Physiology 1.11

Question 1

How can the length constant λ be increased in a neuron?

Answer 1

• bigger fibers (reduce internal resistance)
• increase myelination (increase membrane resistance)
• increase # of nodes of Ranvier

Question 2

How can the time constant τ be decreased in a neuron?

Answer 2

• lower capacitance

- increase myelination (increase membrane resistance)

Question 3

What does myelin do in terms of membrane resistance and capacitance?

Answer 3

• decrease capacitance

- increase resistance

Question 4

What is a Node of Ranvier?

Answer 4

regions of axon which separate the stretches of myelin on the myelinated axon

Question 5

How are action potentials shut off in the periphery?

Answer 5

• fast inactivation of Na+ channel

- large outward K+ leakage current

Question 6

What is the site on a neuron where the input is integrated?

Answer 6

soma

Question 7

What is the membrane length constant λ?

Answer 7

decay of conductance over space

Question 8

What is the time constant τ ?

Answer 8

time required to charge the membrane

Question 9

What is capacitance?

Answer 9

amount of charge required to create a given voltage change

Question 10

How do action potentials differ in myelinated axons of neurons versus the trigger zone between the muscle spindle and axon?

Answer 10

threshold is raised in trigger zone (called spike threshold) and does not need to repolarize before firing again