NeuralCommunication: Action Potential

Lesson 10

Neural Signaling: Axon

Action Potentials propagated electrical signal regenerated

Large & rapid changes in Em depolarization repolarization ~

Action Potentials Electrically-gated channels

or voltage-gated Characteristics

all-or-none relatively slow non-decremental ~

Threshold of Excitation

also: threshold potential Triggered at axon hillock

point of decision integration

Threshold potential Depolarization; approximately 10 mV EPSPs AP ~

-70

-60

0

+40

-80

Time

Em

-70

-60

0

+40

-80

Time

Depolarization

Na+ influx

C & E gradientsdrive Na+ into cell

Em

Na+

K+

+

-

Na+

K++

-

-70

-60

0

+40

-80

Time

Repolarization

K+ efflux Em

Na+

K++

-

Na+

K++

-

-70

-60

0

+40

-80

Time

After- hyperpolarization

Em

Refractory Period

After AP time-out prohibits or resists AP absolute & relative ~

Refractory Period

Absolute refractory period Na+ channels deactivate will not trigger AP must reset one-way transmission of signal

Ball & Chain Model ~

Na+ channel deactivation

Na+ channel deactivation

Refractory Period

Relative refractory period during after-hyperpolarization requires greater depolarization to

reach threshold ~

Frequency Code

Intensity of stimulus frequency of APs Pattern

Type of stimulus Brain area that receives signal Visual, auditory, pain, etc. Doctrine of Specific Nerve Energies ~

FREQUENCY CODE

1.

2.

3.

Weak stimulus

Moderate stimulus

Strong stimulus

Saltatory Conduction

Myelinated neurons oligodendrocytes & Schwann cells

Long distances transmission APs relatively slow, regenerates EPSPs - fast, decremental

Saltatory: combines both types of current speed without loss of signal ~

Saltatory Conduction

Nodes of Ranvier action potentials no myelin

Myelinated portions passive current decremental but triggers AP at

next node ~

Saltatory Conduction

Nodes of Ranvier

PSPs vs APs

GradedSummation

longer duration10-100 msec

chemical-gated passive spread

instantaneousdecremental

All-or-none

short1-2 msec

voltage-gated propagated

slownondecremental