NMJ and EMG

Question 1

what is a neuromuscular junction?

Answer 1

synapse between motor neurone and muscle fibre

Question 2

difference between synapse and NJM

Answer 2

Nerve terminal bouton releases acetylcholine into the synaptic cleft, and binds to acetylcholine receptors (nicotinic) on the post synaptic endplate, which has junctional folds.

Question 3

what is a motor unit?

Answer 3

one motor neurone branches to form many junctions with many muscle fibres.

Question 4

where is acetylcholinesterase found?

Answer 4

on the end plate membrane, it breaks down Ach to stop its effects.

Question 5

what are miniature end plate potentials (EPPs)?

Answer 5

at rest there is a small amount of acetylcholine still released due to intracellular calcium.

Question 6

describe the structure of skeletal muscle

Answer 6

one muscle fibre cell is surrounded by the endomysium, a group of these muscle fibres is called a fascicle surrounded by a perimysium. a group of fascicles make up the muscle itself which is surrounded by an epimysium.

Question 7

what is in the sarcoplasm?

Answer 7

T tubules of the sarcolemma, network of Sarcoplasmic Reticulum, myoglobin, myofibrils, mitochondria.

Question 8

how wide are myofibrils?

Answer 8

1-2um

Question 9

what is the A band?

Answer 9

Dark Bands of myosin that are a constant width after contraction.

Question 10

what is the I band?

Answer 10

light bands of actin that decreases when contraction occurs.

Question 11

what is the H zone?

Answer 11

Area in the middle of the A band that gets smaller when contraction occurs.

Question 12

why is ATP always used even when muscle relaxed?

Answer 12

SER continuously pumps calcium back in, even when contraction occurs.

Question 13

what is Botulism?

Answer 13

botulinum toxin produced by pathogen which causes irreversible release of Ach from presynaptic terminal this leads to paralysis

Question 14

what is Myastenia Gravis (MG)?

Answer 14

autoimmune disorder against Ach Receptor this leads to muscle weakness

Question 15

what is Lambert-Eaton Myastenic Syndrome (LEMS)?

Answer 15

associated with lung cancer, autoimmune diseases against VGCCs.

Question 16

what is an EMG?

Answer 16

electromyography, extracellular reading of action potentials that govern skeletal muscle contraction.

Question 17

how does an EMG work?

Answer 17

two extracellular probes places apart on the skin which is positively charges when the muscles beneath are at resting potential (-70mV). As an AP moves along, the first probe will be in a negative region and the second will be in the positive region hence a potential difference is measured. When this AP moves along to the second probe, the second probe will detect a negative current and the first probe will detect a positive current causing the potential difference to flip.

Question 18

as the force of muscle contraction increases, what happens to the EMG peaks?

Answer 18

frequency and amplitude increases.

Question 19

as you increase the magnitude of stimulus provided to the muscle (eg adductor pollicis) what happens to twitch force?

Answer 19

increases

Question 20

As you increase frequency of stimulus, what happens to the twitch force?

Answer 20

at first you increase the frequency of twitching, then there is summation of force, then at higher frequencies there is tetanus.

Question 21

why are EMGs clinically important?

Answer 21

helps distinguish between myopathies and neuropathies.