Topic 19: Action Potentials Flashcards
What is membrane potential?
the potential to do work
What is voltage?
a measurement of membrane potential
What are excitable cells?
cells that can rapidly change membrane potential
What is the resting potential?
MP of a cell at rest
-70mV
Why is the inside more negative than the outside?
because of the Na/K pump
and ion channels
What is the sodium-potassium pump? Where is it found? What does it do in relation to action potentials? Active or passive?
transmembrane transport protein
found of PM throughout neuron
3 Na+ out and 2 K+ in
Active transport (charged ions cannot diffuse)
What does hyperpolarization do?
becomes more negative inside the cell
MP decreases below RP
it is inhibitory
What does depolarization do?
becomes less negative inside cell
MP increases above RP
it is excitatory
What is action potentials?
electrical signal within neuron
How are voltage gated ion channels opened?
by a stimulus
-> facilitated diffusion of that ion down concentration gradient
What forms the concentration gradient?
Na/K pump
What happens when the VG sodium channels open?
Na+ rushes into the cell
-> inside becomes more positive (depolarization)
What happens when the VG potassium channels open?
K+ rushes out of cell
-> inside becomes less positive (hyperpolarization)
What is the membrane potential when the neuron is at rest?
-70 mV
What happens when there is a small stimulus?
FEW Na+ gates opne
weak depolarization
MP does not reach -55 mV
No AP
What happens when there is a strong stimulus?
MANY VG Na+ channels open
Strong depolarization
if MP reaches -55 mV -> AP
During the rising phase, what voltage does the depolarization reach?
+35 mV
What happens after the rising phase, when the voltage reaches +35 mV?
Na+ gates close K+ gates begin to open by +35 mV, K+ gates now fully open K+ diffuses out repolarization
What happens during the undershoot phase?
Na+ gates closed
K+ gates start to close slowly
hyperpolarization occurs
when the K+ gates fully close, it then returns to RP
Where does continuous conduction occur in?
unmyelinated axons
What happens during continuous conduction?
every spot on axon depolarizes, repolarizes
Where does saltatory conduction occur in?
myelinated axons with myelin sheath
What are internodes?
regions covered in myelin - no depolarization
What are nodes of ranvier?
no myelin - lots of Na+, K+, VG channels
depolarization only occurs at nodes
