Action potentials Flashcards
what is the RMP of a neuron
-65 mV
what is the RMP determined by (2 main factors)
primarly permeable to K+ via leak channels (K+ flowing at rest)
K+ is more concentrated inside than outside
what is the permeability of an ion proportional to
how many ion channels are open for that ion
rank Cl-, K+, and Na+ from most to least permeable at rest
K+ (1.0) —> Cl- (0.45) —> Na+ (0.04)
4 steps of an AP
- all v-gated channels closed (RMP)
- small amount of Na+ enters the neuron, MP becomes more positive, more v-gated Na+ channels open (depolarisation)
- Na+ channels begin to inactivate while slower K+ channels open, MP becomes more negative (repolarisation)
- Most v-gated channels closed but K+ leak channels and some v-gated still open, MP more negative than RMP because K+ is more permeable than at rest
which blocker blocks Na+ (hodgkin and huxley)
tetrodotoxin (puffer fish)
which blocker blocks K+ (hodgkin and huxley)
tetraethylammonium (sea snails)
how did hodgkin and huxley know sodium was entering the cell
when sodium was removed, there was no more inward current
how do APs propagate
spreads down axon like a wave in one direction
why do APs only move in one direction
Na+ channels are inactive for a brief moment after AP so AP can’t propogate back
why are active APs slower than passive diffusion
APs are slow because of gates but passive diffsion is insufficient because they decay
how does passive diffusion effect voltage at neighbouring locations
voltage decays exponentially due to leaking ions
what is saltatory conduction
AP jumping donw the axon from node of ranvier to node of ranvier
fast under myelin, slow AP, fast under myelin, slow AP
3 factors that affect conduction velocity
membrane capacitance (stickiness)
membrane resistance (leakiness)
axoplasmic resistance (ion resistance to flow)
how does membrane capacitance negatively affect conduction velocity in axons
high membrane capacitance (sticky)
small distance between + and - ions inside and outside = strong force
ions sticking to the sides decreases conduction velocity
how does membrane resistance negatively affect conduction velocity in axons
low membrane resistance (hard to hold ions inside)
leak channels for K+ and Na+/K+ pumps
how does axoplasmic resistance negatively affect conduction velocity in axons
high axoplasmic resistance - axons are thin
resistance for ion to flow (4 lanes of traffic on a 2 lane highway)
how did invertebrates increase conduction velocity
larger diameter axons = decreased axoplasmic resistance
how did vertebrates increase conduction velocity
adding myelin
increases membrane resistance (leakiness) by plugging leak channels
decreases membrane capacitance (stickiness) by increasing the distance from inside to outside
