ANATOMY FINAL PRACTICAL – Flashcards
Unlock all answers in this set
Unlock answersquestion
Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels.
answer
increasing the extracellular K+ reduces the steepness of the concentration gradient and so less K+ diffuses out of the neuron.
question
Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value.
answer
The membrane potential became less negative because less K+ diffused out. If more K+ stays in it is more positive or less negative.
question
Explain why a change in extracellular Na+ did not alter the membrane potential in the resting neuron.
answer
There are less Na+ leakage channels than K+ leakage channels, and more K+ leakage channels are open.
question
Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
answer
A change in K+ conductance would have a greater effect on the resting membrane potential than a change in Na+ conductance would due to the greater number of K+ channels.
question
Sensory neurons have a resting membrane potential based on the efflux of K+ ions (as demonstrated in Activity 1.) What passive channels are likely found in the membrane of the olfactory receptor, in the membrane of the Pacinian corpuscle, and in the membrane of the free nerve ending?
answer
The efflux of K+ ions is maintained by passive K+ channels.
question
What is meant by the term graded potential?
answer
Graded potentials are brief, localized changes in the membrane potential that can be either depolarizing or hyperpolarizing.
question
Identify which of the stimulus modalities would induce the largest amplitude receptor potential in the Pacinian corpuscle.
answer
The moderate intensity pressure modality would induce a receptor potential of the largest magnitude in the pacinian corpuscle.
question
identify which of the stimulus modalities would induce the largest amplitude receptor potential in the olfactory receptors.
answer
The moderate intensity chemical modality would induce a receptor potential of the largest magnitude in the olfactory receptors.
question
The olfactory receptor also contains a membrane protein that recognizes isoamyl acetate and, via several other molecules, transduces the odor stimulus into a receptor potential. Does the Pacinian corpuscle likely have this isoamyl acetate receptor protein? Does the free nerve ending likely have this isoamyl acetate receptor protein?
answer
The Pacinian corpuscle and the free nerve ending are not likely to have this receptor protein because they did not respond to chemical stimuli in activity 2.
question
What type of sensory neuron would likely respond to a green light?
answer
Photosensory neurons would likely respond to a green light.
question
Define the term threshold as it applies to an action potential.
answer
Threshold is the voltage that must be reached in order to generate an action potential.
question
What change in membrane potential (depolarization or hyper polarization) triggers an action potential?
answer
A depolarization in the membrane potential results in an action potential. The membrane potential must become less negative in order to trigger an action potential.
question
How did the action potential at R1 (or at R2) change as you increased the stimulus voltage above the threshold voltage?
answer
The action potential didn't change as the stimulus voltage increased. This is because once the threshold is met, the even is all or none, not graded.
question
What part of a neuron was investigated in this activity?
answer
The trigger zone was investigated. This is where the axon hillock and the initial segment come together.
question
What does TTX do to voltage-gated Na+ channels?
answer
TTX blocks the diffusion of Na+ through voltage-gated Na+ channels. This blockage is irreversible.
question
What does lidocaine do to voltage-gated Na+ channels? How does the effect of lidocaine differ from the effect of TTX?
answer
Lidocaine blocks the diffusion of Na+ through voltage-gated Na+ channels. The difference between TTX and lidocaine is that lidocaine's effect is reversible.
question
Lidocaine blocks the diffusion of Na+ through voltage-gated Na+ channels. The difference between TTX and lidocaine is that lidocaine's effect is reversible.
answer
With a compound action potential, the results would not necessarily be zero because some axons could remain unaffected.
question
Define the absolute refractory period
answer
The absolute refractory period is the time in which no action potential can be generated regardless of the strength of the stimulus.
question
How did the threshold for the second action potential change as you further decreased the interval between the stimuli?
answer
The threshold for the second action potential will be higher, which indeed requires increased strength in the stimulus.
question
Why is it harder to generate a second action potential during the relative refractory period?
answer
Voltage gated K+ channels that oppose depolarization are open during this time, this opposition requires a stronger stimulus.
question
How did the conduction velocity in the C fiber compare with that in the B fiber?
answer
At 3omv the C fiber fiber was slower than the B fiber because the C fiber has a small diameter and less myelination
question
How did the conduction velocity in the B fiber compare with that in the A fiber?
