Action potential Flashcards
factors increasing speed of conduction of neurons?
presence of myelin
increased heat
increased axon thickness
why are channels selectively permeable?
due to shape and chemical properties
two types of ____ gated ion channels?
ligand and voltage gated
channel for water?
aquaporins.
describe equilibrium when an electrical field is applied?
equilibrium between voltage AND concentration is established
describe nernst equation
measures ionic equilibrium potential
- potential difference when equilibrium (voltage and conc) is reached when the membrane is permeable to one ion
- depends on relative concs and ionic charge
describe goldman equation
measures membrane potential
- potential difference when equilibrium (voltage and conc) is reached when the membrane is permeable to multiplie ions
- depends on relative concs and permeability
what two membrane proteins set resting membrane potential?
two pore domain potassium pump and Na/K-ATPase
what is resting membrane potential
-65mV
describe how Na/K-ATPase works
- 3 intracellular Na bind
- Pi attaches
- conformational change and release
- extracellular K bind
- pi releases
- conformational change
- -> membrane potential nears EK+
4 types of K channels?
2 pore domain potassium channels
voltage gated K channels
inward rectifying K channels
calcium activated K channels
describe 2 pore domain channels
have 2 pore loop domains, which are open, contributing to ongoing K+ channel
describe voltage gated K channels
delayed rectifier
- open some time after membrane reaches a certain voltage
- returns to resting potential
describe voltage gated sodium channels
closed at -65mV
open at -40mV for 1ms
inactivate at -65mV (globular protein blocks)
returns
pros and cons of passive conduction?
doesnt require energy but strength of AP reduces (since its done by diffusion)
pros and cons of active conduction?
requires energy, but propagates
describe depolarisation to threshold
membrane potential increases due to physically Na channels opening or due to inheritance somewhere in the cell
during resting membrane potential, what controls the membrane potential?
Na/K-ATPase and two pore domain potassium pumps
what happens during rapid depolarisation
membrane potential increases, voltage gated sodium channels open FOR ONE MS; sodium enters cell, increases membrane potential (positive feedback)
what happens during repolarisation?
voltage gated sodium channels close. only K2p channels open, so membrane potential falls.
what happens in hyperpolarisation
voltage gated (delayed rectifier) K channels open
what happens during absolute refractory period
Na+ channels are inactivated (globular protein blocks channel), limiting second AP from firing for atleast 1ms
describe relativle refractory period
voltage gated potassium channels close
are channel openings stoichastic?
yes
where is the threshold reached? why?
axon hillock/spike initiation zone
because Na+ channels are open the most here and hence its easiest to reach threshold.
why do APs propagate in one direction?
inactivated sodium channels prevent back propagation of AP
in terms of axons and the myelin sheath, where are sodium channels most densely found?
in the nodes of ranvier
describe saltatory conduction
AP’s jump from node to node
why is saltatory conduction quicker than when there’s no myelin
AP’s dont have to happen constantly, only in nodes
what happens if the nodes are too far apart?
strength of AP will decline as ions have to diffuse intracellularly to get to the node
what happens when you inject a current and
- it doesnt reach threshold
- reaches threshold?
doesnt reach threshold = no AP
reaches threshold - frequency proportional to strength of injected current
