NSCS 307 Exam 2 Study Guide 2026: Action
Potentials, Myelination & Ion Channels
Description:
Struggling to master neurophysiology for your NSCS 307 Exam 2? This targeted 2026 study
guide delivers clear, concise explanations of key concepts—from action potential propagation
and refractory periods to the role of myelination and voltage-gated ion channel structure. We
break down complex topics like saltatory conduction, length and time constants, and
channelopathies such as Multiple Sclerosis and Dravet Syndrome. Each answer is paired
with a straightforward explanation to ensure you not only memorize but truly understand the
material. Whether you're reviewing for finals or prepping for a quiz, this guide is tailored to help
you excel.
Stop stressing and start mastering—download your free copy now and ace your exam with
confidence!
, Neurophysiology Exam 2 Study Guide: Action Potentials & Ion
Channels
1. Explain the process by which an electrical signal travels along a neuronal axon.
a) Potassium ions enter the axon, followed by sodium ions exiting, repeating this cycle.
b) Sodium channels open at one point, and the resulting depolarization passively spreads to the
next segment.
c) A wave of depolarization is actively regenerated at successive segments along the axon.
d) The action potential diffuses from the cell body to the axon terminals without ion channels.
Answer: c) A wave of depolarization is actively regenerated at successive segments along the
axon.
Explanation: Action potential propagation is not passive diffusion. When one segment of the
axon depolarizes due to sodium influx, it creates a local current that depolarizes the adjacent
segment. If this depolarization reaches the threshold voltage, it triggers voltage-gated sodium
channels in that new segment to open, regenerating the action potential. This cycle of local
current flow and active regeneration continues down the entire length of the axon.
2. What defines the absolute refractory period, and what is its primary biophysical cause?
a) A period of reduced excitability caused by the slow closing of potassium channels.
b) A period where a stronger-than-normal stimulus can trigger an action potential, caused by
sodium channel deactivation.
c) A period where no new action potential can be initiated, caused by the temporary inactivation
of voltage-gated sodium channels.
d) A period of hyperexcitability caused by an overshoot of potassium efflux.
Answer: c) A period where no new action potential can be initiated, caused by the temporary
inactivation of voltage-gated sodium channels.
Explanation: Immediately after an action potential, the ball-and-chain inactivation gates of
voltage-gated sodium channels block the pore. These channels cannot be re-opened, regardless of
stimulus strength, until the membrane repolarizes, which allows the inactivation gate to swing
away. This ensures the action potential travels in one direction and limits the maximum firing
rate of the neuron.
, 3. In a typical neuron, can an action potential propagate backward from the axon hillock into the
dendrites? Explain.
a) Yes, because the axon hillock has the highest density of voltage-gated sodium channels.
b) No, because the absolute refractory period in the recently activated axon hillock prevents
backward propagation.
c) Yes, but only if the stimulus is applied directly to the axon terminal.
d) No, because dendrites lack voltage-gated sodium channels entirely.
Answer: b) No, because the absolute refractory period in the recently activated axon hillock
prevents backward propagation.
Explanation: Action potentials are initiated at the axon hillock and propagate forward along the
axon. The membrane segment just behind the action potential (toward the cell body) is in its
absolute refractory period due to sodium channel inactivation. This refractory state makes it
impossible for the depolarization to spread backward, enforcing one-way communication.
4. Which structural feature of a myelinated axon is essential for saltatory conduction?
a) Continuous coverage of myelin along the entire axon length.
b) A high density of voltage-gated sodium channels under the myelin sheath.
c) Periodic gaps called Nodes of Ranvier with a high concentration of voltage-gated sodium
channels.
d) Schwann cells that completely engulf the axon terminal.
Answer: c) Periodic gaps called Nodes of Ranvier with a high concentration of voltage-gated
sodium channels.
Explanation: Myelin acts as an insulator, preventing ion flow across the membrane it covers.
The Nodes of Ranvier are unmyelinated gaps where voltage-gated sodium channels are highly
concentrated. The action potential "jumps" from node to node, as the depolarization spreads
rapidly through the insulated internode and is actively regenerated only at each node.
