Action Potentials

Action Potentials and Impulse Conduction

Excitable tissues

muscle

nerve

Graded potentials

properties

proportional to magnitude of triggering event

show decremental decay and propagation

can be depolarizing or hyperpolarizing

can be summed

important examples

postsynaptic potentials

receptor potentials

end-plate potentials

pacemaker (ramp) potentials

Action potentials

terminology

polarization

depolarization

hyperpolarization

repolarization

threshold potential

channel gating

types

voltage-gated channels

chemical-messenger gated channels [ligand-gated channels]

gates are all-or-nothing

depolarization results from opening voltage-gated Na⁺ channels

Na⁺ permeability increases to 600 × K⁺ permeability

duration 0.5 msec

closing of inactivation gates

repolarization results from opening voltage-gated K⁺ channels

K⁺ permeability increases to 300 × Na⁺ permeability

Na⁺ channels return to original configuration

K⁺ channels close

Na⁺- K⁺ pump restores ion concentration gradients

propagation

role of the axon hillock

conduction by local current flow

nondecremental

saltatory conduction

myelination

multiple sclerosis

refractory period

role of the Na⁺ activation gates

all-or-nothing law

Synapses

morphology

presynaptic neuron

synaptic knob

synaptic vesicles

neurotransmitter substance

postsynaptic neuron

subsynaptic membrane

synaptic cleft

unidirectional transmission

excitatory synapses

excitatory postsynaptic potential (EPSP)

Parkinsonism

dopamine deficiency

treatment with L-dopa

inhibitory synapses

inhibitory postsynaptic potential (IPSP)

strychnine

competes with glycine at postsynaptic receptor

no IPSPs generated

results in unchecked excitatory input

tetanus toxin

prevents release of gamma-aminobutyric acid (GABA)

results in unchecked excitatory input

synaptic delay

neurotransmitter removal from the synaptic cleft

cholinesterase

monoamine oxidase

catechol-O-methyltransferase (COMT)

the grand postsynaptic potential (GPSP)

temporal summation

spatial summation

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