PSYC 273 Lecture Notes - Lecture 4: Substantia Nigra, Neurotransmitter Receptor, Basal Forebrain
Chapter 4 Notes
A Dream of Soups and Sparks: how neurons communicate.
• Exogenous: arising from outside the body. (drugs)
• Endogenous: produced inside the body. (neurotransmitters)
Electrical Signals are Turned into Chemical Signals at Synapses
• Presynaptic: located on the transmitting side of a synapse.
• Synapse: the cellular location at which information is transmitted from a neuron to
another cell.
• Neurotransmitter: a signaling chemical, released by a presynaptic cleft after the
functioning of the postsynaptic neuron.
• Exocytosis: a cellular process that results in the release of a substance into the
extracellular space (the synaptic cleft).
• Neurotransmitter Receptors: a specialized protein that is embedded in the cell
membrane, allowing it to selectively sense and react to molecules of the corresponding
neurotransmitter. THESE ARE INHIBATORY OR EXCITATORY.
• Postsynaptic: located on the receiving side of the synapse.
• Reuptake: the reabsorption of molecules of neurotransmitter by the neurons that released
them, thereby ending the signaling activity of the transmitter molecules.
o Transporter: a specialized membrane component that returns transmitter
molecules to the presynaptic neuron or reuse.
• Receptor proteins recognize transmitters and their mimics.
o Receptors can be categorized in 2 ways.
▪ Ionotropic Receptors: a receptor protein containing an ion channel that
opens when the receptor is bound by an agonist. Faster than metabotropic
because it’s a very simple opening a channel.
• Ligand: a substance that binds to receptor molecules.
o Exogenous: arising from outside the body.
o Endogenous: produced inside the body.
o Agonist: any molecule that binds to a receptor and initiates
the same response as another molecule.
o Antagonist: molecules that interferes with normal
neurotransmitter receptor activity.
▪ Metabotropic Receptors: a receptor protein that does not contain ion
channels, but may, when activated, use a second messenger (a chemical)
system to open nearby ion channels or to produce other cellular effects.
• Still requires ligand binding, but conformational change does lead
directly control ion flow.
• The binding site for the neurotransmitter in extracellular space.
Intracellular binding for G proteins.
• Use secondary messengers that form biochemical cascade.
• Slower process but has longer lasting effects that can amplify and
modulate responses.
• Most often G-Protein coupled receptors.
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o G-Protein: proteins that adjacent to the intracellular portion
of a receptor. When activated they
▪ Can open ion channels.
▪ Can activate other internal chemical signals which
can then affect ion channels or other cellular
processes.
• Depending on receptor, the target may be a second-messenger
system or an ion channel.
o Second-Messenger System: a slow acting substance in the
postsynaptic cell that amplifies the effects of synaptic
activity within the cell.
• Many neurotransmitters have been identified. Has an indirect effect on the cell.
o Qualifications for a substance to be a transmitter:
▪ It can be synthesized by presynaptic neurons and stored in axon terminals.
▪ Exocytosis: It is released when action potentials reach the terminals.
▪ It is recognized by specific receptors located on the postsynaptic
membrane.
▪ It causes changes in the postsynaptic cell.
▪ Blocking its release interferes with the ability of the presynaptic cell to
affect the postsynaptic cell.
o Categories of neurotransmitters:
▪ Amino Acid Neurotransmitter: a neurotransmitter that is itself an amino
acid. The most common neurotransmitter. (Glycine, glutamic acid,
GABA)
▪ Peptide Neurotransmitter: a neurotransmitter consisting of a short chain
of amino acids. (Oxytocin, Vasopressin)
▪ Amine Neurotransmitter: a neurotransmitter based on modifications of a
single amino acid nucleus. (ex: dopamine, serotonin)
• Acetylcholine: first transmitter to be discovered. A
neurotransmitter that is produced and released by the autonomic
nervous system, by motoneurons and by neurons throughout the
brain.
▪ Gas Neurotransmitter: a neurotransmitter that is a soluble gas. (Nitric
Oxide, Carbon Monoxide)
Neurotransmitter Systems Form a Complex Array in the Brain
• The most abundant excitatory and inhibitory neurotransmitters are amino acids.
o Glutamate: an amino acid transmitter, the most common excitatory transmitter.
