concept 48.3: action potentials are the signals conducted by axons

intracellular recording

can be used to monitor the changes in membrane potential

gated ion channels

open or close in response to stimuli

what does a neuron having gated ion channels result in

changes in membrane potential

voltage- gated channels

open/close in response to a change in voltage across the plasma membrane

ligand- gated channels

open/ close in response to a chemical stimulus

mechanically- gated channels

open/ close in response to physical stimuli

microelectrodes

by inserting one electrode into the cell and one outside of the cell you can measure the difference in membrane potential

hyperpolarization

increase in magnitude of membrane potential, the membrane potential gets more negative

the diffusing of K+ out of the cell does what

makes it more negative

depolarization

opening a Na+ channel, makes the inside of the cell to be less negative, more positive

what direction do ions flow through an open gate

from higher to lower concentration, down the concentration gradient

graded potentials

changes in polarization where the magnitude of the change varies with the strength of the stimulus

action potentials

nerve signals that travel down axons

what affect do graded potentials have on action potentials

graded potentials effect whether action potentials can be generated

what happens when a gated K+ channel is open for a long time

more K+ can leave, more hyperpolarization

what causes an action potential

a massive change in membrane voltage resulting from depolarization shifting the membrane potential significantly

describe action potentials

they are always the same strength and either happen or not, and transmit signals over long distances

what is the threshold voltage for most neurons

approx -55mV

what is occurring when a cell is at resting potential

most voltage-gated Na+ and K+ channels are closed

what happens when action potential is generated

Na+ channels open first, and Na+ flows in, the depolarizing phase rises, the threshold is cross and the membrane potential increase. then the repolarizing phase happens, where Na+ channels become inactivated and the Na+ gates close and the K+ channels open

what happens during hyperpolarization/ undershoot

membrane permeability to K+ is at first higher, and this lets K+ exit the cell, the then the channels close and resting potential is restored

what does the frequency of the action potential rely on

the strength of the stimulus

what can affect the height of the action potential in a neuron

nothing, it is always the same height, just different frequency

refractory period following an action potential

a second action potential cannot be initiated because the Na+ channels have been temporarily inactivated

what is the site where the action potential typically generated

the axon hillock

what is the ONLY way an action potential can travel

down the axon and towards the synaptic cleft

what prevents the action potential from going backwards

the inactivated voltage gated Na+ channels

what causes an action potentials speed

the axons diameter makes it faster, bigger axon= faster action potential velocity

myelin sheath

insulated the axons and causes an action potentials speed to increase

oligodendrocytes

glia making up the myelin sheaths in the CNS

Schwann cell

glia making up the myelin sheaths in the PNS

what macromolecule makes up myelin sheaths

lipids, they are poor conductors

nodes of ranvier

the gaps between the myelin sheath where action potentials are found and voltage gated Na+ are found

saltatory conduction

action potentials in myelinated axons jumping between the nodes of Ranvier

continuous conduction

unmyelinated axons carry action potentials by this when each part of the axon has to generate action potential

which is more efficient saltatory conduction or continuous conduction

saltatory conduction is faster, continuous conduction is very slow