Nerve and Muscle Physiology

Question 1

Axonal transport for membrane-bound organelles and mitochondria

Answer 1

Fast Axonal Transport

Question 2

Axonal transport for substances that are dissolved in the cytoplasm

Answer 2

Slow Axonal Transport

Question 3

Axonal transport driven by dynein
Returns recycled synaptic vesicle membrane to the soma for lysosomal degradation
Movement towards cell body

Answer 3

Retrograde transport

Question 4

Axonal transport driven by kinesin
Allows replenishment of synaptic vesicles and enzymes responsible for the synthesis of neurotransmitters in synaptic terminals
Movement towards synapse

Answer 4

Anterograde transport

Question 5

How to elicit an action potential (AP)? There are 3 ways.

Answer 5

1. Mechanical disturbance of the membrane (e.g. excitation of sensory nerve endings in skin)
2. Chemical effects on the membrane (e.g. chemical neurotransmitters transmit signals from one neuron to the next)
3. Passage of electricity through the membrane (e.g. electric current transmit signals between successive muscle cells in <3 and intestine)

Question 6

Explain the general mechanism behind skeletal muscle contraction

Answer 6

1. AP travels along a motor nerve to its endings on muscle fibers
2. Nerve endings secrete the neurotransmitter substance acetylcholine
3. ACh locally opens the ‘ACh-gated’ cation channels
4. Opened channels allow Na ions to diffuse into the muscle fiber, initiating an AP, causing local depolarization, opening of voltage-gated Na channels
5. AP travels along muscle fiber membrane
6. Depolarization of the membrane leads to release of stored Ca ions by the sarcoplasmic reticulum
7. Ca ions initiate attractive forces between actin and myosin filaments to slide alongside each other -> CONTRACTION
8. Ca ions are pumped back to the reticulum by Ca membrane pump (relaxation)

Question 7

Proteins in the 'dock' important in neurotransmitter release
Functions: 
-allow fusion and exocytosis
-dock targeted proteins
-restrain vesicles

Answer 7

VAMP - inhibited by tetanus toxin and botulinum toxin
SNAP 25 - inhibited by botulinum toxin

Tetanus toxin - leads to spastic paralysis
Botulinum toxin - flaccid paralysis

Question 8

Autoimmune disease in which antibodies destroy Ach receptors
Dominant in women in their 30s
Leads to fatigue and muscular weakness that fluctuates (e.g. ptosis/drooping of eyelids)
In the morning, there are enough receptors for muscular contraction; in the afternoon, immune system has depleted Ach receptors

Answer 8

Myasthenia Gravis