aditus: Latin ad = to, towards, iter = a way, hence an opening or entrance.
adrenal: Latin ad = towards, at, ren = kidney, hence situated near the kidney (see suprarenal)
adrenergic: adjective, Latin ad = at, ren = kidney, and Greek ergon = work, hence, stimuli which cause the adrenal (suprarenal) gland to produce adrenaline. Used to specify neurons or pathways which use adrenaline as a transmitter.
afferent: adjective, Latin ad = to, and ferent = carrying (cf. ferry), hence, carrying to, e.g., axons carrying information from retina to lateral geniculate nucleus are afferents to that nucleus.
aorta: Latin aorta, from Greek aorte = literally 'what is hung up,' from aeirein 'to lift, heave, raise,' of uncertain origin. Originally applied by Aristotle to the great artery of the heart, earlier by Hippocrates to the bronchial tubes.
aponeurosis: Greek apo = from, and neuron = tendon (later applied to nerve cell and its fibres), used for sheet-like tendons. Adjective - aponeurotic.
apophysis: Greek apo = from, and physis = growth, hence, a bony process - reserved for the articular process of a vertebra; adjective - apophysial.
appendage: Latin appendere = to hang on, supplement.
appendix: Latin appendere = to hang on, supplement.
apposition: Latin appositus = placed at, hence, in contact, in juxtaposition.
aqueduct: Latin aqua = water, and ductus = drawn or led off, hence a channel for conducting fluid, e.g. the cerebral aqueduct of the midbrain, which transmits fluid from the 3rd to the 4th ventricle.
arachnoid: adjective, Greek arachne = spider, and eidos = shape or form, hence like a spiders web. This middle layer of the three meninges is spread web-like over the brain when the dura has been removed.
arbor vitae: Latin arbor = tree, and vita = life, hence, resembling the tree of life. This colourful term is used to describe the pattern of cerebellar folia seen in a median section.
archaeocerebellum: Greek archi = first, hence the oldest part of the cerebellum, which is the flocculonodular lobe.
archaeopallium: Greek archi = first, and pallium = cloak, hence the cortex which developed first in vertebrates. Often synonymous with hippocampal formation.
archicerebellum: Greek archi = first, hence the oldest part of the cerebellum, which is the flocculonodular lobe.
archipallium: Greek archi = first, and pallium = cloak, hence the cortex which developed first in vertebrates. Often synonymous with hippocampal formation.
archistriatum: Greek archi = first, and Latin striatum = streaked or fluted.
astrocyte: Greek astron = star, and kytos = cell, hence a star-shaped (neuroglial) cell.
ataxia,: Greek a = negative, and taxis = order, hence inability to co-ordinate the voluntary muscles.
atlas: Greek atlao = I sustain. Atlas was a mythical god who sustained the globe on his shoulders. The 1st vertebra sustains the skull, and its upper surface bears 2 concavities which suggest Atlas' palms, not shoulders.
atresia: Greek a = negative, and tresis = a hole, hence an absence or closure of a body orifice or tubular organ
atrium: Latin = entrance hall, adjective - atrial.
atrophy: Greek a = negative, and trophe = food, hence wasting from starvation.
auditory: Latin audire = to hear, hence, pertaining to the ear.