white substance


substance

 [sub´stans] 1. physical material that has form and weight; called also matter.2. the material constituting an organ or body.3. substance" >psychoactive substance.substance Abuse and Mental Health Services Administration (SAMHSA) an agency of the United States Department of Health and Human Services, created in 1992 to oversee the quality and availability of programs for prevention, treatment, and rehabilitation of abuse" >substance abuse and related mental health problems.black substance substantia nigra.controlled substance a psychoactive substance that is regulated under the controlled substances act. See table at drug dependence.depressor substance 1. vasodepressor.2. depressant.gray substance matter" >gray matter.ground substance the gel-like material in which connective tissue cells and fibers are embedded.substance-induced disorders a subgroup of the substance-related disorders" >substance-related disorders comprising a variety of behavioral or psychological anomalies resulting from ingestion of or exposure to a drug of abuse, medication, or toxin. Included are substance intoxication, substance withdrawal, and other mental disorders such as dementia, mood disorder, and psychotic disorder when they are specifically caused by a substance. See also substance use disorders.medullary substance 1. the white matter of the central nervous system, consisting of axons and their myelin sheaths.2. the soft, marrow-like substance of the interior of such structures as bone, kidney, and adrenal gland.müllerian inhibiting substance a glycoprotein produced by the Sertoli cells of the fetal testis that acts ipsilaterally in the male to suppress the müllerian ducts, consequently preventing development of the uterus and fallopian tubes, thus helping to control formation of the male phenotype.substance P a peptide composed of 11 amino acids, present in nerve cells scattered throughout the body and in special endocrine cells in the gut; it increases the contractions of gastrointestinal smooth muscle and causes vasodilatation; it is one of the most potent vasoactive substances known, and it seems to be a sensory neurotransmitter involving pain, touch, and temperature.perforated substance 1. anterior perforated substance, an area anterolateral to each optic tract, pierced by branches of the anterior and middle cerebral arteries.2. posterior perforated substance, an area between the cerebral peduncles, pierced by branches of the posterior cerebral arteries.pressor substance vasopressor (def. 2).psychoactive substance (psychotropic substance) any chemical compound that affects the mind or mental processes, particularly a drug used therapeutically in psychiatry, or any of various other types of mind-altering substances such as drugs of abuse and some toxins. See also table at drug dependence. Called also psychoactive agent or drug and psychotropic agent or drug.

There are several different classes of psychoactive substances: antidepressants are used for the relief of symptoms of major depression. lithium is the most common agent used to treat manic episodes of bipolar disorder" >bipolar disorder. antipsychotic agents (or major tranquilizers) are used for management of the manifestations of psychotic disorders such as schizophrenia" >schizophrenia. antianxiety agents (called also minor tranquilizers), such as diazepam" >diazepam (Valium), are used for relief of anxiety disorders. While none of these drugs can effect a cure, they can reduce the severity of symptoms and permit the patient to resume more normal activity.
Also included in the category of psychotropic drugs are many other substances that affect the mind but are not used to treat mental disorders, including stimulants" >stimulants such as caffeine, amphetamines, and cocaine" >cocaine; opiates" >opiates; and hallucinogens" >hallucinogens.substance-related disorders any of the mental disorders associated with excessive use of or exposure to psychoactive substances, including drugs of abuse, medications, and toxins. The group is divided into substance use disorders and substance-induced disorders, each of which is specified on the basis of etiology, such as alcohol use disorders. See also drug abuse and drug dependence.slow-reacting substance of anaphylaxis SRS-A, an inflammatory agent released by mast cells in the anaphylactic reaction. It induces slow, prolonged contraction of certain smooth muscles and is an important mediator of allergic bronchial asthma.threshold s's those substances in the blood, such as glucose, that are excreted when they reach their threshold" >renal threshold.transmitter substance neurotransmitter.substance use disorders a subgroup of the substance-related disorders, in which substance" >psychoactive substance use or abuse repeatedly results in significantly adverse consequences. The group comprises substance abuse (see drug abuse) and substance dependence (see drug dependence); specific disorders or groups of disorders are named on the basis of etiology, e.g., alcohol use disorders, alcohol abuse, and alcohol dependence.white substance matter" >white matter.

white mat·ter

[TA] those regions of the brain and spinal cord that are largely or entirely composed of nerve fibers and contain few or no neuronal cell bodies or dendrites. Synonym(s): alba, substantia alba, white substance

white mat·ter

(wīt mat'ĕr) [TA] Those regions of the brain and spinal cord that are largely or entirely composed of nerve fibers and contain few or no neuronal cell bodies or dendrites.
Synonym(s): substantia alba, white substance.