Neural Communication: Action Potential Lesson 9
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 +40 -80 Time Em
Em drive Na+ into cell +40 -60 -70 -80 Time C & E gradients Depolarization Na+ influx Em -60 -70 -80 Time
Na+ + - K+
Na+ + - K+
+40 Repolarization K+ efflux Em -60 -70 -80 Time
Na+ + - K+
Na+ + - K+
+40 After- hyperpolarization Em -60 -70 -80 Time
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 Weak stimulus 1. Moderate stimulus 2. Strong stimulus 3.
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 Graded Summation longer duration 10-100 msec chemical-gated passive spread instantaneous decremental All-or-none short 1-2 msec voltage-gated propagated slow nondecremental