Lecture 3: Nerve & Muscle Physiology

Question 1

action potentials propagate rapidly along nerve cell ___

Answer 1

axons

Question 2

action potential propagation occurs due to spread of __ charge inside the axon

Answer 2

positive

Question 3

maximization of action potential propagation velocity requires minimizing loss of __ across membrane

Answer 3

passive charge

Question 4

in mammals, ___ of axons increases membrane electrical resistance and greatly increases propagation velocity

Answer 4

myelination

Question 5

action potentials travel along myelinated axons by __

Answer 5

saltatory conduction

Question 6

demyelinating diseases disrupt ___

Answer 6

electrical signalling

Question 7

action potentials begin at the ___

Answer 7

axon initiation site

Question 8

in an action potential, the area of depolarization must move ___ to there parts of the axon

Answer 8

sequentially

Question 9

what sort of potentials can be generated before the axon initiation site?

Answer 9

graded

Question 10

why can’t action potentials be generated before the axon initiation site?

Answer 10

not enough sodium channels

Question 11

the axon initial site contains many __

Answer 11

sodium channels

Question 12

in the axon initiation segment, sodium comes in __ (down/up) its electrochemical gradient

Answer 12

down

Question 13

t/f when sodium enters the axon initial site the + charge spreads in all directions

Answer 13

true

Question 14

what happens to the positive charge that moves backwards at the axon initial segment?

Answer 14

nothing

Question 15

what happens to the + charge that moves forwards at the axon initial segment?

Answer 15

causes AP to spread by brining next segment to threshold causing depolarization

Question 16

why does the influx of sodium cause the + charge to disperse?

Answer 16

electrical repulsion

Question 17

t/f action potential is a one way phenomenon

Answer 17

true

Question 18

why are action potentials one way?

Answer 18

the segment behind will be in refractory

Question 19

spreading activation of VG Na channels is caused by ___

Answer 19

local current flow of + charge

Question 20

explain the phenomenon of current loss

Answer 20

charge leaks out across the membrane and does not contribute to action potential, causing slower propagation

Question 21

give 2 ways to decrease charge loss

Answer 21

1. minimize cytoplasmic resistance (thicker axon)

2. increasing membrane resistance (thicker membrane)

Question 22

why is it not feasible to decrease charge loss by increasing axon size in mammals?

Answer 22

mammals have complex nervous systems with trillions of axons that need to fit into a small bundle

Question 23

what method do mammals typically employ to decrease charge loss across the membrane?

Answer 23

thicker membrane

Question 24

myelin ___ speed of action propagation

Answer 24

increases

Question 25

describe the myelination process of nerve axons

Answer 25

Schwann cells wrap themselves continuously around the axon, leaving nodes in-between cells

Question 26

myelination increases the ___ resistance of the axon membrane

Answer 26

electrical

Question 27

t/f nodes of ranvier are always found in myelinated axons

Answer 27

true

Question 28

____ (myelinated/unmyelinated) axons carry action potentials faster

Answer 28

myelinated

Question 29

____ (smaller/larger) axons carry action potentials faster

Answer 29

larger

Question 30

why are the nodes of ranvier needed in myelinated axons?

Answer 30

myelinated sections are too thick for ion channels needed to allow ion flow to boost action potential

Question 31

what is saltatory conduction?

Answer 31

the “jumping” between fast conduction of ap between nodes of ranvier and the slow conduction within nodes

Question 32

within nodes, conduction is __

Answer 32

slow

Question 33

between nodes, conduction is __

Answer 33

fast

Question 34

name a disease that leads to demyelination

Answer 34

MS

Question 35

what are 2 consequences of loss of myelin?

Answer 35

1. slowed conduction

2. failure of action potential propagation