Week 1: Neurons, Action Potential, Synapic Connections

Question 1

What are some roles of glia cells? (5)

Answer 1

1. regulation of neuron to neuron communication
2. transfer nutrients from blood to neuron
3. cover axons to increase transmission speed of action potentials
4. removal of pathogens and dead cell bodies from brain
5. create high ways for neuron migration during development

Question 2

What is the ratio of glia cells to neurons?

Answer 2

Outnumber neurons but 10:1

Question 3

What does a dendrite do?

Answer 3

Receive input from other neurons

Question 4

Why do dendrites grow like a dendritic tree?

Answer 4

Greater surface area allows it to receive more information

Question 5

What is the soma and what happens there?

Answer 5

‘cell body’ where metabolic work occurs

Question 6

What are the roles and features of an axon? (3)

Answer 6

send output to other neurons
transmits action potential
constant diameter

Question 7

How do neurons communicate?

Answer 7

By chemicals. Axon of presynaptic neuron releases neurotransmitter and dendrite of postsynaptic neuron detects them to change its activity. Synaptic transmission is one-way communication.

Question 8

What is Ohm’s law?

Answer 8

V=IR
V is voltage
I is current
R is resistance. (opposite of conductance)

Question 9

What is the neuron membrane made of?

Answer 9

lipids (fats/oil)

Question 10

When in contact with water/liquid, what does the neuron membrane form?

Answer 10

A phospholipid bilayer.

Question 11

What are the other 2 terms for Equilibrium potential for a specific ion?

Answer 11

Nernst potential/Reversal potential

Question 12

What creates the concentration gradient across the cell membrane?

Answer 12

When ions are present in different concentrations inside and outside of the cell. (Since K+ more concentrated inside cell, concentration gradient drives exit of K+ once gate opens.)

Question 13

What is the role of protein in the cell membrane?

Answer 13

An ion channel that selectively allows passage of certain ions only (eg. only K+)

Question 14

What creates the electrical gradient across the cell membrane?

Answer 14

When there is a charge imbalance inside and outside the cell. (+-). Overall charge inside and outside cell is 0.

Question 15

Briefly describe the equilibrium potential for a specific ion (nernst potential, reverse potential)

Answer 15

when the 2 opposing forces of concentration vs electrical gradient eventually balance out and reach a point of equilibrium. (net flow of ions is 0)

Question 16

What is the resting membrane potential?

Answer 16

the membrane potential at which overall flow of current (counting all ion species) equals 0. (ie. when multiple types of ions reach an equilibrium)

Question 17

How does the cell maintain the difference in concentration of Na+ and K+ across the membrane.

Answer 17

Sodium-Potassium Pump (or Na+/K+ ATPase)
- a membrane protein that pumps K+ into the cell and Na+ out of the cell. Energy (ATP) is needed because the movement of both ions does against their concentration gradients. (active transport)

Question 18

Resting membrane potential is close to the reverse potential of ___?

Answer 18

K+ (around -70mV)

Question 19

At rest, K+ channels are ___ and Na+ channels are ___? (open/close)

Answer 19

open; closed.

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Electrical gradient: pull K+ to negative interior of cell

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

Question 22

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

Answer 22

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

Question 23

What is an action potential?

Answer 23

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

Question 24

What is a voltage-gated channel?

Answer 24

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 25

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

Answer 25

the activation/regulation gate. NOT the the inactivation gate!

Question 26

Why is action potential considered all-or-none?

Answer 26

Because as soon as some Na+ channels open, this drives further depolarization, in turn driving the opening of even more Na+ channels. The magnitude of depolarization will always be the same, as long as threshold is crossed. Amplitude & velocity of action potential are independent of the intensity of the stimulus that initiated it.

Question 27

What is the absolute refractory period?

Answer 27

Period following an action potential in which the neuron cannot fire another action potential as inactivation gates are closed. No matter how depolarized the membrane is, inactivation gates are not opening.

Question 28

What is the relative refractory period?

Answer 28

Period following an action potential in which it is harder (but not impossible) to fire another action potential. Due to extremely negative membrane potential during afterhyperpolarization. Neuron requires much more synaptic input to depolarise it enough to reach the action potential threshold.

Question 29

What is myelin?

Answer 29

Myelin is an insulating sheath around an axon that increases the speed of action potential conduction. It is made of membranes of glia cells.

Question 30

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

Answer 30

node of ranvier

Question 31

Why action potentials cannot regenerate between nodes of ranviers?

Answer 31

because Na+ channels are absent between the notes. This is faster and helps c onserve energy. All the poitive charge when Na+ ions enter will be moved to the next node along the axon.