Chapter 1 - Neurons, Action Potentials and Synapses Flashcards
Describe 5 functions of glial cells.
Regulation of neuron-to-neuron communication.
Transfer of nutrients from the blood to the neurons.
Covering the axons to increase the transmission speed of action potentials.
Removal of pathogenic and dead cell bodies from the brain.
Creating highways for neuron migration during development.
What is the soma and what does it do?
Cell body. Contains cell’s nucleus with the DNA of the cell.
What are dendrites and what are their functions?
Structures that receive input from other neurons (they look like branches)
What is the axon?
Part of the cell that sends the output of the neuron to other neurons. Transmits the cell’s action potential.
Describe how neurons communicate with each other (3)
- Neurons communicate with each other using synapses. The main way in which neurons communicate between them is by means of chemicals.
- One neuron releases small molecules called neurotransmitters, and a second neuron detects these molecules to change its activity.
- Synaptic transmission is one-way communication, from axon of presynaptic neuron, which releases neurotransmitters, to the dendrite of the postsynaptic neuron, which detects the neurotransmitters.
Define Ohm’s law.
V = I x R
V = voltage, I = current, R = resistance
Define equilibrium potential.
The membrane potential that leads to zero ionic current (or equilibrium) given a certain ionic concentration.
Depends on the concentration gradient of ion and the ion’s charge.
What mechanism is being used by the brain to transmit information? Define the mechanism.
Through electrical impulses/action potentials. This is the movement of changes in membrane voltage down the axon.
The membrane of a neuron is primarily composed of ________.
Lipids/fats.
How is the interior of a cell linked with the exterior of the cell?
There are proteins inserted inside membranes which are able to link inside and outside together.
What creates a concentration gradient within the cell?
What are the roles of ion channels?
Ions are present in different concentrations inside and outside of the cell.
K+ is more concentrated inside, hence creating a concentration gradient.
Proteins that selectively allows ion to pass through.
What does the presence of a concentration gradient lead to?
The concentration gradient drives K+ out of the cell once K+ ion channels open. –> because K+ is more concentrated inside the cell.
However, when K+ ions exit the cell, what happens?
As K+ starts exiting, this creates a charge imbalance inside and outside the cell, such that the inside becomes negative and the outside becomes positive.
This creates an electrical gradient, as positive ions are attracted to negative ions. K+ ions outside will then want to enter the cell as the cell is more negative.
What happens with the creation of a concentration gradient and an electrical gradient?
Both forces eventually balance out and reach a point of equilibrium, where both forces are identical and the net flow of ions is zero
For every K+ that goes out of the cell, another K+ will enter the cell. This is called the equilibrium potential for a specific ion.
Define equilibrium potential/Nernst potential.
The membrane potential at which the net flow of ions or current is zero, given a specific intra- and extracellular concentration of the ion.
When a neuron is at rest, it is at ___________
Dynamic equilibrium.
Define resting membrane potential.
The membrane potential at which there is zero net ionic current, when considering all ions.
How does the cell manage to maintain this difference in concentration of Na+ and K+ across the membrane?
Another membrane protein, the Na+/K+ ATPase, pumps K+ into the cell and Na+ outside.
- Requires energy to do so since it’s against each of their concentration gradients.
- To do this, body has to burn ATP, which is the main source of energy of all cells in our bodies.
Does the K+ channel require energy to work?
No. things just flow.
As long as the channel is open, K+ will freely flow down its electrochemical gradient (goes outside as it’s more negative outside).
importantly, when neurons are at rest, only K+ channels are open, and Na+ channels are closed. Hence, RMP is close to K+ reverse potential of =70mV.
At rest, K+ channels are ________ whereas Na+ channels are _______
open, closed
How does the electrical and concentration gradient act on Na+ at rest?
Electrical gradient: Na+ is attracted to interior of cell which is negative
Concentration gradient: Na+ is more concentrated outside than inside. Flow in.
How does the electrical and concentration gradient act on K+ at rest?
Electrical gradient: pull K+ to negative interior of cell
Concentration gradient: drives K+ out as it is more concentrated inside the cell
What is the resultant force of electrical and concentration gradient of K+?
Small net flow out of cell. Sodium potassium pump continues pulling K+ into cell, so it’s always a little more concentrated inside.
What is an action potential?
refers to movement of changes in membrane voltage down the axon.
What is a voltage-gated channel?
Refers to an ion channel that opens in response to an increase of the membrane potential (depolarization) as long as this increase crosses a certain threshold.
Which gate opens and close in response to changes in membrane potential??
Activation gate
At which point does the neuron start depolarizing rapidly, and what occurs at this point?
-60mV –> cross this threshold.
Opening of voltage-gated Na+ channels.
Why does the neuron repolarize quickly following rapid depolarization?
Voltage-gated Na+ channels closer due to inactivation.
Voltage-gated K+ open.
Why does the neuron afterhyperpolarizes?
membrane voltage overshoots the RMP, going even more negative and closer to K+ reversal potential at around -80mV.
because both voltage-gated K+ channels are still open –> increases conductance available for K+, considering that there are also always-open K+ channels, which maintains the RMP.
Why is the action potential described as “all or none”
Once you cross the threshold, the action potential goes the whole way, meaning there are no half action potentials.
As soon as some voltage-gated Na+ channels open, this drives further depolarization –> opens up more Na+ channels in turn
Magnitude of depolarization still remains the same, as long as threshold is crossed.
Depolarization is caused by the ____________.
Repolarization is caused by the __________ and ____________.
Opening of voltage-gated Na+ channels.
Closing of voltage-gated Na+ channels and opening of voltage-gated K+ channels.
The action potential propagates down the axon due to _______ that enter during the depolarization phase.
diffusion of ions
Describe how the action potential is propagated
Change in membrane potential propagates down the axon towards the axon terminals.
The action potential begins all the way to the left, close to the cell body.
- Nat+ enters the cell through the voltage-gated Na+ channels.
- When Na+ enters in that segment, there will be a higher concentrations of Na+ compared to adjacent locations.
- So, Na+ will diffuse left and right down its concentration gradient.
Now, since Na+ diffused to the right, this new piece of membrane becomes depolarized, which in turns opens voltage-gated Na+ in that new segment.
What is the absolute refractory period?
A period following an action potential in which the neuron cannot fire another action potential (ie impossible)
What is the relative refractory period?
The period following an action potential in which it is harder (but not impossible) to fire another action potential.
This is due to the extremely negative membrane potential during the afterhyperpolarization, which means that if the neuron wants to initiate an action potential, it requires much more synaptic input to depolarize it enough to reach the action potential threshold.
It is an insulating sheath around an axon, and it increases the speed of action potential conduction.
Myelin
With myelin, action potentials will jump from one _____ to the next.
node of ranvier
Why action potentials cannot regenerate between nodes of ranviers?
because Na+ channels are absent between the notes. This is faster and helps conserve energy. All the positive charge when Na+ ions enter will be moved to the next node along the axon.
