Chapter 5 - The Eye and Muscle

Question 1

• The mammalian eye

The mammalian eye is …

Answer 1

A complex sense organ.

Question 2

• The mammalian eye

The mammalian eye is a complex sense organ. Only a very small section of the eye contains …

Answer 2

The photoreceptors that are sensitive to light.

Question 3

• The mammalian eye

The mammalian eye is a complex sense organ. Only a very small section of the eye contains the photoreceptors that are sensitive to light. The rest of the eye contains …

Answer 3

Structures that ensure that the receptors in the retina at the back of the eye receive focused light rays at the correct intensity to form an image.

Question 4

Draw a diagram showing the structure of the mammalian eye in cross-section

Answer 4

Textbook page 69

Question 5

What is the conjunctiva?

Answer 5

Thin transparent membrane covering the cornea

Question 6

What is the function of the conjunctiva?

Answer 6

Protects the cornea from damage

Question 7

What is the sclera?

Answer 7

Tough opaque connective tissue covering the eye - replaced by transparent cornea at front

Question 8

What is the function of the sclera?

Answer 8

Protects against damage; site of attachment of eye muscles

Question 9

What is the cornea?

Answer 9

Front transparent part of sclera

Question 10

What is the function of the cornea?

Answer 10

Transparent and most refraction (bending) of light occurs here

Question 11

What is the aqueous humour?

Answer 11

Transparent watery fluid between cornea and lens

Question 12

What is the function of the aqueous humour?

Answer 12

Maintains the shape of the front part of the eye

Question 13

What is the iris?

Answer 13

Muscular layer with both circular and radial muscle; contains pigment that absorbs light

Question 14

What is the function of the iris?

Answer 14

Adjusts the size of the pupil to control the amount of light entering the eye

Question 15

What is the pupil?

Answer 15

Gap within the iris

Question 16

What is the function of the pupil?

Answer 16

The area through which light reaches the lens and enters the centre of the eye

Question 17

What is the ciliary body?

Answer 17

Contains a muscular ring of (ciliary) muscle around the eye; suspenseful ligaments extend from the ciliary body and hold the lens in place

Question 18

What is the function of the ciliary body?

Answer 18

Adjusts the shape of the lens to focus light rays

Question 19

What are the suspensory ligaments?

Answer 19

Ligaments that connect the ciliary body to the lens

Question 20

What is the function of the suspensory ligaments?

Answer 20

Transfers tension in the wall of the eyeball to make the lens thinner; important when focusing on distant objects

Question 21

What is the lens?

Answer 21

Transparent biconcave structure with refractive properties

Question 22

What is the function of the lens?

Answer 22

Refracts light and focuses light rays on the retina

Question 23

What is the vitreous humour?

Answer 23

Transparent, jelly-like material between the lens and the back of the eye

Question 24

What is the function of the vitreous humour?

Answer 24

Maintains the shape of the rear part of the eye and supports the lens

Question 25

What is the retina?

Answer 25

Inner layer of the eyeball containing the light sensitive receptor cells (rods and cones)

Question 26

What is the function of the retina?

Answer 26

When stimulated the rods and cones initiate impulses in associated neurones

Question 27

What is the fovea?

Answer 27

Region in the centre of the retina that is particularly rich in cones and does not contain rods

Question 28

What is the function of the fovea?

Answer 28

Part of eye that gives the clearest daylight colour vision

Question 29

What is the choroid?

Answer 29

A layer of pigmented cells between the retina and the sclera

Question 30

What is the function of the choroid?

Answer 30

Contains blood vessels that supply the retina; prevents reflection of light back through the eye

Question 31

What is the optic nerve?

Answer 31

Bundle of sensory nerve fibres that leave the retina

Question 32

What is the function of the optic nerve?

Answer 32

Transmits impulses from the retina to the brain

Question 33

What is the blind spot?

Answer 33

Part of the retina where the sensory neurones that unite to form the optic nerve leave the eye

Question 34

What is the function of the blind spot?

Answer 34

Contains no light sensitive cells so is not sensitive to light

Question 35

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some ...

Answer 35

Bending (refraction) of light automatically takes place.

Question 36

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place ...

Answer 36

In the cornea

Question 37

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes ...

Answer 37

Through the lens

Question 38

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be ...

Answer 38

Focused on the retina

Question 39

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of ...

Answer 39

Their angle as they enter the eye

Question 40

Draw a diagram showing how the eye focuses on distant objects

Answer 40

Textbook page 71, first diagram

Question 41

Draw a diagram showing how the eye focuses on near objects

Answer 41

Textbook page 71, second diagram

Question 42

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains ...

Answer 42

A ring of muscle (ciliary muscle)

Question 43

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running ...

Answer 43

Around the inside of the eyeball and surrounding the lens

Question 44

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to ...

Answer 44

The ciliary body

Question 45

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by ...

Answer 45

Suspensory ligaments

Question 46

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble ...

Answer 46

Small pieces of nylon thread

Question 47

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, ...

