Chapter 1 - Neurons, Action Potentials and Synapses

Question 1

Describe 5 functions of glial cells.

Answer 1

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.

Question 2

What is the soma and what does it do?

Answer 2

Cell body. Contains cell’s nucleus with the DNA of the cell.

Question 3

What are dendrites and what are their functions?

Answer 3

Structures that receive input from other neurons (they look like branches)

Question 4

What is the axon?

Answer 4

Part of the cell that sends the output of the neuron to other neurons. Transmits the cell’s action potential.

Question 5

Describe how neurons communicate with each other (3)

Answer 5

1. Neurons communicate with each other using synapses. The main way in which neurons communicate between them is by means of chemicals.
2. One neuron releases small molecules called neurotransmitters, and a second neuron detects these molecules to change its activity.
3. 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.

Question 6

Define Ohm’s law.

Answer 6

V = I x R

V = voltage, I = current, R = resistance

Question 7

Define equilibrium potential.

Answer 7

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.

Question 8

What mechanism is being used by the brain to transmit information? Define the mechanism.

Answer 8

Through electrical impulses/action potentials. This is the movement of changes in membrane voltage down the axon.

Question 9

The membrane of a neuron is primarily composed of ________.

Answer 9

Lipids/fats.

Question 10

How is the interior of a cell linked with the exterior of the cell?

Answer 10

There are proteins inserted inside membranes which are able to link inside and outside together.

Question 11

What creates a concentration gradient within the cell?

What are the roles of ion channels?

Answer 11

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.

Question 12

What does the presence of a concentration gradient lead to?

Answer 12

The concentration gradient drives K+ out of the cell once K+ ion channels open. –> because K+ is more concentrated inside the cell.

Question 13

However, when K+ ions exit the cell, what happens?

Answer 13

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.

Question 14

What happens with the creation of a concentration gradient and an electrical gradient?

Answer 14

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.

Question 15

Define equilibrium potential/Nernst potential.

Answer 15

The membrane potential at which the net flow of ions or current is zero, given a specific intra- and extracellular concentration of the ion.

Question 16

When a neuron is at rest, it is at ___________

Answer 16

Dynamic equilibrium.

Question 17

Define resting membrane potential.

Answer 17

The membrane potential at which there is zero net ionic current, when considering all ions.

Question 18

How does the cell manage to maintain this difference in concentration of Na+ and K+ across the membrane?

Answer 18

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.

Question 19

Does the K+ channel require energy to work?

Answer 19

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.

Question 20

At rest, K+ channels are ________ whereas Na+ channels are _______

Answer 20

open, closed

Question 21

How does the electrical and concentration gradient act on Na+ at rest?

Answer 21

Electrical gradient: Na+ is attracted to interior of cell which is negative
Concentration gradient: Na+ is more concentrated outside than inside. Flow in.

Question 22

How does the electrical and concentration gradient act on K+ at rest?

Answer 22

Electrical gradient: pull K+ to negative interior of cell

Concentration gradient: drives K+ out as it is more concentrated inside the cell

Question 23

What is the resultant force of electrical and concentration gradient of K+?

Answer 23

Small net flow out of cell. Sodium potassium pump continues pulling K+ into cell, so it’s always a little more concentrated inside.

Question 24

What is an action potential?

Answer 24

refers to movement of changes in membrane voltage down the axon.

Question 25

What is a voltage-gated channel?

Answer 25

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.

Question 26

Which gate opens and close in response to changes in membrane potential??

Answer 26

Activation gate

Question 27

At which point does the neuron start depolarizing rapidly, and what occurs at this point?

Answer 27

-60mV –> cross this threshold.

Opening of voltage-gated Na+ channels.

Question 28

Why does the neuron repolarize quickly following rapid depolarization?

Answer 28

Voltage-gated Na+ channels closer due to inactivation.

Voltage-gated K+ open.

Question 29

Why does the neuron afterhyperpolarizes?

Answer 29

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.

Question 30

Why is the action potential described as “all or none”

Answer 30

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.

Question 31

Depolarization is caused by the ____________.

Repolarization is caused by the __________ and ____________.

Answer 31

Opening of voltage-gated Na+ channels.

Closing of voltage-gated Na+ channels and opening of voltage-gated K+ channels.

Question 32

The action potential propagates down the axon due to _______ that enter during the depolarization phase.

Answer 32

diffusion of ions

Question 33

Describe how the action potential is propagated

Answer 33

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.

Question 34

What is the absolute refractory period?

Answer 34

A period following an action potential in which the neuron cannot fire another action potential (ie impossible)

Question 35

What is the relative refractory period?

Answer 35

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.

Question 36

It is an insulating sheath around an axon, and it increases the speed of action potential conduction.

Answer 36

Myelin

Question 37

With myelin, action potentials will jump from one _____ to the next.

Answer 37

node of ranvier

Question 38

Why action potentials cannot regenerate between nodes of ranviers?

Answer 38

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.