Action Potential

supply of nutrients, metabolic buffering, electrical insulation, prinicipal cells responsible for repair and scar formation

astrocytes

supporting cells, involved in processing and signaling

glial cells

tranmission, storage, processing of info, communicate mainly via ?

neurons, chemical synpapses

macrophage system of CNS

microglia

form myelin sheaths around axons in CNS

oligodendrocytes

line ventricles

ependmyal cells

grey matter

cell bodies

white matter

myelinated axons

cell body performs?

integration

receive signals and send to body

dendrites

Myelin sheath function

increase rate of conduction

Where does the AP start in a neuron?

hillock

Graded potentials

localized, variable amplitude, passive conduction, decreases with distance

can have stronger or weaker based on stimulus, max distance: 5 mm

Threshold potential: definition

membrane potential at which AP is fired

Action potentials are ?

all or none (either fires or doesnt)

Action potential signal travels by?

active propagation: energy to keep signal going stored along axon, energy far from site is same as energy close, amplitude is constant over distance

Na+ channel: what happens?

• closed channel (quickly)

• when threshold is reached, they open rapidly and membrane highly depolarizes (sodium flows into cell)

• inactivation: Prevents sodium from flowing into channel even if it is open, has to be reset to be activated again

K channel: “?”

delayed rectifier

opens slowly to let potassium out, DONT deactivate. Close slowly

Threshold: when happens?

once sodium conductance is greater than K conductance

Rising phase of AP

rapid opening of sodium channels, depolarizes up to 0 membrane potential

Overshoot

hyperpolarization: after 0 potential

peak phase

max amount of Na channels open (not every channel but most open at one time that there will be)

Repolarization

K channels are opened, sodium channels are inactivate

afterhyperpolarization

more K channels open that at rest, but are closing to return to normal leak rate

sodium channel activation are considered what kind of feedback? whats the endpoint?

positive, deactivation

Refractory periods: Absolute

impossible to fire another AP, sodium channels are inactive

Relative Refractory period

more K+ channels are open than at rest, need higher threshold to fire AP, so more difficult

unmyelinated axons AP propogation?

passive depolarization is very fast and travels first, brings it to threshold for the AP to follow, behind it is in refractory which keeps signal in one direction

nodes of ranvier

where AP occurs in myelinated axons, high sodium concentration

Saltatory conduction

jumping conduction: underneath myelin there is passive conduction that is very rapid, when it hits a node another AP is fired through node keep large amplitude being propogated

factors that affect speed?

myelinated vs unmyelinated, size of axons. Larger, myelinated axons are fastest