Action Potential Flashcards
polarized
plasma membrane at rest
one side has a different charge than the other side
resting potential
axon is not conducting an impulse
difference in electrical charge equal to about -70mV
charge is negative because the charge on the inside of the axon’s cell membrane is 70 millivolts less than the outside of the membrane
sodium-potassium pump
active transport to carry ions across the plasma membrane
pump works uses an integral carrier protein
for every three sodium (Na+) ions pumped out, two potassium (K+) ions are pumped in
pump must keep in constant operation because the Na+ and K+ ions will naturally diffuse back to where they originated
a relative positive charge develops and is maintained on the outside of the membrane
action potential
change in polarity
resting potential becomes an action potential if the membrane becomes depolarized
Once an action potential occurs, it continues through the entire length of the axon
depolarization
inside of the membrane is now more positive than the outside
re-polarization
potential returns to normal
indicating that the inside of the axon is negative again
Phases of Action Potential
Phase 1: Resting Potential: During the resting phase, both sodium and potassium gates are closed.
Phase 2: Depolarization: The sodium gates open, and sodium rushes into the axon during the depolarization phase of the action potential. Voltage travels to zero and then on up to +40 mV.
Phase 3: Repolarization: The sodium gates close, and potassium gates open allowing potassium to rush out of the axon. This returns a negative voltage to the inside of the axon
Phase 4: Afterpolarization, also called hyperpolarization. Potassium gates are slow to close, and there is an undershoot of the potential. The voltage drops below -70mV and then returns to -70mV as the resting state begins
self-propagating
ion channels are prompted to open whenever the membrane potential decreases (depolarizes) in an adjacent area
Action potential (all or nothing)
response, either occurring or not.
Since no variation exists in the strength of a single impulse, intensity of a sensation (minor or major pain) is distinguished by the number of neurons stimulated and the frequency with which the neurons are stimulated
synapse
minute fluid-filled space
electrochemical
transmission of nerve impulses is electrochemical in nature as chemicals called neurotransmitters allow the signal to jump the synaptic gap
signal moves from electrical (through the neuron) to chemical (in the synapse) to electrical again once the signal reaches the next neuron
Nerve Impulse Journey
1) nerve impulse reaches the end of an axon
2) voltage-gated calcium channels open. As calcium ions (Ca2+) rushes in, it causes vesicles containing the neurotransmitters to fuse with the plasma membrane and release the neurotransmitter into the synapse.
3) When the neurotransmitter released binds with a receptor on the next neuron, sodium ion (Na+) channels in the receiving dendrites open
* depolarization occurs at next neuron
acetylcholinesterase (enzyme)
aka simply cholinesterase,
breaks down the neurotransmitter acetylcholine
synapses contain enzymes that rapidly inactivate the neurotransmitter
Neurons actions w/neurotransmitters
- neurons repackage the neurotransmitters in synaptic vesicles
- others chemically breakdown the neurotransmitters
- The short existence of neurotransmitters in the synapse prevents continuous stimulation of postsynaptic membranes
inhibition
Prevention of continuous stimulation
