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abducens (VI) nerve: Cranial nerve; axons innervate the lateral rectus muscle.

abducens nucleus: Contains lateral rectus motor neurons and internuclear neurons; located in pons.

accessory cuneate nucleus: Relays somatic sensory information from upper trunk, arm, and neck to the cerebellum; located in medulla.

accessory (XI) nerve: Cranial nerve that innervates the sternocleidomastoid muscle and the upper part of the trapezius muscle.

accessory optic system: Transmits visual information to brain stem nuclei for eye movement control.

accommodation-convergence reaction: A complex response that prepares the eyes for near vision by (1) increasing lens curvature, (2) constricting the pupils, and (3) coordinating convergence of the eyes.

accommodation reflex: Increase in lens curvature that occurs during near vision.

acetylcholine: Neurotransmitter used by motor neurons and neurons in several nuclei, including the basal nucleus and the pedunculopontine nucleus.

acetylcholinesterase: Enzyme that inactivates acetylcholine.

acousticomotor function: Motor behavioral response triggered or controlled by sound such as orienting toward a sound.

adrenergic: Neuron that uses adrenalin as a neurotransmitter or neuromodulator.

adhesion: Union of two surfaces that are normally separate, such as in wound healing or in some pathological process.

afferent: Axons that transmit information toward a particular structure; afferent is not synonymous with sensory, which means related to processing information from a receptor sheet (e.g., body surface or retina).

airway protective reflex: Closure of the larynx to prevent fluid and food from entering the trachea.

akinesia: Impairment in initiating voluntary movement.

alar plate: Dorsal portion of the neuroepithelium that gives rise to sensory nuclei of the spinal cord and brain stem.

allocortex: Cortex having a variable number of layers, but always fewer than six.

alveus: Thin sheet of myelinated axons covering hippocampal formation; axons of pyramidal neurons in the hippocampus and subiculum.

Alzheimer disease: Presenile dementia.

amacrine cells: Retinal interneuron.

amygdala: Telencephalic structure that plays an essential role in emotions and their behavioral expression; has three component nuclear divisions: basolateral, central, and corticomedial.

amygdaloid nuclear complex: Another name for the amygdala.

anastomosis: A network of interconnected arteries.

aneurysm: An abnormal ballooning of a part of an artery due to weakening of the arterial wall.

angiogram: Radiological image of vasculature.

anosmia: Absence of the sense of smell.

ansa lenticularis: Output pathway of the internal segment of the globus pallidus; axons terminate in the thalamus.

anterior: Toward the abdomen; synonymous with ventral.

anterior cerebral artery: Supplies blood to the medial frontal lobes and underlying deep structures.

anterior choroidal artery: Supplies blood to the choroid plexus in ...

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