action potentials Flashcards
depolarization
the cell becomes less negative
hyperpolarization
the eletrical force becomes stronger as the cell gets more negative, potassium starts to flow in and equalise again
action potential
small change in the membrane potential due to a stimulation through electrical currents or chemical messengers, resulting in a less negative cell
action potential threshold
when the neuronal cell is stimulated above -60mv and voltage gated channels open
process of an action potential
- neuron is stimulated above a threshold
- voltage gated channels for na and k open up
- sodium starts to flow into the cell (both concentration and electrical gradient)
- cell starts to depolarize
- potassium starts to flow out of the cell (concentration gradient)
- membrane potential rises until it reaches 20mv and voltage gated channels close again
- sodium influx stops immediately but potassium continues to flow through leaky channels
-electrical and concentration gradient push potassium out - continues until eletcrical and concentration force are in equilibrium again (-70mv)
- sodium/potassium pump, pump sodium out and potassium into the cell to restore chemical balance
what causes the increase in positivity in the cell
sodium flows back into the cell much stronger than potassium flowing out
what causes hyperpolarization
the potassium outflux is stronger than sodium influx so the cell becomes negative
why do we need protein pumps
to pump the sodium from a low concentration to a high concentration
protein pumps
actively moves sodium out and potassium in
how do protein pumps work
binds two potassium on the outside, flips around to put the two potassium inside the cell and binds three soidum, then flips again to move the sodium outside the cell
all or none response
you cant have a little action potential. cells only differentiate by how many actions they produce, not by size
action potential propogation
how electrical activity moves down the axon to the terminal region
axon hillock
where the initial sodium ion channels start
steps of an action potential propogating
- as the area of the neuron thats activated depolarizes, that part of the membrane reaches -60mv
- at -60mv, the ion channel next to it opens up
- as sodium flows in the cell depolarizes
- this spreads to the next sodium channel that reaches the thresh hold and so on
- once one ion channel has opened up, the area on the membrane close by opens up, all along the axon
what is propogation
-once the action potential has been generated it moves along by activating the next ion channel like dominoes in a row, until it moves so far that the membrane reaches 20mv and the channels close again
what state to sodium ion channels go into when they close
the refractory state
types of refractory state
absoloute, relative
absoloute refractory state
not response at all, about 1ms
relative refractory state
only responsive to strong stimuli (2-4ms)
what is the purpose of the refractory state
allows the membrane potential to go back to -70mv, so the cell doesnt continue firing
why is the refractory state important
stops information from moving from the axon to the terminal and and back to the axon
myelinated neurons
neurons with a myelin sheet wrapped around the axon to insulate them
nodes of ranvier
gaps in mylein sheets on myelinated neruons that action potentials jump between when propogated
why are myelinated neurons good
propogate action potentials about 10x faster, helps communicate over a long distance faster
saltatory conduction
the way an electrical impulse skips from node to node down the full length of an axon
