A&p I - Vocab_Ch.12

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Acetylcholine (ACh)

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A neurotransmitter liberated by many peripheral nervous system neurons and some central nervous system neurons. It is excitatory at neuromuscular junctions but inhibitory at some other synapses.

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Action potential (AP)

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An electrical signal that propagates along the membrane of a neuron or muscle fiber (cell); a rapid change in membrane potential that involves a depolarization followed by a repolarization.

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All-or-none principle

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If a stimulus depolarizes a neuron to threshold, the neuron fires at its maximum voltage (all); if threshold is not reached, the neuron does not fire at all (none). Given above threshold, stronger stimuli do not produce stronger action potentials.

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Astrocytes

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A neuroglial cell having a star shape that participates in brain development and the metabolism of neurotransmitters, helps form the blood–brain barrier, helps maintain the proper balance of K+ for generation of nerve impulses, and provides a link between neurons and blood vessels.

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Autonomic nervous system (ANS)

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Visceral sensory (afferent) and visceral motor (efferent) neurons. Autonomic motor neurons, both sympathetic and parasympathetic, conduct nerve impulses from the central nervous system to smooth muscle, cardiac muscle, and glands. So named because this part of the nervous system was thought to be self-governing or spontaneous.

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Axon

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The usually single, long process of a nerve cell that propagates a nerve impulse toward the axon terminals.

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Axon terminals

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Terminal branches of an axon where synaptic vesicles undergo exocytosis to release neurotransmitter molecules. Also called telodendria (tel′-Å0DEN-drÄ“-a)

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Axoplasm

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Cytoplasm of an axon.

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Axosomatic

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From axon to cell body.

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Central nervous system (CNS)

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That portion of the nervous system that consists of the brain and spinal cord.

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Cerebral cortex

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The surface of the cerebral hemispheres, 2–4 mm thick, consisting of gray matter; arranged in six layers of neuronal cell bodies in most areas.

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Chromatolysis

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The breakdown of Nissl bodies into finely granular masses in the cell body of a neuron whose axon has been damaged.

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Continuous conduction

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Propagation of an action potential (nerve impulse) in a step-by-step depolarization of each adjacent area of an axon membrane.

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Convergence

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A synaptic arrangement in which the synaptic end bulbs of several presynaptic neurons terminate on one postsynaptic neuron. The medial movement of the two eyeballs so that both are directed toward a near object being viewed in order to produce a single image.

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Cranial nerves

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One of 12 pairs of nerves that leave the brain; pass through foramina in the skull; and supply sensory and motor neurons to the head, neck, part of the trunk, and viscera of the thorax and abdomen. Each is designated by a Roman numeral and a name.

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Dendrites

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A neuronal process that carries electrical signals, usually graded potentials, toward the cell body.

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Divergence

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A synaptic arrangement in which the synaptic end bulbs of one presynaptic neuron terminate on several postsynaptic neurons.

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Effectors

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An organ of the body, either a muscle or a gland, that is innervated by somatic or autonomic motor neurons.

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Enteric nervous system (ENS)

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The part of the nervous system that is embedded in the submucosa and muscularis of the gastrointestinal (GI) tract; governs motility and secretions of the GI tract.

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Ependymal cells

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Neuroglial cells that cover choroid plexuses and produce cerebrospinal fluid (CSF); they also line the ventricles of the brain and probably assist in the circulation of CSF.

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Epinephrine

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Hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation.

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Ganglion

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Usually, a group of neuronal cell bodies lying outside the central nervous system (CNS).

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Gray matter

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Areas in the central nervous system and ganglia containing neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia

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Guillain-Barré syndrome (GBS)

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An acute demyelinating disorder in which macrophages strip myelin from axons in the PNS. It is the most common cause of acute paralysis in North America and Europe and may result from the immune system's response to a bacterial infection. Most patients recover completely or partially, but about 15% remain paralyzed.

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Interneurons

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Neurons whose axons extend only for a short distance and contact nearby neurons in the brain, spinal cord, or a ganglion; they comprise the vast majority of neurons in the body. Also called association neurons.

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Microglial cells

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Neuroglial cells that carry on phagocytosis.

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Microtubules

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Cylindrical protein filament, from 18 to 30 nm in diameter, consisting of the protein tubulin; provides support, structure, and transportation.

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Motor neuron

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Neurons that conduct impulses from the brain toward the spinal cord or out of the brain and spinal cord into cranial or spinal nerves to effectors that may be either muscles or glands.

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Muscle action potential

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A stimulating impulse that propagates along the sarcolemma and transverse tubules; in skeletal muscle, it is generated by acetylcholine, which increases the permeability of the sarcolemma to cations, especially sodium ions (Na-).

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Myelin sheath

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Multilayered lipid and protein covering, formed by Schwann cells and oligodendrocytes, around axons of many peripheral and central nervous system neurons.

