many branching dendrites found in the cortex of the cerebellum, and for his 1839 discovery of Purk-inje fibers, the unusual tissue that conducts the pacemaker stimulus along the inside walls of the ventricles to all parts of the heart. Purkinje introduced the terms plasma to describe the clear liquid remaining after blood has been cleared of its various corpuscle components, and protoplasm, used to describe young animal embryos.
Purkinje described the effects of camphor, opium, belladonna, and turpentine on humans in 1829. An early user of the improved compound microscope, he also discovered the sweat glands of the skin (1833) and the germinal vesicles (1825). He recognized fingerprints as a means of identification in 1823, and noted the protein-digesting power of pancreatic extracts in 1836. Purkinje died at the age of 82 on July 28, 1869.
pyramidal cells cortical cell type involved in motor activity; the neurons are named for their pyramidal shape.
pyroglutamate (2-oxo-pyrrolidone carboxylic acid, or PCA) This amino acid is an important flavor enhancer found naturally in a wide variety of fruits and vegetables, dairy products and meat; it is found in large amounts in the brain, cerebrospinal fluid, and blood. It is also a suspected enhancer of cognitive ability.
PCA is able to penetrate the blood-brain barrier, where some researchers believe it stimulates cognitive function, improving memory and learning in rats. At least one study has shown it is effective in alcohol-induced memory deficits in humans and in patients suffering from multi-infarct dementia. Administration of this amino acid increased attention and improved short- and long-term retrieval and long-term memory storage.
When compared with a placebo in studies of memory deficits in 40 aged patients, results indicated that PCA improved verbal memory functions in those who were already affected by an age-related memory decline.
One form of the substance has been used in Italy to treat senility, mental retardation, and alcoholism, where it is found in health food and vitamin stores in a variety of preparations under several names.
pyrrolidone derivatives A class of nootropic drugs including piracetam and its analogues OXIRACETAM, PRAMIRACETAM, ANIRACETAM and others. The mechanism behind their memory-enhancing properties seems to be the increase in transmissions at all synapses; most research suggests that the drugs affect the cholinergic system and the adrenal cortex in the brain.
Pythagoras (c. 580 B.c.-c. 500 B.C.) Greek philosopher who suggested that the mind was located in the brain and that the brain was the home of the soul.
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