neurotransmitter/ meuromusclular junction

Describe the structure of a neuromuscular junction

● Receptors are on muscle fibre instead of postsynaptic membrane and there are more

● Muscle fibre forms clefts to store enzyme eg. acetylcholinesterase to break down neurotransmitter

Compare transmission across cholinergic synapses and neuromuscular

junctions

Cholinergic synapse

Neurone to neurone (or effectors, glands)

Neurotransmitters can be excitatory or inhibitory

Action potential may be initiated in postsynaptic neurone

Neuromuscular junction

(Motor) neurone to muscle

Always excitatory

Action potential propagates along sarcolemma down T tubules

explain the effect of drugs on a synapse

○ Similar shape to neurotransmitter

○ Stimulate release of more neurotransmitter

○ Inhibit enzyme that breaks down neurotransmitter → Na+ continues to enter

● Some drugs inhibit the nervous system, leading to fewer action potentials, eg:

○ Inhibit release of neurotransmitter eg. prevent opening of calcium ion channels

○ Block receptors by mimicking shape of neurotransmitter

neuromuscular pathway

1. action potential reaches pre synaptic membrane

2. calcium ion channels open and it diffuses in

3. vesicles containing neurotransmitter (ACh) fuses with pre synaptic membrane, ACh released into neuromuscular junction

4. ACh diffusese across junction and binds to receptors on sarcolemma

5. sodium ion channels open, sodium ions enter

6. depolarises muscle fibre membrane, action potential travesl down T TUBULES

7. opens gated calcium ion channels in membrane of sarcoplasmic reticulum; calcium ions out and into sarcoplasm

8. muscle contracts