6.12 Neurotransmitters and Neuromodulators

Acetylcholine (ACh)

Major neurotransmitter in the peripheral nervous system at the neuromuscular junction and in the brain; released by pre-and postganglionic parasympathetic neurons, preganglionic sympathetic neurons, somatic neurons, and some central nervous system neurons

Acetylcholinesterase

Enzyme that breaks down acetylcholine into acetic acid and choline

Alpha-Adrenergic Receptors (Alpha-Adrenoceptors)

Subtype of plasma membrane receptors for epinephrine and norepinephrine

AMPA Receptors

Receptor proteins found in the membrane of some brain neurons, named for their binding to alpha-amino-3 hydroxy-5 methyl-4 isoxazole proprionic acid

Beta-Adrenergic Receptors (Beta Adrenoceptors)

Plasma membrane receptors for epinephrine and norepinephrine

Beta-Endorphin

Putative hormone released from the anterior pituitary gland, believed to play a role in adaptation to stress and pain relief; also acts as a neurotransmitter

Biogenic Amines

Neurotransmitters having basic formula R-NH2; include dopamine, norepinephrine, epinephrine, serotonin, and histamine

Carbon Monoxide (CO)

Gas that binds to hemoglobin; decreases blood oxygen-carrying capacity and shifts oxygen-hemoglobin dissociation curve to the left; also acts as an intracellular messenger in neurons

Catecholamines

Dopamine, epinephrine, and norepinephrine, all of which have similar chemical structures

Cholinergic

Pertaining to acetylcholine; a compound that acts like acetylcholine or a neuron that contains acetylcholine

Dopamine (DA)

Biogenic amine (catecholamine) neurotransmitter and hormone; precursor of epinephrine and norepinephrine

Dynorphrins

Endogenous opioid peptides that act as neuromodulators in the brian

Endogenous Opioids

Certain neuropeptides-endorphin, dynorphin, and enkephalin

Enkaphalins

Peptide neurotransmitters at some synapses activated by opiate drugs; endogenous opioids

Epinephrine

Amine hormone secreted by adrenal medulla and involved in regulation of organic metabolism; a biogenic amine (catecholamine) neurotransmitter

Excitatory Amino Acids

Amino acids that as excitatory (depolarizing) neurotransmitters in the nervous system

GABA (Gamma-Aminobutyric Acid)

An amino acid neurotransmitter commonly occurring at inhibitory synapses in the central nervous system

Glutamate

Anion formed from the amino acid glutamic acid; a major excitatory central nervous system neurotransmitter

Glycine

An amino acid; a neurotransmitter at some inhibitory synapses in the central nervous system

Hydrogen Sulfide

A type of gas that sometimes functions as a neurotransmitter

L-Dopa

L-dihydroxyphenylalanine; precursor to dopamine formation

Long-Term Potentiation (LTP)

Process by which certain synapses undergo long-lasting increase in effectiveness when heavily used

Monoamine Oxidase (MAO)

Enzyme that breaks down catecholamines in axon terminal and synapse

Muscarinic Receptors

Acetylcholine receptors that respond to the mushroom poison muscarine; located on smooth muscle, cardiac muscle, some central nervous system neurons, and glands

Neuromodulators

Chemical messengers that act on neurons, usually by a second-messenger system, to alter response to a neurotransmitter

Neuropeptides

Family of more than 50 neurotransmitters composed of 2 or more amino acids; often also function as chemical messengers in nonneural tissues

Nicotinic Receptors

Acetylcholine receptors that respond to nicotine; primarily, receptors at motor end plate and on postganglionic autonomic neurons

Nitric Oxide

A gas that functions as intracellular messenger, including neurotransmitters; is endothelium-derived relaxing factor; destroys intracellular microbes

NMDA Receptors

Ionotropic glutamate receptors involved in learning and memory; N-methyl-D-aspartate receptors

Norepinephrine

Biogenic amine (catecholamine) neurotransmitter released at most sympathetic postganglionic endings, from adrenal medulla, and in many central nervous system regions

Peptidergic

Neuron that releases peptides

Serotonin

Biogenic amine neurotransmitter; paracrine agent in blood platelets and digestive tract; also called 5-hydroxytryptamine