Skeletal neuromuscular junction Flashcards
____ is the neurotransmitter released at the neuromuscular junction (NMJ).
ACh
What enzyme is responsible for rapid termination of transmission at the skeletal neuromuscular junction?
ACh esterase
_____ _______ synthesises ACh from choline and acetyl coenzyme A
choline acetyltransferase
What channels are open in the motor neurone terminal in response to action potential (depolarisation)?
voltage-activated Calcium channels
What are the effects of Calcium entry in the motor neurone terminal?
- Fusion of ACh-containing vesicles with presynaptic membrane
- Resultant release of ACh into synaptic cleft
_____ ___ receptors are activated by ACh at the NMJ. These are __/__ channels
Nicotinic ACh receptors
Na/K channels
ACh binding to the post synaptic receptor induces __ influx, resulting in depolarisation, known as the ____ ____ ____
Na influx
end plate potential
The electrical response to one quantum of ACh (from one pre-synaptic vesicle) is known as the ___ ___ ____
miniature endplate potential
Minature end plate potentials summate to produce the ______ _____. If this exceeds the threshold, an ‘all or none’ _____ _____ is triggered.
endplate potential.
action potential
-initiates contraction
Achieving the threshold by the endplate potential triggers the opening of _____-_____ _ channels.
This allows AP propagation along the length of the muscle fibre.
voltage activated Na channels
What’s the name of the invaginations of the sarcolemma that enable AP spread to the sarcoplasmic reticulum?
Transverse (T) tubules
What does the action potential induce at the sarcoplasmic reticulum?
release of Calcium
What is the cause of the prolonged relaxation period of the skeletal muscle twitch?
It takes time for Ca to be reabsorbed and for cross bridges to be released
An autoimmune disease with antibodies against voltage-activated K+ channels in the motor neurone, resulting in muscle tiwtches, cramps and stiffness describes…
Neuromyotonia
-treatment: anti-convulsants (carbamezepine, phenytoin)
Antibodies against voltage-activated Ca2+ channels in the motor neuron terminal results in reduced Ca2+ and thus reduced ACh release, muscle weakness in the limbs describes…
Lambert-Eaton Myasthenic Syndrome
-treatment:
anticholinesterases, K channel blockers
