Membrane Potentials Flashcards
(41 cards)
What is a neuron (nerve cells)
What are most neurons found in
A specialized cell that is used for communication with other cells in the form of electrical impulses (that a formed by changes in ion gradients)
Most neuron are part of the central nervous system and peripheral nervous system (brain and spinal cord)
What is a neuron composed of
Dendrites
Axons
Terminal knobs
Myelin sheaths
What are dendrites
They are the parts of the neuron than branch out from the neuron body and receive information (from other neurons)
What are axons
The long end of the nerve cell that extends from the body to the terminal knobs
It conducts outgoing information
What are terminal knobs
Thing where the impulses are transmitted to the target cells
One neuron can have many terminals knobs that interact with many different cells
What is the myelin sheath
It’s a lipid rich membrane that wraps around most vertebrate axons
All cells have a ___
Membrane potential/ membrane voltage
What is a membrane potential/voltage
The difference in charge across a membrane
The outside of the cell has different charge than the inside of the cell
What is the resting potential
The potential of the membrane when a nerve cell is in an unexcited state (not stimulated)
What is the axon membrane voltage diffence between the inside of the membrane and the outside
If just outside?
The voltage is -70
0 because there’s no charge difference
What is the voltage of the inside of the cell compared to the outside
-70
Means the cell in more Negative on inside
What is the resting potential of a neuron
-70mV
What contributes to the difference in charge across the membrane?
- The sodium potassium pump in the membrane pumps 3 sodium ions out of the cell per every 2 k+ going in. Creating a gradient and making the voltage more negative
This means that overall more positive charges are going out of the cell, making the outside more +
- The k+ ions have the most permeability in a resting nerve cell
they flow out of the cell through potassium leak channels (following their concentration gradient)
This cause more postive charges on the outside of the cell
How is equilibrium reached if more postive is outside the nerve cell membrane than the outside
the concentration gradient favours k+ going out
The electrical gradient favours the k+ going in
So a balance between k in and k out occurs so overall voltage doesn’t change much from -70
What is an action potential
It is the changes in the axons membrane potential after a stimulus (poke, heat) is introduced
The basic for neural communication
Includes depolarization and repolarization and takes 5ms in a squids axon
What are the step of what happens for an action potential
Resting potential
Depolarization
Repolarization
What is the resting potential part of action potentials
The k plus is leaving the cell through the leak channel, the inside of the membrane is more negative than outside
The membrane is not very permeable to sodium or potassium through the sodium or potassium gates (gates are closed)
What is depolarization
The electrical potential/voltage difference across the membrane decreases
meaning the inside of the membrane is more postive like the outside, and the voltage is less negative
How does depolarization happen
What happened if there a larger stimulus
In response to the stimulus, sodium channels In The cell membrane open and the sodium diffuses into the cell through a voltage gated na Channel
The inside of the cell has become more postive
If larger stimulus more sodium in the cell
If lower stimulus less sodium into cell and depolarization doesn’t happen
What is the threshold value to depolarization to happen and what happens after
Enough na has to come in so that the membrane potential goes from -70 to -50mV
Once this happens, the voltage gated sodium channels open and wayyy more sodium comes into the cell to make the potential go to +40mV
The sodium channel close spontaneously after 1ms
What happens to the permeability of NA and K during depolarization
The na is wayyyy more permeable then the k+
What happens during repolarization
Want more negative on inside of the cell to get more negative voltage
After the depolarization occurs, this triggers the the voltage gated K channels of open and the sodium’s channels close
This makes it so that more + is now LEAVING the cell and creating the polarity. This causes the membrane potential to go to -80mV
Because the membrane potential becomes very largely NEGATIVE now due to charge difference (more negative on inside) the voltage gated potassium channels CLOSE
What happens to the permeability of potassium and NA during repolarization
The K is initially very high permeable and sodium is low
Then after a while the K get lower and the na gets lower
What is hyperpolarization
The potassium channels are slow to close so the potential over shoots and goes to -80 during repolarization
