Synapses

How Impulses Cross Synapses: How Impulses Cross Synapses:
An action potential arrives at the synaptic
knob of the presynaptic neurone.
The voltage-gated Ca+ channels open,
causing Ca+ to diffuse into the neurone.
This causes vesicles containing
acetylcholine to move to the presynaptic
membrane.
These vesicles fuse with the presynaptic
membrane & release acetylcholine into
the synaptic cleft.
Acetylcholine diffuses across the synaptic
cleft to the postsynaptic membrane.
Acetylcholine binds to receptors in the
postsynaptic membrane.
+
Na channels open & the membrane
becomes depolarised – generating an
action potential in the postsynaptic
neurone.
Acetylcholinesterase is an enzyme found in
the synaptic cleft that breaks down the
remaining acetylcholine into acetic acid &
choline.
They diffuse back into the presynaptic
neurone to re-form acetylcholine.


Roles of Synapses: Roles of Synapses:
Transport of info between neurones.
Unidirectional:
Synapses only pass impulses one way.
The presynaptic neurone has the
neurotransmitter.
the postsynaptic neurone has the
receptors.