Neuromuscular Junctions Flashcards
(3 cards)
Where are neuromuscular junctions located?
> They are located between a neurone and a muscle cell
Transmission across a neuromuscular junction
> When an impulse travelling along the axon of a motor neurone arrives at the presynaptic membrane, the action potential causes Ca2+ to diffuse into the neurone
> This stimulates vesicles containing the neurotransmitter acetylcholine (ACh) to fuse with the presynaptic membrane
> The ACh that is released diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma (surface membrane of the muscle fibre cell)
> This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in
> This depolarises the sarcolemma, generating an action potential
What happens after the sarcolemma is depolarised and an action potential is generated?
> Action potentials cause voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum to open
> Ca2+ diffuse out of the sarcoplasmic reticulum (SR) and into the sarcoplasm surrounding the myofibrils
> Ca2+ bind to troponin molecules, stimulating them to change shape
> This causes the troponin and tropomyosin proteins to change position on the thin (actin) filaments
> The myosin-binding sites are exposed to the actin molecules
> The process of muscle contraction (known as the sliding filament model) can now begin
