Neurotransmitters – Physiology, Synthesis & Inactivation

Vocabulary flashcards summarizing key terms, enzymes, neurotransmitters and mechanisms related to neurotransmitter physiology, synthesis, action and termination.

Neurotransmitter

Endogenous chemical that carries a nerve signal across a chemical synapse.

Synapse

Junction where a presynaptic neuron communicates with a postsynaptic cell.

Presynaptic Neuron

Nerve cell that releases neurotransmitter into the synaptic cleft.

Postsynaptic Neuron

Cell possessing receptors that bind the released neurotransmitter.

Synaptic Vesicle

Membrane-bound sac that stores neurotransmitter in the presynaptic terminal.

Synaptic Cleft

Tiny extracellular gap between pre- and postsynaptic membranes where neurotransmitter diffuses.

Autoreceptor

Presynaptic receptor that binds its own neurotransmitter to inhibit further release.

Excitatory Neurotransmitter

Chemical that increases the likelihood of postsynaptic action potential generation.

Inhibitory Neurotransmitter

Chemical that decreases the likelihood of postsynaptic action potential generation.

Reuptake

Transport of released neurotransmitter back into the presynaptic neuron for reuse or degradation.

Enzymatic Degradation

Inactivation of neurotransmitter by specific synaptic enzymes.

Simple Diffusion (Termination)

Passive dispersal of neurotransmitter away from the synapse, common for neuropeptides.

Acetylcholinesterase (AChE)

Enzyme that hydrolyzes acetylcholine into acetate and choline in the synaptic cleft.

Monoamine Oxidase (MAO)

Mitochondrial enzyme that deaminates catecholamines and serotonin; inhibited by some antidepressants.

Catechol-O-methyltransferase (COMT)

Enzyme that adds a methyl group to catecholamines during their metabolism.

Tyrosine Hydroxylase

Rate-limiting enzyme in catecholamine synthesis converting tyrosine to L-DOPA.

DOPA Decarboxylase

Enzyme converting L-DOPA to dopamine; deficiency linked to Parkinson’s disease.

Dopamine β-Hydroxylase

Enzyme that converts dopamine to norepinephrine within storage granules.

Phenylethanolamine N-methyltransferase (PNMT)

Enzyme that methylates norepinephrine to form epinephrine in adrenal medulla.

Choline Acetyltransferase

Synthesizes acetylcholine from choline and acetyl-CoA in cholinergic neurons.

Glutamate

Most common excitatory neurotransmitter in the brain; re-uptaken by specific transporters.

GABA (γ-Aminobutyric Acid)

Major inhibitory neurotransmitter of the brain; opens Cl⁻ channels to hyperpolarize neurons.

Glycine

Inhibitory neurotransmitter of spinal cord and brain stem; increases Cl⁻ permeability.

Acetylcholine (ACh)

Neurotransmitter that is excitatory at neuromuscular junctions and inhibitory in parasympathetic pathways.

Dopamine

Catecholamine involved in reward, movement control; usually inhibitory.

Norepinephrine

Catecholamine acting in fight-or-flight response and brain alertness; mostly excitatory.

Epinephrine

Hormone/neurotransmitter synthesized from norepinephrine; enhances sympathetic responses.

Serotonin (5-HT)

Monoamine derived from tryptophan; modulates mood, appetite, pain pathways (inhibitory in spinal cord).

Nitric Oxide (NO)

Gaseous neurotransmitter from arginine causing vasodilation and metabolic signaling.

Substance P

Neuropeptide that transmits pain signals in the nervous system.

Opioid Peptides

Endogenous peptides (e.g., endorphins) that modulate pain by binding opioid receptors.

Vanillylmandelic Acid (VMA)

Major urinary metabolite of epinephrine and norepinephrine after MAO/COMT action.

Homovanillic Acid (HVA)

Principal metabolite of dopamine formed via MAO and COMT pathways.

Astrocyte

Glial cell that uptakes GABA from synapses for inactivation.

Fight-or-Flight Response

Sympathetic reaction mediated partly by norepinephrine release.

Ligand-Gated Ion Channel

Membrane protein that opens when a neurotransmitter binds, altering ion flow.

G-protein Coupled Receptor (GPCR)

A mechanism of neurotransmitter action involving a receptor that indirectly affects ion channels or enzyme activity via a G-protein.

Calcium (Ca²⁺) in Neurotransmitter Release

Essential ion that triggers the fusion of synaptic vesicles with the presynaptic membrane, leading to neurotransmitter release.

Fast Synaptic Transmission

Synaptic transmission mediated by ligand-gated ion channels, resulting in rapid changes in postsynaptic membrane potential.

Slow Synaptic Transmission

Synaptic transmission mediated by G-protein coupled receptors, resulting in slower, longer-lasting changes in postsynaptic excitability.

Exocytosis (Synaptic)

The process by which synaptic vesicles fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft.

Neurotransmitter

Endogenous chemical that carries a nerve signal across a chemical synapse.

Synapse

Junction where a presynaptic neuron communicates with a postsynaptic cell.

Presynaptic Neuron

Nerve cell that releases neurotransmitter into the synaptic cleft.

