lecture 8 conduction

Question 1

what does an oscilloscope do

Answer 1

shows voltage vs time

Question 2

what is conductance

Answer 2

ability of ions to flow through channels

Question 3

what is conduction

Answer 3

movement of action potential from one part to another (axon hillock to presynaptic terminal)

Question 4

what is capacitance

Answer 4

the ability of a system to store an electric charge.

Question 5

difference between distance and time flipped action potential graph

Answer 5

distance is flipped graph (where undershoot is drawn first because that’s the way the direction of propagation of action potential is)

Question 6

how long does an action potential take

Answer 6

2 ms

Question 7

how is an action potential conducted

Answer 7

na enters through VGna and causes charge reversal through depolarization
positive charge displaces negative charge both locally at the site of charge entry and in both directions along the axon cylinder
within a few ms the na channels activate at the site of na entry and that region of axon membrane becomes refractory to further depolarization

Question 8

cable properties of an axon

Answer 8

an axon is like a leaky hose
water pressure is like the voltage
bulgability is like the capacitance
hose leaks like leak ion conductance in axon

Question 9

what is axial resistance inversely related to

Answer 9

caliber (diameter) so bigger axon means bigger flow of charge

Question 10

what is membrane resistance inversely related to

Answer 10

the number of open leak channels

Question 11

what is membrane capacitance inversely related to

Answer 11

distance between intra and extracellular sites that store charge

Question 12

what does the flow of na in during the rising phase do

Answer 12

causes a nearly instantaneous change in membrane

Question 13

voltage is largest at site of na entry and gradually weakens over distance due to

Answer 13

axial resistance (thinner axon more resistance), passive leak channels, membrane capacitance

Question 14

when would smaller axons be needed even if they have a larger axial resistance and slower conduction

Answer 14

optic nerve

Question 15

how can axonal membrane resistance and capacitance be altered by

Answer 15

myelin

Question 16

what is myelin made by

Answer 16

oligodendrocytes in cns and schwann cells in

Question 17

what does myelin do

Answer 17

creates low membrane capacitance and creates high membrane resistance
essentially plugs leaks and makes conduction faster

Question 18

what are nodes of ranvier

Answer 18

myelin is broken up into nodes of ranvier where sodium can flow in again to ensure action potential can reach full amplitude

Question 19

what is saltatory conduction

Answer 19

action potential recharges at nodes (goes fast slow fast)
na chemicals concentrates by nodes, k channels along internodes

Question 20

what is a demyelinating disease

Answer 20

multiple schlerosis (ms) nerve impulses slow or slop, sodium cant come in

Question 21

how does na enter membrane

Answer 21

This spread of charge occurs in the backward direction (toward the
soma) where Na+ channels have already opened and inactivated (the membrane is refractory),
and the forward direction where Na+ channels are simply closed (not inactivated). Within a few
milliseconds (ms), the Na+ channels inactivate at the site of Na+ entry and that region of the
axon membrane becomes refractory to further depolarization (temporarily). But in the forward
direction the positive charges change the membrane potential causing an increase in gNa+
(additional channels opening) to allow local Na+ entry and action potential propagation

Question 22

Attenuation

Answer 22

reduction in current magnitude due to distance and/or time

Question 23

Membrane resistance (Rm) -

Answer 23

the opposition of ionic flow across the membrane. The more
channels in the membrane, the lower the membrane resistance. The lower the membrane
resistance, the more the signal will attenuate over distance

Question 24

Axial resistance (Ra)

Answer 24

the opposition of ionic flow down the axon or neurite. The greater
the diameter of the neurite, the lower the axial resistance. The greater the axial resistance,
the more the signal will attenuate over distance

Question 25

Membrane capacitance (Cm)

Answer 25

property of the membrane that allows for the storage of
charge. Determines how quickly a neuron’s membrane potential can respond to changes in
current. The membrane capacitance is proportional to the surface area. The greater the
capacitance, the more the signal will attenuate over distance.

Question 26

How does an action potential alter the membrane potential along an axon (voltage vs
distance)?

Question 27

Explain the ways in which an axon’s passive properties: membrane resistance, membrane
capacitance, and internal resistance alter the voltage change with distance from the site
where an action potential is peaking.

Question 28

How and why does axon caliber affect conduction velocity?

Question 29

Describe multiple sclerosis, including biologic and physiologic symptoms

Answer 29

Examples of typical MS relapses include blurring of vision in one eye (optic neuritis), persistent numbness or tingling of a body part (sensory system relapse), weakness of a body part (motor system relapse), or loss of coordination (cerebellar system relapse).