Action potential mechanisms, synaptic transmission, and sensory receptor physiology tested on USMLE Step 1.
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- What is the typical resting membrane potential of a neuron?
- About -70 mV
- Which ion channels open first during the depolarization phase of an action potential?
- Voltage-gated Na+ channels
- What two events cause repolarization after an action potential?
- Voltage-gated Na+ channels inactivate and voltage-gated K+ channels open
- What is the threshold potential?
- The membrane voltage at which enough Na+ channels open to make depolarization self-sustaining, triggering an action potential
- What happens if a stimulus arrives during the absolute refractory period?
- No new action potential can be generated, no matter how strong the stimulus
- What is the relative refractory period?
- A period after the absolute refractory period when only a stronger-than-normal stimulus can trigger another action potential
- What causes the absolute refractory period?
- Inactivation of voltage-gated Na+ channels
- Using the Nernst equation, what is the approximate equilibrium potential for Na+ in a neuron?
- About +60 mV
- Using the Nernst equation, what is the approximate equilibrium potential for K+ in a neuron?
- About -90 mV
- What does the Na+/K+ ATPase pump transport per cycle?
- 3 Na+ out of the cell and 2 K+ into the cell
- How does myelination increase nerve conduction velocity?
- It enables saltatory conduction, where the action potential jumps between nodes of Ranvier
- Where are voltage-gated Na+ channels concentrated on a myelinated axon?
- At the nodes of Ranvier
- How does increasing axon diameter affect conduction velocity?
- It increases conduction velocity by reducing internal (axoplasmic) resistance
- How does hyperkalemia affect the resting membrane potential of excitable cells?
- It depolarizes the resting membrane potential, making it less negative
- What is the mechanism of action of local anesthetics such as lidocaine?
- They block voltage-gated Na+ channels, preventing action potential propagation