Membrane Potential

dendrites

input

cell body of a neuron contains its

nucleus

the axon hillock is where

an Ap starts

the axon of a neuron

carries AP out

a neurons terminals

contact next cell’s dendrites, often multiple cells at once

K+ concentration is high

inside the cell

K+ concentration is low

outside of the cell

chemical potential

energy generated by an ion moving with its concentration gradient

electrical potential

energy generated by an ion moving with its electrical gradient

electrochemical gradient

combination of electric and chemical gradient

Nernst equation

equilibrium potential

Na+ concentration is low

in the cell

Na+ concentration is high

outside of the cell

Vm represents

potential difference between inside and outside of cell, with outside being set to 0

Goldman equation

membrane potential

Vrest is

membrane potential with no AP

leak channels

channels open at rest

Pion is determined by

number of open leak channels

at rest, there are more channels open of which ion, K or Na

K, meaning Pk>PNa

Vrest is approximately

-70 mV

Vm=Eion when

only one ion is able to cross the membrane

to depolarize means to

increase Vm, flip charges so that the outside is now more negative than the inside of a cell

to repolarize means to

decrease Vm back towards Vrest, where inside of the cell is more negative than the outside

to hyperpolarize means to

overshoot Vrest, where inside of cell is more negative than usual

Ionic current, Iion

number of ions crossing a membrane

Force, F ion

force driving ion movement

conductance, Gion

similar to permeability

according to the Fion equation, when Vm is far from Eion

there is a large force on the ion

according to the Fion equation, when Vm=Eion

the same amount of ion enters the cell that leaves, so there is no net ion movement, hence no force on ion

when a cation leaves the cell, I (current) is

positive

when a cation enters the cell, I (current) is

negative

when an anion enters the cell, I (current) is

positive

when an anion leaves the cell, I (current) is

negative

when deciding whether ionic current is negative or positive

outside of cell is used as reference, keep in mind whether it is an anion or a cation

What are two ways to depolarize a cell

increase Na ionic current, decrease K ionic current

how can Na ionic current be increased

increase Na conductance (most common) or increase force on Na by increasing ENa

how can K ionic current be decreased

decrease K conductance (most common) or decrease force on K by increasing EK

V-I plots

plot I against Vm, slope is conductance

what is steady state for a neuron

when Vm is stable, cations going into cell=cations going out of cell, IK=-INa

how is Vrest maintained

active transport

how much Na+ is pumped out for how much K+ pumped in?

3Na+ out for 2 K+ in

Can pumps create a rapid repolarization?

No, they are too slow