4- Nmj, Mucle Contraction And EMG Flashcards Preview

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Flashcards in 4- Nmj, Mucle Contraction And EMG Deck (14):

What is the neuromuscular junction

A specialised synapse between a motor neuron and a muscle fibre.


Describe the structure of the NMJ

A specialized structure incorporating the distal axon terminal and the muscle membrane that allows for the unidirectional chemical communication between peripheral nerve and muscle

•Main structures constituting the NMJ:
–presynaptic nerve terminal
–synaptic cleft
–postsynaptic endplate region on the muscle fibre which has folds


Describe the 7 steps in muscle contraction

1.Action potential open V-gated Ca2+ channels
2.Ca2+ enters
3.Ca2+ triggers exocytosis of vesicles
4.Acetylcholine diffuses in cleft
5.Acetylcholine binds to receptor-cation channel & opens channel
6.Local currents flow from depolarized region and adjacent region; action potential triggered and spreads along surface membrane
7.Acetylcholine broken down by acetylcholine esterase (enzyme). Muscle fibre response to that molecule of Acetylcholine ceases


Describe myasthenia gravis

An autoimmune disorder where antibodies are directed against the acetylcholine receptor.
•There may be a personal or family history of other autoimmune diseases. It cause fatigable weakness (i.e. becomes more pronounced with repetitive use) and may affect the ocular, bulbar, respiratory or limb muscles.
•Antibodies are detected in nearly 90% of cases and EMG examination will confirm the diagnosis.
•In severe cases the antibodies in the blood can


Describe Lambert-Eaton myastenic syndrome

•an autoimmune disease caused by antibodies directed against the voltage-gated calcium channel (VGCC) - associated with lung cancer.


What is the neurotransmitter in voluntary striated muscle



Describe muscular activation and relaxation

“Action potential propagates along surface membrane and into T-tubules
DHP (dihydropyridine) receptor in T-tubule membrane: senses V & changes shape of the protein link to Ryanodine receptor, opens the Ryanodine receptor Ca2+ channel in the SR membrane; Ca2+ released from SR into space around the filaments
Ca2+ binds to Troponin & Tropomyosin moves allowing
Crossbridges to attach to actin
Ca2+ is actively transported into the SR continuously while action potentials continue. ATP- driven pump (uptake rate < or = release rate).
Ca2+ dissociates from TN when free Ca2+ declines; TM block prevents new crossbridge attachment; Active force declines due to net crossbridge detachment


Describe botulism

Botulinum toxin produces an irreversible disruption in stimulation-induced acetylcholine release by the presynaptic nerve terminal


How are MEPPS caused

At rest vesicles release ACh at a low rate causing membrane end plate potentials, causing small changes in membrane potential


Describe what happens to the bands in the myofibril during muscle contraction

I band shortens( actin)
A band doesn’t shorten (actin and myosin)
H band narrows and disappears (myosin)


What is an electrocardiography used for

Recording a.p. In skeletal muscles


Describe ECG and EEG

ECG: a.p. In heart, electrodes on limbs or chest
EEG (electroencephalogram): a.p. In brain, electrodes on scalp


What happens as stimulus is increased up to 25hz

Twitch force plateaus


What is tetanus

TETANUS = the prolonged contraction of a muscle caused by rapidly repeated stimuli
• In other words, it is the fusing of lots of twitches such that the
time between one twitch and the next is too short for the contraction to have died off before the next one comes
• If you increase the frequency of the stimuli, you can build up the force because the force of contraction doesn't return to zero before the next stimulus arrives
• This leads to a build up of force and it is called an UNFUSED TETANUS
• It is unfused because you can still see the ripples where the force decreases slightly before the next stimulus comes
• If you further increase the frequency (around 30 Hz) you can start to see
FUSED TETANUS - the muscle will contract and continue to contract with no decrease in force
• Fused Tetanus is how people die when they get electrocuted
• The force summates but the action potentials DO NOT