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Chapter 3

BIOL 4309 Chapter 3: Ch. 3 Notes

Course Code
BIOL 4309
qing lin

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Ch. 3 Chemical Signaling by neurotransmitters and hormones
Synapse anatomical basis of chemical signaling between neurons
Basic structures of the synapse:
1) Presynaptic membrane
2) Synaptic vesicles
3) Synaptic cleft
4) Postsynaptic membrane and receptors
One way travel structural features determine that chemical transmission only occurs in one
direction i.e. from the presynaptic cell to the postsynaptic cell
- The sending (presynaptic) and receiving (postsynaptic) cells don’t actually
touch eachother
Chemical signaling (transmission) is done by the release of a neurotransmitter stored in the
synaptic vesicles into the synaptic cleft and then act on receptors located on the postsynaptic
-- in neuronal communication, the receiving cell may be another neuron, but it may also be a
muscle or a cell specialized to release a hormone or other secretory product.
Neuromuscular junction the connection point between a neuron and a muscle which has
many structural and functional similarities to a synapse
Three major types of the synapse:
1) Axondendritic synapse
2) Axonsomatic synapse
3) Axonaxonal synapse permits the presynaptic cell to alter transmitter release in the
postsynaptic cell directly at the terminals
Criteria to be named as a synapse - the following are anatomical and physiological features of
the synapse:
1) Synthesis there’s a mechanism for synthesis of the classical transmitter (S vesicles)
and neuropeptide (L vesicle)
2) Release the substance can be released from the axon terminal upon stimulation of the
3) Binding site there are receptors for the substance (neurotransmitter) on the
postsynaptic cell
4) Direct application of the substance or an agonist drug that acts on its receptors should
have the same effect on the postsynaptic cell as stimulating the presynaptic neuron

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5) Applying an antagonist drug that blocks the receptors should inhibit both the action of
the applied substance and the effect of stimulating the presynaptic neuron
6) Inactivation there is a mechanism for inactivating the substance
*these points can also be the criteria used for identifying a neurotransmitter
Extrasynaptic receptors receptors that are localized to non-synaptic sites on the neuronal
cell surface. These are usually activated when a neurotransmitter spills out from the synaptic
How the classical neurotransmitter is synthesized and released at a synapse:
How is the classical neurotransmitter synthesized and released at typical synapse
Neurotransmitter is synthesized
and then stored in vesicles.
An enzymatic reaction occurring
anywhere in the cell. Typically
occurs in the axon terminal.
An action potential invades
the presynaptic terminal.
Depolarization of presynaptic terminal
causes opening of voltage-gated Ca2+
Rapid influx of Ca2+ ions
through channels.
Increase in intracellular Ca2+
triggers for release: vesicles
fuse with presynaptic
is released into
synaptic cleft via
a fusion of the
vesicle membrane
with the membrane
of the axon
Neurotransmitter binds
to receptor molecules in
postsynaptic membrane.
Opening or closing of
postsynaptic channels.
Postsynaptic current causes
excitatory or inhibitory
postsynaptic potential that
changes the excitability of
the postsynaptic cell.
Transmitter release does not
occur anywhere along
the terminal, but only at
specialized regions near the
postsynaptic cell, which
stain darkly in the electron
micrograph. These release
sites are called active zones.
Retrieval of vesicular membrane
from plasma membrane.

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Features of neurotransmission using neuropeptides
Neuropeptides serve as neurotransmitters including a family of endogenous opioid and
inflammatory substances, such as calcitonin gene-related peptide & substance P
Precursors of neuropeptides are proteins that have to be synthesized in the cell body. The
precursor is packed into large vesicles and travel (by axonal transport) to the terminal where
the enzyme breaks down into peptides
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