Download Synaptic Transmission

What is a Synapse?
 The spaces between neurons and adjacent neurons or
effectors are known as synapses.
 Synapses usually involve many neurons.
What happens at a Synapse?
1) The nerve impulse
(action potential)
moves along the
presynaptic neuron
towards the synapse.
2) This causes calcium
ions to enter the
neuron.
What happens at a Synapse?
3) Calcium ions cause
chemicals called
neurotransmitters
that are stored in
vesicles at the end of
the presynaptic axon to
be released into the
synapse (synaptic
cleft).
What happens at a Synapse?
4) They diffuse across the
synaptic cleft and attach
to membrane receptors
on the postsynaptic
neuron.
5) This opens up sodium
channels and allows
sodium into the postsynaptic neuron which
causes the depolarization
to continue on.
What happens at a Synapse?

Sometimes
neurotransmitters can
work against sending a
message and can be
inhibitory. When they
bind to the post-synaptic
neuron, they let
potassium out instead of
sodium in, which makes
the neuron even more
negative!

This is called
hyperpolarization.
What happens at a synapse?
6) Once the message has been sent across the
synapse, the neurotransmitters either get
recycled back into the pre-synaptic neuron or get
broken down.
Time lag…
 The diffusion of neurotransmitters is a slow process, so
a neural response that involves many synapses takes a
relatively longer time than a simple reflex arc.
And in summation…
 Summation is when two
or more neurons are
needed to create an
action potential in a
further neuron. The sum
of their firing causes an
action potential in the
postsynaptic neuron.