| lower motor neuron | Clinical term used to indicate the final motor neuron's that innervate the skeletal muscles; distinguished from upper motor neuron's of the motor cortex that contribute to the pyramidal or corticospinal tract. See: motor neuron. (05 Mar 2000) |
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| lower motor neuron dysarthria | Dysarthria caused by dysfunction of the motor nuclei and the lower pons or medulla, or other neural connections, central and peripheral to the muscles of articulation. (05 Mar 2000) |
| lower motor neuron lesion | Injury to motor cells in the brainstem or spinal cord, or of the axons derived from them. (05 Mar 2000) |
| absolute system of units | A system based on absolute units accepted as being fundamental (length, mass, time) and from which other units (force, energy or work, power) are derived; such system's in common use are the foot-pound-second, centimeter-gram-second, and meter-kilogram-second system's. (05 Mar 2000) |
| absorbent system | <anatomy> The tissues and organs (including the bone marrow, spleen, thymus and lymph nodes) that produce and store cells that fight infection and the network of vessels that carry lymph. (12 May 1997) |
| alimentary system | The organs that are responsible for getting food into and out of the body and for making use of food to keep the body healthy. These include the mouth, oesophagus, stomach, liver, gallbladder, pancreas, small intestine, colon, and rectum. (12 Dec 1998) |
| anterolateral system | A composite bundle of fibres, located in the ventrolateral part of the lateral funiculus, containing spinothalamic, spinohypothalamic, spinoreticular, and spinomesencephalic (spinotectal, spinal to periaqueductal grey, etc.) fibres; occupies the combined areas of the spinal white matter historically divided into anterior and lateral spinothalamic tracts; located in white matter ventral to the denticulate ligament, hence the anatomical basis for the anterolateral cordotomy; concerned with the transmission of nociceptive and thermal information and with crude (nondiscriminative) touch. (05 Mar 2000) |
| anti-allergic and respiratory system agents | A collective term for drugs used to treat allergic reactions as well as those drugs that produce an effect on the respiratory system. (12 Dec 1998) |
| arch-loop-whorl system | See: Galton's system of classification of fingerprints. (05 Mar 2000) |
| association system | Groups or tracts of nerve fibres interconnecting different regions of one and the same major subdivision of the central nervous system, such as the various areas of the cerebral cortex or the various segments of the spinal cord. (05 Mar 2000) |
| autonomic nervous system | <anatomy> Neurons that are not under conscious control, comprising two antagonistic components, the sympathetic and parasympathetic nervous systems. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: 1. The sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. 2. The parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. (03 Jul 1999) |
| autonomic nervous system diseases | Diseases that have their major effects on the autonomic nervous system. The autonomic nervous system may be seriously affected in many other disorders including other peripheral nervous system diseases, infectious diseases (e.g., tetanus, diphtheria), immunologic diseases (e.g., acquired immunodeficiency syndrome), and systemic disorders (e.g., diabetic neuropathy, amyloid neuropathy, thyroid diseases). Disorders of central autonomic control also contribute substantially to a wide variety of problems (e.g., eating disorders, panic disorder, water-electrolyte imbalance, cardiovascular diseases). (12 Dec 1998) |
| balanced lethal system | <genetics> A population with non-linked, recessive alleles of a gene, where an individual who has two copies of the recessive allele and is therefore homozygous is dead, while an individual who has only one copy of it, and one copy of a different allele (and is heterozygous) survives. (09 Oct 1997) |
| Bethesda system | Recent classification for categorizing cervical Papanicolaou smears. Origin: Bethesda, Maryland, site of NIH (05 Mar 2000) |
| blood-vascular system | The heart and the blood vessels by which blood is pumped and circulated through the body. (12 Dec 1998) |