Answer 47

Tension in the wall of the eyeball is transferred through the suspensory ligaments to the lens

Question 48

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, ...

Answer 48

The ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut).

Question 49

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, ...

Answer 49

The suspensory ligaments pull the lens into a thinner shape that has less refractive power.

Question 50

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens ...

Answer 50

Fatter when a greater degree of refraction is required.

Question 51

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle ...

Answer 51

Contracts

Question 52

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form ...

Answer 52

A tighter circle

Question 53

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a ...

Answer 53

Smaller diameter

Question 54

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are ...

Answer 54

Not pulled taught so relax

Question 55

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on ...

Answer 55

The lens

Question 56

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to ...

Answer 56

Spring back to its 'normal' thicker shape.

Question 57

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its 'normal' thicker shape. The adjustment of lens thickness to ensure that ...

Answer 57

The light rays are focused on the retina

Question 58

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its 'normal' thicker shape. The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of ...

Answer 58

The angle of light rays reaching the eye

Question 59

- Function of the eye Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye. The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power. The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its 'normal' thicker shape. The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of the angle of light rays reaching the eye, is called ...

Answer 59

Accommodation

Question 60

What happens as light rays enter and pass through the cornea?

Answer 60

Some bending (refraction) of light automatically takes place.

Question 61

Where in the eye does most refraction of light take place?

Answer 61

In the cornea

Question 62

As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Where in the eye does further refraction take place?

Answer 62

As light passes through the lens

Question 63

In simple terms, how can light be focused on the retina?

Answer 63

By adjusting the thickness of the lens, light rays can be focused on the retina, irrespective of their angle as they enter the eye.

Question 64

Comment on the angle of light rays as they enter the eye from a distant object

Answer 64

Light rays arrive parallel

Question 65

Comment on the angle of light rays as they enter the eye from a near object

Answer 65

Light rays diverge from a close-up object

Question 66

Why is the lens thin when focusing light rays from a distant object?

Answer 66

Lens is thin as little additional refraction is necessary to focus light on the retina

Question 67

Why is the lens thick when focusing light rays from a near object?

Answer 67

Lens is thicker as further refraction is necessary to focus light on the retina

Question 68

What does the ciliary body contain?

Answer 68

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens.

Question 69

How is the lens attached to the ciliary body?

Answer 69

The lens is attached to the ciliary body by suspensory ligaments.

Question 70

What do suspensory ligaments resemble?

Answer 70

Small pieces of nylon thread

Question 71

What happens if the ciliary body relaxes?

Answer 71

* If the ciliary body relaxes, the tension in the wall of the eyeball is transferred through the suspensory ligaments to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taught). * When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

Question 72

What happens if the ciliary body contracts?

Answer 72

* The ciliary muscle contracts to form a tighter circle with a smaller diameter. * The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its 'normal' thicker shape. * This makes the lens fatter when a greater degree of refraction is required.

Question 73

What is accommodation?

Answer 73

The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of the angle of light rays reaching the eye.

Question 74

Comment on the state of the ciliary muscles, suspensory ligaments and the lens when the eye is: a) Focusing on a distant object b) Focusing on a near object

Answer 74

a) Ciliary muscles relaxed Suspensory ligaments stretched Lens pulled thin b) Ciliary muscles contracted Suspensory ligaments slack Thick lens

Question 75

Draw a diagram showing the state of the lens, ciliary muscles and suspensory ligaments within the mammalian eye as it is focusing on a distant object. Furthermore, draw a diagram showing only the lens, ciliary muscles and suspensory ligaments in cross-section during this accommodation.

Answer 75

Textbook page 72, first diagram

Question 76

Draw a diagram showing the state of the lens, ciliary muscles and suspensory ligaments within the mammalian eye as it is focusing on a near object. Furthermore, draw a diagram showing only the lens, ciliary muscles and suspensory ligaments in cross-section during this accommodation.

Answer 76

Textbook page 72, second diagram

Question 77

Describe the structural composition of ligaments and how it relates to their role in the mammalian eye

Answer 77

* Ligaments are tough and flexible but they do not stretch. * Not being stretchable is important as this ensures that the suspensory ligaments pull the lens thin when the ciliary muscle contracts.

Question 78

Controlling the amount of light that enters the eye - It is important that ...

Answer 78

The correct intensity of light enters the eye

Question 79

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches ...

Answer 79

The retina

Question 80

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will ...

Answer 80

Prevent an image being formed

Question 81

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light ...

Answer 81

Can damage the sensitive light receptor cells in the retina

Question 82

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows ...

Answer 82

As much light as possible to enter the eye

Question 83

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure ...

Answer 83

That there is sufficient light to stimulate the photoreceptors in the retina

Question 84

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is ...

Answer 84

Reduced to a small size

Question 85

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to ...

Answer 85

Restrict the amount of light entering

Question 86

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of ...

Answer 86

The size of the iris

Question 87

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can ...

Answer 87

Contract or relax

Question 88

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can contract or relax to ...

Answer 88

Change the size of the pupil

Question 89

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of ____ types of muscle.

