Neural Communication Action Potential Lesson 11 Action Potentials

Action Potentials Large and rapid change in membrane potential n electrically-gated channels n EPSPs

AP Characteristics Voltage-gated channels n All or none n Slow n Non-decremental n Self

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

+40 0 Vm Depolarization Amplitude = 105 m. V - 65 m. V to

+40 0 Repolarization K+ efflux Vm -55 -65 -75 Time

+40 0 Afterhyperpolarization Vm -55 -65 -75 Time

$Refractory Period after AP l won’t fire again l relative & absolute n Relative$

$Relative Refractory Period +40 0 Vm -55 -65 -75 Time$

$Absolute refractory period Na+ channels deactivate l will not trigger AP l must reset$

Frequency Code Pattern = Intensity of stimulus l frequency of APs n Place =

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

Saltatory Conduction Myelinated neurons l oligodendroglia & Schwann cells n Transmit long distances l

Saltatory Conduction Nodes of Ranvier l action potentials n Myelinated l like electricity through

PSPs n Graded l n n n l n All-or-none n short *10 -100

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Neural Communication Action Potential Lesson 11

Action Potentials Large and rapid change in membrane potential n electrically-gated channels n EPSPs l threshold potential n Occurs in axon l triggered at axon hillock ~ n

axon hillock

AP Characteristics Voltage-gated channels n All or none n Slow n Non-decremental n Self Propagated l regenerated ~ n

+40 0 Vm -55 -65 -75 Time

+40 0 Vm -55 -65 75 Time

+40 0 Vm C & E gradients drive Na+ into cell Depolarization Na+ influx -55 -65 -75 Time

+40 0 Vm Depolarization Amplitude = 105 m. V - 65 m. V to +40 m. V Na+ influx -55 -65 -75 Time

+40 0 Repolarization K+ efflux Vm -55 -65 -75 Time

+40 0 Afterhyperpolarization Vm -55 -65 -75 Time

$Refractory Period after AP l won’t fire again l relative & absolute n Relative$

Refractory Period after AP l won’t fire again l relative & absolute n Relative l during after hyperpolarization l requires greater depolarization ~ n

$Relative Refractory Period +40 0 Vm -55 -65 -75 Time$

Relative Refractory Period +40 0 Vm -55 -65 -75 Time

$Absolute refractory period Na+ channels deactivate l will not trigger AP l must reset$

Absolute refractory period Na+ channels deactivate l will not trigger AP l must reset n Ball & Chain Model ~ n

Na+ channel deactivation

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

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

Saltatory Conduction Myelinated neurons l oligodendroglia & Schwann cells n Transmit long distances 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 n Myelinated l like electricity through wire l decremental but triggers AP at next node n Safety factor - trigger AP across 5 nodes l. 2 - 2 mm apart n larger neurons farther apart ~

Saltatory Conduction Nodes of Ranvier

PSPs n Graded l n n n l n All-or-none n short *10 -100 msec chemical-gated passive spread l APs Summation longer duration l vs instantaneous decremental l n n 1 -2 msec voltage-gated propagated l l slow nondecremental