7 propagated signaling: the action potential

abstract

the action potential is generated by the flow of ions through voltage-gated channels

sodium and potassium currents through voltage-gated channels are recorded with the voltage clamp

voltage-gated sodium and potassium conductances are calculated from their currents

the action potential can be reconstructed from the properties of sodium and potassium channels

variations in the properties of voltage-gated ion channels expand the signaling capabilities of neurons

the nervous system expresses a rich variety of voltage-gated ion channels

gating of voltage-sensitive ion channels can be influenced by various cytoplasmic factors

excitability properties vary between regions of the neuron

excitability properties vary between types of neurons

the mechanisms of voltage-gating and ion permeation have been inferred from electrophysiological measurements

voltage-gated sodium channels open and close in response to redistribution of charges within the channel

voltage-gated sodium channels select for sodium on the basis of size, charge, and energy of hydration of the ion

voltage-gated potassium, sodium, and calcium channels stem from a common ancestor and have similar structures

X-ray crystallographic analysis of voltage-gated channel structures provides insight into voltage-gating

the diversity of voltage-gated channel types is generated by several gentic mechanisms

an overall view

content

148

action potentials have four properties important for neuronal signaling. first, they have a threshold for initiation. as we saw in chapter 6, in many nerve cells the membrane behaves as a simple resistor in response to small hyperpolarizing or depolarizing current steps. second, the action potential is an all-or-none event. the size and shape of an action potential initiated by a large depolarizing current is the same as that of an action potential evoked by a current that just surpasses the threshold. third, the cation potential is conducted without decrement. it has a self-regenerative feature that keeps the amplitude constant, even when it is conducted over great distances. fourth, the action potential is followed by a refractory period. for a brief time after an action potential is generated, the neuron’s ability to fire a second action potential is suppressed. the refractory period limits the frequency at which a nerve can fire action potentials, and thus limits the information-carrying capacity of the axon

the action potential is generated by the flow of ions through voltage-gated channels

sodium and potassium currents through voltage-gated channels are recorded with the voltage clamp

voltage-gated sodium and potassium conductances are calculated from their currents

the action potential can be reconstructed from the properties of sodium and potassium channels

158

the specific value of Vm at which the net ionic current ( INa+ IK+ IL) just changes from outward to inward, depositing a net positive charge on the inside of the membrane capacitance, is the threshold

variations in the properties of voltage-gated ion channels expand the signaling capabilities of neurons

the nervous system expresses a rich variety of voltage-gated ion channels

gating of voltage-sensitive ion channels can be influenced by various cytoplasmic factors

excitability properties vary between regions of the neuron

excitability properties vary between types of neurons

the mechanisms of voltage-gating and ion permeation have been inferred from electrophysiological measurements

voltage-gated sodium channels open and close in response to redistribution of charges within the channel

voltage-gated sodium channels select for sodium on the basis of size, charge, and energy of hydration of the ion

voltage-gated potassium, sodium, and calcium channels stem from a common ancestor and have similar structures

X-ray crystallographic analysis of voltage-gated channel structures provides insight into voltage-gating

the diversity of voltage-gated channel types is generated by several gentic mechanisms

an overall view