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Neuroscience: Action Potential Propagation

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Neuroscience: Action Potential Propagation

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Questions and Answers

What is the primary difference in how action potentials propagate along unmyelinated and myelinated axons?

Action potential propagation in unmyelinated axons is bidirectional, whereas in myelinated axons it is unidirectional.

Myelinated axons experience a slower propagation speed due to the myelin sheath, whereas unmyelinated axons have faster conduction.

Unmyelinated axons transmit action potentials using saltatory propagation, while myelinated axons use continuous propagation.

Action potentials in myelinated axons jump from node to node, and action potentials in unmyelinated axons travel along the entire axon membrane. (correct)

During the peak of an action potential, what is the electrical charge of the membrane potential?

The membrane potential becomes strongly negative

The membrane potential becomes neutral

The membrane potential becomes positive (correct)

The membrane potential remains unchanged

Why does an action potential propagate in only one direction along the axon?

The direction of the local current influences the direction of propagation

The myelin sheath blocks backward propagation.

The potassium ion concentration gradients prevent backward propagation.

The refractory period of the previous segment prevents backward propagation. (correct)

Why can't the axon hillock generate an action potential?

It does not have enough voltage-gated sodium channels. (B) Signup and view all the answers

What role do local currents play in the propagation of the action potential?

They depolarize adjacent portions of the membrane, pushing the action potential forward. (C) Signup and view all the answers

What is the speed of action potential propagation with continuous propagation?

Approximately 1 meter per second (D) Signup and view all the answers

Where does the action potential initiate?

At the axon's initial segment (A) Signup and view all the answers

What is the main purpose of the myelin sheath in myelinated axons?

Block ion flow across the membrane between nodes. (D) Signup and view all the answers

Study Notes

Action Potential Propagation

Action potentials affect the entire axon membrane, unlike graded potentials that diminish with distance.
Action potentials begin at the axon's initial segment.
At the peak, the membrane potential briefly becomes positive.
Sodium ion movement in the cytosol and extracellular fluid creates a local current, depolarizing adjacent membrane segments.
This process continues in a chain reaction, propagating the action potential along the axon away from its origin.
The previous segment's refractory period prevents backward movement.
This method is called continuous propagation, occurring slowly along unmyelinated axons (about 1 meter/second).

Myelinated Axon Propagation

Myelinated axons are wrapped in myelin, interrupted by nodes of Ranvier.
Myelin sheath lipids block ion flow between the nodes.
Continuous propagation is impossible in myelinated axons.
Saltatory propagation occurs, where the action potential jumps from node to node.
This process is much faster than continuous propagation (18 to 140 meters/second).
The name "saltatory" is derived from the Latin word for "to leap."

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Description

Explore the crucial concepts of action potential propagation in both unmyelinated and myelinated axons. Understand the mechanisms behind continuous and saltatory propagation, including how myelin and nodes of Ranvier influence signal transmission. Test your knowledge of these fundamental neuroscience principles.