Time is required to re-establish the resting potential after
an action potential has been initiated.
no other action potential may be initiated, no matter how
strong the signal
Different neurons have differing threshold levels before
an action potential will proceed.
Sensitive neurons will have low threshold values.
all-or-none response – neurons will or will not fire
greater axon diameter = greater axon surface area
Larger surface area results in more ion channels and
therefore less time to depolarize and repolarize.
Na+ and K+ exchange can only occur where the axons
are exposed to the extracellular fluid.
allows for faster signal conduction along the axon
synapse – structure
formed by two adjacent
action potentials cause
axon terminals to
the synaptic cleft
Types of Na+ Channels
postsynaptic cells receive chemical signals
ion channels opened due to membrane
acetylcholine – common neurotransmitter
released upon neuron depolarization
from presynaptic neuron
causes Na+ channels to be opened
in the postsynaptic neuron
How does the postsynaptic neuron know when the
signal has stopped?
enzymes released will degrade the chemical
cholinesterase – released by postsynaptic neuron
causes action potential to proceed in postsynaptic
prevents action potential to proceed
hyperpolarization – membrane is more negative;
therefore stronger signal needed
Putting it all Together
positive and negative signals collect (summation) on
Why are negative signals important?
experience has told you what should be concentrated
on and what can be ignored