Lecture 3-4: Action Potentials Flashcards
List and describe the 3 characteristics of action potentials
all or none principle
self-propagating - each depolarization generates the next action potential on both sides
non-decremental - does not decrease in strength
name the 2 types of gated ion channels
ligand gated
voltage gated
voltage gates have ___ number of gates, name them
2 gates
activation gate
inactivation gate
Action potentials can travel is all directions from the point of stimulation, what does orthodromic direction mean?
the direction normally taken = toward the distal end of the axon —> dendrites
Action potentials can travel is all directions from the point of stimulation, what does antidromic direction mean?
opposite of the direction normally taken = toward the axon hillock/neuron cell body
why do action potentials typically travel in the orthodromic direction even though they are capable of all directions?
because of refractory period
define refractory period
period during which a second action potential cannot be generated until the cell returns to resting state
how are nodes of Ranvier significant to propagation speed of action potentials?
they are unmyelinated junctions between schwann cells on axons, thus allowing the signal to jump from node to node. resulting in an increase in propagation speed
why do small diameter axons conduct action potential slower than large diameter axons?
a large diameter allows for multiple pathways, thus resulting in less resistance, allowing a faster conductance
what would be the characteristic of the fastest conducting axon vs the slowest conducting axon in humans?
fast = large diameter & myelinated
slow = small diameter & non-myelinated
what are the two subsets of refractory period?
absolute & relative refractory period
define relative refractory period and explain why it is different than absolute refractory period?
relative - period of time right after the abs period in which a second action potential is inhibited but not impossible = requires a stronger than normal stimuli
in abs period = impossible to make a second AP no matter how strong a stimuli
-90mV
resting membrane potential
+35mV
apex of depolarization
-65mV
threshold for action potential
describe sodium voltage gated channels at rest
sodium voltage gates have 2 gates
activation gate is closed at rest
inactivation gate is open at closed
describe sodium voltage gated channels at +35mV
activation gate in open
inactivation gate is closed
describe sodium voltage gates during depolarization and what is voltages?
going from -90 to +35
activation gate opens at -70 and stays open
inactivation gate is open from rest and closes at +35
describe sodium voltage gates during repolarization and what is voltages?
going from +35 to -90
inactivation gate closes at +35
activation gate is open and does not close until rest at -90
once a channel inactivates, it cannot re-open until it transitions back to resting state
refractory period
how can an axon increase speed of conduction?
increase axon diameter
increase axolemma resistance
how does increasing axon diameter effect conduction rate?
large diameter = large cross-sectional area for internal flow
a lot of different paths to take = less resistance
how does increasing axolemma resistance effect conduction rate?
the current will flow at points of least resistance, which will be the unmyelinated junctions between schwann cells, allowing the AP to jump from node to node
how can an axolemma resistance be increased?
by having layers of insulation = myelination or myelin sheath
creating a capacitor effect
explain the difference between absolute and relative refractory period
abs - no 2nd AP can be conducted no matter how strong the stimulus is
relative - period right after abs, where a stronger that normal stimulus can produce a 2nd AP
describe relative refractory period
in this period a second action potential is inhibited but not impossible
method = increased K+ conductance
Na, K, Ca, Cl - permeability at resting potentials
Na - low
K - more than Na
Ca - low
Cl - moderate
the intracellular environment is always more _____ than the intercellular environment.
more negative
the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane
Nernst potential
as long as a concentration gradient exists, diffusion will continue
diffusion potential
equilibrium will be reached when the electrical force driving ions out, exactly equals the force driving those same ions in
equilibrium potential
the sum of cation concentrations must be equal to the anion concentrations within the same compartment
electrical neutrality
equilibrium is only satisfied when equilibrium potentials for both ions is equal
Donnan equilibrium
resting membrane potential of nerves
-90mV
electrical potential across the membrane must exactly balance the concentration gradients for both ions, when there are two different ion concentrations on each side of the membrane
Donnan equilibrium
Nernst equation
=61.5 x log ( [outside] // [inside] )
