neuron /neu·ron/ (noor´on) nerve cell; any of the conducting cells of the nervous system, consisting of a cell body, containing the nucleus and its surrounding cytoplasm, and the axon and dendrites. neuro´nal
Neuron
neuron
neuron [noor´on]
afferent neuron one that conducts a nervous impulse from a receptor to a center.
efferent neuron one that conducts a nervous impulse from a center to an organ of response.
Golgi neurons
1. (type I): pyramidal cells with long axons, which leave the gray matter of the central nervous system, traverse the white matter, and terminate in the periphery.
2. (type II): stellate neurons with short axons that are particularly numerous in the cerebral and cerebellar cortices and in the retina.
motor neuron motoneuron.
multisensory neuron a neuron in the cerebral cortex or subcortical regions that can receive input from more than one sensory modality.
postganglionic neurons neurons whose cell bodies lie in the autonomic ganglia and whose purpose is to relay impulses beyond the ganglia.
preganglionic neurons neurons whose cell bodies lie in the central nervous system and whose efferent fibers terminate in the autonomic ganglia.
sensory neuron any neuron having a sensory function; an afferent neuron conveying sensory impulses. The first in an afferent pathway is the primary sensory n. and the second is the secondary sensory n.
neu·ron (n r  n ) or neu·rone (- n)n. Any of the impulse-conducting cells that constitute the brain, spinal column, and nerves, consisting of a nucleated cell body with one or more dendrites and a single axon. Also called nerve cell, neurocyte. |   |
Neuron
The cells within the body which make up the nervous system, specifically those along which information travels.
neuron
[noo͡r′on]
Etymology: Gk, nerve
the basic nerve cell of the nervous system, containing a nucleus within a cell body and extending one or more processes. Neurons can be classified according to the direction in which they conduct impulses or according to the number of processes they extend. Sensory neurons transmit nerve impulses toward the spinal cord and the brain. Motor neurons transmit nerve impulses from the brain and the spinal cord to the muscles and the glandular tissue. Multipolar neurons, bipolar neurons, and unipolar neurons are classified according to the number of processes they extend to the different kinds of neurons. Multipolar neurons have one axon and several dendrites, as do most of the neurons in the brain and the spinal cord. Bipolar neurons, which are less numerous than the other types, have one axon and only one dendrite. Unipolar neurons have one axon and no dendrites. All primary sensory afferents and some autonomic neurons are unipolar. All neurons have one axon, and most have one or more dendrites and have a slightly gray color when clustered, as in the nuclei of the brain and the spinal cord. As the generators and carriers of nerve impulses, neurons function according to electrochemical processes involving positively charged sodium and potassium ions and the changing electrical potential of the extracellular and the intracellular fluid of the neuron. Also spelled neurone. neuronal, adj.
neuron [noor´on]
a highly specialized cell of the nervous system, having two characteristic properties: irritability (ability to be stimulated) and conductivity (ability to conduct impulses). They are composed of a cell body (called also neurosome or perikaryon), containing the nucleus and its surrounding cytoplasm, and one or more processes (nerve fibers) extending from the body. Called also nerve cell. adj., adj neuro´nal.
The nerve fibers are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar; this type is widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated to action. Many processes are covered with a layer of lipid material called the myelin sheath. Peripheral nerve fibers have a thin outer covering called neurilemma.
The nerve fibers are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar; this type is widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated to action. Many processes are covered with a layer of lipid material called the myelin sheath. Peripheral nerve fibers have a thin outer covering called neurilemma.
Types of Neurons. Neurons that receive stimuli from the outside environment and transmit them toward the brain are called afferent or sensory neurons. Those that carry impulses in the opposite direction, away from the brain and other nerve centers to muscles, are called efferent neurons, motor neurons, or motoneurons. Another type, the interneuron, found in the brain and spinal cord, conducts impulses from afferent to efferent neurons.
Synapses. The point at which an impulse is transmitted from one neuron to another is called a synapse. The transmission is chemical in nature; that is, there is no direct contact between the axon of one neuron and the dendrites of another. The cholinergic nerves (parasympathetic nervous system) liberate at their axon endings a substance called acetylcholine, which acts as a stimulant to the dendrites of adjacent neurons. In a similar manner, the adrenergic nerves (sympathetic nervous system) liberate epinephrine or related substances. The synapse may involve one neuron in chemical contact with many adjacent neurons, or it may involve the axon terminals of one neuron and the dendrites of a succeeding neuron in a nerve pathway. There are many different patterns of synapses.
