Neural Communication Action Potential Lesson 10 Neural Signaling

Neural Signaling: Axon Action Potentials l propagated electrical signal l regenerated n Large &

Action Potentials Electrically-gated channels l or voltage-gated n Characteristics l all-or-none l relatively slow

Threshold of Excitation also: threshold potential n Triggered at axon hillock l point of

+40 0 Em C & E gradients drive Na+ into cell Depolarization Na+ influx

+40 0 Repolarization K+ efflux Em -60 -70 -80 Time

+40 0 Afterhyperpolarization Em -60 -70 -80 Time

$Refractory Period n After AP l time-out l prohibits or resists AP l absolute$

$Refractory Period Absolute refractory period l Na+ channels deactivate l will not trigger AP$

$Refractory Period n Relative refractory period l during after-hyperpolarization l requires greater depolarization to$

Frequency Code Intensity of stimulus l frequency of APs l Pattern n Type of

FREQUENCY CODE Weak stimulus 1. Moderate stimulus 2. Strong stimulus 3.

Saltatory Conduction Myelinated neurons l oligodendrocytes & Schwann cells n Long distances transmission l

Saltatory Conduction Nodes of Ranvier l action potentials l no myelin n Myelinated portions

PSPs n n Graded l. Summation longer duration l 10 -100 msec chemical-gated passive

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Neural Communication: Action Potential Lesson 10

Neural Signaling: Axon Action Potentials l propagated electrical signal l regenerated n Large & rapid changes in Em l depolarization l repolarization ~ n

Action Potentials Electrically-gated channels l or voltage-gated n Characteristics l all-or-none l relatively slow l non-decremental ~ n

Threshold of Excitation also: threshold potential n Triggered at axon hillock l point of decision l integration n Threshold potential l Depolarization; l approximately 10 m. V l EPSPs AP ~ n

+40 0 Em -60 -70 -80 Time

+40 0 Em C & E gradients drive Na+ into cell Depolarization Na+ influx -60 -70 -80 Time

Na+ + K+

Na+ + K+

+40 0 Repolarization K+ efflux Em -60 -70 -80 Time

Na+ + K+

Na+ + K+

+40 0 Afterhyperpolarization Em -60 -70 -80 Time

$Refractory Period n After AP l time-out l prohibits or resists AP l absolute$

Refractory Period n After AP l time-out l prohibits or resists AP l absolute & relative ~

$Refractory Period Absolute refractory period l Na+ channels deactivate l will not trigger AP$

Refractory Period Absolute refractory period l Na+ channels deactivate l will not trigger AP l must reset l one-way transmission of signal n Ball & Chain Model ~ n

Na+ channel deactivation

$Refractory Period n Relative refractory period l during after-hyperpolarization l requires greater depolarization to$

Refractory Period n Relative refractory period l during after-hyperpolarization l requires greater depolarization to reach threshold ~

Frequency Code Intensity of stimulus l frequency of APs l Pattern n Type of stimulus l Brain area that receives signal l Visual, auditory, pain, etc. l Doctrine of Specific Nerve Energies ~ n

FREQUENCY CODE Weak stimulus 1. Moderate stimulus 2. Strong stimulus 3.

Saltatory Conduction Myelinated neurons l oligodendrocytes & Schwann cells n Long distances transmission l APs relatively slow, regenerates l EPSPs - fast, decremental n Saltatory: combines both types of current l speed without loss of signal ~ n

Saltatory Conduction Nodes of Ranvier l action potentials l no myelin n Myelinated portions l passive current l decremental but triggers AP at next node ~ n

Saltatory Conduction Nodes of Ranvier

PSPs n n Graded l. Summation longer duration l 10 -100 msec chemical-gated passive spread linstantaneous ldecremental vs APs n All-or-none n short l 1 -2 msec voltage-gated propagated lslow lnondecremental n n