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Questions and Answers
What is the primary reason why no action potential can be elicited during the absolute refractory phase?
What is the primary reason why no action potential can be elicited during the absolute refractory phase?
- The neuron is in a state of hyperpolarization
- The voltage-gated sodium channels are unresponsive (correct)
- The potassium channels are open
- The voltage-gated sodium channels are closed
What is the effect of the potassium outflow during the relative refractory phase?
What is the effect of the potassium outflow during the relative refractory phase?
- It has no effect on the cell's membrane potential
- It makes the inside of the cell more positive
- It makes the inside of the cell more negative (correct)
- It closes the voltage-gated sodium channels
What is the minimum voltage required for the action potential to occur?
What is the minimum voltage required for the action potential to occur?
- -50mV
- -60mV
- -40mV (correct)
- -30mV
What is the mechanism by which action potentials are transmitted down the axon?
What is the mechanism by which action potentials are transmitted down the axon?
What is the result of the depolarization of the neuron during the action potential?
What is the result of the depolarization of the neuron during the action potential?
What is the role of the voltage-gated sodium channels in the axon?
What is the role of the voltage-gated sodium channels in the axon?
During which phase of the action potential can another action potential be elicited with strong stimulation?
During which phase of the action potential can another action potential be elicited with strong stimulation?
What is the effect of the strong stimulation on the neuron during the relative refractory phase?
What is the effect of the strong stimulation on the neuron during the relative refractory phase?
What is the significance of the -40mV threshold in the action potential?
What is the significance of the -40mV threshold in the action potential?
What is the purpose of the voltage-gated sodium channels in the transmission of action potentials?
What is the purpose of the voltage-gated sodium channels in the transmission of action potentials?
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Study Notes
Membrane Potential
- Hyperpolarization: an increase in membrane potential, making the interior of the membrane more negative relative to the outside.
- Depolarization: a decrease in membrane potential, making the interior of the cell less negative.
Action Potential
- An action potential is an extremely fast reversal of a resting membrane potential, making the inside of the membrane more positive relative to the outside.
- Threshold: the point at which the membrane potential reaches -40mV, triggering an action potential.
- All or none property: an action potential either fires at full amplitude or not at all.
Action Potential Characteristics
- The size and amplitude of an action potential are not dependent on the size of the stimulus.
- The action potential is still occurring down the axon, but with smaller strength.
Origin of Action Potential
- Changes in membrane potential can send electrical signals through the axon.
- Action potentials originate in the axon hillock.
Explanation of Action Potential
- The movement of sodium ions into the cell through ion channels generates an action potential.
- The sum of EPSPs and IPSPs determines the direction of the membrane potential change.
Synapses and Local Changes
- Synapses cause local, graded changes in the postsynaptic membrane potential.
- Spatial summation: the summing of potentials from different parts of the cell.
- Temporal summation: the summing of potentials that arrive at the axon hillock at different times.
Refractory Phases
- Absolute refractory phase: a short period after an action potential during which no new action potentials can be produced.
- Relative refractory phase: a period during which only strong stimulation can produce an action potential.
Action Potential Transmission
- Axons have many voltage-gated Na+ channels.
- The action potential is a spike that strongly depolarizes the next segment of the axon, creating a new action potential.
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