Answer 89

Two

Question 90

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - ...

Answer 90

Radial and circular

Question 91

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - radial and circular. Radial muscles are like ...

Answer 91

The spokes of a wheel moving out from the edge of the pupil through the iris

Question 92

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris. The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - radial and circular. Radial muscles are like the spokes of a wheel moving out from the edge of the pupil through the iris, and circular muscles form ...

Answer 92

Rings within the iris around the pupil

Question 93

In low light intensities the radial muscles ...

Answer 93

Contract

Question 94

In low light intensities the radial muscles contract (and the circular muscles ...

Answer 94

Relax

Question 95

In low light intensities the radial muscles contract (and the circular muscles relax) - this makes the pupil ...

Answer 95

Larger (dilated)

Question 96

In bright light the circular muscles ...

Answer 96

Contract

Question 97

In bright light the circular muscles contract (and the radial muscles ...

Answer 97

Relax

Question 98

In bright light the circular muscles contract (and the radial muscles relax) - this makes the pupil ...

Answer 98

Smaller (constricted)

Question 99

Draw a cross-section of the iris and pupil in dim light. Your diagram should include the state of the radial and circular muscles in the iris.

Answer 99

Textbook page 72. Diagram on the bottom left.

Question 100

Draw a cross-section of the iris and pupil in bright light. Your diagram should include the state of the radial and circular muscles in the iris.

Answer 100

Textbook page 72. Diagram on the bottom right.

Question 101

Accommodation and the control of the amount of light entering the eye are both examples of ...

Answer 101

Reflex action

Question 102

Accommodation and the control of the amount of light entering the eye are both examples of reflex action. They are ...

Answer 102

Automatic responses, not under voluntary control

Question 103

Give two examples of reflex actions

Answer 103

Accommodation | The control of the amount of light entering the eye

Question 104

What is a reflex action?

Answer 104

An automatic response, not under voluntary control.

Question 105

Why is it important that the correct intensity of light enters the eye and reaches the retina?

Answer 105

* Too little or too much light will prevent an image being formed. * In addition, too much light can damage the sensitive light receptor cells in the retina.

Question 106

Why is the pupil dilated in low light intensities?

Answer 106

In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina.

Question 107

Why is the pupil constricted in bright light?

Answer 107

In bright light the pupil is reduced to a small size to restrict the amount of light entering.

Question 108

The size of the pupil is a direct consequence of what?

Answer 108

The size of the iris

Question 109

How many types of muscle does the iris consist of?

Answer 109

Two

Question 110

How do the muscles of the iris change the size of the pupil?

Answer 110

The muscles of the iris can contract or relax to change the size of the pupil.

Question 111

What two types of muscle does the iris consist of?

Answer 111

Radial and circular

Question 112

How is the size of the pupil adjusted when the eye is exposed to a low light intensity?

Answer 112

In low light intensities the radial muscles contract (and the circular muscles relax) - this makes the pupil larger.

Question 113

How is the size of the pupil adjusted when the eye is exposed to bright light?

Answer 113

In bright light the circular muscles contract (and the radial muscles relax) - this makes the pupil smaller.

Question 114

- The retina in detail The retina contains ...

Answer 114

Millions of light sensitive cells and the neurones with which they synapse.

Question 115

- The retina in detail The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are ...

Answer 115

Specialised photoreceptors (photosensitive cells)

Question 116

- The retina in detail The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are specialised photoreceptors (photosensitive cells) in that ...

Answer 116

Light energy brings about change in the level of polarisation of their membranes

Question 117

- The retina in detail The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are specialised photoreceptors (photosensitive cells) in that light energy brings about change in the level of polarisation of their membranes - they act as ...

Answer 117

Transducers converting a light stimulus to a nerve impulse in their associated neurones.

Question 118

- The retina in detail Rod cells - In rods the light sensitive pigment ...

Answer 118

Rhodopsin

Question 119

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is ...

Answer 119

Packed into an array of membranes in the outer part of the rod cell.

Question 120

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from ...

Answer 120

A protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A.

Question 121

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin ...

Answer 121

Breaks down into its retinal and opsin components

Question 122

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This ...

Answer 122

Changes the membrane potential of the rod cell

Question 123

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates ...

Answer 123

A generator potential

Question 124

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates a generator potential. If ...

Answer 124

A threshold level is achieved

Question 125

- The retina in detail Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates a generator potential. If a threshold level is achieved, this can ...

Answer 125

Cause the adjacent linking neurone (bipolar neurone) to become depolarised to the extent that it will conduct an action potential.

Question 126

What is a generator potential?

Answer 126

* A generator potential is the degree of depolarisation a stimulated receptor can produce. * Only if the generator potential reaches a threshold level will it produce an action potential in the neurone.

Question 127

- The retina in detail The inner segment of the rod contains ...

Answer 127

The cell's nucleus and mitochondria

Question 128

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in ...

Answer 128

Producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Question 129

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for ...

Answer 129

Vision in low light intensities

Question 130

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have ...

