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Chapter 3

Psychopharmacology chapter 3 textbook notes

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Ryerson University
PSY 214
Tara M Burke

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: o Axosomatic synapses: synapses between a nerve terminal and a nerve cell body o Axoaxonic 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: o Mechanism for inactivating the substance o Substance should be released from the axon terminal upon stimulation of the neuron o Receptors should be present on the postsynaptic cell Neurotransmitters encompass several different kinds of chemical substances ­ Major types of CLASSICAL neurotransmitters: o Amino acids: the individual building blocks of proteins, play other metabolic roles other than their role as a neurotransmitter o Monoamines: derived from amino acids, but they undergo a chemical rxn and removal of (-COOH) ­ NONCLASSICAL neurotransmitters o Neuropeptides: peptides found in the nervous system o Lipids: fatty substances o Gaseous transmitters: ­ The neuron has two different types of synaptic vesicles: o Small vesicles: contain only the classical transmitter o Large vesicles: contain the neuropeptide along with the classical transmitter Classical transmitters and neuropeptides are synthesized by different mechanisms ­ Their precursors are protein molecules ­ Steps: o Protein precursors are made in the cells body o Protein is then packaged into large vesicles, along with enzymes to break down the precursor o Vesicles are transported to the axon terminals o New 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: o a vesicle must be transported to an active zone o there, the vesicle must “dock” at the active zone o Docking is followed by priming o Caenorhabditis elegans: have shown that ethanol can acutely affect neurotransmitter release by acting on at least 2 different presynaptic proteins involved in the exocytosis process Endocytosis ­ Endocytosis: quickly retrieves the vesicle membrane from the terminal  membrane ­ Vesicle recycling*** Several mechanisms control the rate of neurotransmitter release by nerve cells 1) Rate of cell firing 2) Probability of a transmitter release from the terminal 3) Presence of autorecptors on axon terminals or cell bodies and dendrites ­ Neurons may have 2 different types of autoreceptors: o terminal autoreceptors: located on axon terminals. They inhibit  further transmitter release o somatodendritic autoreceptors: found on the soma (cell body.  They slow the rate of cell firing 4) Heteroreceptors: they may either enhance or reduce the amount of transmitter  being released from the axon terminal  Neurotransmitters are inactivated by reuptake and by enzymatic breakdown Several processes responsible for neurotransmitter removal… ­ enzymatic breakdown ­ removal from the synaptic cleft by a transport process that makes use of  specialized proteins called transporters ­ Depending on the neurotransmitter, terminati
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