6.1/2 Extra Flashcards
(23 cards)
- What is a generator potential?
The change in potential difference across the cell-surface membrane of a receptor as a result of a stimulus.
(If the generator potential is large enough it will reach threshold and result in an action potential in the sensory neurone)
Draw PC
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- Write a flow-chart to describe what happens in a Pacinian Corpuscle to generate an action potential in the sensory neurone:
- Pressure from touch causes the corpuscle to change shape
- Stretches the membrane of the neurone
- This causes the stretch-mediated Na+ channels to widen and open
- So Na+ ions flood into the axon
- The axon becomes depolarised
- A generator potential is established
- If threshold is reached Na+ VG channels open
- Na+ diffuse in and cause an action potential
- What is the retina and where is it found?
The retina is the layer of photoreceptor cells found at the back of the eye
- Where are rod cells found in the eye?
In the periphery of the retina
- Where are cone cells found in the eye?
In the fovea
Rod cells Cone cells
Name of pigment Rhodopsin Iodopsin
What happens to pigment when it absorbs light? What’s the consequence? Is broken down to form retinal and opsin
This causes an impulse to be sent down the optic nerve to the brain Is broken down
This causes an impulse to be sent down the optic nerve to the brain
Which wavelength of light does it absorb? A broad range of wavelengths There are three types of iodopsin.
One that absorbs red light.
One that absorbs green light.
One that absorbs blue light.
Which pigment requires more light to be broken down? Requires less light (so more sensitive) Requires more light (so it is not so much use at low light levels)
Rod cells Cone cells
Name of pigment Rhodopsin Iodopsin
What happens to pigment when it absorbs light? What’s the consequence? Is broken down to form retinal and opsin
This causes an impulse to be sent down the optic nerve to the brain Is broken down
This causes an impulse to be sent down the optic nerve to the brain
Which wavelength of light does it absorb? A broad range of wavelengths There are three types of iodopsin.
One that absorbs red light.
One that absorbs green light.
One that absorbs blue light.
Which pigment requires more light to be broken down? Requires less light (so more sensitive) Requires more light (so it is not so much use at low light levels)
- Write an equation to describe what happens to rhodopsin in the light and in the dark
In the light: Rhodopsin retinal + opsin
(when this happens, we say that rhodopsin is ‘bleached’)
In the dark: retinal + opsin rhodopsin
- Why do rod cells give greater visual sensitivity?
Because several rod cells converge on the same bipolar cell
This is a type of spatial summation
This means that even in low light intensities, threshold is more likely to be exceeded in the bipolar cell so an impulse will be sent through the optic nerve to the brain
AND
Rhodopsin needs a lower intensity of light to bebroken down
- Why do cone cells give less visual sensitivity?
Because there is only one cone cell synapsed to each bipolar cell
There is no spatial summation
This means that in low light intensities, threshold is not likely to be reached or exceeded in the bipolar cell so no impulse is sent through the optic nerve to the brain
- Why do cone cells give greater visual acuity?
Because there is only one cone cell synapsed to each bipolar cell
- Why do rod cells give less visual acuity?
Because several rod cells converge on the same bipolar cell
This is a type of spatial summation
(Therefore the light hitting several points in the retina result in the same impulse being transmitted to the brain)
- What does myogenic mean?
‘Myogenic’ means nervous stimulation originating in the muscle tissue (rather than from neurones).
This means that the muscle of the heart is able to generate its own electrical impulses without the need for stimulation from nerves
- Write a summary of how the cardiac cycle is controlled by the SAN and the AVN
- The SAN acts as a pacemaker and initiates the heartbeat
- The SAN sends a wave of electrical impulses across the atria, causing them to contract
- The non-conducting tissue between atria and ventricles prevents the impulse reaching the ventricles
- There is a short delay at the AVN, allowing the atria to empty and the ventricles to fill before they contract
- The AVN sends a wave of electrical activity down the Bundle of His and up the Purkyne fibres
- This causes the ventricles to contract from the base upwards
- Where are the chemoreceptors and pressure receptors which are involved in controlling heart rate found?
In the aortic arch and the carotid artery
- What is the effect of impulses from the parasympathetic nerve on heart rate? Which neurotransmitter is involved?
Decreases heart rate
The nerve releases acetylcholine onto the SAN
- What is the effect of impulses from the sympathetic nerve on heart rate?
Increases heart rate
The nerve releases noradrenaline onto the SAN
- Write a flow-chart to describe what happens if there is an increase in CO2 concentration in the blood (e.g. following exercise)
- Decrease in pH detected by chemoreceptors in aortic arch and carotid artery
- More Impulses sent to the medulla
- Higher frequency of impulses sent down the sympathetic nerve to the SAN
- So more noradrenlin released onto the SAN
- So the SAN produces a higher frequency of impulses and heart rate increases
- Write a flow-chart to describe what happens if there is a decrease in CO2 concentration in the blood
- Increase in pH detected by chemoreceptors in aortic arch and carotid artery
- fewer Impulses sent to the medulla
- Higher frequency of impulses sent down the parasympathetic nerve to the SAN
- So more acetylecholine is released onto the SAN
- So the SAN produces a lower frequency of impulses and heart rate decreases
- Write a flow-chart to describe what happens if there is an increase blood pressure
- increase in blood pressure detected by pressure receptors in aortic arch and carotid artery
- fewer Impulses sent to the medulla
- Higher frequency of impulses sent down the parasympathetic nerve to the SAN
- So more acetylcholine released onto the SAN
- So the SAN produces a lower frequency of impulses and heart rate decreases
- Write a flow-chart to describe what happens if there is a decrease blood pressure
- increase in blood pressure detected by pressure receptors in aortic arch and carotid artery
- more impulses sent to the medulla
- Higher frequency of impulses sent down the sympathetic nerve to the SAN
- So more noradrenalin released onto the SAN
- So the SAN produces a higher frequency of impulses and heart rate increases
- Describe the series of events which take place at a neuromuscular junction
- Depolarization causes Ca2+ voltage gated channels in the pre-synaptic knob open
- Ca2+ move in and cause vesicles to move towards the presynaptic membrane and fuse with it
- Acetylcholine is released into the neuromuscular junction
- Acetylcholine binds to receptors on the sarcolemma, so the ion channels open
- Na+ flood into the sarcolemma
- Depolarization spreads along the sarcolemma and down the t-tubules
- This causes the Ca2+ voltage gated channels on the sarcoplasmic reticulum to open
- So Ca2+ ions are released into the sarcoplasm from the sarcoplasmic reticulum allowing muscle contraction to take place
- Compare and contrast transmission across a cholinergic synapse and across a neuromuscular junction
Cholinergic Synapse Neuromuscular junction
Neurone to neurone Neurone to muscle
An action potential occurs in the post-synaptic neurone There is no action potential in the muscle/sarcolemma
The response in the post-synaptic neurone could be excitatory or inhibitory The response in the muscle is always excitatory
A cholinergic synapse always uses acetylcholine as the neurotransmitter Some neuromuscular junctions have different neurotransmitters
