Membrane Potentials Flashcards
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
During the action potential how is the voltage and na and k concentration gradients affected
The voltage gradient changes but the concentration gradients are barley affected
How does the action potential travel down the axon
Through a nerve impulse
the action potential is sent along the neuron by the triggering of action potentials in adjacent portions of the membrane
What are the two way a nerve impulse can happen
Continuous conduction
Saltatory conduction
what is continuous conduction
Happens in unmyleinated axons (with no myelin sheet)
The flow of current during the action potential will make the membrane region next to where the action potential is happening to become depolarized
The action potential that was induced along the axon doesnt lose its intensity but
The part of the membrane that previously had the action potential is in a refractory period where the sodium channels can’t reopen to move the action potential backwards.
What happens in a saltatory conduction
Happens myelinated axons where the nerve impulses are 20x faster than in unmyelinated because
The myelin (lipid rich) prevents ions from passing across the membrane
This means the the na and k channels are found in or near unmyelinated region of the axon called nodes of ranvier.
The action potential at this NODE induced action potential at another NODE (faster propagation of the action potential down the axon)
Can nerve impulses be amplified
No
What determines the direction of the nerve impulse down the axon
The refractory period
What is a synapse
The junction (interaction) of a neurons terminal knob with its target cell
What is a pre synaptic cell
The neuron that conducts the impulse (action potential) towards a synapse
What is the synaptic cleft
The space separating the neuron from the target cell
What is the postsynaptic cell
The cell that takes in the impulse
What is the synaptic vesicles
The things that store neurotransmitters in the terminal knobs of the axons
What are neurotransmitters
The chemical that’s released from the synaptic vesicles and binds to the postsynaptic cell
What happens after the nerve impulse is propragted along the axon and goes to the terminal knob
The impulse causes depolarization to happen in the knob which leads to the voltage gated calcium channels to open in the presynatic cell (knob)
This leads to calcium diffusing into the presynatpic cell since initially ca concentration was low in the cell
After the ca goes into the presynaptic cell after the nerve impulse what happens
The influx of ca into the presynaptic cell triggers the synaptic vesicles to fuse with the plasma membrane of the presynaptic cell
This releases the neurotransmitters (acetylcholine) in the synaptic vesicle to the recipient cells and allows them to bind to the ligand gated ion channels or the postsynaptic cells membrane
After the neurotransmitters are binded to the ligand gated ion channels on the postsynaptic cell what 2 things can happen
Excitatory effect: The neurotransmitters cause an influx of na (+) ion into the postsynaptic cell which depolarizes the cell and bring it to form action potential/nerve impulse
Inhibitory effect : negative ions (cl) are influx instead and do hyperpolarization where action potential less likely to happen
What stops the postsynaptic cell from continually being stimulated once neurotransmitters have entered the synaptic cleft
The neurotransmitters have a short half-life
enzymes destroy them in the synaptic cleft
Or they are taken back up into the presynaptic cell by transporters in the presynaptic cell
