Lecture 4

Question 1

What 4 factors influence nerve conduction?

Answer 1

1) Conduction is faster in a larger diameter axon
2) Conduction is faster if the time is shorter
3) Conduction is faster if the length constant is longer
4) Mylenation speeds up conduction.

Question 2

What factors affect the decline of the graded synaptic potentials?

Answer 2

1) Low membrane resistance decreases the graded potential as it leaks out.
2) High internal resistance decreases the graded potential.

Question 3

Unlike AP, Graded potential can change with time in terms of amplitude and distance. What two parameters explain that effect on graded potential?

Answer 3

1) Space constant

2) time constant

Question 4

What is the time constant?

Answer 4

The time constant is the time period when a graded potential (The voltage) reaches 63% of its original value.

Question 5

What is space constant?

Answer 5

its the distance of how long a graded potential crosses until it reaches 37% of its amplitude.

Question 6

What is the ideal graded potential conduction?

Answer 6

Ideal neuronal conduction would have high space constant and short time constant.

Question 7

What is passive conduction?

Answer 7

passive conduction in the axon is when the gates of the axons are closed and that inhibits leaking out so the conduction is like an ocean cable. the only thing that affects the voltage is the space constant.

Question 8

Lambda is the space constant. What could be manipulated to increase the space potential?

Answer 8

• increasing PM resistance and decreasing internal resistance increases the space constant and decreases the speed where it loses voltage.
• longer space constants results in larger conductions.

Question 9

what are the relationships of Plasma membrane resistance, internal resistance, and radius of an axon? What effect does that have on conduction?

Answer 9

PM resistance is inversely proportional to radius
-Internal resistance is inversely proportional to radius squared.

-Increasing the diameter decreases both resistances that affect the space constants, therefore, space constant becomes longer and conduction becomes faster.

Question 10

What effect does capacitance have time? do we want to increase or decrease capacitance?

Answer 10

Capacitance and time have a direct relationship, therefore, decreasing capacitance mean we decrease time. We want to decrease capacitance because we want to decrease the time constant.

Question 11

Can voltage increase or decrease through time?

Answer 11

It can exponentially increase and decrease. Membrane with high membrane capacitance means they have large time constant (bad for conduction)

Question 12

Why is myelin so beneficial?

Answer 12

Myelin reduces membrane capacitance therefore increasing the speed of conduction by lowering the time constant.

Question 13

If the membrane is explained as an RC circuit, what is resisitance and what is capacitance and what are their effects?

Answer 13

• Resitance is determined by ion channels and it influnces the graded potentials amplitude and speed.
• Capacitance is determined by membrane lipids. and it influnces the speed of conduction and response.

Question 14

What are a larger axons properties in terms of capacitance and resistance?

Answer 14

-Larger Axon has larger capacitance and lower resisitance. Because as we increase surface area, stored charges increase

Question 15

What is myelin?

Answer 15

Myelin is wrappings of glial cells around an axon. It reduces capacitance thereby speed up conduction along the axon.

Question 16

What are nodes of ranvier?

Answer 16

They are charge stations between consecutive myelin sheathes on an axon. its about 1-2 um in size and it has sodium channels that recharge the voltage of action potential.

Question 17

What type of conduction is found in myelinated axons?

Answer 17

saltatory conduction which is hopping conduction.

Question 18

What is the effect of myelin sheath combined with nodes of ranvier?

Answer 18

-Myelin reduces capactitance and that allows the “Spike hopping” or “Saltatory conduction” between the nodes of ranvier.

Question 19

What effects does demyelination have on conduction?

Answer 19

-It slows down conduction and if we lose couple of consecutive myelin sheaths then we lose conduction.

Question 20

What is the relationship between axon diameter and conduction speed?

Answer 20

-Increasing the diameter; decreases resistance; increases space constant and speed is amazingly enhanced if axon is myelinated.

Question 21

What speed do sensory nerve fibers from muscles spindles travel?

Answer 21

120 m/s

Question 22

What is a field potential?

Answer 22

-synchronized activity of a large number of neurons oriented in the same direction.

Question 23

What are two types of sensory evoked responses?

Answer 23

• ERG (electroretinogram)

- BAER (Brainstem Auditory Evoked Response)