Answer 130

High sensitivity

Question 131

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as ...

Answer 131

The rhodopsin will break down readily in low light levels

Question 132

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring ...

Answer 132

Only a small amount of light energy

Question 133

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to ...

Answer 133

The phenomenon of dark adaptation

Question 134

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light ...

Answer 134

Virtually all the rhodopsin is broken down (bleached)

Question 135

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it ...

Answer 135

Takes time for it to be re-synthesised

Question 136

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why ...

Answer 136

If we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves.

Question 137

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves. In effect, ...

Answer 137

Our eyes have changed from being light-adapted (when in bright light) to being dark-adapted

Question 138

- The retina in detail The inner segment of the rod contains the cell's nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation. Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves. In effect, our eyes have changed from being light-adapted (when in bright light) to being dark-adapted, ie ...

Answer 138

Adapted for functioning in low light intensities.

Question 139

Give a definition of transduction

Answer 139

Transduction is the process of changing energy from one form to another.

Question 140

What does the retina contain?

Answer 140

The retina contains millions of light sensitive cells and the neurones with which they synapse.

Question 141

What are rods and cones?

Answer 141

Rods and cones are specialised photoreceptors (photosensitive cells)

Question 142

What makes rods and cones specialised photoreceptors (photosensitive cells)?

Answer 142

Light energy brings about change in the level of polarisation of their membranes - they act as transducers converting a stimulus to a nerve impulse in their associated neurones.

Question 143

Name the light sensitive pigment found in rods

Answer 143

Rhodopsin

Question 144

Describe the arrangement of rhodopsin in rods

Answer 144

In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell.

Question 145

What is rhodopsin made up of?

Answer 145

Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A.

Question 146

What happens to rhodopsin when it is stimulated by light?

Answer 146

The rhodopsin breaks down into its retinal and opsin components.

Question 147

When will rhodopsin break down?

Answer 147

When stimulated by light, the rhodopsin breaks down into its retinal and opsin components.

Question 148

What happens to the rod cell when a light stimulus breaks down rhodopsin into its retinal and opsin components?

Answer 148

* This changes the membrane potential of the rod cell and creates a generator potential. * If a threshold level is achieved, this can cause the adjacent linking neurone (bipolar neurone) to become depolarised to the extent that it will conduct an action potential.

Question 149

What does the inner segment of the rod cell contain?

Answer 149

The cell nucleus and numerous mitochondria

Question 150

What is the role of the mitochondria found in the inner segment of rod cells?

Answer 150

Produce ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Question 151

What are rod cells adapted for?

Answer 151

Vision in low light intensities

Question 152

Why do rods have high sensitivity?

Answer 152

As the rhodopsin will break down readily in low light levels requiring only a small amount of light energy.

Question 153

Describe how the phenomenon of dark adaptation arises

Answer 153

* Rods are adapted for vision in low light intensities. * They have high sensitivity as the rhodopsin will break down readily in low lights levels requiring only a small amount of light energy. * In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. * This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves. * In effect, our eyes have changed from being light-adapted (when in bright light) to being dark-adapted, ie adapted for functioning in low light intensities.

Question 154

Name the pigment found in cone cells

Answer 154

Iodopsin

Question 155

Where in the cone cell is iodopsin situated?

Answer 155

In the membranes of the outer segment

Question 156

How does iodopsin compare with rhodopsin?

Answer 156

Iodopsin is less readily broken down and will only produce a generator potential in bright light.

Question 157

- Cone cells The same general principles apply ...

Answer 157

To the functioning of cone cells

Question 158

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones ...

Answer 158

A different pigment, iodopsin, is situated in the membranes of the outer segment.

Question 159

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is ...

Answer 159

Less readily broken down and will only produce a generator potential in bright light.

Question 160

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are ...

Answer 160

Not sensitive to colour and provide monochromatic vision

Question 161

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide ...

Answer 161

Colour vision

Question 162

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in ...

Answer 162

Three different forms

Question 163

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being ...

Answer 163

Sensitive to different wavelengths of light

Question 164

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of ...

Answer 164

The three different types of cone

Question 165

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with ...

Answer 165

A different type of iodopsin)

Question 166

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to ...

Answer 166

The colours blue, green and red

Question 167

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the ...

Answer 167

Trichromatic theory of colour vision).

Question 168

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will ...

Answer 168

Only break down the 'blue' iodopsin

Question 169

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will only break down the 'blue' iodopsin but of course ...

Answer 169

Most light is not pure blue, green or red

Question 170

- Cone cells The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light. While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision. Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will only break down the 'blue' iodopsin but of course most light is not pure blue, green or red. In effect, ...

Answer 170

It is the degree of stimulation of each type of cone that determines colour vision.

Question 171

Draw a diagram of a rod cell. Your diagram should indicate the direction of the light rays entering the retina and reaching the cell.

Answer 171

Diagram on textbook page 73 | Light ray moving from inner segment towards outer segment (direction)

Question 172

What is the role of cone cells?

