Lab #7: Neurophysioogy of Nerve Impulse

Question 1

Which neuroglial cells are responsible for producing a myelin sheath?

What division of the NS are they in?

Answer 1

• Schwann Cells: PNS
• Oligodendrocytes: CNS

Question 2

What part of the neuron receives the information/stimulus

Answer 2

dendrites

Question 3

Where part of the neuron does a true AP start?

Answer 3

axon hillock

Question 4

What part of the neuron are NT released?

Answer 4

axon terminals

Question 5

What device is use to measure membrane potential?

Answer 5

voltmeter (mV)

Question 6

Define membrane potential

Answer 6

the charge difference between the inside and outside of the cell

Question 7

What is membrane potential when a neuron is at rest/RMP?

Answer 7

-70mV

Question 8

Define depolarization

Answer 8

occurs when MP becomes more positive (influx of Na+)

Question 9

Define repolarization

Answer 9

occurs when MP becomes more negative (efflux of K+)

Question 10

Define hyperpolarization

Answer 10

occurs when repolarization overshoots and MP becomes more negative than RMP

Question 11

How do MP changes occur?

Answer 11

when ions flow through membrane channel (LG and VG ion channels)

Question 12

When do VG ion channel open?

Answer 12

open at a certain charge/by depolarization

Question 13

What type of channel is chemically regulated?

Answer 13

LG ion channels; open when bound to ligand/neurotransmitter

Question 14

What type of channel is voltage regulated?

Answer 14

VG ion channels; respond to charge/voltage

Question 15

T/F: ions can flow across myelinated parts of the axon

Answer 15

F, myelin inhibits VG Na+ channels, therefore ions can only flow around unmyelinated parts of axon (Nodes of Ranvier)

Question 16

What are the Nodes of Ranvier?

Answer 16

unmyelinated areas of axon

Question 17

Will an AP be conduced faster through a myelinated or unmyelinated axon?

Answer 17

myelinated because AP will travel from node to node, thus increasing speed

Question 18

Define threshold

Answer 18

the minimum MP required for an AP (the “rapid” depolarization part)

Question 19

What is the voltage value for threshold? What happens at this point?

Answer 19

-55mV; VG Na+ channel open -> influx Na+ -> rapid depolarization

Question 20

Is the amplitude of the AP in activitiy 3 generated the same as you would expect in an intact neuron inside the human body?

Answer 20

No, because human neuronal AP peaks at +30-40mV, but the exercise peaked at 100mV

Question 21

In activity 3, you increased the voltage of the stimulus beyond the minimum voltage needed to trigger an AP. Did the amplitude of the AP change? Why/why didn’t it change?

Answer 21

• increasing stimulus did NOT increase amplitude of AP -> AP are “all or none” (either happens or doesnt)
• a change in size/strength of stimulus only increases frequency of AP

Question 22

Compare the effects of tetrodotoxin (TTX) and Lidocaine. What do they do the same, and what do they do differently?

Answer 22

BOTH: block/inhibit VG Na+ channels; inhibit AP (but not equal)

TTX: irreversible and faster inhibition of VG Na+ channels

Lidocaine: slow inhibition of VG-Na channls

Question 23

Define inactivation

Answer 23

a channel is open but is blocked, so NO ions can travel through -> act as if it were closed

Question 24

Why is it harder to generate a second action potential during the relative refractory period?

Answer 24

in RRP, it is difficult to generate a 2nd AP because you are further away from threshold because VG-K+ are slow to close (must be at threshold; -55mV to have AP)

Question 25

Why is it important that a neuron has a refractory period?

Answer 25

limits how many AP + signals can be sent; controls release of NT

Question 26

What two main factors determine AP conduction velocity?

Answer 26

presence of myelin and diameter of axon

-> large diameter means increased AP conduction velocity

Question 27

Which well-known disease is caused by the deteroration of myelin?

Answer 27

multiple sclerosis

Question 28

In what ways would breakdown of myelin affect functions of the nervous system?

Answer 28

if no myelin along axon -> slower AP because no saltatory conduction

Question 29

What was the effect of lowering/removing Ca++ ions from the extracellular fluid?

Answer 29

if no Ca++ -> no fusion of vesicles with pre-synaptic membrane -> no NT released into synaptic cleft -> no AP

Question 30

What was the effect of adding Mg++ ions to the extracellular fluid?

Answer 30

• Mg++ prolongs duration of AP -> decrease freq of AP
• suppresses activity of neuron (excitability)

Question 31

T/F “When a neuron is stimulated with a high-intensity stimulus, a large action potential is produced, and more neurotransmitters are released at the axon terminal.”

Explain your answer

Answer 31

False

large stimulus = increase freq of AP (does not generate a “large AP”)

however, increase in freq of AP = increase release of NT

Question 32

How does the increase in frequency of an AP affect NT release?

Answer 32

more NT will be released