The Action Potential - II

Question 1

What is Ohm’s Law?

Answer 1

g = I / (Em-Eion)

Question 2

What is Em-Eion?

Answer 2

The electrochemical driving force action on the ion

Question 3

With knowledge of Vm, Ena, and Ek, what three things were learned?

Answer 3

1. Both conductances are voltage dependent
2. Both conductances change over time
3. Activation saturates

Question 4

The coincidence of the initial increase in g-na with the rapid rising phase of the action potential demonstrates what?

Answer 4

A selective increase in gNa is responsible for AP initiation

Question 5

Increased gNa causes Na to ______ the neuron

Answer 5

Enter

Question 6

What causes the rate of gNa to fall? (2 reasons)

Answer 6

the electrochemical driving force on Na decreases

gNa inactivates

Question 7

What does depolarization slowly activate? What happens?

Answer 7

gK, allowing K+ to leave the cell

Question 8

gK being higher than in resting condition causes….

Answer 8

undershoot

Question 9

Undershoot causes what to occur?

Answer 9

Voltage dependent gK to turn off, mem. pot return to resting level

Question 10

Which ion cycle is regenerative?

Answer 10

Na

Inward Na Current –> Depolarization –> Increase in gNa –> Inward Na Current

Question 11

Which ion cycle is not regenerative?

Answer 11

K

Depolarization –> Increase in gK –> outward K current –> repolarization

Question 12

What stops the Na positive feedback?

Answer 12

Na+ conductance inactivation

Question 13

What is passive spread?

Answer 13

Current conduction in the absence of an action potential

Question 14

How does potential change change over increasing distance.

Answer 14

Exponentially decays

Question 15

What is lambda?

Answer 15

sqrt((Rm/Ri))

Question 16

Though there is a decrement of APs spreading along the axon, local depolarization….

Answer 16

is still large enough spread to depolarize adjacent regions of the axon above threshold and generate an AP nextdoor

Question 17

How long will the AP regeneration process continue?

Answer 17

Until the AP travels the full length of the axon

Question 18

Is action potential instantaneous?

Answer 18

No. Action potentials occur later at greater distances down the axon.

Question 19

What is the measurement of the rate of AP transmission?

Answer 19

Conduction Velocity

Question 20

What causes a nerves conduction velocity to vary?

Answer 20

Size and Myelination of the Nerve

Question 21

What causes the refractory period?

Answer 21

Transient inactivation of the Na and K channels

Question 22

What do refractory periods limit?

Answer 22

Number of APs a given cell can produce at a time

Inability to reverse direction of signal

Question 23

Why can’t APs reverse direction?

Answer 23

Inactivated Na channels left in the APs wake

Question 24

Axon diameter is ______ related to internal resistace

Answer 24

Inversely

Question 25

Large axons with low resistance will conduct at ____ rates.

Answer 25

Higher

Question 26

Electrically, what does myelination do for the neuron.

Answer 26

Prevents leakage of current out of the axon

Question 27

Where are neuron Na/K channels located on an axon?

Answer 27

Node of Ranvier

Question 28

How do Schwann cells get nutrients to their most wrapped components? What happens when this goes awry?

Answer 28

Gap Junctions

Charcot Marie Tooth

Question 29

Name the type of conduction seen in myelinated nerves.

Answer 29

Saltatory Conduction

Question 30

Why are dendrites less likely to develop AP?

Answer 30

Few voltage gated channels.

Question 31

Highest density of voltage gated channels?

Answer 31

Axon Hillock

Question 32

How does local anesthesia work?

Answer 32

Temporarily blocking the voltage gated sodium channels of neuronal axons

Question 33

What do anesthetics bind?

Answer 33

Small lipid soluble molecules bind hydrophobic sites og the transmembrane protein involved in activation.

Question 34

Normal WBC count?

Answer 34

5-6

Question 35

What is Guillone Barre? Treatment?

Answer 35

Ab against myelin

Plasmaphoresis, IgG to downreg. Ab production

Question 36

What is MS? Treatment?

Answer 36

Ab against central myelin, lose function, no repair

Selective Immunosuppressive Drugs may stop progression

Question 37

A bilateral Babinski sign in an adult means….

Answer 37

Pyramidal Tract Damage