Neurophysiology of Nerve Impulses Essay
1. What happens to the resting membrane potential when extracellular K+ concentration is increased? -The resting membrane potential will become more positive when K+ concentration is increased.
2. Explain why the resting membrane potential had the same value in the cell body and in the axon. -The resting membrane potential has the same value in the cell body and the axon because the typical resting membrane potential is the same throughout the entire neuron.
3. Describe what would happen to the resting membrane potential if the sodium-potassium transport pump was blocked. -If the potassium transport pump was blocked the leakage channels would still be open allowing Na+ to leak in while K+ would be leaking out based on diffusion.
4. Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels. -Increasing extracellular K+ reduces the net diffusion through the leak channels because if there are an increased amount of K+ ions outside of the cell, the amount coming from the leak channels needs to decrease so it can be balanced.
5. Explain why a change in extracellular Na+ did not alter the membrane potential in the resting neuron. -A change in Na+ did not alter the membrane potential in the resting neuron because there are less leakage sodium channels than leakage potassium channels, and more of the potassium channels are open.
1. Define graded potential. How does your data show that stimulation of the olfactory receptor is graded? Graded potential are local changes in membrane potential or short duration. These can be depolarizing which are less negative or hyperpolarizing which are more negative. The data that I collected shows that the olfactory receptor is graded because the resting potential, peak value response, and the amplitude of response are all very close in number.
2. In your experiment which receptors are stimulated by: high pressure? high chemicals? high heat?
-The receptors that are stimulated by high pressure are: Pacinian corpuscle
-The receptors that are stimulated by high chemicals are: Olfactory
-The receptors that are stimulated by high heat are: Free nerve ending
1. Does the action potential increase at R1 (or R2) with increasing voltage? -Both R1 and R2 had increasing action potential with increasing voltage. With 10mv of voltage there was no action potential, but with 20 mv of voltage both R1 and R2 had 100 as their peak value.
2. Explain how your data shows that initiation of an action potential is an all or nothing event. -My data shows that the initiation of an action potential is all or nothing because the response to stimuli only occurs above a certain threshold, and both R1 and R2 responded when the voltage was over a certain amount.
3. What change in membrane potential must happen to trigger an action potential? -The membrane potential must depolarize from the resting voltage of -70mv to a threshold value that is -55mv. When it depolarizes, the channels are able to open.
1. Define the absolute refractory period.
-The period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied
2. What happens to voltage gated Na+ channels during stimulation? refractory period? -During stimulation the voltage gated Na+ channels are
3. What happens to voltage gated K+ channels during stimulation? refractory period ? -During stimulation the voltage gated K+ channels are
4. Explain how an absolute refractory period ensures directionality of action potential propagation. -An absolute refractory period ensures directionality of action potential propagation because once the action potential comes through, that section is in in refractory period and has to wait to go again. This ensures that things keep moving forward because the action potential has nowhere else to go but forward.
5. Looking at your data. Under what conditions is a second action potential generated? -From my data, the conditions that a second action potential requires are a larger interval between stimuli and a smaller stimulus voltage. For example, there was a second action potential when the interval between stimuli was 250 and the stimulus voltage was 20. There wasn’t a second action potential when the interval between stimuli was 60 and the stimulus voltage was 20.
6. Why is it harder to generate a second action potential during the relative refractory period???? -It is harder to generate a second action potential during the relative refractory period because a greater stimulus is required because voltage-gated K+ channels that oppose depolarization are open during this time.
1. Rank the conduction velocity in the axons A, B, C from fastest to slowest.
-A: Type A fibers
-B: Type C fibers
-C: Type B fibers
2. Why did the time between the stimulation and the action potential at R1 differ for each axon? -The time between the simulation and the action potential at R1 differed for each axon because the axon diameter and amount of myelination varied for each axon.
3. The squid utilizes a very large-diameter unmyelineated axon to execute a rapid escape response when it perceives danger. How is this possible, given that the axon is unmyelinated? -The conduction velocity is dependent upon both myelination and the diameter of the axon. The large diameter of the squid axon contributes to its fast reaction.
4. When you burn your finger on a hot stove, you feel sharp, immediate pain, which later becomes slow, throbbing pain. These two types of pain are carried by different pain axons. Speculate on the axonal diameter and extent of myelination of these axons. -The axons that respond to the pain first are myelinated which carries the signal faster. That is why you feel immediate pain. The axons that are active later on, causing the throbbing, are unmyelinated and move slowly.
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