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Chapter 5

Chapter 5

Course Code
Suzanne Erb

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Chapter 5
Neuroactive Ligands and the Nervous System
Neurotransmitters, Neuromodulators, and Neurohormones
-chemicals located in specific regions of neurons that are released under specific stimulation
-act on specific receptors and induce short term changes in membrane potential
-chemicals synthesized in one area of the nervous system and are released into circulation
-travel to site that is distant from release site and produce effect on brain or body
-chemicals with characteristics of neurotransmitters and neurohormones
-have no intrinsic activity on their own
-modify responses of other transmitters pre-synaptically or post-synaptically
-a chemical can act as a neuromodulator in one area of the nervous system and a neurotransmitter in
another part
-therefore, collectively known as neurotransmitters:
-in order for a chemical to be designated as a neurotransmitter:
oShould be found in presynaptic neurons
oEnzymes necessary for synthesis must also be present
oShould be a mechanism for terminating its action
oDirect application to post synaptic neuron must be same as stimulation to pre synaptic neuron
oWhen presynaptic neuron is stimulated, synaptic cleft should contain the NT
oDrugs that interfere with synthesis or reaction should block the effects of presynaptic neuronal
oDrugs blocking the actions of inactivating enzyme should prolong transmitters actions
-a psychoactive drug can alter many processes such as:

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oIncrease/decrease the rate of neurotransmitter synthesis
oIncreases/decrease amount of NT release
oEnhance or prevent storage of NT
oIncrease/decrease NTs rate of metabolic breakdown
oBind to post synaptic / pre synaptic receptor and accentuate/blunt neurotransmitter’s effects
oReduce/enhance NTs reuptake
oServe as neurotoxin or neurotoxic agentsubstance causes destruction of neural tissue
Specific Neurotransmitters
Acetylcholine (Ach)
-found in various parts of the PNS and many areas of the CNS
-in PNS, has excitatory effects (causes depolarization)
-in CNS, can have excitatory and inhibitory effects
-undergoes inactivation through enzyme acetylcholinestrase
-important NT for memory functions, aggression, and grand mal seizures
has 2 main receptors
- easily activated by drug muscarine
-slow receptors
- easily activated by nicotine
-fast receptors
-other drugs including curare, atropine, and some antidepressants alter cholinergic activity
-cholinergic system is in the brain and increases ability to focus on environment and respond to it
-major influence on CNS and PNS
-CNS: mainly inhibitory
-PNS: mainly excitatory
-NE activity may enhance physiological activity – crucial role in arousal and mood
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