NRSC 277 - Lecture 5: The Action Potential and its Propagation

Neural code (how a neuron encodes information)

frequency (Hz) and pattern of APs

In a neuron, cytosol is more negatively charged than

the extracellular space

depolarization

making intracellular side more positive

hyperpolarization

making intracellular side more negative

action potentials mediated by

sodium and calcium gated channels

four phases of action potential

rising, overshoot, falling, undershoot

what are action potentials caused by

depolarization of membrane beyond threshold

generation of multiple action potentials

artificially inject current into a neuron using a microelectrode

Ion channel number is proportional to

electrical conductance

rising phase

Inward sodium current

falling phase

outward potassium current

hodgkin and huxley

used the giant squid axon to learn generation of action potential through voltage clamp

The relative refractory period has

a higher threshold for action potential to fire

during absolute refractory period

sodium channels are inactivated

potassium gates open _________ than sodium gates

later

potassium channels =

four subunits

Membrane potential is sensitive to

extracellular K+ (Nernst equation)

action potentials _______ along the axon

propogate

Orthodromic:

action potential travels in one direction - down axon to the axon terminal

Antidromic (experimental):

backward propagation

length of an action potential

about 2 msec

action potential conduction is faster inside myelinated axon than...

across axonal membrane

sodium channels are concentrated at

the nodes

there are no _______ channels at the nodes

potassium

potassium channels conc. at

juxtaparanodes

patch clamp method is used to:

study ion channel properties

Neuronal membrane (excitable membrane)

capacitor

Ion channels are

series of resistors