Biopsychology: Neurotransmission and Endogenous Ligands

Vocabulary practice flashcards covering neurotransmitter classifications, criteria, biosynthesis, receptor mechanisms, and major anatomical projection systems.

Neurotransmitter

A chemical substance that acts locally to convey information between neurons and fulfills all criteria of an endogenous signaling agent.

Neurohormone

A chemical messenger that acts distal to its site of release (often carried through the bloodstream) but otherwise fulfills all criteria of a neurotransmitter to influence behavior.

Neuromodulator

A substance co-released with a neurotransmitter that does not exert an effect of its own, but instead modifies receptor responsiveness and regulates the duration of graded ion channel opening.

Criterion for a True Neurotransmitter

A set of physiological standards requiring presynaptic presence, synthetic precursors and enzymes within the neuron, action potential-dependent release, identical effects upon direct application, proximity of receptors producing post-synaptic potentials ($\text{PSPs}$), specific inactivation mechanisms, and response to agonists and antagonists.

Neuropeptides

Large signaling molecules containing peptide bonds (such as endorphins, substance P, cholecystokinin, insulin, vasopressin, and oxytocin) that are synthesized exclusively in the neuronal cell body and transported to terminals via axonal transport.

Gaseous Neurotransmitters

Unconventional neurotransmitters (including nitric oxide and carbon monoxide) synthesized in terminal boutons/end feet that freely diffuse across cell membranes rather than being packaged into vesicles.

Life Cycle of a Neurotransmitter

The multi-step process consisting of precursor uptake, enzymatic synthesis, vesicular storage in the Golgi apparatus, exocytotic release, receptor interaction, and clearance via reuptake transporters or enzymatic degradation into metabolites.

Glutamate

The brain's primary excitatory amino acid neurotransmitter, synthesized from glucose, whose receptor activation allows $Na^+$ influx into the postsynaptic cell.

Excitotoxicity

Neuronal damage and cell death resulting from an excessive synaptic release and accumulation of excitatory amino acid neurotransmitters such as glutamate and aspartate, frequently implicated in epilepsy.

Gamma-Aminobutyric Acid (GABA)

The major inhibitory amino acid neurotransmitter of the brain, synthesized directly from glutamate, which functions by mediating $Cl^-$ and $K^+$ movement across the membrane.

Glycine

An inhibitory amino acid neurotransmitter in the central nervous system that plays a critical role in sleep and dreaming.

GABA Receptors ($GABA_A$, $GABA_B$, $GABA_C$)

The three classes of receptors for GABA: $GABA_A$ and $GABA_C$ are ionotropic receptors coupled to $Cl^-$ influx, whereas $GABA_B$ is a metabotropic G-protein-coupled receptor.

Ionotropic Glutamate Receptors

Ligand-gated channel complexes comprising AMPA (GluR1–4 subunits, mediating learning and memory), NMDA (NR1, NR2A–D, NR3A subunits), and Kainate (GluR5–7, KA1,2 subunits).

Metabotropic Glutamate Receptors (mGluRs)

G-protein-coupled receptors responsive to glutamate categorized into Group I (mGlu1, mGlu5), Group II (mGlu2, mGlu3), and Group III (mGlu4, mGlu6, mGlu7, mGlu8).

Choline Acetyltransferase (ChAT)

The enzyme responsible for the biosynthesis of acetylcholine from dietary choline and acetyl coenzyme A.

Acetylcholinesterase (AChE)

The synaptic enzyme that rapidly inactivates and degrades acetylcholine into choline and acetate at the synapse and neuromuscular junction.

Cholinergic Pathways

Neuronal projection networks originating in the basal forebrain and cholinergic nuclei of the pons and midbrain that project to the neocortex, amygdala, and hippocampus; degradation along these pathways is associated with Alzheimer's disease and dementia.

Nicotinic Acetylcholine Receptor

An ionotropic cholinergic receptor subtype that opens directly to allow cation influx, generating an excitatory (+) postsynaptic potential.

Muscarinic Acetylcholine Receptor

A metabotropic cholinergic receptor bound by muscarine (found in mushrooms) that can produce excitatory (+) or inhibitory (-) effects and makes up $90\%$ of all acetylcholine receptors in the brain.

Tyrosine Hydroxylase

The rate-limiting biosynthetic enzyme that catalyzes the initial conversion of dietary tyrosine into DOPA in the catecholamine synthesis pathway.

Catecholamine Biosynthesis Pathway

The enzymatic pathway converting tyrosine to DOPA via tyrosine hydroxylase, DOPA to dopamine via dopa decarboxylase, and dopamine to norepinephrine via dopamine-beta-hydroxylase.

COMT and MAO

Catechol-O-methyltransferase and monoamine oxidase, the two principal enzymes responsible for the enzymatic degradation and metabolic breakdown of catecholamines.

Mesolimbocortical Pathway

A major dopaminergic pathway originating in the ventral tegmental area (VTA) and projecting to the limbic system (nucleus accumbens, amygdala, hippocampus) and cortex, mediating reward and reinforcement.

Mesostriatal Pathway

A dopaminergic motor circuit originating in the substantia nigra and projecting to the striatum of the basal ganglia; loss of dopamine in this pathway produces Parkinson's disease.

Locus Coeruleus

A major noradrenergic nucleus located in the pons whose widespread ascending and descending projections innervate the cortex, thalamus, hypothalamus, and cerebellum; hyperactivation is linked to anxiety.

Raphe Nuclei

A cluster of serotonergic cell bodies located in the brainstem that project throughout the brain and spinal cord to modulate arousal, sleep, and mood.

Serotonin (5-HT)

An indoleamine monoamine neurotransmitter synthesized from dietary tryptophan via tryptophan-5-hydroxylase and aromatic L-amino acid decarboxylase, critical for regulating sleep and arousal states.