Chapter 3: Action Potential

Action Potential

rapid electric depolarization that is sent down the axon

• neuron quickly depolarizes (becomes more positive)

• triggered by an electrical stimulus passing the threshold of excitation

Voltage sensative Ions channels

membrane-protein channels that have permiability based on voltage differences

types of voltage senastive Ion channels

• voltage snesative Na+ ion channels

• Voltage-sensitive K+ ion channels

Voltage-sensative Na+ cahnnels

These channels quickly open and let in Na+ when the depolarizing potential is ~-40

• This makes the neuron more positive, triggers the action potential

Voltage-sensative K+ cahnnel

Open much more slowly, used as a way to hyperpolarize the membrane

• Potassium flows OUT

Ion channel process

1. at people of depolarization during the AP, V-sensitive Na+ channels SHUT

2. positive charges stop entering the neuron

3. V-sensitive K+ channels open

4. K+ flows out of the neuron, hyperpolarizing the neuron again

Afterpolerization

occurs when K+ channels stay open slightly longer than needed, so the membrane is suddenly MORE negative than normal

refractory period

a time after AP where the nueron resists producing another AP

• 2 parts

refractory period parts

• absolute refractory period

• relative refractory period

Absolute refractory period

the first part of the period; no AP can be produced bc the Na+ channels have been shut and cannot be opened for a hot second

• depolerization can’t occur to trigger another AP

relative refractory period

second part of the period; Na+ channels are still closed but K+ channels are opened

• k+ is flowing OUT of membrane; the membrane is being hyperpolarized again

All or none law

the strength and spped of the AP is comteplty indepdnet from the size of the stimulus

• If you shock a neuron with 10000 volts, it won’t matter, the AP will be the same size

Factors that affect AP direction/velocity

• Nueron size/shape

• neuron diameter

• myleanation

Nodes of Ranvier

interruptions in the mylean sheath that cause the AP to be psuehd along to the next sheath segment; acts as a boost

saltatory conduction

When APs “jump” from neuron to nueron; provides a faster conduciton of impulses

multiple sclerosis

When your autoimmune system attacks CNS myelin, slowing AP conduction and fucking up the axons

local nuerons/interneurons

neurons with very short axis that only exchange info with close neighbors

Graded potentials

produced by some neurons, the complete opposite of all or nothing