Receptor End-Organs. The dendrites of the sensory neurons are designed to receive stimuli from various parts of the body. These dendrites are called receptor end-organs and are of three general types: exteroceptors, interoceptors, and proprioceptors. The exteroceptors are located near the external surface of the body, receive impulses from the skin, and transmit information about the senses of touch, heat, cold, and other factors in the external environment. The interoceptors are located in the internal organs and receive information from the viscera, e.g., pressure, tension, and pain. The proprioceptors are found in muscles, tendons, and joints and transmit “muscle sense,” by which one is aware of the position of one's body in space.
Neurons and Effectors. The axons of motor neurons form synapses with skeletal fibers to produce motion. These junctions are called motor end-plates or myoneural junctions. The axon of a motor neuron divides just before it enters the muscle fibers and forms synapses near the nuclei of muscle fibers. These motor neurons are called somatic efferent neurons. Visceral efferent neurons form synapses with smooth muscle, cardiac muscle, and glands.
Upper and lower motor neurons. From Damjanov, 2000.
Golgi n's
1. (type I): pyramidal cells with long axons, which leave the gray matter of the central nervous system, traverse the white matter, and terminate in the periphery.
2. (type II): stellate neurons with short axons in the cerebral and cerebellar cortices and in the retina.
motor neuron motoneuron.
postganglionic n's neurons whose cell bodies lie in the autonomic ganglia and whose purpose is to relay impulses beyond the ganglia.
preganglionic n's neurons whose cell bodies lie in the central nervous system and whose efferent fibers terminate in the autonomic ganglia.
neuron (nyoo´ron),
n a nerve cell; the basic structural unit of the nervous system. There is a wide variation in the shape of nerve cells, but they all have the same basic structures: cell body, protoplasmic processes, axons, and dendrites. The neuron is the only body cell whose principal function is the conduction of impulses. It cannot regenerate when the cell body is destroyed; however, cell processes such as axons and dendrites can often regenerate.
neuron, sensory,
n See neuron, afferent.
neuron
a nerve cell; any of the conducting cells of the nervous system, consisting of a cell body, containing the nucleus and its surrounding cytoplasm, and the axon and dendrites.
Neurons are highly specialized cells having two characteristic properties: irritability, which means that they are capable of responding to stimulation; and conductivity, which means that they are able to conduct impulses. They are composed of a cell body (the neurosome or perikaryon), containing the nucleus and its surrounding cytoplasm, and one or more processes (nerve fibers) extending from the cell body.
The processes are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar, this type of neuron being widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a long single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated into action.
Many processes are covered with a layer of lipid material called myelin. Peripheral nerve fibers have a thin outer covering called the neurilemma.
adrenergic neuron
nerve cells which secrete norepinephrine as a neurotransmitter; they are mostly sympathetic postganglionic nerves plus some within specific brainstem foci.
association neuron
see internuncial neuron (below).
cholinergic neuron
nerves which synthesize the neurotransmitter acetylcholine in their terminals; they include α-motor neurons of the spinal cord, cranial nerves innervating skeletal muscle, preganglionic sympathetic and postganglionic parasympathetic neurons.
internuncial neuron
neurons found in the brain and spinal cord that conduct impulses between neurons such as from afferent to efferent neurons. Called also association neurons or interneurons.
Golgi n's
see golgi neurons.
lower motor n's
see lower motor neuron.
motor neuron
see motor neuron.
neurosecretory neuron
neurons of the hypothalamus that receive nervous impulses from higher centers and translate them into the regulation of hormone secretion.
nonadrenergic-noncholinergic (NANC) n's
release nitric oxide as a neurotransmitter.
parvicellular neuron
in the hypothalamus; regulate the secretion of adenohypophyseal hormones via releasing and inhibiting factors.
postganglionic n's
neurons whose cell bodies lie in the autonomic ganglia and which relay impulses beyond the ganglia to the effector organ.
preganglionic n's
neurons whose cell bodies lie in the central nervous system and whose efferent fibers terminate in the autonomic ganglia.
neuron transmission
the transmission of impulses along axons by means of electrical impulses and across synapses by neurotransmitters, especially norepinephrine and acetylcholine.
upper motor n's
see upper motor neuron.
neuron
Structural unit of the nervous system consisting of the nerve cell body and its various processes, the dendrites, the axon and the ending (also called bouton, end foot or axon terminal). There are many types of neurons within the nervous system; some transmit afferent nerve impulses to the brain (e.g. those carrying information from the photoreceptors to the visual cortex), or to the spinal cord (e.g. those carrying information from the receptors in the skin to the spinal cord). They are called sensory neurons. Others transmit efferent motor nerve impulses to a muscle (e.g. those carrying information from the Edinger-Westphal nucleus to the sphincter pupillae and ciliary muscles). These are called motor neurons. Other neurons carry nerve impulses from one neuron to another (internuncial neurons). Note: also spelt neurone. See action potential; synapse.
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