4 - The Nerve Action Potential

Velocity of an AP is determined by the ___ and ___ of a neuron, ___ relative to ___, and degree of ___.

resistance, diameter; stimulus, capacitance; myelination

K+ channel activation depends on ___.

voltage

List the phases of the action potential

(threshold) Depolarization, (overshoot) Repolarization, (after) Hyperpolarization

Explain what is meant by the cable properties of nerves and describe how cable properties affect conduction of the AP.

Cable Properties are: Membrane Resistance Axon Diameter (and Axial Resistance) Capacitance

Term for when the cell interior becomes more positive as compared to the resting membrane potential.

Depolarization

Differentiate between electrotonic conduction, AP conduction and saltatory conduction.

Electrotonic conduction = the passive conduction of charge along an axon (Na+ ions diffusing down the length of the cytoplasm) Saltatory conduciton = the jumping of electrotonic conduction from Node to Node in myelinated axons AP conduction = general term for both of these

Term for when the cell interior becomes more negative as compared to the resting membrane potential.

Hyperpolarization

Cell repolarization results from an increase in ___ ___.

K+ conductance

For a nerve cell, the upstroke of the AP is due to ___ influx, with the maximum Na+ ___ at the peak of the AP.

Na+, conductance

What does threshold mean?

Stimulus required to initiate an AP.

___ and ___ (drugs) block action potentials.

TTX, TEA

What is the membrane space constant?

The distance over which the membrane is depolarized (longer space constant = faster propagation)

APs proceed in an ___-___-___ manner.

all-or-none

Describe the role of myelin in motor nerves.

allow saltatory conduction

Describe how changes in extracellular ion concentration or toxins/drugs can affect the AP.

can make cells hyperpolarizable or hypopolarizable

Propogation of an AP depends on the degree of ___ ___ of the current.

electrotonic spread

With increased blood K+ (hyperkalemia), neural membranes become ___ and action potentials occur at a ___ rate.

hypopolarized (depolarized), higher

Myelin sheaths cause the speed of the AP to ___ because it greatly increases nerve ___ as well as the ___ ___.

increase, resistance, space constant

During hyperpolarization is the ___ ___ ___, where membrane potential is closer to ___. Therefore you need a higher stimulus to elicit an action potential.

relative refractory period, E(K+)

When both ___ and ___ are high, the ___ ___ is greatest and conduction takes the longest.

restistance, capacitance, time constant

What is the membrane time constant?

the speed with which the membrane potential changes (shorter T = faster propagation)

Cell potential must reach ___ in order to fire an AP.

threshold

Na+ channel inactivation depends on ___.

time

AP depends on simple diffusion of ions down their electrochemical gradients through ___-gated membrane channels.

voltage

K+ channel inactivation depends on ___.

voltage

Na+ channel activation depends on ___.

voltage

The absolute refractory period is due to the unresponsiveness of the ___-___ ___ ___.

voltage-gated Na+ channel