26: Receptors

Question 1

Define Stimulus:

Answer 1

• detectable change in the environment that is capable of causing a response by the nervous system

Question 2

How do Receptors work?

Answer 2

• specific stimulus causes the membrane potential to change via depolarisation
• the more intense the stimulus, the greater the generator potential
• if the membrane potential exceeds the threshold value, it will cause an action potential to be produced
• this can then be transmitted to a sensory neurone via synaptic transmission
• a larger generator potential, increases the frequency of action potentials in the sensory neurone

Question 3

What us a Pacinian Corpuscle?
How do they work?

Answer 3

-mechanoreceptor - allows you to detect firm pressure changes
- stretch mediated (gated) Na+ protein channels, are found in the membrane of the sensory nerve ending
- when under pressure, the membrane is stretched and this causes the channels to change shape and open
- this leads to Na+ diffusing into the axon
- this leads to the generator potential which, if above the threshold leads to an action potential
- the greater the pressure, the greater the generator potential

Question 4

What happens in the Pacinian Corpuscle when no pressure?
What is the function of the gel-filled lamellae

Answer 4

• Na+ channels are too narrow for the diffusion of Na+
• the gel-filled lamellae, filter the stimuli so they reform the membrane from the deformation from the action potential

Question 5

Name 2 Photoreceptors:
Where are the 2 Photoreceptors located?
What do they Synapse with?

Answer 5

1. rods + cones
2. cones are mainly in the fovea, whilst the rods are in the periphery of the retina
3. they both synapse with bipolar neurone, which then synapses with a sensory neurone (ganglion cells), which bundle together to form the optic nerve

Question 6

Describe Rod Cells functionality:

Answer 6

• they contain the pigment rhodopsin, which is very sensitive to light
• this breaks down when it absorbs light, leading to action potentials in bipolar neurones
• then in the sensory neurone
• when the stimulation from light ends, the rhodopsin reforms (requiring ATP), spatial summation

Question 7

What happens to Rods in Bright Light?

Answer 7

• in bright light, the breakdown of rhodopsin happens faster than rhodopsin can reform, so the rod cells will not function and are bleached
• this is when the eyes are light-adapted

Question 8

Describe Cone Cells Functionality:

Answer 8

• pigment is one of 3 types of iodopsin, which is sensitive to high light intensities
• they absorb light of different wavelengths, blue (445nm), green (535nm) & red (575nm)
• these different wavelengths break down iodopsin, leading to action potentials in the bipolar neurone
• then in the sensory neruones
• brain interprets colour according to the proportion of each type of cone stimulated
• iodopsin reforms (requiring ATP), temporal summation

Question 9

Why is colour vision poor in the dark?

Answer 9

• iodopsin does not break down in dim light

Question 10

Why does it take a while before you can see reasonably well after entering a dark room?

Answer 10

• takes time for rhodopsin to reform

Question 11

Why do Rod Cells have Retinal Convergence?

Answer 11

• many rod cells connect with the same bipolar neurone
• if several rods are stimulated at the same time, (spatial summation), there is a greater chance of producing an action potential
• this gives rods great sensitivity to low light intensity

Question 12

Do Cone cells show Retinal Convergence?
Why?

Answer 12

• no because they are not sensitive to light at low levels

Question 13

Why do Cone cells have High Visual Acuity?

Answer 13

• image has high resolution, and fine detail can be seen
• this is due to each cone only synapsing with a separate bipolar neurone, which in turn generates impulses in separate neurones in the optic nerve (temporal summation)
• this is why cone cells have sensitivity to only high light intensity

Question 14

Describe the Events that control the Cardiac Cycle:

Answer 14

1. A wave of electrical impulse/activity is sent to the Sinoatrial Node (SAN)
2. This spreads across both atria, causing atrial contraction
3. A band of non-conducting tissue prevents the impulse from passing into the ventricles directly
4. The electrical activity/impulse reaches the AV node, where it is delayed
5. This delay allows the atria to fully empty, and the ventricles to fill with blood BEFORE they contract
6. After this delay, the impulses spread down the ventricles into the Bundle Of His
7. The impulse is then transmitted to the base (apex) of ventricles, where it is passed up the Purkyne Fibres
8. This causes the ventricles to contact from the base upwards
9. Blood is forced up arteries

Question 15

Cardiac Muscle is _______, meaning it can _______ on its own, but the rate __ _________ is controlled by impulses from the ____ _____ _____

Answer 15

• myogenic
• contract
• of contraction
• Autonomic Nervous System

Question 16

Describe the 2 Nerves used in control of Heart Rates:
1. names
2. neurotransmitter
3. function

Answer 16

1. sympathetic nerve:
   
   • noradrenaline
   • excitatory
2. parasympathetic nerve:
   
   • acetylcholine
   • inhibitory

Question 17

Describe the Control of the Heart Rate:

Answer 17

1. controlled by the cardiac centre in the medulla oblongata
2. they send impulses to the SAN via 2 different nerves, that are apart of the autonomic nervous system
3. the sympathetic nerve increases the heart rate, and the parasympathetic nerve decreases the heart rate
4. more frequent impulses in the sympathetic nerve and/or fewer impulses in the parasympathetic nerve will result in a faster heart rate
5. conversely, more frequent impulses in the parasympathetic nerve and/or fewer impulses in the sympathetic nerve will result in a slower heart rate

Question 18

Describe the location and function:
- Chemoreceptors
- Baroreceptors

Answer 18

chemoreceptors:
- found in the carotid artery (supplies blood to brain) and aorta
- receptors cluster together to form carotid and aortic bodies
- sensitive to changes in blood pH, resulting from changes in CO2 concentration

baroreceptors:
- found in carotid + aortic bodies
- sensitive to changes in blood pressure

Question 19

Describe the Control of Blood pH by Chemoreceptors:

Answer 19

• blood CO2 increases, H+ concentration increases, so pH decreases
• detected by chemoreceptors, which send more impulses to the cardiac centre in the medulla via sensory neurones
• this causes an increase in frequency of impulses via sympathetic nerves to the SAN, increasing heart rate
• increased blood flow leads to more CO2 being removed by lungs, turning pH back to normal
• chemoreceptors then reduce impulses to medulla, therefore reducing impulses to SAN via sympathetic nerve, therefore bringing heart rate back to normal

Question 20

Describe the role of Baroreceptors in the control of Blood Pressure:
(fall in blood pressure)

Answer 20

• fall in blood pressure in aorta detected by baroreceptors
• impulses carried in sensory neurone to cardiac centre in medulla
• more frequent impulses along sympathetic nerve to the SAN
• noradrenaline releases from sympathetic nerve endings onto SAN
• SAN increases its rate of activity causing an increase in heart rate + blood pressure

Question 21

Describe the role of Baroreceptors in the control of Blood Pressure:
(gain in blood pressure)

Answer 21

• fall in blood pressure in aorta detected by baroreceptors
• impulses carried in sensory neurone to cardiac centre in medulla
• more frequent impulses along parasympathetic nerve to the SAN
• acetylcholine releases from parasympathetic nerve endings onto SAN
• SAN decreases its rate of activity causing an decrease in heart rate + blood pressure