Chapter 3: Chemical Signaling by Neurotransmitters and hormones

presynaptic cell

neuron at a synapse that transmits a signal to the postsynaptic cell

postsynaptic cell

neuro at a synapse that receives a signal from the presynaptic cell

pyramidal neuron

serves as the principal type of output neuron in several brain areas, notably the cerebral cortex, hippocampus, and amygdala

postsynaptic density

rich in neurotransmitter receptors along with other proteins that help anchor the receptors in place

axosomatic synapses

junctions used for communication between a nerve terminal and a nerve cell body

presynaptic inhibition

signaling by the presynaptic cell to reduce neurotransmitter release by the axon terminal of the postsynaptic cell

presynaptic facilitation

signaling by the presynaptic cell to increase neurotransmitter release by the axon terminal of the postsynaptic cell

amino acids

essential building blocks of proteins, some of which also act as neurotransmitters

monoamines

refers to a compound or transmitter that contains a single amine group

neuropeptides

small proteins (3 to 40 amino acids long) in the nervous system that act as neurotransmitters or neuromodulators

neuromodulators

chemicals that don’t follow the typical neurotransmitter model. They may regulate neurotransmitter activity or act at distant sites from their point of release

volume transmission

phenomenon characrterized by the diffusion of a chemical signal through the extracellular fluid to reach target cells at some distance from the point of release

wiring transmission

point-to-point communication between neurons in which the neurotransmitter acts locally within the synapse to affect the target cell.

exocytosis

fusion of the vesicle and the cell membrane, specifically the axon terminal membrane in the case of neurotransmitters. the vesicle opens toward the synaptic cleft allowing neurotransmitter molecules to diffuse out

vesicle recycling

multi-step process consisting of removal of synaptic vesicle membrane components from the membrane of the axon terminal after exocytosis, followed by formation of new vesicles

reuptake

process that involves transport of a neurotransmitter from the extracellular fluid back into the same cell that released it

receptors

proteins located on the surface of or within cells that bind to specific ligands to initiate biological changes within the cell

exicitatory

increasing the probability of an action potentiali

inhibitory

decreasing the probability of an action potential

agonist

drug mimics the actions of the neurotransmitter in activating the receptor

antagonist

drug blocks or inhibits the ability of the neurotransmitter to activate the receptor

ionotropic receptors

fast-acting receptor type comprised of several subunits that come together in the cell membrane

• ion channel at its center, which is regulated by neurotransmitters binding to specific sites on the receptor causing the channel to open

• aka ligand-gated channel receptor

metabotropic receptors

slow-acting receptor type composed of a single large protein in the cell membrane that activates G proteins.

desensitization

remains closed despite the presence of an agonist bound to the receptor. cannot respond again until it leaves the desensitized state

g proteins

necessary for neurotransmitter signaling

• operate by regulating ion channels or effector enzymes involved in the synthesis or breakdown of second messengers

how do G proteins operate? what are the two major mechanisms

• stimulating or inhibiting the opening of ion channels in the cell membrane

• stimulating or inhibiting certain enzymes in the cell membrane (effector enzymes)

allosteric modulators

compounds that bind to a receptor site distinct from the main agonist binding site, may or may not have an effect on the receptor when administered alone, and either enhance or reduce the effectiveness of an agonist on the receptor

allosteric sites

binding sites on a receptor protein that modulate the receptor’s response, either positively or negatively, to a receptor agonist