The synapse
The synapse
- A synapse is a tiny gap between two neurones.
- The electrical impulse can't jump the gap — so it's carried across by a chemical.
- The same idea connects a neurone to a muscle.
A cholinergic synapse
- the impulse arrives and makes calcium ions enter the first neurone.
- this makes vesicles release a neurotransmitter, acetylcholine, into the gap.
- acetylcholine diffuses across and binds receptors on the next neurone.
- this starts a new impulse in the next neurone.
Practice
When an impulse arrives at a synapse, the first thing that happens is:
Ca²⁺ entering the presynaptic neurone causes vesicles to release acetylcholine into the cleft.
Practice
Acetylcholine carries the signal across the synapse by:
The neurotransmitter diffuses across the cleft and binds receptors, starting a new impulse.
Practice
Put the events at a cholinergic synapse in order.
Impulse → Ca²⁺ in → ACh released → ACh binds receptors → new impulse.
The neuromuscular junction
- A neuromuscular junction works just like a synapse.
- But it is between a motor neurone and a muscle.
- The neurotransmitter triggers the muscle to contract.
Practice
A neuromuscular junction is a synapse between:
It works like any synapse, but the second cell is a muscle that is made to contract.
You've got it
Key idea
- a synapse is a gap between neurones; the signal crosses it as a chemical
- cholinergic synapse: impulse → Ca²⁺ in → vesicles release acetylcholine → binds receptors → new impulse
- a neuromuscular junction is a synapse between a motor neurone and a muscle