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Chapter 3

PSY 214 Chapter Notes - Chapter 3: Axon Terminal, Neuropeptide, Neuromodulation


Department
Psychology
Course Code
PSY 214
Professor
Tara M Burke
Chapter
3

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Chapter 3: Chemical Signaling by Neurotransmitters and Hormones
-Neurotransmitter: Chemical substance released by a neuron to communicate with
another cell, which may be a different neuron, a muscle cell, or a hormone-producing cell
in an endocrine gland
Chemical signaling between nerve cells
-Synapse: structural unit of information transmission between two nerve cells. It consists
of the presynaptic nerve terminal, the synaptic cleft, and a small area of the postsynaptic
cell (typically associated with a dendrite or region of the cell body) that receives
incoming signal).
-Presynaptic cell: Neuron at a synapse that transmits a signal to the postsynaptic cell
-Postsynaptic cell: Neuron at a synapse that receives a signal from the presynaptic cell
-Axodendritic synapses: The most common synapses in the brain; in these synapses, an
axon terminal from the presynaptic neuron communicates with a dendrite of the
postsynaptic cell
-Synaptic Cleft: Small gap between the presynaptic and postsynaptic cells
-Synaptic Vessels: In the axon terminal, many small saclike objects, each one is filled
with several thousand molecules of a neurotransmitter- normally the source of transmitter
release
-Mitochondria: the cellular organelles responsible for energy
-Other types of synapses present in the brain:
oAxosomatic synapses: synapses between a nerve terminal and a nerve cell body
oAxoaxonic synapses: involve one axon synapsing on the terminal of another
axon
-Presynaptic inhibition: Signaling by the presynaptic cell to reduce neurotransmitter
release by the axon terminal of the postsynaptic cell
-Presynaptic facilitation: Signaling by the presynaptic cell to increase neurotransmitter
release by the axon terminal of the postsynaptic cell
-Neuromuscular Junction: connection point between a neuron and a muscle
Neurotransmitter Synthesis, Release and Inactivation
-Verifying a chemical’s status as a neurotransmitter, criteria:
oMechanism for inactivating the substance
oSubstance should be released from the axon terminal upon stimulation of the
neuron
oReceptors should be present on the postsynaptic cell
Neurotransmitters encompass several different kinds of chemical substances
-Major types of CLASSICAL neurotransmitters:
oAmino acids: the individual building blocks of proteins, play other metabolic
roles other than their role as a neurotransmitter
oMonoamines: derived from amino acids, but they undergo a chemical rxn and
removal of (-COOH)
-NONCLASSICAL neurotransmitters
oNeuropeptides: peptides found in the nervous system
oLipids: fatty substances
oGaseous transmitters:

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-The neuron has two different types of synaptic vesicles:
oSmall vesicles: contain only the classical transmitter
oLarge vesicles: contain the neuropeptide along with the classical transmitter
Classical transmitters and neuropeptides are synthesized by different mechanisms
-Their precursors are protein molecules
-Steps:
oProtein precursors are made in the cells body
oProtein is then packaged into large vesicles, along with enzymes to break down
the precursor
oVesicles are transported to the axon terminals
oNew neuropeptide molecules can be generated only in the cell body
Neuromodulators are chemical that don’t act like typical neurotransmitters
-Neuromodulators: describe substances that don’t act exactly like typical
neurotransmitters ( i.e. they don’t have a direct effect itself on the postsynaptic cell).
-Volume transmission: a common property of a neuromodulator. It is diffusion away
from the site of release to influence cells more distant from the releasing cell than is the
case at a standard synapse
-Wiring transmission: tight cell-to-cell synaptic interactions
Neurotransmitter relsease involves the exocytosis and recycling of synaptic vesicles
-Exocytosis: fusion of the vesicle membrane with the membrane of the axon terminal,
which exposes the inside of the vesicle to the outside of the cell
-Active Zones: Area along the axon terminal, near the postsynaptic cell that is specialized
for neurotransmitter release
-For exocytosis to take place:
oa vesicle must be transported to an active zone
othere, the vesicle must “dock” at the active zone
oDocking is followed by priming
oCaenorhabditis elegans: have shown that ethanol can acutely affect
neurotransmitter release by acting on at least 2 different presynaptic proteins
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