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SYNAPSES (Transmission across cholinergic synapse (Common in the CNS (and…
SYNAPSES
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
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.
summation and control
Spatial summation
Occurs when a number of presynaptic neurones connect to one postsynaptic neurone
Temporal summation
Where
two
ore more
nerve impulses arrive in
quick succession
from the
same presynaptic neurone
This makes an
action potentia
l
more likely
as
more neurotransmitters
are
released
into the
synaptic cleft