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Nervous System

Definition: The entire nerve apparatus, composed of a central part, the brain and spinal cord, and a peripheral part, the cranial and spinal nerves, autonomic ganglia, and plexuses. (Stedman, 26th ed)
Notes: GEN only; /innerv is available for organs: Manual 19.8.39, 21.7+; for "nerves" but not for a specific nerve nor NERVE TISSUE; NERVOUS SYSTEM /anat as a SPEC = NEUROANATOMY, NERVOUS SYSTEM /chem as a SPEC = NEUROCHEMISTRY, NERVOUS SYSTEM /physiol as a SPEC

Nervous System Categories.
Central Nervous System - The main information-processing organs of the nervous system, consisting of the brain, spinal cord, and meninges.
Ganglia - Clusters of multipolar neurons surrounded by a capsule of loosely organized CONNECTIVE TISSUE located outside the CENTRAL NERVOUS SYSTEM.
Nerve Net - A meshlike structure composed of interconnecting nerve cells that are separated at the synaptic junction or joined to one another by cytoplasmic processes. In invertebrates, for example, the nerve net allows nerve impulses to spread over a wide area of the net because synapses can pass information in any direction.
Nerve Tissue
Neural Pathways - Neural tracts connecting one part of the nervous system with another.
Neuroglia - The non-neuronal cells of the nervous system. They not only provide physical support, but also respond to injury, regulate the ionic and chemical composition of the extracellular milieu, participate in the BLOOD-BRAIN BARRIER and BLOOD-RETINAL BARRIER, form the myelin insulation of nervous pathways, guide neuronal migration during development, and exchange metabolites with neurons. Neuroglia have high-affinity transmitter uptake systems, voltage-dependent and transmitter-gated ion channels, and can release transmitters, but their role in signaling (as in many other functions) is unclear.
Neurons - The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.
Peripheral Nervous System - The nervous system outside of the brain and spinal cord. The peripheral nervous system has autonomic and somatic divisions. The autonomic nervous system includes the enteric, parasympathetic, and sympathetic subdivisions. The somatic nervous system includes the cranial and spinal nerves and their ganglia and the peripheral sensory receptors.
Synapses - Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate through direct electrical connections which are sometimes called electrical synapses; these are not included here but rather in GAP JUNCTIONS.

Nervous System Definitions and Terms

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