Chemical Signaling by Neurotransmitters and Hormones

Flashcards covering vocabulary terms, mechanisms, receptor structures, second-messenger pathways, and modes of transmission from the Chemical Signaling lecture.

Axodendritic Synapse

A synaptic connection between the axon terminal of one neuron and a dendrite of another neuron.

Axosomatic Synapse

A synaptic connection between the axon terminal of one neuron and the cell body (soma) of another neuron.

Axoaxonic Synapse

A synaptic connection between the axon terminal of one neuron and the axon terminal of another neuron.

Ionotropic Receptor

A transmitter receptor type consisting of 4 or 5 subunits surrounding a central pore that functions directly as an ion channel, enabling fast signaling.

Metabotropic Receptor

A transmitter receptor type consisting of a single protein subunit with 7 trans-membrane domains (7-TM receptors) that signals through G proteins and downstream effectors.

Terminal Autoreceptor

A receptor located on the presynaptic axon terminal that is activated by the neurotransmitter released by that neuron to inhibit further transmitter release.

Somatodendritic Autoreceptor

An autoreceptor located on the cell body or dendrites of a neuron that slows the rate of cell firing when activated by the neuron's own neurotransmitter.

Retrograde Messenger

A lipid or gaseous chemical transmitter released by the postsynaptic cell that travels backward across the synapse to alter function in the presynaptic cell.

Clathrin-Mediated Endocytosis

A synaptic vesicle recycling mechanism involving full fusion of the vesicle membrane with the nerve terminal followed by coat formation and retrieval taking 15 to 20 seconds.

Ultrafast Endocytosis

A rapid mechanism of synaptic vesicle retrieval occurring within 100 milliseconds in an area close to the release site, followed by endosomal budding.

Kiss-and-Run

A mode of vesicle recycling where the synaptic vesicle fuses with the nerve terminal membrane for an extremely brief time (1 to 2 seconds) to release transmitter before pinching off.

Synaptobrevin

A protein in the membrane of synaptic vesicles that helps the vesicle fuse with the axon terminal membrane.

Positive Allosteric Modulator

A molecule that binds to an allosteric site on a receptor and increases receptor signaling in response to agonist binding.

Negative Allosteric Modulator

A molecule that binds to an allosteric site on a receptor and decreases receptor signaling in response to agonist binding.

Cyclic AMP (cAMP)

A second messenger molecule synthesized by adenylyl cyclase that stimulates Protein Kinase A (PKA).

Cyclic GMP (cGMP)

A second messenger molecule regulated by nitric oxide (NO) gas that stimulates Protein Kinase G (PKG).

Phosphoinositide System

A second messenger system in which breakdown of membrane phospholipids generates diacylglycerol (DG) and inositol trisphosphate ($IP_3$), leading to increased $Ca^{2+}$ ions and activation of Protein Kinase C (PKC).

Calcium/Calmodulin Kinase II (CaMKII)

An intracellular protein kinase associated with and activated by calcium ($Ca^{2+}$) acting as a second messenger.

Mitogen-Activated Protein Kinase (MAPK) System

An intracellular signaling cascade consisting of MKKK (Raf), MKK (MEK), and MAPK (ERK) that plays a major role in synaptic plasticity and nuclear gene transcription.

Synaptic Plasticity

Functional and structural synaptic changes including changes in synaptic strength, growth of new synapses, or growth of axon terminals, dendrites, and spines.

Volume Transmission

Chemical communication where neuromodulators diffuse away from the site of release through extracellular fluid to influence distant target cells.

Neuromuscular Junction

The specialized synapse formed between a motor neuron axon terminal and the sarcolemma of a muscle fiber.

Endocrine Communication

A mode of cellular communication where hormones are secreted into the bloodstream by endocrine glands to act on distant target cells.

Receptor Subtypes

The distinct structural variants of receptors to which a given neurotransmitter can bind.

Estradiol

An estrogenic sex hormone that can modify dopamine-related signaling and alter behavioral responses to stimulant drugs.