Action Potentials

Vt is

threshold potential, Vm at which AP is triggered

Depolarization is caused by

activation of Na+ channels and Na+ rushing into the cell

Depolarization is what kind of feedback loop

positive, Na+ influx activates more Na+ channels

Repolarization is caused by

Na+ channels being inactivated, K+ channels being activated, allowing K+ to flow out

hyperpolarization is caused by

excess K+ flowing out of cell, making Vm more negative than Vrest

How does the cell return to Vrest

K+ channels are deactivated, Na+ channels are deactivated

Does AP firing affect chemical gradients?

No, not enough ions cross the membrane to disrupt chemical gradients

Do ATPase pumps cause repolarization?

No, they are too slow

Na+ channel inactivation is

time dependent and fast

K+ channel deactivation is

voltage dependent, not time dependent

Na+ channel deactivation is

voltage dependent, required to activate channels again

Activation of ion channel is

opening the pore, voltage dependent, done during depolarization

deactivation of ion channels is

closing the pore, voltage dependent, done during repolarization

inactivation of ion channel is

plugging the pore with ball and chain, time dependent, requires deactivation for removal

Do K+ channels inactivate?

No, they have no ball and chain, so they only deactivate

Is AP graded?

No, it is all or nothing

Which channel type has a higher activation potential, Na or K

K channels, they are activated after Na channels are activated

A greater stimulus creates

greater AP frequency

Absolute refractory period

period in which an AP cannot be triggered

What causes the absolute refractory period

Na+ channels have not had a chance to deactivate, which removes ball and chain/inactivation

Relative refractory period

period after first AP where a stronger stimulus can trigger another AP

What causes a relative refractory period?

some K+ channels are still activated from previous K+, which raises Vt

max AP frequency is set by

absolute refractory period

How does calcium affect Na+ channels

negative amino acids can be weakened when bound by calcium, which makes it more difficult for channel to activate

high external calcium causes

decreased excitability

low external calcium causes

hyperexcitability

As AP moves down the membrane, why can’t it move backwards?

The absolute refractory period prevents this

How does myelin affect axons

a myelinated axon is insulated and allows an AP to travel faster

PNS myelination cells

Schwann cells

CNS myelination cells

oligodendrocytes

Nodes of Ranvier

gaps between myelin, lots of NA+ channels

Saltatory conduction

when AP jumps from node to node (travels quickly under myelin and is restored in nodes)

thicker myelin causes

increased conduction velocity

greater axon diameter

increased conduction velocity

neuron fiber types from largest axon diameter to smallest

Aa, Ab, Ag, Ad

neuron fiber types from thickest myelin to thinnest

Aa, Ab, Ag, Ad

neuron fiber types from fasts to slowest conduction velocity

Aa, Ab, Ag, Ad

Aa neurons

skeletal muscles

Ab neurons

touch and pressure

Ag neurons

muscle spindles

Ad neurons

pain, temp, and low touch

B neurons

moderate myelination, autonomic preganglionic

C neurons

no myelination, low temp pain touch, autonomic postganglionic

CAP

compound action potential, summation of individual APs

in many neurons, a very small stimulus will

generate no CAP

in many neurons, a small stimulus will

generate a small CAP

in many neurons, increase of stimulus

increases CAP, more neurons reach Vt