Receptors

Question 1

What are receptors?

Answer 1

Specialised cells that detect a specific stimulus and generate electrical impulses in response

Question 2

Describe the general action of receptors

Answer 2

Receptors detect a stimulus, cause a generator potential across the axon membrane
If reaches threshold, action potential is reached and impulse travels along the neurone
The larger the stimulus, the higher the frequency of action potentials

Question 3

What are pacinian corpuscles? Where are they found

Answer 3

A type of mechanoreceptor found deep in the skin, they response to changes in pressure

Fingers, ligaments, joints, tendons

Question 4

What are mechanoreceptors?

Answer 4

Receptors that respond to changes in pressure (the stimulus)

Question 5

Describe the structure of pacinian corpuscles

Answer 5

Layers of lamellae (connective tissue) with gel between them, that surround the un-myelinated end of a myelinated sensory neurone
Lamellae are surrounded by a capsule
A membrane surrounds the un-myelinated axon and contains stretch mediated sodium ion protein channels

Question 6

How do pacinian corpuscles respond to changes in pressure?

Answer 6

At rest, membrane surrounding the axon contains stretch mediated Na+ channels that are the wrong shape to allow ions to pass through

When pressure is applied, the membrane stretches and channels change shape. They can now open and allow ions to diffuse into the axon. This causes a generator potential which can cause an action potential (impulse) if the threshold is reached
The larger to pressure the larger the frequency of action potentials

Once pressure registered, no more action potentials until pressure is released (membrane sprung to an elongated shape so membrane becomes deformed again)n

Question 7

In pacinian corpuscles, why are more action potentials generated when pressure is released?

Answer 7

When released, the membrane is sprung into an elongated shape
The membrane becomes deformed again, so sodium channels change shape and open
Sodium ions diffuse into the axon and cause a generator potential, which becomes an action potential if it reached the threshold

Question 8

In pacinian corpuscles, what are the gel filled lamellae used for?

Answer 8

To filter the stimuli
If a slow pressure is applied, the gel flows away from the stimulus and the membrane is not deformed
If a fast pressure is applied, the membrane will deform before the gel can move away from the stimulus, so action potentials will be generated until the gel returns the membrane to its normal shape

Question 9

What is the eye? What are the components of the eye?

Answer 9

A sense organ, that contains photoreceptors in the retina

Optical nerve
Retina
Fovea
Iris
Lens
Pupil
Cornea
Vitreous gel

Question 10

What are photoreceptors?

Answer 10

Receptors that respond to light stimuli

Question 11

Why is there a blind spot in the retina?

Answer 11

Where there are no photoreceptors, because this is where the optical nerve leaved the retina

Question 12

What are the two types of pohotoreceptors in the retina, and the differences between them?

Answer 12

Cone receptors- found in the fovea
Can distinguish colour
Contains three types of iodopsin pigment

Rod receptors- found all around the periphery of the retinal
Cannot distinguish colour
Contains rhodopsin pigment

Question 13

Explain how rod cells in the receptor detect light

Answer 13

The contain a pigment called rhodopsin
Rhodopsin breaks down when it detects light, and sends action potentials along the optic nerve
Impulses are transmitted to the brain
If no further stimuli detected, rhodopsin reforms (requires ATP)

Question 14

Why do rod cells not function well in bright light?

Answer 14

In bright light, rhodopsin breaks down much quicker than it can reform. Therefore they are said to be bleached and cannot function. This process is called bleaching
Eyes become light adapted

Question 15

Why does it take time for your eyes to see in dark spaces?

Answer 15

Cone cells do not brea down in dim light
In rod cells, it takes time for rhodopsin to reform

Question 16

Explain how cone cells detect coloured light

Answer 16

Cone cells contain one of three types of iodopsin pigment. Each absorbs different wavelengths that approximate to either blue green or red. This is called the trichromatic theory
Iodopsin does not break down in dim light
When iodopsin breaks down, action potentials are sent along the optical nerve and impulses are transmitted to the brain
The brain interprets colour depending on the proportion of each type of cone cell stimulated

Question 17

Explain what the trichromatic theory is

Answer 17

Cone cells receive waves of light and translate them into one of three colours (red green blue) that can be combined to create an entire visible spectrum
The range of wavelengths absorbed by each type of cone cell can overlap

Question 18

What is red-green colour blindness? How is it inherited

Answer 18

A sex linked disease, recessive allele on the X chromosome

The inability to produce red or green sensitive cones.
The light is still detected by the other colours sensitive cones, however the brain will not be able to distinguish between red and green colours

Question 19

What is the structure of the retina?

Answer 19

Rod and cone cells form synapses with a layer of cells called bipolar neurones
The bipolar neurones form synapses with sensory neurones that form the optic nerve

Question 20

How does the structure of rod and cone cells differ in the retina?

Answer 20

Several rod cells synapse with one bipolar neurone. Rod cells are very sensitive to dim light and have retinal convergence
Only one cone cell synapses with one bipolar neurone. Cone cells do not have retinal convergence, and are sensitive to high intensity light. Cone cells have high visual acuity

Question 21

Why are rod cells more sensitive than cone cells?

