Lecture 8 Flashcards
Spatial summation
When currents from nearly simultaneous graded potentials combine
Temporal summation
When two graded potential from one presynaptic neuron occur close in time
What is the overshoot
Region above 0mV
explain membrane potential changes during AP
- we start off at resting membrane potential (-70mV)
- graded potential arrives at axon hillock and membrane depolarizes to threshold (-55mV)
- voltage gated Na+ channels open at -55mV (Na rushes in) which causes permeability of Na+ to increase and massive depolarization
- now we’re in overshoot (+30mV), so voltage gated Na+ channels inactivate causing a decrease in Na+ permeability
- voltage gated k+ channels open (k moving out of cell) increasing k+ permeability and repolarizing back towards -70mV
- one ce we blow past -70mV at almost -90mV K+ channels will close and permeability to K+ will decrease
- membrane potential will go back to -70mV because potassium-sodium pump and k+ leak channels are still in effect
How can voltage gated Na+ channels act as a positive feedback loop once activated?
- depolarization triggers activation of Na+ channel
- Na+ enters the cell
- more depolarization
It would end up getting to Ena (+60mV) and stay there
refractory period
limits how soon after an action potential another can be triggered
Na+ channels open and close _______ than the k+ channels
faster
absolute refractory period
- most voltage gated Na+ channels are inactivated
- no stimulus regardless of strength can trigger AP
- excitatory = 0
relative refractory period
- 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
what is key for propagation
- high membrane resistance because we don’t want leak channels
- low internal resistance because we want a large cell
myelin is a ________
insulator
loss of myelin
- decrease membrane resistance
- increase membrane capacitance
- increased loss of current and voltage along axon
myelin is an insulator and enhances action potential propagation because:
- it increases membrane resistance (Rm)
- decreases membrane capacitance (Cm)
membrane capacitance is
a measure of how much charge should be separated across the membrane to produce a given voltage