Nerve impulses and Synaptic Transmission

Question 1

Where is the action potential initiated?

Answer 1

axon hillock

Question 2

What does the propagation of the action potential depend on?

Answer 2

local current speed depolarizing the membrane potential of adjacent sections of the axon above threshold

Question 3

How does synaptic transmission at a chemical synapse occur?

Answer 3

• synthesis of the neurotransmitter and packaging into vesicles
• action potential arrives at nerve terminal
• voltage gated Ca2+ channels open
• Rise in Ca2+ in nerve terminal triggers release of transmitter
• Transmitter diffuses across synaptic cleft and binds to receptors on the postsynaptic membrane
• Transmitter diffuses away, is broken down by enzymes or taken up by cells which terminate the response

Question 4

The neuromuscular junction

Answer 4

• specialised synapse between motor neurones and skeletal muscle
• transmitter released is ACh
• ACh binds to nicotinic acetylcholine receptors (nAChR) on the membrane of the skeletal muscle
• nAChR ae ligand gated ion channels- permeable to cations
• activation of nAChR causes membrane depolarisation called the end plate potential
• the end plate potential initiates an action potential in the skeletal muscle