18 Questions
What happens during the rising phase of the action potential?
Threshold is crossed, membrane potential increases, Na⁺ channels open, Na⁺ rushes in, cytosol becomes positive, action potential is triggered.
Describe the falling phase of the action potential.
Na⁺ channels become inactivated, K⁺ channels open, K⁺ leaves the cell, cytosol becomes more negative.
What occurs during hyperpolarization/undershoot phase of the action potential?
Voltage-gated K⁺ channels remain open, K⁺ continues to leave the cell, membrane becomes more negative than the resting potential.
Explain the All-or-none Law in relation to action potentials.
Action potentials either occur fully or not at all, regardless of the stimulus strength.
What is the refractory period in the context of action potentials?
Refractory period is a brief time after an action potential when the neuron is resistant to firing another action potential.
How do voltage-gated Na⁺ channels contribute to the speed of impulse conduction?
Voltage-gated Na⁺ channels opening allow for rapid depolarization and propagation of the action potential.
What is an action potential?
Nerve impulse that travels rapidly along an axon in response to stimuli.
What are the two types of voltage-gated channels involved in generating an action potential?
i. Voltage-gated sodium ion (Na⁺) channels, ii. Voltage-gated potassium ion (K⁺) channels
What happens during depolarization in the context of an action potential?
A stimulus opens some voltage-gated Na⁺ channels, leading to Na⁺ influx into the cell and membrane depolarization.
Describe the resting state of a neuron.
Most voltage-gated sodium (Na⁺) and potassium (K⁺) channels are closed, maintaining a membrane potential around -70mV.
What is the threshold membrane potential that triggers an action potential?
-50 mV
What is the role of ligand-gated channels in neurotransmission?
Ligand-gated channels open or close in response to specific neurotransmitters binding to them.
What is the role of Na+ in the propagation of action potentials?
Na+ entering the cell depolarizes the next neighboring region above threshold, producing a new action potential in the forward direction.
Why can't an action potential induce another action potential in the previous region/behind?
The previous region undergoes repolarization followed by a refractory period.
Describe how an action potential is transmitted along an axon.
An action potential is transmitted as a wave of depolarization that travels down the axon.
What happens as an action potential progresses along the axon?
Repolarization occurs quickly behind it.
Explain the concept of wave of depolarization in relation to action potentials.
Action potential is regenerated along an axon, creating a wave of depolarization.
How does the termination of neurotransmission occur?
Neurotransmitters are removed from the synaptic cleft or degraded to terminate neurotransmission.
Study Notes
Action Potential
- An action potential is a nerve impulse that travels rapidly along an axon in response to stimuli, involving changes in membrane potential from -70 mV to +40 mV.
- It involves the opening and closing of specific voltage-gated channels: voltage-gated sodium ion (Na⁺) channels and voltage-gated potassium ion (K⁺) channels.
Phases of Action Potential
- Resting state: Most voltage-gated sodium (Na+) and potassium (K+) channels are closed, maintaining a resting potential of around -70 mV.
- Depolarization: A stimulus opens some voltage-gated Na⁺ channels, allowing Na⁺ to diffuse into the cell and depolarize the membrane.
- Rising phase: The membrane potential increases as more voltage-gated Na⁺ channels open, and Na⁺ rushes into the cytosol, making it more positive relative to the outside.
- Falling phase: Most voltage-gated Na⁺ channels become inactivated, and most voltage-gated K⁺ channels open, allowing K⁺ to leave the cell and making the cytosol more negative than the outside.
- Hyperpolarization/Undershoot: The slow-acting voltage-gated K⁺ gates remain open, allowing K⁺ to continue moving out of the cell, making the membrane more negative (-80 mV) than the resting potential.
Propagation of Action Potentials
- An action potential in one region can depolarize the next region to threshold, producing a new action potential in the forward direction.
- The action potential is regenerated along the axon as a wave of depolarization that travels down the axon.
- As an action potential progresses along the axon, repolarization occurs quickly behind it.
Characteristics of an Impulse
- All-or-none Law:
- Refractory Period:
- Speed of Conduction:
Test your knowledge on action potential, a nerve impulse that travels rapidly along an axon in response to stimuli. Learn about the changes in membrane potential across the axon and the role of voltage-gated sodium and potassium ion channels.
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