SYNAPSES

TYPES OF NEUROTRANSMITTERS

Excitatory- Theses neurotransmitters result in the depolarisation of the postsynaptic neurone

If the threshold is reached in the postsynaptic membrane an action potential is triggered

An example is acetylcholine

Inhibitory- These neurotransmitters result in the hyperpolarisation of the postsynaptic membrane.

This prevents an action potential being triggered.

Gamma-aminobutyric acid is an example.

Transmission across cholinergic synapse

They use the transmitter acetylcholine

Common in the CNS

and at neuromuscular junctions where a motor neurone and a muscle cell meet.

(1) Acetylcholine is realised from the vesicles in the presynaptic knob

(2) It then diffuses across the synaptic cleft where it binds to specific receptors in the postsynaptic membrane

(3) This triggers an action potential in the postsynaptic neurone or muscle cells

(4) Ones the action potential has been triggered acetylcholine is hydrolysed

summation and control

Spatial summation

Temporal summation

Occurs when a number of presynaptic neurones connect to one postsynaptic neurone

Where two ore more nerve impulses arrive in quick succession from the same presynaptic neurone

This makes an action potential more likely as more neurotransmitters are released into the synaptic cleft