Inhibitory interneurons of the cerebellar cortex at the top of the granular layer deep to the Purkinje cells containing the neurotransmitter GABA. These cells have extensive processes that extend well into the molecular layer and the lower parts of the granular layer. They are activated by mossy fibers and climbing fibers so as to provide …
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Gonadotropin releasing hormone (GnRH)
Also called lutenizing hormone-releasing hormone, it is a peptide hormone or neurohormone consisting of 10 amino acids that when released from the hypothalamus stimulate the gonadotrope cells of the anterior pituitary gland to produce lutenizing hormone and follicle-stimulating hormone. Thus, while very low during childhood, its intermittent secretion at the onset of puberty triggers sexual …
Golgi tendon organ
A proprioceptive receptor found embedded in muscle tendons consisting of encapsulated bundles (or fibrils) of collagen, which attach some 3 to 50 muscle fibers to tendons (see figure below). Innervated by a single, large, rapidly conducting afferent fiber (afferent Ib fiber so labeled to distinguish it from the Ia primary afferent that supplies the muscle …
Go/no go test
Originally devised by Alexander R. Luria (1902-1977), this simple task involves forming an habitual response to a stimulus (e.g., pressing a button in response to a light) and then suppressing that pre-potent response on selected trials. Performance is rated by error frequency and type (e.g., errors of commission or omission) as well as reaction times. …
Golgi apparatus (body or complex or organ)
A cell organelle consisting of a system or stack of interconnected smooth-surfaced, double-membraned vesicles (cistern) in the cytoplasm of eukaryote cells situated between two complex networks of tubules (cis and trans Golgi networks), and usually connected to the endoplasmic reticulum. It stores and transports lipids and (ribosomal) proteins and has a role in the formation …
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Glycoproteins
Any group of conjugated proteins containing a carbohydrate as the non-protein component. They occur in a variety of different forms in many different species, and are particularly important in the maintenance of mammalian tissue as well as in immune cell recognition in mammals. Many proteins released by cells into the blood and other fluids are, …
Glycine
A non-essential amino acid and a major inhibitory transmitter in the central nervous system, but not as widespread as gamma amino butyric acid. Binds to receptor sites on alpha (α) motoneurons. See Alpha (α) motoneuron, Amino acids, Aspartate (or aspartic acid), Gamma amino butyric acid (GABA), Glutumate (or glutamate), Neurotransmitters
Glycogen
Sometimes referred to as ‘animal starch’, it is a polysaccharide that is the chief carbohydrate store in animal cells and produced from glucose by hydrolysis. It is broken down into lactic acid (and thus is useful for endurance athletes) when it is used as an energy source in the liver or muscles. It has also …
Glutumate (or glutamate)
An amino acid derived from the diet. In certain neurons, it is converted to GABA by an enzymatic reaction that depends on vitamin B6. Consequently, a severe deficiency in this vitamin can lead to convulsions due to lack of GABA-mediated inhibition in the brain. This effect was witnessed on a large scale when an artificial …
Glucocorticoids
Steroid hormones produced by the adrenal cortex, which play a role in carbohydrate metabolism in normal conditions. Stress induces increased levels, which results in an elevation of blood pressure and a suppression of immunological and inflammatory responses. They play a crucial role in the regulation of glucose, and when used in treatment (e.g., asthma, as …