Neurons & Action Potentials

Equilibrium potential

membrane voltage when there is no net ion movement

determining factors of equilibrium potential

electrical valence/charge of ion and concentration of the ion

the electrical gradient (neg. intracellular volatge)

at resting potential, what drives K+ to enter cells?

concentration gradient (higher inside than out)

at resting potential, what drives K+ to leave cells

concentration & electrical gradient

at resting potential, what drives Na+ into the cell?

no forces

at resting potential what drives Na+ to leave cells?

-90mV

approx. equilibrium potential for K+

-90mV

approx. equilibrium potential for K+

K+ leak channels contributing to more neg. resting potential

why is resting potential of the membrane close to K+ equilibrium potential

driving factors of membrane potential

ion concentrations**, ion valance, membrane permeability** (**=greatest effect)

direction of net movement of ions if equilibrium does not equal membrane potential

net movement will shift the membrane potential to the ions equilibrium potential

net movement of an ion if the equilibrium and membrane are opposite signs

ions will move down both concentration and electrical gradients

determined by voltage

Opening & closure of voltage gated channels is

determined by time

inactivation of voltage-gated channels is

summation of all graded potential at a given point in time

what determines whether threshold potential is reached

temporal summation

high frequency stimulation by a single pre-synaptic neron

spatial summation

simultaneous stimulation by several presynaptic neurons

axon hillock

where summation of all PSPs occurs (determines if AP will travel down axon)

channels at resting membrane potential

voltage-gated Na+: closed, voltage-gated K+: closed, leak K+: open (net movement out)

channels at depolarization phase

voltage-gated Na+: opened at threshold, voltage-gated K+: closed, leak K+: open (net movement out)

channels at repolarization phase

voltage-gated Na+: inactivation, voltage-gated K+: opened (attained threshold), leak K+: open (net movement out)

channels at hyperpolarization phase

voltage-gated Na+: closed, voltage-gated K+: still open (net movement out), leak K+: open

channels at return to resting potential

voltage-gated Na+: closed, voltage-gated K+: closing as approaching resting membrane potential, leak K+: open