Action Potential/impulse

Front 1

How is a neuronal membrane electrically assessed?

Back 1

By placing electrodes on the two sides of the axon membrane. They register a voltager difference of about 70mv across the membrane with the inside negative potential about -70mv.

Front 2

What happens when the axon is stimulated?

Back 2

The voltage reverses itself, moving momentarily to positive inside and then quickly back to the resting negative state. This change in membrane potential is the action potential.

Front 3

The action potential begins at the stimulus and travels along the axon toward the muscle. TRUE/FALSE

Back 3

TRUE. At the height of the action potential, the outside of the membrane is negatively charged, and this negative region moves along the axon.

Front 4

How do action potentials arise?

Back 4

At rest the membrane potential is about -70mv. Because of this polarity,(negative inside, positive outside), the membrane is said to be polarized.

Front 5

What about the intracellular fluid of neurons?

Back 5

The intracellular fluid of neurons(axons) has high K+ and low Na+ concentrations, the reverse is true for extracellular fluid which is rich in Na+ and poor in K+.

Front 6

At rest, most operative channels allow passage of K+, but not of Na+. TRUE/FALSE

Back 6

TRUE. K+ diffuses down its concentration gradient, delivering a positive charge on the outside surface while leaving negatively charged partners behind on the inner surface. The membranes become polarized, with the inside negative, with respect to the outside.

Front 7

How does a stimulus affect Na+ channels?

Back 7

It causes a brief increase in the number of open Na+ channels. If the stimulus is weak, only a few channels open, and the potential is hardly perturbed. If threshold level is reached, then the number of Na+ channels become substantial.

Front 8

Na+ ions poised at high concentration outside the axon, leave their negatively charged partners behind on the outside and rush in fast enough to overwhelm the K+ moving out. TRUE/FALSE

Back 8

TRUE.The inside of the cell is inundated with positive charge so that the polarity is reversed, now the inside is positive and the outside is negative.

Front 9

What is the next phase of events?

Back 9

A moment later the Na+ channels close and extra K+ channels open. The membrane becomes very permeable to potassium. K+ moves out, making the membrane potential even more negative than it was a t rest, driving it very close to the K+ equilibrium potential.

Front 10

As a consequence of the above scenario, after several milliseconds, the extra potassium channels close, and the membrane permeability returns to its resting condition. TRUE/FALSE

Back 10

TRUE.

Front 11

What is the selectivity filter?

Back 11

Each membrane channel recognizes the appropriate ion, and allows it to pass while restraining others.

Front 12

What are the 2 types of potassium channels?

Back 12

1. One type is voltage activated, but most of these are closed during rest, when the membrane potential is about -70mv.
2. The other type is not voltage activated. It is always open and provides the pathway for the small but continuous K+ leakage that creates the resting potential.

Front 13

A resting potential of -70mv implies what?

Back 13

It implies that the inside is negative while the outside is positive.

Front 14

Because of this electrical distinction between the membranes inner and outer surfaces, the membrane is said to be polarized. TRUE/FALSE

Back 14

TRUE.

Front 15

When is the membrane depolarized?

Back 15

Whenever the magnitude of this membrane potential becomes smaller than the resting potential(close to zero), and conversely, when the magnitude is increased, the membrane is hyperpolarized.