Voltage-Gated Channels

When cell is at rest

potassium leak channels open —> keep cell polarized

V-gated Sodium Channels - 3 things

Activation gate

Selectivity filter

Inactivation gate

Activation gate

Opens in response to change in voltage

Selectivity filter

Mostly only sodium ions pass through

Inactivation gate

Even when open can be inactivated to stop ions

At least 3 states for V-gated sodium channels

Open

Inactivated

Closed

V-gated sodium and calcium are a

single polypeptide

V-gated sodium and calcium have

4 domains that are subunit-like

Voltage sensing region for v-gated sodium and calcium channels

S4

Mutations in v-gated sodium and calcium channels can cause

channelopathies

Why do APs propagate in only one direction?

Once it hits a section of membrane, that membrane will be refractory until it repolarizes —> sodium channels unavailable

Orthodromic

Going from axon hillock to dendrites

Antidromic

Going from dendrites to axon hillock

Only in artificial lab setting

V-gated Potassium Channels

Opens slower than sodium

Stays open longer

Returning the membrane to normal after depolarization

V-gated calcium channels

Expressed at neuron terminals - synaptic release

Expressed in muscle cells - muscle contraction

Expressed in astrocytes

Real channels

flutter (open and close)

Does the sodium-potassium ATPase directly contribute to changes in membrane potential?

NO

Does it take a large flow of ions to create the elctrical events of an action potential?

NO