answer
At 30mv the B fiber was 7.78 m/s slower than the A fiber.
question
What is the effect of axon diameter on conduction velocity?
answer
Axon diameter is positively correlated with conduction velocity.
question
What is the effect of the amount of myelination on conduction velocity?
answer
Conduction velocity is positively correlated with the extent of myelination
question
Why did the time between the stimulation and the action potential at R1 differ for each axon?
answer
The time between the stimulation and action potential at R1 differed for each axon because each differed in diameter and extent of myelination
question
Why did you need to change the timescale on the oscilloscope for each axon? pa
answer
The timescale needed to be changed for each axon because as conduction velocity slowed a longer time scale was required to capture the action potential.
question
When the stimulus intensity is increased, what changes: the number of synaptic vesicles released or the amount of neurotransmitter per vesicle?
answer
Increasing stimulus intensity results in a greater number of synaptic vesicles being released.
question
How does Mg2+ block the effect of extracellular calcium on neurotransmitter release?
answer
Magnesium acts as an antagonist to calcium in the nervous system
question
Why is the resting membrane potential the same value in both the sensory neuron and the interneuron?
answer
The resting membrane potential is the same value in both sensory and interneurons because the potential is generally typical of neurons.
question
Describe what happened when you applied a very weak stimulus to the sensory receptor.
answer
A small depolarizing response occurred at R1 with no depolarization recorded by downstream sensors.
question
Describe what happened when you applied a moderate stimulus to the sensory receptor.
answer
A depolarizing response occurred at R1 and R3 and action potentials occurred at R2 and R4.
question
Identify the type of membrane potential (graded receptor potential or action potential) that occurred at R1, R2, R3, and R4 when you applied a moderate stimulus.
answer
Graded receptor potentials occurred at R1 and R3, while action potentials occurred at R2 and R4.
question
Describe what happened when you applied a strong stimulus to the sensory receptor.
answer
A relatively larger depolarizing response occurred at R1 and R3, with action potentials recorded at R2 and R4.
question
an action potential is all or nothing
answer
this means that the action potential will either happen or not happen at all. it cannot slightly happen.
question
A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (a compound action potential). Would the response at R2 after lidocaine application necessarily by zero? Why or why not?
answer
Given compound action potential and that some nerves are less sensitive to lidocaine, the response at R2 after lidocaine application would not necessarily be zero because some of the axons may not be sensitive to lidocaine
question
Why are fewer action potentials recorded at R2 when TTX is applied between R1 and R2? How well did the results compare with your prediction?
answer
Fewer action potentials are recorded at R2 when TTX is applied between R1 and R2 because it prevents propagation of the action potential by blocking voltage-gated Na+ channels.
The same applies when lidocaine is applied between R1 and R2.
question
Pain-sensitive neurons (nociceptors) conduct action potentials from the skin or teeth to sites in the brain involved in pain perception. Where should a dentist inject lidocaine to block pain perception?
answer
A dentist should inject lidocaine near the receptors of nociceptors.
question
Define inactivation as it applies to a voltage-gated Na+ channel.
answer
Voltage-gated Na+ channels are inactivated when they no longer allow Na+ to diffuse through.
question
Why are multiple action potentials generated in response to a long stimulus that is above threshold?
answer
Multiple action potentials are generated in response to a long stimulus that is above threshold provided the length of stimulus is greater than the relative refractory period and the intensity exceeds threshold.
question
Why does the frequency of action potentials increase when the stimulus intensity increases? How well did the results compare with your prediction?
answer
The frequency of action potentials increases with stimulus intensity because the increasing stimulus intensity can trigger additional action potentials within the relative refractory period.
question
How does threshold change during the relative refractory period?
answer
Threshold increases during the relative refractory period
question
What is the relationship between the interspike interval and the frequency of action potentials?
answer
The relationship between the interspike interval and the frequency of action potentials is reciprocal.
question
What happened to the amount of neurotransmitter release when you switched from the control extracellular fluid to extracellular fluid with no Ca2+?
answer
decreased
question
What happened to the amount of neurotransmitter release when you switched from the extracellular fluid with no Ca2+ to the extracellular fluid with low Ca2+?
answer
increased
question
How did neurotransmitter release in the Mg2+ extracellular fluid compare to that in the control extracellular fluid?
answer
less than
