CHAPTER 3 — CHEMICAL SIGNALING BY NEUROTRANSMITTERS AND HORMONES

Neurotransmitter signaling sequence

Synthesis → storage → release → receptor interaction → inactivation.

Neurotransmitter synthesis

Production of a neurotransmitter inside a neuron.

Neurotransmitter storage

Neurotransmitters can be stored in synaptic vesicles before release.

Vesicular exocytosis

Process in which synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter into the synapse.

Neurotransmitter release

Release of neurotransmitter into the synaptic space, usually triggered by an action potential.

Receptor interaction

Released neurotransmitter binds to receptors on a target cell and changes its activity.

Neurotransmitter inactivation

Processes that terminate neurotransmitter signaling, including reuptake, enzymatic breakdown, and diffusion.

Autoreceptor

Receptor located on a neuron that responds to the neuron's own neurotransmitter and regulates its release or synthesis.

Autoreceptor function

Provides feedback that can decrease or otherwise regulate further neurotransmitter release.

Heteroreceptor

Receptor that responds to a neurotransmitter or signal different from the neurotransmitter released by the neuron containing the receptor.

Firing rate

Rate at which a neuron generates action potentials; can influence neurotransmitter release.

Release probability

Likelihood that neurotransmitter will be released when an action potential reaches the terminal.

Ionotropic receptor

Receptor that directly controls an ion channel and produces relatively rapid effects.

Metabotropic receptor

Receptor that activates intracellular signaling, usually through G proteins, and produces slower and often longer-lasting effects.

Ionotropic versus metabotropic receptors

Ionotropic receptors directly control ion channels and act quickly; metabotropic receptors activate intracellular signaling pathways and act more slowly.

G-protein-coupled receptor

Metabotropic receptor that activates G proteins and intracellular signaling pathways.

G protein

Signaling protein activated by many metabotropic receptors that helps regulate intracellular processes.

Second messenger

Intracellular molecule that carries a signal from an activated receptor to other parts of the cell.

Second-messenger signaling

Process in which receptor activation triggers intracellular molecules that amplify or spread the signal inside the cell.

Metabotropic effects

Effects that can last longer because receptor activation triggers intracellular signaling cascades.

Allosteric modulation

Regulation of a receptor by a substance binding to a site different from the neurotransmitter's primary binding site.

Positive allosteric modulator

Substance that binds to an allosteric site and increases the receptor's response to its neurotransmitter.

Negative allosteric modulator

Substance that binds to an allosteric site and decreases the receptor's response to its neurotransmitter.

Drug effects on neurotransmission

Drugs can alter neurotransmitter synthesis, storage, release, receptors, reuptake, metabolism, ion channels, or intracellular signaling.

Drug effect on synthesis

A drug can increase or decrease how much neurotransmitter is produced.

Drug effect on storage

A drug can alter how neurotransmitters are packaged and stored in vesicles.

Drug effect on release

A drug can increase or decrease neurotransmitter release.

Drug effect on receptors

A drug can activate, block, or modify neurotransmitter receptors.

Drug effect on reuptake

A drug can prevent neurotransmitter removal from the synapse and prolong its effects.

Drug effect on metabolism

A drug can inhibit neurotransmitter breakdown and increase its availability.

Synaptic plasticity

Functional or structural changes in synapses that alter the strength of communication between neurons.

Functional synaptic plasticity

Changes in the strength or efficiency of an existing synapse.

Structural synaptic plasticity

Physical changes such as formation or growth of synapses, dendrites, dendritic spines, or axon terminals.

Hormone

Chemical messenger released by endocrine cells that can influence distant tissues, including the brain.

Hormonal signaling

Chemical signaling in which hormones travel through the bloodstream to influence target tissues.

Hormones and behavior

Hormones can influence brain activity and therefore affect behavior and physiological states.