Answer 172

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Question 173

How many different forms of iodopsin are there?

Answer 173

Iodopsin exists in three different forms

Question 174

How are the three different forms of iodopsin different from each other?

Answer 174

* Each form is sensitive to different wavelengths of light. | * The absorption peaks of the three types of iodopsin correspond to the colours blue, green and red.

Question 175

What wavelength of light will break down 'blue' iodopsin?

Answer 175

Blue light

Question 176

What determines colour vision?

Answer 176

The degree of stimulation of each type of cone

Question 177

- The arrangement of rods and cones in the retina It is not only the ...

Answer 177

Differences in structure and sensitivities of rod and cone cells

Question 178

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are ...

Answer 178

Important in their functioning.

Question 179

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their ...

Answer 179

Distribution across the retina

Question 180

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and ...

Answer 180

The different ways in which they are arranged with linking neurone cells

Question 181

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are ...

Answer 181

Also crucial.

Question 182

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form ...

Answer 182

A layer immediately inside the choroid.

Question 183

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of _______ ________ lies immediately inside the photosensitive cells

Answer 183

Bipolar neurones

Question 184

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is ...

Answer 184

Another layer of sensory cells (ganglion cells).

Question 185

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is ...

Answer 185

The axons of the ganglion cells that group together to make up the optic nerve

Question 186

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that ...

Answer 186

Carries impulses from the retina to the brain

Question 187

Draw a diagram of a cross-section through the retina and choroid showing photoreceptor cells and their associated neurones

Answer 187

Textbook page 74

Question 188

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that ...

Answer 188

Each cone cell can synapse individually with its own bipolar neurone

Question 189

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie ...

Answer 189

Each provides its own discrete image in vision.

Question 190

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of ...

Answer 190

High visual acuity

Question 191

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - ...

Answer 191

The ability of cones to provide highly precise (colour) vision of high resolution

Question 192

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling ...

Answer 192

The brain to distinguish between two points that are very close together

Question 193

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show ...

Answer 193

Retinal convergence

Question 194

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves ...

Answer 194

A number of rods having a common bipolar neurone

Question 195

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and ...

Answer 195

A number of bipolar cells having a common ganglion cell).

Question 196

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows ...

Answer 196

The generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone

Question 197

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of ...

Answer 197

Rhodopsin

Question 198

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in ...

Answer 198

Rods

Question 199

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to ...

Answer 199

Break down more easily than iodopsin

Question 200

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in ...

Answer 200

Cones

Question 201

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of ...

Answer 201

The sensitivity that rods show.

Question 202

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is ...

Answer 202

Not enough to stimulate the bipolar cell sufficiently

Question 203

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but ...

Answer 203

Stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone.

Question 204

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains ...

Answer 204

Another feature of rods

Question 205

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains another feature of rods - ...

Answer 205

Their lack of visual acuity or high resolution

Question 206

- The arrangement of rods and cones in the retina It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial. As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain. The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone. Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains another feature of rods - their lack of visual acuity or high resolution as ...

Answer 206

The individual rods in each 'convergence unit' only provide as much detail as one cone cell.

Question 207

What factors are important in the functioning of rod and cone cells?

Answer 207

1. The differences in the structure and sensitivities of rod and cone cells. 2. The distribution of rod and cone cells across the retina along with the different ways in which they are arranged with linking neurone cells.

Question 208

Comment on the position of the rod and cone cells relative to the choroid layer

Answer 208

The rods and cones form a layer immediately inside the choroid.

Question 209

Comment on the position of the layer of bipolar neurones relative to the photosensitive cells

Answer 209

The layer of bipolar neurones lies immediately inside the photosensitive cells

Question 210

Comment on the position of the ganglion cells relative to the layer of bipolar neurones

Answer 210

The layer of sensory cells (ganglion cells) lies immediately inside the layer of bipolar neurones.

Question 211

What is the optic nerve composed of?

Answer 211

The axons of ganglion cells group together to form the optic nerve.

Question 212

How many cone cells can synapse with a bipolar neurone?

Answer 212

One

Question 213

How many rod cells can synapse with a bipolar neurone?

Answer 213

Many

Question 214

The different properties of rods and cones, and their retinal arrangement, explains why we can see detailed colour vision during daytime (...

Answer 214

The light intensity is sufficient to break down iodopsin

Question 215

The different properties of rods and cones, and their retinal arrangement, explains why we can see detailed colour vision during daytime (the light intensity is sufficient to break down iodopsin) but can only see less detailed black and white image during the night (...

Answer 215

Light intensity sufficient to break down rhodopsin but not iodopsin

Question 216

Describe the structure of a 'convergence unit'

Answer 216

Single ganglion cell which synapses with two or more bipolar neurones which individually synapse with many rod cells.

Question 217

What is the structural basis of high visual acuity in the mammalian eye?

Answer 217

Each cone cells can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision.

Question 218

What is high visual acuity?

Answer 218

The ability of cones to provide highly precise (colour) vision of high resolution

Question 219

How can the brain distinguish between two points that are very close together?

