Post on 07-Jan-2016
description
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