NeuralCommunication

Action Potential

Lecture 11

Action Potentials Large and rapid change in membrane

potential electrically-gated channels EPSPs

threshold potential Occurs in axon

triggered at axon hillock ~

AP Characteristics

Voltage-gated channels All or none Slow Non-decremental Self Propagated

regenerated ~

-70

-60

0

+40

-80

Time

Vm

-70

-60

0

+40

-80

Time

Vm

-70

-60

0

+40

-80

Time

Depolarization

Na+ influx

C & E gradientsdrive Na+ into cell

Vm

-70

-60

0

+40

-80

Time

Repolarization

K+ efflux Vm

-70

-60

0

+40

-80

Time

After- hyperpolarization

Vm

Refractory Period

after AP won’t fire again relative & absolute

Relative during after hyperpolarization requires greater depolarization ~

Relative Refractory Period

-70

-60

0

+40

-80

Time

Vm

Absolute refractory period

Na+ channels deactivate will not trigger AP must reset

Ball & Chain Model ~

Na+ channel deactivation

Na+ channel deactivation

Frequency Code

Pattern = Intensity of stimulus frequency of APs

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

FREQUENCY CODE

1.

2.

3.

Weak stimulus

Moderate stimulus

Strong stimulus

Saltatory Conduction

Myelinated neurons oligodendroglia & Schwann cells

Transmit long distances 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 Myelinated

like electricity through wire decremental but triggers AP at next node

Safety factor - trigger AP across 5 nodes .2 - 2 mm apart

larger neurons farther apart ~

Saltatory Conduction

Nodes of Ranvier

PSPs vs APs

GradedSummation

longer duration*10-100 msec

chemical-gated passive spread

instantaneousdecremental

All-or-none

short1-2 msec

voltage-gated propagated

slownondecremental