Answer 219

* Each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. * This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together.

Question 220

The arrangement of rod cells within the mammalian eye displays what phenomenon?

Answer 220

Retinal convergence

Question 221

What is retinal convergence?

Answer 221

A number of rod cells have a common bipolar neurone (and a number of bipolar cells have a common ganglion cell).

Question 222

What does retinal convergence facilitate in the mammalian eye?

Answer 222

Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone, therefore facilitating the sensitivity that rods show.

Question 223

What factors contribute to the sensitivity that rod cells show?

Answer 223

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show.

Question 224

Comment on the stimulation of rod cells when light enters the eye with reference to retinal convergence

Answer 224

The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone.

Question 225

Why do rods display a lack of visual acuity?

Answer 225

Rod cells display a lack of visual acuity (or high resolution) as the individual rods in each 'convergence unit' only provide as much detail as one cone cell.

Question 226

Do not confuse sensitivity with visual acuity. What is sensitivity? What is visual acuity?

Answer 226

Sensitivity is the ability to operate in very low light intensities. Visual acuity is the ability to provide precision vision.

Question 227

What can be noted about the arrangement of photosensitive cells and neurones in the retina?

Answer 227

Light rays have to pass through layers of neurones before reaching the light sensitive cells.

Question 228

If you look again at the arrangement of photosensitive cells and neurones in the retina, you will note that the light rays have to pass through layers of neurones before reaching the light sensitive cells. Why is this the case?

Answer 228

This 'inverted' arrangement appears to be less efficient than if it was the opposite way round with the photosensitive cells being on the inside and the neurone 'cabling' behind. Perhaps, but the arrangement in mammals is a consequence of the evolutionary development of the eye.

Question 229

Draw a graph showing the distribution and abundance of rod and cone cells across the retina of the human left eye

Answer 229

Textbook page 75

Question 230

The graph on page 75 of the textbook shows how the cones and rods are distributed across the retina. What phenomena does this distribution explain?

Answer 230

The distribution explains phenomena such as the blind spot and why we can distinguish shapes but not colour at the periphery of our vision, ie when the light rays are focused on the edge of the retina

Question 231

Comment on the distribution of rods across the retina of the human left eye

Answer 231

There are more rods at the right side of the retina (closer to centre of head) compared to the left. This facilitates peripheral vision on the left side of the head - the converse arrangement exists in the right eye.

Question 232

The presence of two eyes in mammals provides what type of vision?

Answer 232

Binocular or stereoscopic vision

Question 233

What is the advantage of the two eyes creating a single image?

Answer 233

If the two eyes create a single image it allows accurate judgement of distance. Stereoscopic vision, the ability to form three-dimensional images, is also possible.

Question 234

Comment on the position of the eyes in humans and other primates

Answer 234

In humans and other primates, and also in most predatory species, the eyes are positioned on the front of the head.

Question 235

In humans and other primates, and also in most predatory species, the eyes are positioned on the front of the head. What is the advantage of this?

Answer 235

This facilitates excellent judgement of distance and 3-D vision.

Question 236

Comment on the position of the eyes in prey species

Answer 236

Many prey species, such as rabbits, have their eyes positioned on the side of their heads rather than at the front.

Question 237

Many prey species, such as rabbits, have their eyes positioned on the side of their heads rather than at the front. What is the advantage of this?

Answer 237

This provides a wider field of view, a greater priority for prey aiding the detection of potential predators than 3-D vision.

Question 238

What are muscles?

Answer 238

Muscles are specialised effectors that bring about movement through contraction.

Question 239

What is the main type of muscle in the body?

Answer 239

Skeletal muscle

Question 240

What is skeletal muscle?

Answer 240

Muscle that is attached (via tendons) to the skeleton. Skeletal muscle is voluntary muscle in that it is under conscious control.

Question 241

Comment on the size of skeletal muscle

Answer 241

Skeletal (voluntary) muscle can vary considerably in size, for example, compare the triceps and biceps muscles with the muscles controlling the eyeball. However, the basic structure of all skeletal muscle is the same.

Question 242

Describe the structure of skeletal muscle

Answer 242

* Skeletal muscle consists of many muscle fibres bunched together. * Each fibre is surrounded by a cell surface membrane (sarcolemma). * Each fibre is multinucleate with the nuclei typically arranged just inside the sarcolemma. * The fibre, which is effectively a very specialised 'cell', contains the cell organelles typically found in any cell, but is particularly rich in mitochondria. * At intervals, the sarcolemma folds deeply inwards to form transverse tubules or T-tubules. * The bulk of the muscle fibre is filled with highly specialised contractile units called myofibrils. * Muscle fibres are very large structures and can be up to many centimetres long.

Question 243

Draw a simple diagram showing the macrostructure of a skeletal muscle

Answer 243

Textbook page 76

Question 244

How many proteins make up the myofibril?

Answer 244

The myofibril consists largely of two types of protein

Question 245

The myofibril consists largely of two types of protein. What are these two proteins?

