Exam 1: Lecture 4

Question 1

How is an increase in sodium conductance an example of positive feedback?

Answer 1

The elevated sodium ion conductance causes more sodium channels to open causing depolarization to continue further

Question 2

How do axons increase the speed of the action potential as it travels along the neuron?

Answer 2

Increasing the diameter of the axon and increasing membrane resistance through myelination

Question 3

Explain how increasing the diameter of axon increases the speed of action potential

Answer 3

The increased diameter offers a larger cross-sectional area causing less resistance to the flow of the current

Question 4

Explain how mylenation increases the speed of the action potential, especially considering it increases membrane resistance?

Answer 4

Current will flow along the axons through the path of least resistance. Myelination forces the charge to jump along the myelin-free junctions called nodes that exist between the myelin forming schwann cells; (i.e. myelin sheaths force saltatory conduction jumping current)

Question 5

Define threshold and the membrane potential at which it is reached

Answer 5

Threshold is the point when the local potential causes an action potential; occurs between -65mV to -70mV

Question 6

What are the differences between Absolute refractory period and Relative refractory period?

Answer 6

Absolute refractory period exists during depolarization and the early part of repolarization when no stimulus would be able to elicit a 2nd action potential; Relative refractory period is throughout the repolarization phase when only stronger than normal stimulus could cause an action potential