Module 2

Question 1

What are the three rules regarding injected current

Answer 1

1. If injected current does not depolarize the membrane to threshold, no action potential will be generated
2. If injected current depolarizes the membrane beyond threshold, action potentials will be generated
3. The action potential firing rate increases as the depolarizing current increases

Question 2

Explain the role of the separate gates in Voltage-gated Na+ channels

Answer 2

As the membrane potential depolarizes, the inactivation gate will slowly close, while the activation gate quickly opens.

Question 3

Explain the role of gates in Voltage gated K+ channels

Answer 3

First, it only has one gate. That gate opens as the membrane depolarizes

Question 4

What main purpose do K+ channels play in an action potential?

Answer 4

When the cell depolarizes, they open, causing a hyper-polarization, and bring the action potential back down towards rest.

Question 5

Defined the K+ channel called the Delayed Rectifier

Answer 5

opens slowly in response to changes in membrane potential, closes slowly. Responsible for repolarizing axonal membrane following an action potential

Question 6

Defined the K+ channel called the A-channel

Answer 6

Opens when the membrane is depolarized, closes rapidly, influences neuron excitability

Question 7

Defined the K+ channel called the Inward Rectifier

Answer 7

Opens when membrane is hyperpolarized, influences duration of action potential

Question 8

Defined the K+ channel called the Ca2+ activated channel

Answer 8

Opens in the presence of Ca2+, influences the excitability of the neuron

Question 9

Defined the K+ channel called the M-channel

Answer 9

Opens when the membrane is depolarized, closes slowly. Regulated by neurotransmitters

Question 10

Defined the K+ channel called the ACh channel

Answer 10

Opens when membrane is exposed to ACh, involved in regulation of heartbeat

Question 11

Defined the K+ channel called the Kv3 subfamily

Answer 11

Activated only at high voltages, they have fast recovery (deactivation).
Result is fast repolarization without compromising AP amplitude

Question 12

In terms of electrochemical significance, define Ca2+

Answer 12

Located in large conc. outside the cell. Therefore, it generally causes cell depolarization when it’s channels open, like Na+

Question 13

Define Voltage-gated Ca2+ channels

Answer 13

Open with similar time dependence as voltage-gated channels

Ca2+ current is more sustained

Question 14

What are the four steps of an action potential in a neuron

Answer 14

1. Signal reception
2. Signal integration
3. Signal conduction
4. Signal transmission

Question 15

Where does the signal integration (initiation of AP in cell) usually occur?

Answer 15

Axon hillock

Question 16

What are the four steps of a graded potential?

Answer 16

1. Neurotransmitter binds to ligand-gated Na+ channel
2. Na+ enters the cell
3. Current spreads through the cell
4. Strength of the signal decreases with distance

Question 17

What are Five differences between graded potentials and action potentials?

Answer 17

Graded potentials

1. Vary in magnitude
2. Vary in duration
3. Decay with distance
4. Occur dendrites or cell body (as opposed to axons)
5. Caused by opening and closing of many kinds of channels (APs are controlled just by voltage-gated ion channels)

Question 18

Define a threshold potential

Answer 18

Found with APs, it is the minimum level of membrane depolarization required for an AP to be generated

Question 19

What is the length constant (lambda) in a neuron?

Answer 19

The length constant is a measure of how far the voltage travels down the axon before it decays to zero.

Question 20

When will length constant be highest?

Answer 20

When Ri is low, and Rm is high

Question 21

What kind of conduction speeds do squid giant axons have?

Answer 21

High

Question 22

Define myelin

Answer 22

An insulating wrapping around axons that increases membrane resistance by decreasing current loss through leak channels

Question 23

How does myelin differ between CNS and PNS

Answer 23

CNS: oligodendrocytes
PNS: Schwann cells

Question 24

Define the nodes of Ranvier

Answer 24

Areas of exposed axonal membrane in between insulated regions that are rich in ion channels. they are required to continue the propagation of the AP.

Question 25

Define saltatory conduction

Answer 25

APs leap from node to node