Lecture 16

Question 1

What are Cable (Passive) properties

Answer 1

The physical and electrical properties of a neuron’s dendrites and axon that determine signal propagation, similar to how electricity travels through a cable

Question 2

What 3 factors do cable properties depend on

Answer 2

1. axial resistance Ri: internal, longitudinal resistance due to axoplasm
2. transmembrane resistance Rm: phospholipid bilayer and myelin
3. membrane capacitance Cm

Question 3

cable properties and signals

Answer 3

Cable properties shape how neurons integrate and transmit signals

Question 4

What is the length constant

Answer 4

λ
how FAR a voltage spreads (distance current travels) before it decays to about 37% of its initial voltage

in a membrane, its exponential decay of a change in voltage (ΔV) with distance

Question 5

What is the time constant

Answer 5

𝜏
how LONG it takes for a change in membrane voltage to reach 63% of its final value

or to discharge to 37% of its full charge

Question 6

What is capacitance

Answer 6

Cm
the ability to store charge

Question 7

What properties does the plasma membrane ahve

Answer 7

capacitative
resistive

Question 8

What is the physical structure of a capacitor

Answer 8

2 parallel plates separated by a dielectric insulator

proportional to the size
inversely proportional to the distance between the plates.

Question 9

What direction does current flow

Answer 9

from (+) to (-) terminal

Question 10

Describe the initial circuit of a plasma membrane

Answer 10

Capacitive current dominates
Capacitor starts to charge and current flowing through resistor increases (change in membrane voltage

Question 11

What happens when the capacitor is fully charged

Answer 11

all current flows through the resistor and maximal voltage change is achieved

Question 12

What would indicate that a membrane has capacitive properties

Answer 12

the redistribution of charges during the current pulse (I) occurs more slowly than would be expected if the membrane acted as a pure resistor

Question 13

Describe the membrane components that correspond to resistance and capacitance

Answer 13

resistance corresponds to ion channels through which ions can flow

dielectric capacitor corresponds to the lipid bilayer that separates charges on the surface

Question 14

How long is the time constant 𝜏 in neurons

Answer 14

2-20 ms

Question 15

describe the voltage change in relation to distance

Answer 15

the amplitude of a voltage change decreases with distance from point of stimulation

Question 16

What is measured if a third electrode is added to a microelectrode setup

Answer 16

V2 measures the potential change at some distance from the source of current (I)

Question 17

What does the magnitude of lambda depend on

Answer 17

1. transmembrane resistance Rm
2. Axonal resistance Ri
   λ = sqrt(Rm/Ri)

Question 18

What does the distance current travels depend on

Answer 18

1. voltage applied
2. membrane resistance including transmembrane resistance (Rm) and membrane capacitance (Cm)
   𝜏 = Rm x Cm

Question 19

What is the effect of membrane myelination

Answer 19

myelination increases Rm and decreases Cm

Question 20

What is multiple sclerosis and its effect on length constant

Answer 20

destruction of myelin
decreases length constant (how far)

Question 21

What is Guillain-Barre Syndrome

Answer 21

body attacks Schwann cells causing loss of signal conduction

Question 22

What can a prolonged time constant indicate

Answer 22

the loss of dendritic branches and result in a decrease in total cell surface area