48.3 Action potentials are the signals conducted by axons

gated ion channels

ion channels that open or close in response to stimuli, altering membrane potential

voltage-gated ion channel

a gated ion channel that opens or closes in response to a shift in voltage

gated potassium channels in a resting neuron

opens and increases permeability for K+

hyperpolarization

more negative in the cell because K+ goes out (E_K+ -90 mV @37 degrees celsius)

depolarization

sodium goes in, changing membrane gradient; more positive inside the cell membrane (E_Na+ +62 mV @37 degrees celsius)

graded potential

a shift in the membrane potential, magnitude depends on stimulus

action potential (resting state, depolarization, rising phase, falling phase, and undershoot)

5 stages: 1. at resting potential, voltage-gated sodium and potassium channels are closed and ungated potassium channels are open. 2. the stronger the stimulus, more depolarization, the more gated sodium channels open. 3. after crossing threshold (-55 mV), all sodium gated channels open, causing spike in charge, therefore called the rising phase 4. closes gated sodium channels and opens voltage-gated potassium channels to open, aka falling phase. 5. sodium channels close but potassium channels stay open until resting state

threshold

if stimulated, only some ion channels will open to allow sodium in, but after passing threshold, all will open; threshold being -55 mV

refractory period

inability to trigger action potential due to inactivation of sodium channels

Thought explanation:
through sodium-potassium pump (undershoot), potassium comes back in and sodium goes back out. this membrane gradient is needed to do action potential again alter so that there can be potassium that goes out and sodium that goes back in

myelin sheath

the electrical insulation that surrounds vertebrate axons; produced by glia; mostly lipids

oligodendrocytes

a type of glia in the CNS that produces myelin sheaths

schwann cells

the glia in the PNS that produces myelin sheath

nodes of Ranvier

voltage-gated sodium channels that can go through the myelin sheath

saltatory conduction

the propagation of the action potential due to opening and close of ion channels (nodes of Ranvier)