Glossary of Physiology Terms

Atropine

Atropine is a blocker (i.e., inhibitor) of muscarinic acetylcholine receptors. Therefore, atropine blocks the action of postganglionic parasympathetic neurons.

γ-Aminobutyric acid

GABA

GABA is an inhibitory amino acid neurotransmitter in the central and peripheral nervous systems. It is the most abundant inhibitory neurotransmitter in the nervous system. During embryonic development, GABA acts as an excitatory neurotransmitter at some central synapses. GABA is a classical neurotransmitter. Its action is exerted via the activation of GABA_A, GABA_B, and GABA_C receptors. GABA_A and GABA_C receptors are ligand-gated chloride channels, whereas GABA_B receptors are G protein coupled receptors. At GABAergic synapses, the action of GABA is terminated by GABA transporters (GAT), which transport GABA from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Glycine

Glycine (Gly, G) is one of the standard twenty (20) amino acids. At a molecular weight of 75.07 g/mol, it is the smallest of the 20 amino acids used by cells to synthesize peptides, polypeptides, and proteins.

In the nervous system, glycine is also an inhibitory amino acid neurotransmitter. Glycinergic synapses are most commonly found in brain stem and spinal cord circuits. Glycine is a classical neurotransmitter. Its action is exerted via the activation of ionotropic glycine receptors (GlyR), which are ligand-gated chloride channels. At glycinergic synapses, the action of glycine is terminated by glycine transporters (GlyT), which transport glycine from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Neurotoxin

Neurotoxins are chemical molecules that have an adverse effect on neuron function and, thus, disrupt the normal function of the nervous system. Neurotoxins could be small molecules or peptides and can be derived from a variety of invertebrate and vertebrate animals, as well as plant species.

The following is a short list of some examples of neurotoxins:

α-Bungarotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

Chlorotoxin: A peptide neurotoxin that inhibits chloride channels.

α-Conotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

δ-Conotoxin: A peptide neurotoxin that inhibits voltage-gated sodium channels.

w-Conotoxin: A peptide neurotoxin that inhibits N-type voltage-gated calcium channels.

Picrotoxin: Inhibits GABA_A receptor chloride channels.

Tetrodotoxin: Inhibitor of neuronal voltage-gated sodium channels.

Tetraethyl ammonium

TEA

An inhibitor of voltage-gated potassium (K⁺) channels.

TEA is a quaternary ammonium cation (positively charged ion). It is also commonly used as a cation replacement for sodium (Na⁺) in physiological buffers used in ion replacement experiments.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

Tetrodotoxin

TTX

Inhibitor of fast voltage-gated sodium (Na⁺) channels of neurons and muscle cells. It is an extremely potent and toxic neurotoxin.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

Tetrodotoxin (Wikipedia)

Vanadate

An inhibitor of the Na⁺/K⁺/ATPase (i.e., sodium pump). The form commonly used for this purpose is sodium orthovanadate.

Ouabain

Yohimbine

An antagonist (i.e., inhibitor) of α₂-adrenergic receptor.

Yohimbine (Wikipedia)