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.
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.
