CM09: Action Potential and Signal Propagation

What is a graded potential?

A change in membrane potential (Vm) caused by change in current, where depolarizing or hyperpolarizing determines the direction. (and amplitude determine by stimulus strength)

What is an action potential?

A rapid depolarization/repolarization cycle when threshold membrane potential (Vm) is reached.

What is a stimulus?

Something that elicits a local change in ion channel permeability (e.g. molecule that binds to a receptor).

What is decremental conduction?

….

What does the Ohm’s law describe?

It describes the change in current will produce a proportional change in membrane potential.

What are two things that the intensity of the initial stimulus determine?

• The magnitude of the change in mem. potential.

• The distance along the membrane that the stimulus will affect membrane potential.

What is the threshold?

Depolarized membrane potential at which the specific voltage-gated channels that generate an action potential will open.

How is threshold reached?

• The opening of ligand-gated channels.

• Local current flow from one region of membrane to another.

What are examples of cells that can produce an action potential?

Neurons, muscle cells, certain endocrine, immune, and reproductive cells.

At resting membrane potential, are Na+ and K+ channels open or closed?

Closed

What activates voltage gated channels?

Depolarization

How fast do Na+ and K+ channels open?

Na+: Rapidly

K+: Slowly

What are the phases of an action potential in order?

1. Resting membrane potential: both Na+ and K+ channels closed

2. Depolarizing stimulus → membrane reach threshold: V-gated Na+ channels open

3. Rapid depolarization (Rising phase): additional v-gated Na+ channels open and cause rapid influx of Na+ into cell

4. Peak: Na+ channels inactivate (closed) and K+ channels open.

5. Repolarization: efflux of K+ out of cell

6. Hyperpolarization: K+ channels begin to close.

7. Recovery to resting membrane potential: both Na+ and K+ channels closed.

What is the stimulus-action potential relationship?

Any stimulus that depolarizes past threshold generates an action potential.