AP II

Question 1

What three things does the distance that current propagates depend upon?

Answer 1

1. Internal Resistance (Ri) - Higher Ri –> smaller spread of current
2. Membrane Resistance (Rm) - Higher Rm –> larger spread of current
3. Membrane capacitance (Cm) - Higher Cm –> slower spread of current

Question 2

What is the length constant (lambda) for an axon?

Answer 2

~1mm

Question 3

How does myelin increase conduction velocity?

Answer 3

1. Increases membrane resistance (and therefore length constant)
2. Decreases Cm
3. Allows for saltatory conduction via nodes of Ranvier

Question 4

Where are Na channels located on myelinated axon?

Answer 4

in the Nodes of Ranvier

Question 5

What does conduction velocity depend upon?

Answer 5

1. Myelination

2. Axon width - the wider the axon, the more charge that can flow through per given time

Question 6

Why is there redundancy in # of V-G Na channels?

Answer 6

Allows for:

1. Branching of axons
2. Shorter refractory period

Question 7

How do local anesthetics like lidocaine work?

Answer 7

Bind intracellular portion of V-G Na channels, block Na entry

Question 8

Lidocaine has greatest effect on axons that are?

Answer 8

Smaller (lower safety factor) & more active (channels must open)