Membrane and Action Potential Flashcards
what is the action potential?
a rapid, all or none change in the membrane potential followed by a return to the resting membrane potential
what type of channels are the basis for action potentials?
voltage dependent ion channels
how is an action potential propagated?
with the same shape and size along the entire length of an axon
where are action potentials initiated?
at the initial segment of the axon
what is the action potential the basis for?
the signal carrying ability of nerve cells
the patterns of conducted action potentials encode what?
the information conveyed by the nerve cells
what are the nodes of ranvier?
they help propagate the action potential from the cell body to the axon terminal
what is the purpose of the nernst equation?
it allows the electrical potential across the membrane at equilibrium to be predicted exactly and how sodium is kept outside and potassium ions kept inside
what is the Goldman equation?
determined voltage concentration to keep cells on their respectful side of the cell, intracellular ions vs extracellular ions
at the peak of the membrane potential, what ion runs the show and name corresponding voltage?
sodium at +58
at hyperpolarization, which ion runs the show?
potassium at -90, but other ions play a factor in returning the membrane back to resting potential
how many gates do sodium channels have?
2, M gate (middle) and H gate (cytosolic side)
relate the M gate and H gate to the various states of the membrane potential
Resting state, sodium channels are closed, end gates closed and H gates are opened. During depolarization, M gate opens up to allow sodium influx. For repolarization, H gate closed first to prevent sodium influx. In the undershoot, both are closed. During resting state, H gate opened and M gate closed, easier to open when depolarization happens again.
what is the effect of ischemia on the membrane potential?
In ischemic tissue, rate of recovery is longer because cells stay in the depolarized state. They were going through a systolic process, MI, happens recovery is halted and so less sodium channels participating in the next depolarization state and so erratic passages from atrium to ventricle, translated on the ECG.
resistance is much higher in an axon with a smaller diameter, T/F?
T
You need to change the membrane potential of neurons to carry information (like action potentials). Instead of pumping ions out of equilibrium and opening and closing ion-selective channels (which is difficult to understand) why don’t neurons just use ATP to pump positive ions in to depolarize and out to repolarize during an action potential?
pumps using ATP can not select between positive and negative ions
pumps using ATP are not fast enough to change the membrane potential in 1-2 milliseconds which is the time course of a typical action potential.
there would not be enough ATP available
pumps using ATP can not move significant amounts of ions
pumps using ATP are not fast enough to change the membrane potential in 1-2 milliseconds which is the time course of a typical action potential.
one of the most potent poisons known, specifically blocks the Na+ channel
Tetrodotoxin (TTX)
how does tetrodotoxin (TTX) work?
TTX binds to the extracellular side of the sodium channel
this poison blocks K+ channels
Tetraethylammonium (TEA+)
how does Tetraethylammonium (TEA+) work?
TEA+ enters the K+ channel from the cytoplasmic side and blocks the channel because TEA is unable to pass through it.
what species of animals contain tetrodotoxin (TTX)?
puffer fish, also known as blowfish
You decide to take your chances and have some of that amazing puffer fish you’ve heard so much about. Unfortunately, your sushi chef got his license from a questionable online university and he leaves in too much tetrodotoxin (TTX). The sensory neurons in your lips stop firing action potentials and your lips go numb because:
the TTX blocks potassium channels, hyperpolarizing the membrane
the TTX blocks sodium channels, preventing the membrane from hyperpolarizing
the TTX blocks sodium channels, preventing the membrane from depolarizing.
the TTX opens sodium channels, depolarizing the membrane
the TTX blocks sodium channels, preventing the membrane from depolarizing.
what is the relationship between synaptobrevin and botulinum toxin?
Synaptobrevin can be eliminated or degraded by botulinum toxin, then the muscle cannot be contracted; very popular for wrinkling free treatment of the face like botox
Eating home-canned vegetables or smoked fish is associated with the transmission of botulism. Clostridium botulinum synthesizes its neurotoxin, which is a specific protease affecting the presynaptic protein called synaptobrevin. An individual suffering from botulism with this specific protease would ________?
Be unable to open voltage-gated Ca2+ channels along the presynaptic membrane following an action potential
Have a massive discharge of synaptic vesicles even with low extracellular Ca2+
Be unable to utilize ATP for endocytosis
Result in diminished or absent end-plate potentials on the skeletal muscle membrane.
Result in diminished or absent end-plate potentials on the skeletal muscle membrane.
