Unit 1 (part 2): Neurons and Glia

Neuron

The information-processing cell of the nervous system; also called nerve cell. Most neurons use action potentials to send signals over a distance, and all neurons communicate with one another using synaptic transmission.

Glial cell

A support cell in the nervous system. Glia are classifi ed into four categories: astrocytes, oligodendroglia, Schwann cells, and microglia. Astrocytes regulate the extracellular environment of the brain, oligodendroglia and Schwann cells provide myelin, and microglia scavenge debris.

Cytoarchitecture

The arrangement of neuronal cell bodies in various parts of the brain.It reflects the organization and distribution of neurons and their connections.

Cell body

The central region of the neuron containing the nucleus; also called soma or perikaryon.

Neurite

A thin tube extending from a neuronal cell body; the two types are axons and dendrites.

Axon

A neurite specialized to conduct nerve impulses, or action potentials, normally away from the soma.

Dendrite

A neurite specialized to receive synaptic inputs from other neurons.

Cytosol

The watery fluid inside a cell.

Organelle

A membrane-enclosed structure inside a cell; examples are the nucleus, mitochondrion, endoplasmic reticulum, and Golgi apparatus.

Cytoplasm

Cellular material contained by the cell membrane, including the organelles but excluding the nucleus.

Nucleus

(1) The roughly spherical organelle in a cell body containing the chromosomes. (2) A clearly distinguishable mass of neurons, usually deep in the brain.

Chromosome

A structure in the cell nucleus containing a single linear thread of DNA.

Gene

A unit of heredity; a sequence of DNA that encodes a single polypeptide or protein.

Gene expression

The process of transcribing the information from a gene into messenger RNA; a gene is a segment of DNA carrying the instructions for a single protein.

Ribosomes

A cellular organelle that assembles new proteins from amino acids according to the instructions carried by messenger RNA. They are found in both prokaryotic and eukaryotic cells.

Rough endoplasmic reticulum (RER)

A membrane-enclosed cellular organelle with ribosomes attached to its outer surface; a site of synthesis for proteins destined to be inserted into membrane or to be enclosed by membrane.

Smooth endoplasmic reticulum (SER)

A membrane-enclosed cellular organelle that is heterogeneous and performs different functions in different locations.

Adenosine triphosphate (ATP)

The molecule that is the cell’s energy source. The hydrolysis of ATP to produce adenosine diphosphate (ADP) releases energy that fuels most of the biochemical reactions of the neuron. ADP is converted back to ATP in the mitochondria.

Neuronal membrane

The barrier, about 5 nm thick, that separates the inside of a nerve cell from the outside; consists of a phospholipid bilayer with proteins embedded in it; encloses the intracellular organelles and vesicles.

Cytoskeleton

The internal scaffolding that gives a cell its characteristic shape; consists of microtubules, neurofi laments, and microfi laments.

Microtubule

A polymer of the protein tubulin, forming a straight, hollow tube 20 nm in diameter. Microtubules, a component of the cytoskeleton, play an important role in axoplasmic transport.

Microfilament

A polymer of the protein actin, forming a braided strand 5 nm in diameter; a component of the cytoskeleton.

Neurofilament

A type of intermediate filament found in neurons, 10 nm in diameter; an important component of the neuronal cytoskeleton.

Axon hillock

A swelling of the axon where it joins the soma.

Axon collateral

A branch of an axon.

Axon terminal

The end region of an axon, usually a site of synaptic contact with another cell; also called terminal bouton or presynaptic terminal.

Terminal bouton

The end region of an axon, usually a site of synaptic contact with another cell; also called axon terminal.

Synapse

The region of contact where a neuron transfers information to another cell.

Terminal arbor

Branches at the end of an axon terminating in the same region of the nervous system.

Innervation

The provision of synaptic input to a cell or collection of cells.

Synaptic vesicle

A membrane-enclosed structure, about 50 nm in diameter, containing neurotransmitter and found at a site of synaptic contact.

Synaptic cleft

The region separating the presynaptic and postsynaptic membranes of neurons.

Synaptic transmission

The process of transferring information from one cell to another at a synapse.

Neurotransmitter

A chemical released by a presynaptic element upon stimulation that activates postsynaptic receptors.

Anterograde transport

Axoplasmic transport from a neuron’s soma to the axon terminal.

Retrograde transport

Axoplasmic transport from an axon terminal to the soma.

Receptor

(1) A specialized protein that detects chemical signals, such as neurotransmitters, and initiates a cellular response. (2) A specialized cell that detects environmental stimuli and generates neural responses.

Astrocyte

A glial cell in the brain that supports neurons and regulates the extracellular ionic and chemical environment.

Oligodendroglial cell

A glial cell that provides myelin in the central nervous system.

Schwann cell

A glial cell that provides myelin in the peripheral nervous system.

Myelin

A membranous wrapping, or sheath, around axons provided by oligodendroglia in the central nervous system and Schwann cells in the peripheral nervous system.

Node of Ranvier

A space between two consecutive myelin sheaths where an axon comes in contact with the extracellular fluid.

Ependymal cells

A type of glial cell that provides the lining of the brain’s ventricular system.

Microglial cell

A type of cell that functions as a phagocyte in the nervous system to remove debris left by dead or dying neurons and glia.

Gray matter

The regions of the brain and spinal cord that are primarily made up of neuronal cell bodies, dendrites, and unmyelinated axons.

White matter

The areas of the brain and spinal cord composed mainly of myelinated axons, which facilitate communication between different brain regions.

Commissure

Any collection of axons that connect one side of the brain with the other.

Lemniscus

Tract that meanders through the brain like a ribbon.