5. Demyelination, as seen in Multiple Sclerosis, can lead to action potential failure. Which
biophysical property change best explains this failure?
a) An increase in the time constant, slowing the membrane's charging rate.
b) A decrease in the length constant, causing the depolarizing current to decay too quickly over
Potentials, Myelination & Ion Channels
Description:
Struggling to master neurophysiology for your NSCS 307 Exam 2? This targeted 2026 study
guide delivers clear, concise explanations of key concepts—from action potential propagation
and refractory periods to the role of myelination and voltage-gated ion channel structure. We
break down complex topics like saltatory conduction, length and time constants, and
channelopathies such as Multiple Sclerosis and Dravet Syndrome. Each answer is paired
with a straightforward explanation to ensure you not only memorize but truly understand the
material. Whether you're reviewing for finals or prepping for a quiz, this guide is tailored to help
you excel.
Stop stressing and start mastering—download your free copy now and ace your exam with
confidence!
, Neurophysiology Exam 2 Study Guide: Action Potentials & Ion
Channels
1. Explain the process by which an electrical signal travels along a neuronal axon.
a) Potassium ions enter the axon, followed by sodium ions exiting, repeating this cycle.
b) Sodium channels open at one point, and the resulting depolarization passively spreads to the
next segment.
c) A wave of depolarization is actively regenerated at successive segments along the axon.
d) The action potential diffuses from the cell body to the axon terminals without ion channels.
Answer: c) A wave of depolarization is actively regenerated at successive segments along the
axon.
Explanation: Action potential propagation is not passive diffusion. When one segment of the
axon depolarizes due to sodium influx, it creates a local current that depolarizes the adjacent
segment. If this depolarization reaches the threshold voltage, it triggers voltage-gated sodium
channels in that new segment to open, regenerating the action potential. This cycle of local
current flow and active regeneration continues down the entire length of the axon.
2. What defines the absolute refractory period, and what is its primary biophysical cause?
a) A period of reduced excitability caused by the slow closing of potassium channels.
b) A period where a stronger-than-normal stimulus can trigger an action potential, caused by
sodium channel deactivation.
c) A period where no new action potential can be initiated, caused by the temporary inactivation
of voltage-gated sodium channels.
d) A period of hyperexcitability caused by an overshoot of potassium efflux.
Answer: c) A period where no new action potential can be initiated, caused by the temporary
inactivation of voltage-gated sodium channels.
Explanation: Immediately after an action potential, the ball-and-chain inactivation gates of
voltage-gated sodium channels block the pore. These channels cannot be re-opened, regardless of
stimulus strength, until the membrane repolarizes, which allows the inactivation gate to swing
away. This ensures the action potential travels in one direction and limits the maximum firing
rate of the neuron.
, 3. In a typical neuron, can an action potential propagate backward from the axon hillock into the
dendrites? Explain.
a) Yes, because the axon hillock has the highest density of voltage-gated sodium channels.
b) No, because the absolute refractory period in the recently activated axon hillock prevents
backward propagation.
c) Yes, but only if the stimulus is applied directly to the axon terminal.
d) No, because dendrites lack voltage-gated sodium channels entirely.
Answer: b) No, because the absolute refractory period in the recently activated axon hillock
prevents backward propagation.
Explanation: Action potentials are initiated at the axon hillock and propagate forward along the
axon. The membrane segment just behind the action potential (toward the cell body) is in its
absolute refractory period due to sodium channel inactivation. This refractory state makes it
impossible for the depolarization to spread backward, enforcing one-way communication.
4. Which structural feature of a myelinated axon is essential for saltatory conduction?
a) Continuous coverage of myelin along the entire axon length.
b) A high density of voltage-gated sodium channels under the myelin sheath.
c) Periodic gaps called Nodes of Ranvier with a high concentration of voltage-gated sodium
channels.
d) Schwann cells that completely engulf the axon terminal.
Answer: c) Periodic gaps called Nodes of Ranvier with a high concentration of voltage-gated
sodium channels.
Explanation: Myelin acts as an insulator, preventing ion flow across the membrane it covers.
The Nodes of Ranvier are unmyelinated gaps where voltage-gated sodium channels are highly
concentrated. The action potential "jumps" from node to node, as the depolarization spreads
rapidly through the insulated internode and is actively regenerated only at each node.
5. Demyelination, as seen in Multiple Sclerosis, can lead to action potential failure. Which
biophysical property change best explains this failure?
a) An increase in the time constant, slowing the membrane's charging rate.
b) A decrease in the length constant, causing the depolarizing current to decay too quickly over
