Mod7-Obj4: Major structures of the eye and its physiology

Question 1

Vision is our…

Answer 1

Dominant sense

• 70% of the body’s receptors are in the eye
• Visual processing by half cerebral cortex

Question 2

Accessory structures

Answer 2

• Eyebrows
• Eyelids (Palpebrae)
• Conjuctiva
• Lacrimal apparatus
• Extrinsic eye muscles

Question 3

Eyebrows

Answer 3

• Protect the eye from perspiration

- Shade from direct sunlight

Question 4

Eyelids (Palpebrae)

Answer 4

• Muscular folds of facial skin fringed with hair
• Eyelashes are richly innervated (triggers blinking to prevent damage)
• Glands secret oily lubricant that lubricates eyelid & prevents eyelids from sticking together

Question 5

Conjunctiva

Answer 5

• Transparent mucous membrane lining the eyelids and white of the eye
• Produces lubricating fluid to prevent drying out and friction

Question 6

Lacrimal (tear) Apparatus

Answer 6

• Secretes dilute saline solution (tears) containing mucus, antibodies &lysozyme
• Blinking spreads tears
• Tears provide nutrients and oxygen, cleanse, moisten and protect the surface of the eye

Question 7

Movement of the eyeball

Answer 7

• Six extrinsic muscles which are innervated by cranial nerves III, IV and VI
• These enable the eyes to be fixed on stationary or moving objects and keep both eyes fixed on the same object at the same time

Question 8

Lens

Answer 8

• Lens is bioconvex, transparent and flexible
• Changes shape to focus light
• Spherical unless and outside force is applied
• Held in place by ciliary zonules called suspensory ligaments attached to ciliary muscles

Question 9

Ciliary muscle

Answer 9

Circular muscle surrounding the lens

Question 10

Suspensory ligaments

Answer 10

Extend from muscle to lens to hold in place

Question 11

Ciliary muscles contract

flatten the lens

Answer 11

Suspensory ligaments relax and the lens becomes spherical

Question 12

Ciliary muscles relax

lens become round

Answer 12

Suspensory ligaments tighten, pull at the circumference of the lens. causing it to flatten

Question 13

The lens and ciliary zonules divides the eye into 2 segements

Answer 13

1. ) Anterior segment

2. ) Posterior segment

Question 14

Anterior segment of the lens and ciliary zonules

In front of the lens

Answer 14

-Anterior chamber: Between cornea and iris
-Posterior chamber:
Between iris and lens

Question 15

The anterior segment of the lens and ciliary zonules

Answer 15

Contains aqueous humour that supplies nutrients and oxygen to the lens and cornea

Question 16

Posterior segement of the lens and ciliary zonules

Behind the lens

Answer 16

Contains vitreous humour (gelatinous)

-Maintains the shape of the hollow eyeball and holds the retina into place

Question 17

3 layers of the eyeball

Answer 17

1. ) Fibrous layer (outer layer)
2. ) Vascular layer (middle layer), three regions
3. ) Retina (inner layer): nervous layer

Question 18

Fibrous layer of the eyeball

outer layer

Answer 18

• Sclera: Tough opaque connective tissue

- Cornea: Transparent region

Question 19

Vascular Layer (middle layer), supplies blood to the other two layers

Answer 19

• Choroid: Highly vascularised area
• Ciliary body: Forms muscular rings around lens
• Iris: Adjustable diaphragm that controls diameter of pupil (coloured area)

Question 20

Retina (inner layer): Nervous layer

Answer 20

• Photoreceptors (cones & rodes)
• Fovea centralis (cones for visual acuity)
• Optic disc (no photoreceptors)

Question 21

Rods and cones

Photoreceptors

Answer 21

Photoreceptors: light detecting cells (converting it to an action potential)
-Light reflects off objects and travels through our eyes to the photoreceptors of the retina

Question 22

Rods (photoreceptors)

Answer 22

Receptors for dim light and peripheral vision

Question 23

Cones (photoreceptors)

Answer 23

Receptors for bright light, colour and visual acuity

Question 24

Focusing light on the Retina: 2 processes

Answer 24

1. ) Refraction

2. ) Accommodation

Question 25

Refraction (focusing light on the Retina)

Answer 25

Bending of light when it changes speed passing from one medium to another

Question 26

Accomodation (focusing light on the Retina)

Answer 26

Changing the shape of the lens to direct light rays to the retina

Question 27

Refraction of light

Answer 27

Refractions explains why these objects appear the way they do (why they appear bent)

Question 28

Focussing light on the Retina: Refraction involving 4 changes (Bending of the light, multiple refractions before it reaches the retina)

Answer 28

1. ) Air to cornea 2. ) Cornea to aqueous humour 3. ) Aqueous humour to lens 4. ) Lens to vitreous humour

Question 29

Focussing light on the Retina: Refraction

Answer 29

The amount of refraction is constant for changes except for the amount of refraction through the lens because the lens is highly elastic and changes shape for focussing (changes the bending of the light ray)

Question 30

Combined effects of the refractions...

Answer 30

occur to focus the image on the retina

Question 31

Focussing light on the Retina...Refraction of distant vision | flattened lens

Answer 31

An object that is 6 metres or more away from the eye reflects light rays that are virtually parallel to each other. These light rays will focus on the retina with the lens flattened (ciliary muscles relaxed, suspensory ligaments tightened)

Question 32

Distance vision

Answer 32

Sympathetic activation - Nearly parallel rays from distant object - Lens is flattened for distant vision. Sympathetic input relaxes he ciliary muscle, tightening the ciliary zonule, and flattening the lens

Question 33

Focusing light on the Retina: Close vision | rounder lens

Answer 33

Objects that are nearer than 6m reflect light rays that are on divergent paths. These requirer greater refraction to bring them into focus at the retina - Lens is less thickened (more round) to increase refractory power=accomodation - This is achieved through contraction of the ciliary muscle

Question 34

Close vision

Answer 34

Parasympathetic activation - Divergent rays from close object - Lens bulges for close vision. Parasympathetic input contracts the ciliary muscles, loosing the ciliary zonule, allowing the lens to bulge

Question 35

Focussing for close vision

Answer 35

- Convergence of the eyeballs: turning both eyeballs medially e.g.) looking at the tip of your nose - Constriction of pupil: by iris sphincter muscle to decrease the diameter of the pupil. This prevents most divergent light rays from entering eye and causing blurred vision

Question 36

Converting light to neural impulses

Answer 36

Once an object is focussed light rays are directed on the retina where photoreceptors (rods and cones) are located

Question 37

Rods contain rhodopsin

Answer 37

- Light promotes the breakdown of rhodopsin causing the rod cell membrane to depolarise, which produces and action potential - The visual pigments of cones operate in similar fashion

Question 38

Rhodopsin

Answer 38

Sensitive to light, found in rods