BIOG 1440 Lecture 21: Action Potential

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coralsnail788

12 May 2017

School

Cornell University

Department

Biology: General Courses

Course

BIOG 1440

Professor

Buchon, N

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Document Summary

Action potentials are the signals conducted by axons. Decay with time and with distance from source. Induce a small electric current that leaks out of neuron. Action potential: massive change in membrane potential. Constant magnitude and can regenerate in adjacent regions of the membrane. Can spread along axons well suited for long distances. Voltage -gated ion channels: open/close depending on membrane potential. Occur whenever a depolarization increases membrane voltage to a threshold value. Threshold: value of membrane potential at which neurons fire. Depolarization opens both types of channels but they respond independently and sequentially. Sodium channels open first, initiating action potential. As action potential proceeds, sodium channels become inactivated they remain inactive until resting potential. Potassium channels open more slowly but remain open throughout action potential (see detailed process in page 16 of notes) Refractory period: downtime where a second action potential cannot be initiated. Limits frequency at which action potentials can be generated.

Related Questions

This is the peak depolarization in an action potential. At this point in an action potential two events start to happen.

1. Na+ channels begin to inactivate, which is equivalent to closing.

2. A majority of the K+ channels are beginning to open.

Determine what happens to the membrane potential when voltage-gated K+ channels are open simultaneously with voltage-gated Na+ channels (and the leak K+ channels which are still open). Increase the membrane permeability to K+ by increasing it to 115.

i. What happens to the membrane potential Em? __________________________

j. Why does the membrane potential change in this direction? __________________________ Now inactivate the voltage-gated Na+ channels by reducing the membrane permeability for Na+ back to 1. k. What is the new membrane potential? _____________

l. Is the new membrane potential less negative or more negative than the resting membrane potential listed in line âbâ of this section? _____________

m. Why? (hint: what 2 types of K+ channels are open now?) n. Under the current ionic concentrations given, what is the most negative value that the membrane potential could reach? _____________ (Increase the permeability of the membrane to K+ to confirm your answer.)

o. What equilibrium potential has the same value? _____________

p. At this point in the action potential, when the membrane potential is more negative than the resting potential, the membrane potential is said to be hyperpolarized. What happens to voltage-gated K+ channels (membrane permeability to K+) to bring the membrane potential back to its resting potential near -70mV?_____________

When the membrane potential became more negative than the Threshold potential, the inactivated voltage-gated Na+ channels became reactivated. After the voltage-gated K+ channels closed to enable the membrane potential to return to resting membrane potential they became ready to open again. Both channels are ready to open again in order to fire another action potentia

sapphirepanda54

3. Which of the following is TRUE about a motor neuron?

		It passes information to another motor neuron.
		It passes information to another neuron.
		It stimulates cells associated with muscles or glands.
		It cannot generate an action potential.

2. Choose the immediate event that needs to occur for a nerve to fire an action potential.

		Voltage-gated potassium ion channels need to open.
		A threshold potential will need to be reached.
		Depolarization will need to be happen.
		Voltage-gated sodium ion channels need to close.

1. Choose the TRUE statement with respect to axons and/or dendrites.

		Dendrite is the location that a neurotransmitter moves into the synamptic cleft.
		Action potentials travel along the axon of a neuron.
		A neuron will typically have more axons than dendrites.
		More than one is correct

amaranthmouse537

Please help

29. The action potentialâ¨

a. begins with the membraneâs increased permeability to potassium.

b. returns to resting when the sodium channels open.â¨

c. can be triggered by opening of ligand gated Na and K channels.â¨

d. involves voltage-gated Chloride channels in the membrane.â¨

e. can be triggered by opening of voltage gated Na+ and K+ channels.

30. Which of the following is not a step in the propagation of action potentials?

â¨a. Sufficient local inward current causes the axon to reach threshold.

â¨b. Local depolarization/inward current spreads to adjacent axonal regions.â¨

c. Adjacent regions eventually reach threshold and exhibit an action potential waveform.

â¨d. Current/depolarization continue to spread directionally along the axon, repeating steps aâc

e. All of the above are steps contributing to the propagation of action potentials.

31. Which of the following is important for the unidirectional propagation of action potentials?

a. The voltage dependence of the sodium channels

â¨b. The voltage dependence of the potassium channels

â¨c. The presence of a refractory period at a location where an action potential has just fired

d. Sufficient âleakinessâ of the axons, such that backward propagation of action potentials is prevented

â¨e. The capacity of axons to function as perfect insulators and prevent current leakage and backpropagation

BIOG 1440 Lecture 21: Action Potential

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