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Nerve

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A cordlike bundle of neuronal axons and/or dendrites and associated connective tissue coursing together outside the central nervous system.

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Nerve action potential

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A wave of depolarization and repolarization that self-propagates along the plasma membrane of a neuron.

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Nerve fiber

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General term for any process (axon or dendrite) projecting from the cell body of a neuron.

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Nervous system

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A network of billions of neurons and even more neuroglia that is organized into two main divisions.

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Neuroblastoma

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A malignant tumor that consists of immature nerve cells ; occurs most commonly in the abdomen and most frequently in the adrenal glands. Although rare, it is the most common tumor in infants.

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Neuroglia

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Cells of the nervous system that perform various supportive functions.

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Neurolemma

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The peripheral, nucleated cytoplasmic layer of the Schwann cell. Also called sheath of Schwann (SCHWON).

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Neurology

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The study of the normal functioning and disorders of the nervous system.

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Neurons (nerve cells)

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

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Neuropathy

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Any disorder that affects the nervous system but particularly a disorder of a cranial or spinal nerve.

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Neurosecretory cells

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A neuron that secretes a hypothalamic releasing hormone or inhibiting hormone into blood capillaries of the hypothalamus; a neuron that secretes oxytocin or antidiuretic hormone into blood capillaries of the posterior pituitary.

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Neurotransmitter

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One of a variety of molecules within axon terminals that are released into the synaptic cleft in response to a nerve impulse and that change the membrane potential of the postsynaptic neuron.

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Nodes of Ranvier

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A space along a myelinated axon between the individual Schwann cells that form the myelin sheath and the neurolemma.

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Norepinephrine (NE)

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A hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation.

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Oligodendrocytes

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A neuroglial cell that supports neurons and produces a myelin sheath around axons of neurons of the central nervous system.

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Parasympathetic division

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One of the two subdivisions of the autonomic nervous system, having cell bodies of preganglionic neurons in nuclei in the brain stem and in the lateral gray horn of the sacral portion of the spinal cord; primarily concerned with activities that conserve and restore body energy.

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Peripheral nervous system (PNS)

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The part of the nervous system that lies outside the central nervous system, consisting of nerves and ganglia.

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Postsynaptic neuron

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The nerve cell that is activated by the release of a neurotransmitter from another neuron and carries nerve impulses away from the synapse.

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Presynaptic neuron

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A neuron that propagates nerve impulses toward a synapse.

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Purkinje cells

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Neuron in the cerebellum named for the histologist who first described them.

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Rabies

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A fatal disease caused by a virus that reaches the CNS via fast axonal transport. It is usually transmitted by the bite of an infected dog or other meat-eating animal. The symptoms are excitement, aggressiveness, and madness, followed by paralysis and death.

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Satellite cells

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Flat neuroglial cells that surround cell bodies of peripheral nervous system ganglia to provide structural support and regulate the exchange of material between a neuronal cell body and interstitial fluid.

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Schwann cell

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A neuroglial cell of the peripheral nervous system that forms the myelin sheath and neurolemma around a nerve axon by wrapping around the axon in a jelly-roll fashion.

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Sensory

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Neurons that carry sensory information from cranial and spinal nerves into the brain and spinal cord or from a lower to a higher level in the spinal cord and brain. Also called afferent neurons.

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Somatic nervous system (SNS)

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The portion of the peripheral nervous system consisting of somatic sensory (afferent) neurons and somatic motor (efferent) neurons.

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Spinal nerves

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One of the 31 pairs of nerves that originate on the spinal cord from posterior and anterior roots.

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Stimulus

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Any stress that changes a controlled condition; any change in the internal or external environment that excites a sensory receptor, a neuron, or a muscle fiber.

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Sympathetic division

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One of the two subdivisions of the autonomic nervous system, having cell bodies of preganglionic neurons in the lateral gray columns of the thoracic segment and the first two or three lumbar segments of the spinal cord; primarily concerned with processes involving the expenditure of energy.

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Synapse

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The functional junction between two neurons or between a neuron and an effector, such as a muscle or gland; may be electrical or chemical.

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Synaptic cleft

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The narrow gap at a chemical synapse that separates the axon terminal of one neuron from another neuron or muscle fiber (cell) and across which a neurotransmitter diffuses to affect the postsynaptic cell.

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Synaptic end bulbs

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Expanded distal end of an axon terminal that contains synaptic vesicles. Also called a synaptic knob.

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Synaptic vesicles

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Membrane-enclosed sac in a synaptic end bulb that stores neurotransmitters.

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Tract

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A bundle of nerve axons in the central nervous system.

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Wallerian degeneration

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Degeneration of the portion of the axon and myelin sheath of a neuron distal to the site of injury.

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White matter

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Aggregations or bundles of myelinated and unmyelinated axons located in the brain and spinal cord.