Lecture 3: Nerve & Muscle Physiology Flashcards
action potentials propagate rapidly along nerve cell ___
axons
action potential propagation occurs due to spread of __ charge inside the axon
positive
maximization of action potential propagation velocity requires minimizing loss of __ across membrane
passive charge
in mammals, ___ of axons increases membrane electrical resistance and greatly increases propagation velocity
myelination
action potentials travel along myelinated axons by __
saltatory conduction
demyelinating diseases disrupt ___
electrical signalling
action potentials begin at the ___
axon initiation site
in an action potential, the area of depolarization must move ___ to there parts of the axon
sequentially
what sort of potentials can be generated before the axon initiation site?
graded
why can’t action potentials be generated before the axon initiation site?
not enough sodium channels
the axon initial site contains many __
sodium channels
in the axon initiation segment, sodium comes in __ (down/up) its electrochemical gradient
down
t/f when sodium enters the axon initial site the + charge spreads in all directions
true
what happens to the positive charge that moves backwards at the axon initial segment?
nothing
what happens to the + charge that moves forwards at the axon initial segment?
causes AP to spread by brining next segment to threshold causing depolarization
why does the influx of sodium cause the + charge to disperse?
electrical repulsion
t/f action potential is a one way phenomenon
true
why are action potentials one way?
the segment behind will be in refractory
spreading activation of VG Na channels is caused by ___
local current flow of + charge
explain the phenomenon of current loss
charge leaks out across the membrane and does not contribute to action potential, causing slower propagation
give 2 ways to decrease charge loss
- minimize cytoplasmic resistance (thicker axon)
2. increasing membrane resistance (thicker membrane)
why is it not feasible to decrease charge loss by increasing axon size in mammals?
mammals have complex nervous systems with trillions of axons that need to fit into a small bundle
what method do mammals typically employ to decrease charge loss across the membrane?
thicker membrane
myelin ___ speed of action propagation
increases
describe the myelination process of nerve axons
Schwann cells wrap themselves continuously around the axon, leaving nodes in-between cells
myelination increases the ___ resistance of the axon membrane
electrical
t/f nodes of ranvier are always found in myelinated axons
true
____ (myelinated/unmyelinated) axons carry action potentials faster
myelinated
____ (smaller/larger) axons carry action potentials faster
larger
why are the nodes of ranvier needed in myelinated axons?
myelinated sections are too thick for ion channels needed to allow ion flow to boost action potential
what is saltatory conduction?
the “jumping” between fast conduction of ap between nodes of ranvier and the slow conduction within nodes
within nodes, conduction is __
slow
between nodes, conduction is __
fast
name a disease that leads to demyelination
MS
what are 2 consequences of loss of myelin?
- slowed conduction
2. failure of action potential propagation
