Download 9.3 Synaptic Transmission

Synaptic
Transmission
Homework: Question Handout
#16 - 24
The Synapse

The spaces between
neurons and adjacent
neurons or effectors are
known as synapses.

Synapses usually
involve many neurons.
Synaptic Transmission
1.
When the nerve
impulse reaches the
end of the axon of the
presynaptic neuron it
causes synaptic
vesicles to move to
the presynaptic
membrane.

The vesicles contain
chemicals called
neurotransmitters.
2.
The synaptic
vesicles release the
neurotransmitter into
the synapse by
exocytosis.
3.
The neurotransmitter
diffuses across the
synaptic cleft.
4.
Neurotransmitter
molecules attach to
membrane receptors on
the dendrites of the
postsynaptic neuron.
5.
This leads to increased
permeability of the
postsynaptic membrane
to Na+ and therefore
depolarization.
6.
After the signal has been passed, the sodium
gates must be closed in order to return the
postsynaptic neuron to resting potential.

This is indirectly done by an enzyme that breaks
down the neurotransmitter, clearing it from the
synapse and thereby shuts the sodium gates.
Neurotransmitters

Excitatory
neurotransmitters cause an
action potential in the
postsynaptic neuron to
continue the transmission of
the nerve impulse.

Ex. Acetylcholine

The enzyme that breaks
down acetylcholine in the
synapse is
cholinesterase.

Inhibitory
neurotransmitters stop
signals from transmitting.

They make postsynaptic
neurons more permeable
to potassium.

This causes more
potassium to leave the
cell and the potential to be
even more negative or
hyperpolarized.

Diffusion of neurotransmitters is a relatively
slow process (compared to the depolarization of
the neuron)

a neural response that involves many synapses
takes relatively longer than a simple reflex arc.
Summation

When two or more
neurons are needed
to create an action
potential in the
postsynaptic neuron.

Inhibitory and
Excitatory neurons
work together to
coordinate nerve
impulses.
Reminder!
Homework Questions #16 - 24