When charged particles, such as electrons, are accelerated, they generate an electromagnetic (EM) field. Typically, such a field is produced by alternating current in electrical conductors, which can have various frequency ranges (the standard unit of EM frequency being the hertz). Magnetic resonance imaging (MRI) involves the sophisticated use of EM fields to produce …
Category Archives: Uncategorized
Electroencephalogram (EEG)
An instrument with a variable number of channels designed to record electrical activity (in microvolts) generated in the upper layer of the cortex from electrodes attached to the scalp. In comparison with fMRI, EEG allows more direct and real time measurements of electrical signals generated by brain tissue. These signals are mainly derived from intra- …
Electrolyte
Liquid or gelatinous solution or chemical compound containing the free, primary ions (bicarbonate, calcium, chloride, magnesium, phosphate, and potassium). Most organisms require a complex electrolytic balance between the intercellular and extracellular milieu for normal physiological functioning, and in particular the maintenance of osmotic gradients. These gradients regulate hydration of the body, blood pH, and are …
Electrochemistry
A branch of chemistry devoted to the study of chemical changes generated by electrical currents and the production of electricity by chemical reactions involving ions in solution, including electrolysis and electric cells. Given that all chemical reactions involve changes in the electronic structure of atoms, it therefore follows that all reactions (including organic ones) are …
Ego
According to Freudian psychoanalytical theory, it is a feature of personality, developing during infancy, that operates on the basis of the reality principle. One of three components of the psychic apparatus, it is a way of seeking acceptable means of gratification in dealing with the real world. Originally derived by Freud from the German word …
Elastin (gene)
The main structural protein in elastic tissues of the body such as intestines, large blood vessels (arteries), ligaments, lungs, and tendons. It functions together with collagen in connective tissue: collagen supplies rigidity, whereas elastin allows the tissues to stretch and recoil to their original positions. Once elastin is no longer produced soon after puberty, the ageing …
Egg-tooth (or carbuncle)
A hard tooth-like projection on the top of the beak of embryonic birds or from the upper jaw of pre-hatchling crocodiles, tortoises and turtles (see figure below) that is used to cut the egg membrane and break open the shell so that the animal can hatch. There is a specialized hatching muscle at the back …
Efference copy (or corollary discharge)
A concept introduced into the study of motor control by Erich von Holst (1908-1962) to indicate the sending of a copy of the efferent signal ahead of a movement so that it prepares the system for incoming sensory feedback or for a future motor command. ‘Efferent’ means the conduction of nerve impulses ‘away from the …
Efficacy
The degree to which a clinical intervention relative to an appropriate control has a desired beneficial effect. This term is contrasted with efficiency: whether or not a treatment works after it is implemented in clinical practice. In Piaget‘s theory, ‘efficacy’ refers to a fundamental type of experience in which the child assumes his or her emotions …
Effect size
A family of statistical measures that provides an indication of the magnitude of a treatment effect. In contrast to significance tests, they are independent of sample size, and therefore generally used in meta-analyses. Broadly speaking, effect size boils down to two measurements: the standardised difference between two means of two independent groups, and the effect size …