resting and action potentials

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anatomy and physiology, lesson 7

absolute refractory period

The period during which the neuron is functionally unable to generate a second spike, occurring early in the period of repolarization and afterhyperpolarization.

afterhyperpolarization phase

A period during which the membrane potential is even more inside negative than at rest.

depolarization

Any change in the direction of a less-negative potential.

hyperpolarization

Any change in the direction of an even more inside-negative potential.

polarized

A resting cell's membrane in which it is charged electrically with a positive and negative pole.

resting potential

In the resting cell, the plasma membrane is mainly permeable to K+, and the inside-to-outside concentration gradient tends to drive K+ toward the outside of the cell, giving the membrane a slight excess of positive charge on the outside surface of the membrane and a corresponding slight excess of negative charge on the inside.

spike

When an action potential occurs, the membrane potential changes rapidly from its resting inside-negative value to an inside-positive value (peaking typically in the range of +20 to +50 mV) and just as quickly returns to the resting value.

closed state

An Na+ channel state in which the pore is blocked by an internal activation gate that senses the transmembrane potential and can be opened by depolarization, switching the channel to the open state.

relative refractory period

A period after the absolute refractory period during which a second action potential can be initiated, but the stimulus must be more intense.

open state

One of three states a Na+ channel may exist in which the transmembrane potential and can be opened by depolarization.

resting state

A state in which closed channels could be thought of as available to be opened by depolarization.

inactivation gate

Once the channel has entered the open state this gate can swing into place and close the channel. While the inactivation gate remains closed, the channel cannot be reopened by depolarization.

upstroke

A rapid rise in the membrane potential.

decremental threshold

Stimulation of the dendrites results in a local depolarization that decreases in intensity as it travels through the dendrites to the cell body.

activation gate

Senses the transmembrane potential and can be opened by depolarization.

inactivated state

When the inactivation gate remains closed, the channel cannot be reopened by depolarization.

K+

In the resting cell, the plasma membrane is mainly permeable to _________

outside

in resting potential, the inside-to outside concentration gradient tends to drive K+ toward the ____________ of the cell

positive charge

In resting potential the driving of K+ to the outside of the cell, gives the membrane a slight excess of ________on the outside surface of the membrane and a corresponding slight excess of negative charge on the inside.

polarized

In the resting potential, we could speak of the resting membrane as being electrically ____________________, like a battery with a positive and negative pole.

-70 to -80

The magnitude of the resting potential varies somewhat from one cell to another, but is in the range of ___________ mV.

depolarization

Any change in the direction of a less-negative potential is referred to as____________

hyperpolarization

any change in the direction of an even more insidenegative potential is called__________________

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