Nervous Tissue Terms

Astrocyte: A type of CNS supporting cell with a star shape that assists in exchanges between blood capillaries and neurons, and helps to form the blood-brain barrier.

Axolemma: The plasma membrane of a neuron axon, which transmits a nerve impulse.

Axon: Cell process that conducts nerve impulses away from a neuron cell body.

Axon hillock: The conical area of a neuron cell body, where the axon begins and the nerve impulse is generated.

Axon terminal: The terminal branch of a presynaptic axon containing neurotransmitters in synaptic vesicles, that makes synaptic contact with a postsynaptic cell.

Bipolar neuron: Nerve cell with one dendrite and one axon that extend from opposite sides of its cell body; rare neuron type found only in the retina of the eye, the olfactory region of the nose, and the inner ear.

Central nervous system (CNS): Portion of the nervous system that consists of the brain and spinal cord.

Cerebrospinal fluid (CSF): A fluid produced by ependymal cells covering the choroid plexuses in the ventricles of the brain; the fluid circulates in the ventricles and subarachnoid space around the brain and in the central canal of the spinal cord.

Dendrite: Branching cell process that receives nerve impulses and transmits graded potentials toward a neuron cell body.

Ependymal cell: A type of CNS supporting cell that covers the choroid plexuses and produces cerebrospinal fluid (CSF); it also lines the ventricles of the brain and assist in the circulation of CSF.

Ganglia: Groups of neuron cell bodies in the peripheral nervous system (PNS).

Gray matter: Gray areas in the CNS that contain neuron cell bodies, and unmyelinated processes.

Interneurons: Nerve cell located between sensory and motor neurons that govern coordinated activity. Also called association neurons.

Microglia: A type of CNS supporting cell that can transform into a phagocyte in areas of neural damage or inflammation.

Multipolar neuron: Nerve cell with many processes projecting from its cell body, many dendrites and one axon; most cell bodies reside in the CNS; the most abundant neuron type.

Myelin sheath: Multilayered lipid and protein covering around neuron axons; formed by Schwann cells in the PNS, and oligodendrocytes in the CNS.

Myelinated fiber: Neuron axon with a myelin sheath that conducts nerve impulses very rapidly.

Nerve: Cordlike bundle of myelinated nerve fibers with associated connective tissue in the PNS.

Neurilemma: The outer nucleated cytoplasmic layer of a Schwann cell. Also called neurolemma, or sheath of Schwann.

Neurofibril: Cytoskeletal structure in a neuron, composed of microtubules and intermediate filaments.

Neuroglia: Nonneuronal cells of the nervous system that perform various supportive functions. Also called glial cells.

Neuron: A nerve cell, consisting of a cell body, dendrites, and axon.

Neurotransmitter: Chemical released by the neuron axon terminal, that crosses the synaptic cleft and either excites or inhibits the postsynaptic cell (another neuron, muscle or gland cell).

Nissl bodies: The rough endoplasmic reticulum in neurons. Also called chromatophilic substance.

Node of Ranvier: A space in the myelin sheath of a nerve fiber, between two neighboring Schwann cells in the PNS, or oligodendrocytes in the CNS.

Nuclei: Groups of neuron cell bodies in the central nervous system (CNS).

Oligodendrocyte: A type of CNS supporting cell that forms a myelin sheath around a neuron axon.

Peripheral nervous system (PNS): Portion of the nervous system that consists of nerves and ganglia that lie outside of the central nervous system.

Saltatory conduction: Transmission of an action potential along a myelinated fiber, in which the nerve impulse appears to leap from node to node of Ranvier.

Satellite cell: A type of PNS supporting cell that surrounds a neuron cell body in a ganglion; provides structural support and regulates the exchange of material between the cell body and interstitial fluid.

Schwann cell: A type of PNS supporting cell that forms a myelin sheath around a neuron axon, and is vital to regeneration of a damaged axon.

Synapse: The functional junction between a neuron and postsynaptic cell (another neuron, a muscle, gland, or sensory receptor cell).

Synaptic cleft: The narrow gap at a synapse that separates the neuron axon terminal from a postsynaptic cell, across which a neurotransmitter diffuses to transmit the impulse.

Tract: Bundle of myelinated nerve fibers in the CNS.

Unipolar neuron: Nerve cell with only one process projecting from its cell body; the process divides into a sensory nerve fiber and an axon which synapses with neurons in the CNS; its cell body resides in a ganglion in the PNS.

Unmyelinated fiber: Neuron axon lacking a myelin sheath that conducts nerve impulses very slowly.

White matter: White area of the CNS; contains mostly myelinated nerve fibers.