Lecture 8

Question 1

Spatial summation

Answer 1

When currents from nearly simultaneous graded potentials combine

Question 2

Temporal summation

Answer 2

When two graded potential from one presynaptic neuron occur close in time

Question 3

What is the overshoot

Answer 3

Region above 0mV

Question 4

explain membrane potential changes during AP

Answer 4

1. we start off at resting membrane potential (-70mV)
2. graded potential arrives at axon hillock and membrane depolarizes to threshold (-55mV)
3. voltage gated Na+ channels open at -55mV (Na rushes in) which causes permeability of Na+ to increase and massive depolarization
4. now we’re in overshoot (+30mV), so voltage gated Na+ channels inactivate causing a decrease in Na+ permeability
5. voltage gated k+ channels open (k moving out of cell) increasing k+ permeability and repolarizing back towards -70mV
6. one ce we blow past -70mV at almost -90mV K+ channels will close and permeability to K+ will decrease
7. membrane potential will go back to -70mV because potassium-sodium pump and k+ leak channels are still in effect

Question 5

How can voltage gated Na+ channels act as a positive feedback loop once activated?

Answer 5

1. depolarization triggers activation of Na+ channel
2. Na+ enters the cell
3. more depolarization
   It would end up getting to Ena (+60mV) and stay there

Question 6

refractory period

Answer 6

limits how soon after an action potential another can be triggered

Question 7

Na+ channels open and close _______ than the k+ channels

Answer 7

faster

Question 8

absolute refractory period

Answer 8

• most voltage gated Na+ channels are inactivated
• no stimulus regardless of strength can trigger AP
• excitatory = 0

Question 9

relative refractory period

Answer 9

• some voltage gated Na+ channels are recovered from inactivation and voltage gated k+ channels are still open
• stronger stimulus is required to account for fewer available Na+ channels and hyperpolarizing k+ efflux
• excitatory is recovering

Question 10

what is key for propagation

Answer 10

• high membrane resistance because we don’t want leak channels
• low internal resistance because we want a large cell

Question 11

myelin is a ________

Answer 11

insulator

Question 12

loss of myelin

Answer 12

• decrease membrane resistance
• increase membrane capacitance
• increased loss of current and voltage along axon

Question 13

myelin is an insulator and enhances action potential propagation because:

Answer 13

• it increases membrane resistance (Rm)
• decreases membrane capacitance (Cm)

Question 14

membrane capacitance is

Answer 14

a measure of how much charge should be separated across the membrane to produce a given voltage