Neuromuscular junction Flashcards
How is a muscle contraction triggered?
when an action potential arrives at a neuromuscular junction
What is a neuromuscular junction?
the point where a motor neurone and skeletal muscle fibre meet
How does the muscle contract simulataneously?
- there are many neuromuscular junctions along the length of a muscle to ensure that all the muscle fibres contract simulataneously
What would happen if there was only one neuromuscular junction?
- the muscle fibres would not contract together
- therefore the contraction of the muscle would not be as powerful
- much slower, as a wave of contraction would have to travel across the muscle to stimlate the individual fibres to contract
How is the impulse supplied to muscle fibres?
- all the muscle fibres supplied by a single motor neurone are known as a motor unit
- the fibres act as a single unit
What is done if a strong force is required?
a large number of motor units are stimulated
How is the presynaptic vesicles fused with presynaptic membrane?
- when an action potential reaches the neuromuscular junction it stimulates calcium ion channels to open
- calcium ions then diffuse from the synapse into the synaptic knob
- where they cause synaptic vesicles to fuse with the presynaptic memebrane
What happens after the synaptic vesicles fuse with the presynaptic membrane?
- acetycholine is released into the synaptic cleft by exocytosis and diffuses acorss the synapse
- it binds to receptors on the post synaptic membrane (the sacrolemma)
- opening sodium ion channels, and resulting in depolarisation
What happens to the acetylcholine after binding to the sacrolemma?
- broken down by acetylcholinesterase
- into choline and ethanoic acid
What is the purpose of the breakdown of acetylcholine?
prevents the muscle from being overstimulated
What happens to the choline and the ethanoic acid?
- diffuse back into the neurone
- where they are recombined into acetylcholine
- using the energy provided by mitochondria