Answer 245

Myosin | Actin

Question 246

Briefly describe the ultrastructure of a myofibril

Answer 246

* The myofibril consists largely of two types of protein, myosin and actin. * Myosin forms thick filaments around 15 nm in diameter and actin forms thin filaments about 7 nm in diameter.

Question 247

Comment briefly on the distribution of myosin and actin filaments in a myofibril

Answer 247

* Myosin filaments lie in the central region of each contractile unit and are linked together by a thin disc (the M-line) that runs perpendicular to the orientation of the myosin filaments. * Actin filaments slot between the outer edges of the myosin filaments and they are also held together by a thin disc called the Z-line.

Question 248

What is a sarcomere?

Answer 248

A section of myofibril between two Z-lines (ie the basic contractile unit)

Question 249

How do the myosin filaments affect the appearance of skeletal muscle in electron micrographs?

Answer 249

The thicker myosin filaments form denser or darker striations or bands.

Question 250

How do the actin filaments affect the appearance of skeletal muscle in electron micrographs?

Answer 250

The thinner actin filaments form less dense or lighter regions between the myosin filaments.

Question 251

Why does skeletal (voluntary) muscle display a striated (banded) pattern?

Answer 251

The thicker myosin filaments form denser or darker striations or bands and the thinner actin filaments form less dense or lighter regions between them. It is this alternating pattern of myosin and actin that forms the striated (banded) pattern of voluntary (striated) muscle as seen in electron micrographs.

Question 252

What is the name given to the part of the myofibril containing myosin?

Answer 252

A-band (anisotropic band)

Question 253

What is the A-band?

Answer 253

The part of the myofibril containing myosin is referred to as the A-band (or anisotropic band). The A-band includes those areas where the thinner actin penetrates between the myosin filaments.

Question 254

What is the name given to the part of the myofibril that contains actin only?

Answer 254

The I-band (isotropic band)

Question 255

What is the I-band?

Answer 255

The I-band (isotropic band) is the part of the myofibril that contains actin only.

Question 256

What is the H-zone?

Answer 256

The H-zone is the zone in the centre of the A-band where there is myosin only (the area beyond the ends of the actin filaments).

Question 257

Draw a diagram showing a cross-section of a myofibril through an I-band

Answer 257

Textbook page 77. Diagram A.

Question 258

Draw a diagram showing a cross-section of a myofibril through an A-band area where the thinner actin penetrates between the myosin filaments

Answer 258

Textbook page 77. Diagram B.

Question 259

Draw a diagram showing a cross-section of a myofibril through a H-zone

Answer 259

Textbook page 77. Diagram C.

Question 260

Draw a diagram of multiple sarcomeres in sequence. Include labels.

Answer 260

Textbook page 77. Top diagram.

Question 261

Comment on the relationship between the overlapping actin and myosin within each myofibril

Answer 261

The relationship between the overlapping actin and myosin is very regular with each myosin filament being surrounded by six actin filaments in a regular hexagonal pattern.

Question 262

The relationship between the overlapping actin and myosin is very regular with each myosin filament being surrounded by six actin filaments in a regular hexagonal pattern. Draw a diagram illustrating this.

Answer 262

Textbook page 77

Question 263

Label the structures evident in the TEM of a striated muscle showing series of myofibrils running left to right on page 77 of the textbook.

Answer 263

Textbook page 77

Question 264

What is the basic principle of muscle contraction?

Answer 264

The basic principle of muscle contraction is that the myosin and actin filaments slide past each other so reducing the overall length of the sarcomere (and muscle).

Question 265

What is the process of muscle contraction called?

Answer 265

The sliding filament mechanism

Question 266

Describe the structure of the myosin and actin filaments

Answer 266

Myosin filaments are thick (around 15 nm in diameter). Although mainly a long fibrous molecule, the myosin also has small bulbous heads that protrude at intervals. The thinner actin filaments (around 7 nm in diameter) have small binding sites into which the bulbous heads of the myosin fit.

Question 267

Draw a diagram illustrating the structure of a myosin filament

Answer 267

Textbook page 78

Question 268

Draw a diagram illustrating the structure of an actin filament

Answer 268

Textbook page 78

Question 269

Comment on the state of the myosin head binding sites on the actin filaments when the muscle is not contracting

Answer 269

When not contracting, the actin binding sites are blocked by another ancillary protein (tropomyosin) to prevent binding.

Question 270

Describe the process of muscle contraction

Answer 270

1. An action potential stimulates the muscle fibre as it travels through its extensive system of T-tubules. 2. The action potential causes the calcium ion channels in the sarcoplasmic reticulum (the name given to the specialised endoplasmic reticulum of muscle cells) to open. 3. This causes the calcium ions (Ca2+) that have been stored in the sarcoplasmic reticulum to diffuse into the sarcoplasm (the cytoplasm of muscle cells) down a concentration gradient. 4. The calcium ions cause ancillary protein (tropomyosin) that normally covers the binding sites on the actin filaments to be moved, so enabling the myosin bulbous heads to link with the actin binding sites (forming actomyosin bridges). 5. Once attached, the myosin heads change their angle (rotate or 'rock' back to an angle about 45°) and pull the actin filaments over the adjacent myosin filaments (by about 10 nm). 6. An ATP molecule attaches to each myosin head and the energy released from its hydrolysis enables the myosin head to detach from the stationary actin binding site and return to its original position. 7. The detached myosin heads repeat the process so that the cycle of attachment, rotation and release is repeated in a type of ratchet mechanism, with each cycle occurring about five times each second. 8. The cycle continues as long as the muscle fibre receives nervous stimulation (and has calcium ions present).