Postsynaptic Neuron

Cell possessing receptors that bind the released neurotransmitter.

Synaptic Vesicle

Membrane-bound sac that stores neurotransmitter in the presynaptic terminal.

Synaptic Cleft

Tiny extracellular gap between pre- and postsynaptic membranes where neurotransmitter diffuses.

Autoreceptor

Presynaptic receptor that binds its own neurotransmitter to inhibit further release.

Excitatory Neurotransmitter

Chemical that increases the likelihood of postsynaptic action potential generation.

Inhibitory Neurotransmitter

Chemical that decreases the likelihood of postsynaptic action potential generation.

Reuptake

Transport of released neurotransmitter back into the presynaptic neuron for reuse or degradation.

Enzymatic Degradation

Inactivation of neurotransmitter by specific synaptic enzymes.

Simple Diffusion (Termination)

Passive dispersal of neurotransmitter away from the synapse, common for neuropeptides.

Acetylcholinesterase (AChE)

Enzyme that hydrolyzes acetylcholine into acetate and choline in the synaptic cleft.

Monoamine Oxidase (MAO)

Mitochondrial enzyme that deaminates catecholamines and serotonin; inhibited by some antidepressants.

Catechol-O-methyltransferase (COMT)

Enzyme that adds a methyl group to catecholamines during their metabolism.

Tyrosine Hydroxylase

Rate-limiting enzyme in catecholamine synthesis converting tyrosine to L-DOPA.

DOPA Decarboxylase

Enzyme converting L-DOPA to dopamine; deficiency linked to Parkinson’s disease.

Dopamine β-Hydroxylase

Enzyme that converts dopamine to norepinephrine within storage granules.

Phenylethanolamine N-methyltransferase (PNMT)

Enzyme that methylates norepinephrine to form epinephrine in adrenal medulla.

Choline Acetyltransferase

Synthesizes acetylcholine from choline and acetyl-CoA in cholinergic neurons.

Glutamate

Most common excitatory neurotransmitter in the brain; re-uptaken by specific transporters.

GABA (γ-Aminobutyric Acid)

Major inhibitory neurotransmitter of the brain; opens Cl⁻ channels to hyperpolarize neurons.

Glycine

Inhibitory neurotransmitter of spinal cord and brain stem; increases Cl⁻ permeability.

Acetylcholine (ACh)

Neurotransmitter that is excitatory at neuromuscular junctions and inhibitory in parasympathetic pathways.

Dopamine

Catecholamine involved in reward, movement control; usually inhibitory.

Norepinephrine

Catecholamine acting in fight-or-flight response and brain alertness; mostly excitatory.

Epinephrine

Hormone/neurotransmitter synthesized from norepinephrine; enhances sympathetic responses.

Serotonin (5-HT)

Monoamine derived from tryptophan; modulates mood, appetite, pain pathways (inhibitory in spinal cord).

Nitric Oxide (NO)

Gaseous neurotransmitter from arginine causing vasodilation and metabolic signaling.

Substance P

Neuropeptide that transmits pain signals in the nervous system.

Opioid Peptides

Endogenous peptides (e.g., endorphins) that modulate pain by binding opioid receptors.

Vanillylmandelic Acid (VMA)

Major urinary metabolite of epinephrine and norepinephrine after MAO/COMT action.

Homovanillic Acid (HVA)

Principal metabolite of dopamine formed via MAO and COMT pathways.

Astrocyte

Glial cell that uptakes GABA from synapses for inactivation.

Fight-or-Flight Response

Sympathetic reaction mediated partly by norepinephrine release.

Ligand-Gated Ion Channel

Membrane protein that opens when a neurotransmitter binds, altering ion flow.

G-protein Coupled Receptor (GPCR)

A mechanism of neurotransmitter action involving a receptor that indirectly affects ion channels or enzyme activity via a G-protein.

Calcium (Ca²⁺) in Neurotransmitter Release

Essential ion that triggers the fusion of synaptic vesicles with the presynaptic membrane, leading to neurotransmitter release.

Fast Synaptic Transmission

Synaptic transmission mediated by ligand-gated ion channels, resulting in rapid changes in postsynaptic membrane potential.

Slow Synaptic Transmission

Synaptic transmission mediated by G-protein coupled receptors, resulting in slower, longer-lasting changes in postsynaptic excitability.

Exocytosis (Synaptic)

The process by which synaptic vesicles fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft.

Excitatory Postsynaptic Potential (EPSP)

A transient depolarization of the postsynaptic membrane potential, making an action potential more likely.

Inhibitory Postsynaptic Potential (IPSP)

A transient hyperpolarization or stabilization of the postsynaptic membrane potential, making an action potential less likely.

Ionotropic Receptor

A type of neurotransmitter receptor that is also an ion channel; binding of a neurotransmitter directly opens the channel, leading to rapid changes in membrane potential.

Metabotropic Receptor

A type of neurotransmitter receptor that is not itself an ion channel, but initiates a signaling cascade (often via G-proteins) that indirectly affects ion channels or enzyme activity, leading to slower, longer-lasting effects.

Molecules that relay