Summary: Chemistry of Behaviour

CHAPTER 4: CHEMISTRY OF BEHAVIOUR

Synaptic Transmission Involves Complex Electrochemical Process

Diagram

Description automatically generatedNeurotransmitter receptors can be categorized into 2 kinds

Ionotropic Receptors (ligand-gated ion channel): receptor containing ion channel that opens when bound by agonist, changing membrane potential

-change is depolarization = more likely to produce action potential = excitatory effect

-change is hyperpolarize = less likely to produce action potential = inhibitory effect


Metabotropic Receptors: doesn’t contain ion channel, instead activated metabotropic receptors use second messengers to cause changes

Many Neurotransmitters Have Been Identified

Qualifications to classify as transmitter:

-can be synthesized by presynaptic neurons and stored in axon terminals

-released when action potentials reach terminals

-recognized by specific receptors located on postsynaptic membrane

-causes changes in postsynaptic cell

-blocking its release interferes with ability of presynaptic cell to affect postsynaptic cell

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Description automatically generatedNeurotransmitter Systems Form Complex Array in Brain

-most common transmitters in brain are amino acids; two best studied are

  1. Glutamate: excitatory transmitter
  2. Gamma-Aminobutyric Acid (GABA): inhibitory transmitter


4 Amine Neurotransmitters Modulate Brain Activity

  1. Acetylcholine
  2. Dopamine
  3. Serotonin
  4. Norepinephrine

-each amine neurotransmitter is carried by different set of axons, projected to different brain regions

Co-Localization: synthesis and release of more than one type of neurotransmitter by presynaptic neuron

Diagram

Description automatically generatedAcetylcholine

-plays major role in neurotransmission in forebrain

-cholinergic cells that project to sites like cerebral cortex, amygdala, hippocampus

-loss is associated with Alzheimer’s disease and experimental disruption of cholinergic pathways interfering with learning and memory


Dopamine

-monoamine

-dopaminergic projections include

-mesostriatal pathway: originates in midbrain (mesencephalon) around substantia nigra

and projects axons to striatal cortex (basal ganglia)] which relate to motor control – damage relates to problems of Parkinson’s disease and tremors

-mesolimbocortical pathway: originates in midbrain (ventral tegmental area (VTA)) and projects to various locations in limbic system and cortex, important for processing reward, abnormalities associate with some symptoms of schizophrenia


Serotonin

-wide expanses of the brain are innervated by serotonergic fibers, originating from neurons along midline of midbrain and brainstem

-controls behaviours ex. mood, vision, sexual behaviour, anxiety, sleep,


Norepinephrine

-noradrenergic neurons, accelerate organ activity

-two regions of brainstem and midbrain: locus coeruleus (blue spot) and lateral tegmental area

-project broadly throughout cerebrum, cerebral cortex, limbic system, thalamic nuclei

-control behaviours ranging from alertness to mood to sexual behaviour and more

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Description automatically generatedMany Peptides Function as Neurotransmitters

Opioid Peptides: group of endogenous substances that mimic effects of morphine, reducing perception of pain and have rewarding properties

-diverse group of peptides originally discovered in periphery, also made by neurons in spinal cord and brain, may act as synaptic transmitters and often co-localize ex. substance P, cholecystokinin (CCK), neurotensin, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP)

-various peptide hormones, ex. oxytocin and vasopressin are produced by hypothalamus and pituitary

Some Neurotransmitters are Gases

Different from traditional neurotransmitters in 3 important ways

  1. produced in cellular locations other than axon terminals, especially in dendrites, and not held in vesicles but rather diffuses out of neuron as it is produced
  2. no receptors are involved, instead they diffuse into target cell to trigger second messengers inside
  3. can function as retrograde transmitters – diffuses from postsynaptic neuron back to presynaptic neuron to convey info that physically changes synapse, possibly crucial for memory formation


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