Exam 2 Powerpoint 9

Question 1

Both Na and K are dependent on

Answer 1

depolarizing currents

Question 2

Need 8 to 9 milliseconds to fire another

Answer 2

action potential

Question 3

Refractory Period

Answer 3

Short period following an AP, during which axon is resistant to further excitation 8-9 ms

Question 4

Closed channel

Answer 4

can just open

Question 5

Inactivated channels have to __________ before they can open again.

Answer 5

close

Question 6

Threshold

Answer 6

Threshold is the membrane potential at which enough voltage-gated
sodium channels are open so that the relative permeability of the membrane is
higher for sodium ions than it is for potassium ions.

Question 7

Rising Phase:

Answer 7

Rising Phase: When the inside of the membrane has a negative potential, there is a large driving force for on sodium ions. Therefore, sodium rushes in through the open sodium channels, causing a rapid depolarization of the membrane

Question 8

Overshoot:

Answer 8

Because of the high permeability to sodium, the membrane potential
goes to a value that is close to the Equilibrium potential for sodium (depends on concentrations but somewhere above +50 mV)

Question 9

Falling Phase:

Answer 9

Falling Phase: First, the voltage-gated sodium channels inactivate. Second, the voltage-gated potassium channels open (the delayed-rectifier potassium channels).
The driving force pushes potassium out of the cell, causing the membrane potential
to become negative again.

Question 10

Undershoot:

Answer 10

Undershoot: The open potassium channels add to the normal resting membrane permeability to potassium, and drives the membrane potential close to the equilibrium potential for potassium, thus hyperpolarizing the membrane.

Question 11

At rest, neuronal membranes more
permeable to

Answer 11

K+ than Na

Question 12

During an action potential, membrane more permeable to

Answer 12

Na+
Than K

Question 13

During repolarization,____ more
permeable than ____

Answer 13

K+
Na+

Question 14

Positive feed back is fueled by

Answer 14

Na

Question 15

Negative feed back is fueled by

Answer 15

K

Question 16

AIS is rich in v

Answer 16

oltage-gated Na+ Channels

Question 17

APs typically initiate here at the

Answer 17

AIS

Question 18

Spread of AP down the axon
AP re-generates itself, activating

Answer 18

adjacent Nav channels

Question 19

Leak channels work to________ APs re-generating itself
0.5 to 10m/s top speed (conduction velocity)

Answer 19

oppose

Question 20

Speed at which action potential travels

Answer 20

0.5 to 10m/s

Question 21

MYELIN ________ CONDUCTION VELOCITY to_______

Answer 21

Increases
150 m/s

Question 22

Problem with myelin

Answer 22

Myelin is not a perfect insulator
Some charge leaks out
After a certain distance, the whole signal would be lost

Question 23

Fix for myelin

Answer 23

Nodes of Ranvier – periodic interruption of myelin sheath
Nodes are rich in voltage gated Na+ channels
AP is regenerated at the node.
The current flows through the neuron to the next node at near the speed of light

This is called Saltatory Conduction

Question 24

Multiple Sclerosis

Answer 24

Demyelination of axons in multiple sclerosis. Myelin ordinarily surrounds axons . In MS, axons lose myelin and can break as a result