Neuromuscular junction and muscle contraction Flashcards
What is a neuromuscular junction
Synapse between alpha(lower)-motor neurons (coming from brain) and a muscle fibre
synaptic cleft length
10-50nm
purpose of synapse
contact point for neuron to neuron or neuron to muscle
contact ratio
rangs from 1:1 for mmuscle to 10^3:1 in the CNS
myelin sheath
increases conduction velocity
distal axon
“away from beginning”
unidirectional chemical communication
only from peripheral nerve to the muscle
arrangement of neuron in spinal cord
motor neurons reside in anterior route
number of axons in a muscle fibre
only 1 motor neuron axon attached to each muscle fibre
number of axons in a muscle fibre
only 1 motor neuron axon attached to each muscle fibre
7 steps of synapse action
- Action potential opens Voltage-gated Ca2+ channels
- Ca2+ enters
- Ca2+ triggers exocytosis of vesicles
- Acetylcholine diffuses in cleft
- Acetylcholine binds to receptor-cation channel & opens channel
- Local currents flow from depolarized region and adjacent region; action potential triggered and spreads along surface membrane
- Acetylcholine broken down by acetylcholine esterase (enzyme). Muscle fibre response to that molecule of Acetylcholine ceases
snare proteins
responsible for making membrane of vesicle fuse with the nerve terminal
EMG
electro-myogram - test functioning of neuromuscular system
H-zone
myosin on its own (shortens upon contraction)
A-band
myosin (does not decrease in length when contracted)
I-band
actin on its own (decreases in length when contracted)
Botulism
“Botox”. irreversible disrution in stimulation-induced acetylcholine release by the presynaptic nerve
Myasthenia gravis (MG)
Auto-immune disease. antibodies produced Against acetylcholine receptors - they are blocked by antibodies.
Antibodies detected in 90% cases. EMG examination will confirm diagnosis
Lambert-Eaton myasthenic syndrome (LEMS)
Failure of calcium channels. Antibodies directed against the VGCC - associated with lung cancer.
Lambert-Eaton myasthenic syndrome (LEMS)
Failure of calcium channels. Antibodies directed against the VGCC - associated with lung cancer.
