neuromuscular junctions

• 1. an action potential moves down the myelinated motor neurone towards the presynaptic membrane
• 2. The arrival of the action potential causes voltage-gated calcium channels to open in the membrane on the motor neurone. so Ca2+ diffuses in by facilitated diffusion
• 3. The presence of calcium ions causes vesicles of acetylcholine to move and fuse with the presynaptic membrane. So releasing the acetylcholine into the synapse. this is called exocytosis
• 4. The acetylcholine diffuses across the synapse to the postsynaptic membrane where they bind to receptors
• 5. The binding of acetylcholine causes neurotransmitted-gated channels to open and Na+ to fuse into the post-synaptic neurone
• 6. The influx of Na+ into the neurone causes voltage-gated Na+ channels to open so more ions can diffuse in setting up an action potential in the post synaptic neurone
• 7. Once the acetylcholine has binded to the receptors it’s broken down by enzymes called acetylcholinesterase which are on the membrane of the postsynaptic neurone. so stopping the response from continuously happening
• diagaram

  A) motor neurone

  B) skeletal muscle fibres

  C) motor end plate ( neuromuscular junction )

  
• 1. action potential arrives at the axon terminal of the motor neurone
• 2. arrival of the action potential causes the calcium gated channels to open so calcium ions move in by facilitated diffusion
• 3. calcium ions cause the synaptic vesicles, filled with a neurotransmitter called acetylcholine to move through the cytoplasm and fuse with the presynaptic membrane. this is called exocytosis and requires ATP
• 4. the neurotransmitter diffuses across the neuromuscular junction and binds to their receptor on the sodium gated channels. the latter open and causes sodium ions to diffuse in. this causes depolarisation of the sarcolemma and an action potential is set up