Answer 21

Due to rod cells having retinal convergence.
Several rod cells synapse with one bipolar neurone. If the stimulation of one rod cells is not enough to reach the threshold and generate an action potential, spatial summation can be used to reach the threshold (several rods are stimulated at the same time)

Cone cells do not have retinal convergence, each cone cell synapses with one bipolar neurone so it takes more light tp reach the threshold and generate an action potential.

Question 22

What is visual acuity?

Answer 22

The ability to tell two points apart that are close together

Question 23

Why do cone cells have visual acuity, but rod cells do not?

Answer 23

Each cone cell is very close together, but synapses with its own bipolar neurone. Therefore the brain receives separate information about two close points, from separate sensory neurones

Several rods cells synapse with one bipolar neurone, so the brain does not receive separate information from the close points

Question 24

State two reasons why rod cells have a greater sensitivity than cone cells

Answer 24

Rhodopsin in rod cells breaks down in dim light, iodopsin does not

Rod cells have retinal convergence, cone cells do not

Question 25

State two reasons why cone cells ahve a greater visual acuity than rod cells

Answer 25

There is a very high density of cone cells In the fovea Cone cells have a 1:1 ratio with bipolar neurones

Question 26

What is the autonomic nervous system? What systems is it made up of?

Answer 26

Regulates the internal glands and muscles Made up of two antagonistic systems- the sympathetic system and parasympathetic system

Question 27

Why are the sympathetic and parasympathetic systems antagonistic?

Answer 27

They oppose each other The sympathetic prepares for activity Parasympathetic slows down and conserves energy

Question 28

What are the neurotransmitters used In the two systems of the ANS?

Answer 28

Sympathetic- noradrenaline Parasympathetic- acetylcholine

Question 29

What are the general effects of the two systems of the ANS?

Answer 29

Sympathetic- excitatory Parasympathetic- inhibitory

Question 30

In the ANS, when are the sympathetic and parasympathetic systems dominant?

Answer 30

Sympathetic is dominant during stress, danger and excitement Parasympathetic is dominant during rest

Question 31

Describe the myogenic stimulation of the cardiac cycle

Answer 31

SAN in the Right atrium sends impulses that spread across both atria, causing aria to contract Impulse is delayed at the AV nodes, the aria empty completely with blood (into the ventricle) Impulse travels down to the bundle of hiss at the base of the ventricles, and travels through the purkyn fibres Causes the ventricle to contract from the base upwards- causes blood to move out ventricle down pressure gradient

Question 32

How is the rate of heartbeat changed?

Answer 32

Via impulses from the autonomic nervous system ANS Impulses are sent from the cardiac centre in a region of the brain called the medulla oblongata Impulses are send through the sympathetic nerve to increase heart rate Impulses are send through the parasympathetic nerve to decrease heart rate

Question 33

Using different impulses from the cardiac centre in the medulla oblongata, how can heart rate be increased or decreased?

Answer 33

To increase the heart rate, increase the frequency of impulses sent via the sympathetic nerve, and decrease the frequency sent via the parasympathetic nerve To decrease the hart rate, decrease the frequency of impulses sent via the parasympathetic nerve, decrease the frequency sent via the sympathetic nerve

Question 34

What are the two ways that the cardiac centre receives information from the SAN?

Answer 34

Chemoreceptors on the walls of the aorta or carotid arteries cluster together to form structure called aortic bodies and the carotid. They are sensitive to changes in blood pH that are a result of changes in CO2 concentration Baroreceptors (specific pressure receptors) are found in the carotid and aortic bodies that are sensitive to changes in blood pressure

Question 35

How does carbon dioxide concentration change the blood pH?

Answer 35

Carbon dioxide dissolves in water to form weak acids (carbonic acids) that can dissociate to release hydrogen ions, therefore the higher the conc. of carbon dioxide dioxide the lower the pH

Question 36

Describe how chemoreceptors in the heart can increase heart rate

Answer 36

Increased carbon dioxide concentrations cause the block pH the decrease This is detected by chemoreceptors, which send more impulses to the cardiac centre in the medulla oblongata, via sensory neurones The cardiac centre increases the frequency of impulses sent in the sympathetic nerve to the SAN. This increases the heart rate. Increased blood flow causes carbon dioxide to be removed by the lungs, so the pH returns to normal and the chemoreceptors in turn reduce their input to the medulla

Question 37

Describe how baroreceptors increase heart rate when blood pressure decreases

Answer 37

Decreased blood pressure is detected by baroreceptors in the aorta and carotid arteries. Sends impulses via sensory neurones to the cardiac centre Causes more frequent impulses to be sent along the sympathetic nerve to the SAN Noradrenaline is released by the sympathetic nerve endings into the SAN, causing heart rate to increase so blood pressure increases

Question 38

Decisive how baroreceptors decrease the heart rate when blood pressures increase?

Answer 38

Baroreceptors in the aorta and carotid arteries detect the increase blood pressure Send impulses via sensory neurones to the cardiac centre Causes more frequent impulses to be sent via the parasympathetic nerve to the SAN Acetylcholine is released by the parasympathetic nerve endings into the SAN Causes heart rate and blood pressure to decrease

Question 39

What is the coordinator in the control of heart rate?

Answer 39

The cardiac centre in the medulla oblongata

Question 40

What happens to the Pacinian corpuscles when the pressure is higher

Answer 40

More sodium channels open, so more sodium ions diffuse into the axon. Greater chance of reaching the action potential threshold, so there is a higher frequency of action potentials