Lecture 9

Question 1

Describe the generation of an action potential

Answer 1

neurotransmitter arrives at dendrite, graded potential generated. this diffuses through cell body to axon hillock, depolarizes axon hillock. voltage gated Na channels very dense there, if it is enough voltage to open the channel, neuron will depolarize. if it depolarizes to threshold, will open up all of the voltage gated channels, creating positive feedback loop. As this happens, it opens the activation gate in the Na channel, while simultaneously triggering the K channels and the inactivation gates. these operate slower than the Na channel. depolarization, then as k channels open, repolarization occurs. hyperpolarization, then return to resting membrane potential

Question 2

Describe the refractory periods

Answer 2

absolute: during depolarization/repolarization, most Na channels inactive, K channels open, no strength stimulus can trigger AP
relative: during hyperpolarization, some Na channels reset, K channels open, need stronger stimulus to depolarize

Question 3

Why don’t AP’s move backwards?

Answer 3

due to refractory periods, movement depends on length constant

Question 4

what do myelin sheaths do?

Answer 4

increase membrane resistance, increases speed of conduction, allows for saltatory conduction where AP only generated at nodes of Ranvier

Question 5

What is the speed of teh AP determined by?

Answer 5

diameter of axon, resistance of membrane to ion leakage