IASM 33 34: Nerve Signals

Question 1

What is a motor unit?

Answer 1

All muscle fibres controlled by a single motor neurone

Question 2

Tension applied to individual motor neurone remains relatively _______, although each motor unit cycle between ________ and _______.

Answer 2

Relatively constant

Cycle between contraction and relaxation

Question 3

As contraction progresses, the muscle fibre has higher _______

Answer 3

Tension

Question 4

What is latent period (in muscle contraction)?

Answer 4

time needed for the conduction of action potential and subsequent release of Ca2+ by sarcoplasmic reticulum

Question 5

Compare the Threshold stimulus for depolarizing a nerve, with depolarizing the muscle fibres directly. Which one has lower Threshold Stimulus?

Why

Answer 5

Depolarizing a nerve

Motor units present, you only need to depolarize a few motor neurones, compared to depolarize a lot of muscle fibres.

Question 6

Threshold potential is when ____ (number) motor unit responds

Answer 6

1

Question 7

Maximal potential is when ____ motor unit responds

Answer 7

all

Question 8

What is meant by ‘tetanus’

Answer 8

Relaxation phase to be very brief (incomplete tetanus) or eliminated (complete tetanus)

Question 9

How to measure action potential

Answer 9

Artificially inject current into neuron by a stimulating electrode, and record the membrane potential by recording electrode

Question 10

What are the 4 phases of action potential
With reference to which ions rush in/out
With reference to the ion channels

Answer 10

1. Resting State- All Na+ and K+ channels closed
2. Depolarizing Phase- Na+ channels open, Na+ rushes in
3. Repolarizing Phase- Na+ channels inactivated, K+ channels open, K+ rushes out
4. Hyperpolarizing Phase

Question 11

What’s the resting membrane potential of neurones

Answer 11

-60mV

Question 12

What’s the potential of the neurones after finishing depolarization

Answer 12

+40mV

Question 13

What’s the function of oligodendrocytes

Answer 13

Myelinate CNS axons

Question 14

What’s the function of Schwann cells

Answer 14

Myelinate PNS axons

Question 15

What’s the function of Astrocytes (name 2)

Where is it found (CNS or PNS)

Answer 15

Formation of Blood Brain Barrier
Form scar tissue after injury
Found in CNS

Question 16

What’s the function of microglia

Where is it found (CNS or PNS)

Answer 16

Remove cell waste, debris by phagocytosis

Found in CNS

Question 17

What’s the function of ependymal cells

Where is it found (CNS or PNS)

Answer 17

Producing, monitoring and circulating Cerebrospinal Fluid through formation of Choroid Plexus
Found in CNS

Question 18

What is saltatory conduction

Answer 18

Action potentials jump between nodes on Ranvier

Question 19

Function of myelin?

Answer 19

1. Faster conduction of impulses
2. Use less energy (less Na+ pumped out of cytoplasm)
3. Prevent the loss of information

Question 20

Describe the shape of astrocytes

Answer 20

Star-shaped

Question 21

There are 2 types of astrocytes, name them and where are they found
F
P

Answer 21

Fibrous astrocyte- White matter
Protoplasmic astrocyte- Grey matter

(forward, Postgraduates!)
-FW, PG

Question 22

In CNS, unmyelinated neurones are bare neurones. In PNS, how are axons considered ‘unmyelinated’?

Answer 22

Series of Schwann cells covering the entire length of the axon, such that there are no Nodes of Ranvier.

Entire group of axons are enclosed under the Schwann cell surface

Question 23

For injuries in the PNS, are there regeneration

Answer 23

Yes

Question 24

For injuries in the CNS, what will happen

Are there regeneration

Answer 24

Astrocytes rush in to form glial scar

No regeneration