Question 271

Draw a flow diagram illustrating the sliding filament mechanism of muscle contraction

Answer 271

Textbook page 79

Question 272

Describe how the arrangement of the myosin and actin filaments in each sarcomere change as contraction takes place

Answer 272

* The sarcomere shortens (distance between the Z-lines decreases). * The H-zone becomes shorter. * The I-band becomes shorter. * The A-band remains the same length.

Question 273

Draw a diagram showing a sarcomere in a relaxed and contracted state

Answer 273

Textbook page 79

Question 274

Why is overall muscle contraction considerable despite each sarcomere being microscopic in size?

Answer 274

* With each sarcomere being microscopic in size (approx 2.5 micrometers) it is obvious that the contraction caused by each sarcomere shortening is almost negligible. * However, with many sarcomeres lined end to end in a muscle fibre, and all contracting at the same time, the overall muscle contraction can be considerable.

Question 275

What contributes to the power of muscle contraction?

Answer 275

The power of muscle contraction is due to the many parallel myofibrils lined side by side in a muscle fibre (and many fibres in a single muscle) all contracting at the same time.

Question 276

What contributes to the strength of muscle contraction?

Answer 276

* The strength of muscle contraction depends on a number of factors including for how long the muscle is stimulated but also how many muscle fibres are actually stimulated and contracting. * Although one motor neurone may control contraction in an entire muscle, not all the fibres may be contracted at the one time.

Question 277

What are the different types of muscle in the body?

Answer 277

Skeletal muscle, although the most obvious in terms of size and extent, is not the only type of muscle in the body. Smooth and cardiac muscle also contract and bring about movement but are different in appearance, nervous control, distribution and function to skeletal muscle.

Question 278

Describe the appearance of skeletal muscle

Answer 278

* Striated (banded) | * Multinucleate fibres

Question 279

Describe the appearance of smooth muscle

Answer 279

* Discrete uninucleate cells are spindle-shaped * Not striated * There is a single central nucleus in each cell * Cells are elongated and taper towards their ends

Question 280

Describe the appearance of cardiac muscle

Answer 280

• Striated but branched with intercalated discs (seen as discrete lines) between cells

Question 281

Describe the distribution of skeletal muscle

Answer 281

• Attached to bone throughout the body (most of the muscle in the body)

Question 282

Describe the distribution of smooth muscle

Answer 282

* Lining gut and blood vessels | * Iris and ciliary body in eye

Question 283

Describe the distribution of cardiac muscle

Answer 283

• Wall of heart

Question 284

Describe the nervous control of skeletal muscle

Answer 284

• Voluntary (conscious) control

Question 285

Describe the nervous control of smooth muscle

Answer 285

• Involuntary or automatic (for example, reflex action)

Question 286

Describe the nervous control of cardiac muscle

Answer 286

• Myogenic and involuntary control

Question 287

Draw a simple diagram of skeletal muscle

Answer 287

Textbook page 80

Question 288

Draw a simple diagram of smooth muscle

Answer 288

Textbook page 80

Question 289

Draw a simple diagram of cardiac muscle

Answer 289

Textbook page 80

Question 290

Practical work | - For this topic, what should an A-level biology student be familiar with in terms of practical work?

Answer 290

They must be familiar with prepared slides, photomicrographs and electron micrographs of muscle and muscle components in addition to the different types muscle present in the body.

Question 291

Why can cardiac muscle be difficult to distinguish from skeletal muscle in electron micrograph images?

Answer 291

Cardiac muscle can be difficult to distinguish from skeletal muscle - it is clear in this electron micrograph that the characteristic striated appearance of skeletal muscle is also present in cardiac muscle. However, there are crucial differences. In cardiac muscle: * Cells branch * Intercalated discs run across the myofibrils - these are important in synchronising electrical conduction and contraction in heart muscle * The cells are uninucleate

Question 292

Label the structures evident in the electron micrographs of cardiac muscle on page 81 of the textbook

Answer 292

Cells branch Mitochondrion Intercalated discs

Question 293

Why is smooth muscle not always very obvious in photographs?

Answer 293

Although smooth muscle consists of discrete cells, each with a central nucleus, this is not always very obvious in photographs as many smooth muscle cells are bunched together and intertwined to form smooth muscle tissue as shown in the diagram on page 81 of the textbook.

Question 294

You should also be familiar with preparations of the eye as prepared slides and EM photographs.

Answer 294

Take time to google images now