Also called the amygdaloid nucleus, it is a key, almond-shaped, bilateral structure in the limbic system of the forebrain (see figure below), involved in emotion recognition and other social emotional functions such as fear, aggression and defensive behaviours, as well as learning and memory. Connected with the prefrontal cortex, hypothalamus, hippocampus and cingulate gyrus. Many …
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Amodal
Intermodal information that is not unique to one sensory channel, as when a single event is specified by more than one modality. In essence, amodal properties are putativeproperties of multisensory stimulation, which are argued to be easilyaccessible to the human infant. Amodal properties contrast with arbitrarycross-modal relations and are currently defined as multisensory perceptualproperties that are …
Amnion (or amniotic sac)
The innermost of two transparent membranous sacs that completely surround the developing embryo and fetus (see figure below). It is partly responsible for producing the amniotic fluid that fills the sac. Amniotic sac and related structures See Amniocentesis, Amniotic fluid, Ascending genital tract infection, Chorion, Chorionic villus sampling, Dizygotic twins, Monozygotic twins, Placenta
Amniotic fluid
The watery fluid filling the cavity created by the embryonic membranes (amnion and chorion) that surround the embryo or fetus. Following formation of the amniotic sac some 12 days after conception, it is produced by several sources, including a filtrate from maternal plasma, secretion by the amnion, and urination by the fetus. By the end …
Amniocentesis
A technique, first used in 1882 to remove excess amniotic fluid, that involves extracting by centesis (inserting a hollow needle through the maternal abdominal wall into the uterus) a small amount of the fluid (usually about 1 cc for each week of pregnancy), and then analysing the fetal cells from the sample as a means …
American Sign Language (ASL)
American Sign Language is a system of communication for deaf people in which meaning is conveyed by hand signals and the position of the hands relative to other body parts (see figure below). For historical reasons, many of its signs are more closely related to French sign language than to British sign language. Chimpanzees, gorillas and orang-utans have …
Amino acids
Organic acids or compounds that form short chemical chains made of peptides and polypeptides that in turn form proteins. Thus, they are the fundamental components of peptides and polypetides and proteins that go to make up all living cells. In various combinations, 20 basic amino acids make up all the proteins in the human body. …
Ambidexterity
A confusing term. It literally means a condition of ‘equal hand’ (ambit) dexterity or skill across a range of tasks. For tasks requiring little if any skill (e.g., scratching one’s nose), virtually all adults are ambidextrous. For certain skilled tasks, even writing, many adults, with sufficient practice, might be able to achieve ambidexterity or near …
Alveoli
The tiny vesicles or sacs in the vertebrate lungs in which the exchange of oxygen and carbon dioxide takes place. It is a process of gas diffusion by which oxygen is transported from air in the alveoli (during inspiration), while carbon dioxide diffuses out of the blood into the air in the alveoli (during expiration), …
Alzheimer’s disease
The leading cause of dementia in elderly people, it is a progressive, irreversible, and thus incurable, neurological disease characterised by premature senile dementia that affects brain functions, including short-term memory loss, inability to reason, as well as the deterioration of language and the ability to care for oneself. There is an irreversible loss of neurons in …