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
–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
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
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