Receptors Flashcards
What are receptors?
Specialised cells that detect a specific stimulus and generate electrical impulses in response
Describe the general action of receptors
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
What are pacinian corpuscles? Where are they found
A type of mechanoreceptor found deep in the skin, they response to changes in pressure
Fingers, ligaments, joints, tendons
What are mechanoreceptors?
Receptors that respond to changes in pressure (the stimulus)
Describe the structure of pacinian corpuscles
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
How do pacinian corpuscles respond to changes in pressure?
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
In pacinian corpuscles, why are more action potentials generated when pressure is released?
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
In pacinian corpuscles, what are the gel filled lamellae used for?
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
What is the eye? What are the components of the eye?
A sense organ, that contains photoreceptors in the retina
Optical nerve
Retina
Fovea
Iris
Lens
Pupil
Cornea
Vitreous gel
What are photoreceptors?
Receptors that respond to light stimuli
Why is there a blind spot in the retina?
Where there are no photoreceptors, because this is where the optical nerve leaved the retina
What are the two types of pohotoreceptors in the retina, and the differences between them?
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
Explain how rod cells in the receptor detect light
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)
Why do rod cells not function well in bright light?
In bright light, rhodopsin breaks down much quicker than it can reform. Therefore they are said to be bleached and cannot function
Eyes become light adapted
Why does it take time for your eyes to see in dark spaces?
Cone cells do not brea down in dim light
In rod cells, it takes time for rhodopsin to reform
Explain how cone cells detect coloured light
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
Explain what the trichromatic theory is
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
What is red-green colour blindness? How is it inherited
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
What is the structure of the retina?
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
How does the structure of rod and cone cells differ in the retina?
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
Why are rod cells more sensitive than cone cells?
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.
What is visual acuity?
The ability to tell two points apart that are close together
Why do cone cells have visual acuity, but rod cells do not?
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
State two reasons why rod cells have a greater sensitivity than cone cells
Rhodopsin in cone cells breaks down in dim light, iodopsin does not
Rod cells have retinal convergence, cone cells do not
State two reasons why cone cells ahve a greater visual acuity than rod cells
There is a very high density of cone cells In the fovea
Cone cells have a 1:1 ratio with bipolar neurones
What is the autonomic nervous system? What systems is it made up of?
Regulates the internal glands and muscles
Made up of two antagonistic systems- the sympathetic system and parasympathetic system
Why are the sympathetic and parasympathetic systems antagonistic?
They oppose each other
The sympathetic prepares for activity
Parasympathetic slows down and conserves energy
What are the neurotransmitters used In the two systems of the ANS?
Sympathetic- noradrenaline
Parasympathetic- acetylcholine
What are the general effects of the two systems of the ANS?
Sympathetic- excitatory
Parasympathetic- inhibitory
In the ANS, when are the sympathetic and parasympathetic systems dominant?
Sympathetic is dominant during stress, danger and excitement
Parasympathetic is dominant during rest
Describe the myogenic stimulation of the cardiac cycle
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
How is the rate of heartbeat changed?
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
Using different impulses from the cardiac centre in the medulla oblongata, how can heart rate be increased or decreased?
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
What are the two ways that the cardiac centre receives information from the SAN?
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
How does carbon dioxide concentration change the blood pH?
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
Describe how chemoreceptors in the heart can increase heart rate
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 cycle 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
Describe how baroreceptors increase heart rate when blood pressure decreases
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
Decisive how baroreceptors decrease the heart rate when blood pressures increase?
Baroreceptors in the aorta and carotid arteries detect the decreased 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
What is the coordinator in the control of heart rate?
The cardiac centre in the medulla oblongata