Interact with subtypes of receptors. Important for learning and memory.
▪ AMPA: the most plentiful receptors in the brain.
▪ NMDA: have unique characteristics that suggest they play a central role in
memory formation.
o Aspartate: excitatory transmitter.
o Gamma-Aminobutyric Acid (GABA): a widely distributed amino acid
transmitter. The main inhibitory transmitter in the mammalian nervous system.
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▪ Related to anxiety relief. Drugs that mimic this action of GABA are
effective calming agents.
• Benzodiazepines: drugs that are widely used to reduce anxiety and
aid in muscle relaxation, sleep induction, etc.
o Glycerin: inhibitory transmitter.
• 4 amine neurotransmitters modulate brain activity.
o Acetylcholine: first transmitter to be discovered. A neurotransmitter that is
produced and released by the autonomic nervous system, by motoneurons and by
neurons throughout the brain. Important for learning and memory.
▪ Cholinergic: referring to cells that use Acetylcholine as their synaptic
transmitter. Loss of these can lead to Alzheimer’s. These are excitatory.
Found within the
• Basal Forebrain: a region, ventral to the basal ganglia, that is the
major source of acetylcholine in the brain.
o Dopamine (DA): a monoamine transmitter found in the midbrain—especially the
substantia nigra— and in the basal forebrain.
▪ Dopaminergic: referring to cells that use dopamine as their synaptic
transmitter.
• Mesostriatal Pathway: motor control. Originates in:
o Substantia Nigra: a brainstem structure that innervates the
basal ganglia and is a major source of dopaminergic
projections.
• Mesolimbocortical Pathway: important for the processing of
reward. Feelings of pleasure. Associated with addiction. Important
for learning and shaped by positive reinforcement. originates in:
o Ventral Tegmental Area (VTA): a portion of the midbrain
that projects dopaminergic fibers to the nucleus.
o Serotonin: a synaptic transmitter that is produced in the raphe nuclei and is active
in structures throughout the cerebral hemispheres. Very few of these. Participates
in the control of sleep, mood, vision, sexual behavior, anxiety, etc.
▪ Raphe Nuclei: a string of nuclei in the midline of the midbrain and
brainstem that contain most of the serotonergic neurons of the brain.
• Serotonergic: referring to cells that use serotonin as their synaptic
transmitter.
▪ Drugs that mimic serotonin are usually used for relieving depression and
anxiety.
o Norepinephrine (Noradrenaline) (NE): a neurotransmitter produced and
released by sympathetic postganglionic neurons to accelerate organ activity.
▪ Noradrenergic: referring to cells using Norepinephrine as a transmitter.
▪ Have their cell bodies in two regions of the brainstem and midbrain:
• Locus Coeruleus (blue spot): a small nucleus in the brainstem
whose neurons produce norepinephrine and modulate large areas
of the forebrain.
• Lateral Tegmental Area: a brainstem region that provides some
of the norepinephrine- containing projections of the brain.
• Many peptides function as neurotransmitters or hormones.
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Document Summary
A dream of soups and sparks: how neurons communicate: exogenous: arising from outside the body. (drugs, endogenous: produced inside the body. (neurotransmitters) Has an indirect effect on the cell. postsynaptic cell that amplifies the effects of synaptic activity within the cell: qualifications for a substance to be a transmitter: It can be synthesized by presynaptic neurons and stored in axon terminals: exocytosis: it is released when action potentials reach the terminals. It is recognized by specific receptors located on the postsynaptic membrane. It causes changes in the postsynaptic cell: blocking its release interferes with the ability of the presynaptic cell to affect the postsynaptic cell, categories of neurotransmitters, amino acid neurotransmitter: a neurotransmitter that is itself an amino acid. Gaba: peptide neurotransmitter: a neurotransmitter consisting of a short chain of amino acids. (oxytocin, vasopressin, amine neurotransmitter: a neurotransmitter based on modifications of a single amino acid nucleus. (ex: dopamine, serotonin, acetylcholine: first transmitter to be discovered.
