NMJ and EMG Flashcards
what is a neuromuscular junction?
synapse between motor neurone and muscle fibre
difference between synapse and NJM
Nerve terminal bouton releases acetylcholine into the synaptic cleft, and binds to acetylcholine receptors (nicotinic) on the post synaptic endplate, which has junctional folds.
what is a motor unit?
one motor neurone branches to form many junctions with many muscle fibres.
where is acetylcholinesterase found?
on the end plate membrane, it breaks down Ach to stop its effects.
what are miniature end plate potentials (EPPs)?
at rest there is a small amount of acetylcholine still released due to intracellular calcium.
describe the structure of skeletal muscle
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.
what is in the sarcoplasm?
T tubules of the sarcolemma, network of Sarcoplasmic Reticulum, myoglobin, myofibrils, mitochondria.
how wide are myofibrils?
1-2um
what is the A band?
Dark Bands of myosin that are a constant width after contraction.
what is the I band?
light bands of actin that decreases when contraction occurs.
what is the H zone?
Area in the middle of the A band that gets smaller when contraction occurs.
why is ATP always used even when muscle relaxed?
SER continuously pumps calcium back in, even when contraction occurs.
what is Botulism?
botulinum toxin produced by pathogen which causes irreversible release of Ach from presynaptic terminal this leads to paralysis
what is Myastenia Gravis (MG)?
autoimmune disorder against Ach Receptor this leads to muscle weakness
what is Lambert-Eaton Myastenic Syndrome (LEMS)?
associated with lung cancer, autoimmune diseases against VGCCs.
what is an EMG?
electromyography, extracellular reading of action potentials that govern skeletal muscle contraction.
how does an EMG work?
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.
as the force of muscle contraction increases, what happens to the EMG peaks?
frequency and amplitude increases.
as you increase the magnitude of stimulus provided to the muscle (eg adductor pollicis) what happens to twitch force?
increases
As you increase frequency of stimulus, what happens to the twitch force?
at first you increase the frequency of twitching, then there is summation of force, then at higher frequencies there is tetanus.
why are EMGs clinically important?
helps distinguish between myopathies and neuropathies.
