motor unit

unit (u´nit)

1. a single thing.

2. a quantity assumed as a standard of measurement. Symbol U.

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Angström unit  angstrom.

atomic mass unit  (u) (amu) the unit mass equal to 112 the mass of the nuclide of carbon-12. Called also dalton.

Bethesda unit  a measure of the level of inhibitor to coagulation factor VIII; equal to the amount of inhibitor in patient plasma that will inactivate 50 per cent of factor VIII in an equal volume of normal plasma following a 2-hour incubation period.

Bodansky unit  the quantity of alkaline phosphatase that liberates 1 mg of phosphate ion from glycerol 2-phosphate in 1 hour under standard conditions.

British thermal unit  (BTU) the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit, usually from 39°F to 40°F.

CGS unit  any unit in the centimeter-gram-second system.

CH50 unit  the amount of complement that will lyse 50 per cent of a standard preparation of sheep red blood cells coated with antisheep erythrocyte antibody.

coronary care unit  a specially designed and equipped hospital area containing a small number of private rooms, with all facilities necessary for constant observation and possible emergency treatment of patients with severe heart disease.

intensive care unit  a hospital unit in which are concentrated special equipment and skilled personnel for the care of seriously ill patients requiring immediate and continuous attention; abbreviated ICU.

International unit  (IU) a unit of biological material, as of enzymes, hormones, vitamins, etc., established by the International Conference for the Unification of Formulas.

motor unit  the unit of motor activity formed by a motor nerve cell and its many innervated muscle fibers.

SI unit  any of the units of the Système International d'Unités (International System of Units) adopted in 1960 at the Eleventh General Conference of Weights and Measures.

Somogyi unit  that amount of amylase which will liberate reducing equivalents equal to 1 mg of glucose per 30 minutes under defined conditions.

Svedberg unit  (S) a unit equal to 10−13 second used for expressing sedimentation coefficients of macromolecules.

terminal respiratory unit  the anatomical and functional unit of the lung, including a respiratory bronchiole, alveolar ducts and sacs, and alveoli.

toxic unit , toxin unit the smallest dose of a toxin which will kill a guinea pig weighing about 250 gm in three to four days.

USP unit  one used in the United States Pharmacopeia in expressing potency of drugs and other preparations.

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motor unit

n.

A single somatic motor neuron and the group of muscle fibers innervated by it.

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motor unit,

a functional structure consisting of a motor neuron and the muscle fibers it innervates.

Motor unit

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motor,

n pertaining to a muscle, nerve, or center that produces or affects movement.

motor neuron,

n one of the various efferent nerve cells that transmit nerve impulses from the brain or from the spinal cord to muscular or glandular tissue.

motor neuron disease,

n a progressive disease that tends to affect middle-age men with degeneration of anterior horn cells, motor cranial nerve nuclei, and pyramidal tracts (e.g., amyotrophic lateral sclerosis).

motor output,

n the activity that results from the integrative phenomena associated with brain activity. It is expressed in function as muscle contraction of the smooth and striated muscle and as secretion of the exocrine and endocrine glands and, in effect, represents the total behavioral activity. Whereas sensory phenomena have many avenues that feed into the brain, motor activity is expressed in terms of the simple, direct state of muscle contraction and glandular secretion. Thus muscle activity is expressed in terms of locomotion, hand-learned skills, speaking, mastication, and all forms of activity that involve motion.

motor pathway,

n all reflex actions of muscle are achieved by the passage of nerve impulses through the final common pathway–the muscle fibers. The lower motor neuron (the motor route of the cranial nerve) is the final pathway for the structures that are innervated by the cranial nerves. Impulses traverse these nerves to their respective muscles from every level of the spinal cord, hindbrain, midbrain, and cerebral cortex. The cranial motor neurons collate these multiple stimuli and transmit sequences of stimuli to the motor end-plate, which in the normal muscle effects a smooth, continuous, controlled contraction.

motor skill,

n the ability to make the purposeful movements that are necessary to complete or master a prescribed task.

motor unit,

n the entity consisting of the lower motor neuron, motor end-plate, and muscle fibers supplied by the end-plate. The final motor activity resulting from a sequence of stimulations to the lower motor neuron is considered a function of the motor unit. The proportion of nerve fibers to the muscle fibers in motor units is designated as the innervation ratio. They may have ratios ranging from 1:4 to 1:150. The closer the ratio approximates unity, the greater the finesse of specificity of the muscular action. The eye muscles have the highest ratio of striated muscles, and the tongue, facial, masticatory, and pharyngeal muscles succeed in that order.

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motor

1. pertaining to motion.

2. a muscle, nerve or center that effects movements.

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motor activity

limb movement the most obvious of these forms of activity.

motor alpha-neuron

ventral spinal cord neurons which innervate skeletal muscle. Called also final common pathway, lower motor neuron.

motor depressant anticonvulsant

a drug that depresses motor activity and hence prevents convulsions, e.g. phenobarbital sodium, phenytoin sodium.

motor dysfunction

abnormality of the motor system.

motor end-plate

sites of neuraptic transmission of acetylcholine from nerve to muscle receptors.

motor fibers

innervate the body effectors.

motor lubricating oil

ingestion may cause lead poisoning.

motor nerve conduction

the transmission of impulses along motor nerves to skeletal muscle.

motor unit

includes the motor neuron, neuromuscular junction, and the myofibrils innervated by the neuron.

motor unit action potential

the electrical activity of voluntary muscle contractions recorded by needle electromyography.

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motor unit

A group of muscle fibres that respond to a stimulus from a single motor neuron. In the extraocular muscles a motor unit consists of less than a dozen small fibres, that is considered to be a small unit. It produces a finer degree of neural control over contraction than a larger unit, which produces more powerful gross movements when activated. See neuron.