accommodation:the process of changing the shape of the lens from round and fat to thin and flat, and vice versa, so that light can be focused on the retina to accommodate vision of objects near and far awayacetylcholine:one of the most common neurotransmitters of both the somatic nervous system and the parasympathetic nervous system. Acetylcholine functions by binding to receptors on the postsynaptic membrane and either depolarizing or hyperpolarizing the membrane.action potential:the change in charge that occurs when the gates of the potassium ion channels close and the gates of the sodium ion channels open; a large depolarization event that is conducted along the membrane of a nervecell or a muscle celladaptation:the process by which the iris adjusts the diameter of the pupil based on light conditions, thus controlling the amount of light that enters the eye and strikes the retinaall-or-none response:action that occurs either completely or not at all, such as the generation of an action potential by a neuronamplify:to increase the amplitude or the extent of a vibration; see intensityanterior chamber:the space in front of the iris and behind the cornea that is filled with aqueous humouraqueous humour:a clear, watery fluid in the anterior chamber of the eye that maintains the shape of the cornea andprovides oxygen and nutrients for the surrounding cells, including those of the lens and the corneaastigmatism:an uneven curvature of the cornea or lens, resulting in uneven focusing, which results in poor visionauditory canal:a short channel that funnels sound waves from outside the ear to the tympanum and amplifies soundsauditory nerve:a nerve composed of sensory fibres from the organ of Corti, the vestibular apparatus that conducts impulses to the temporal lobe of the cerebrumautonomic nervous system (ANS):a division of the peripheral nervous system that conducts nerve impulses to cardiac and smooth muscles, as well as to glands; may also be called the involuntary motor systemaxon:the long extension that emerges from the cell body and conducts the nerve impulse away from the cell body. The axon may be up to 1 m long in motor neurons.
axon terminal:numerous endings found at the end of an axon. Axon terminals are enlarged into knobs that are specialized for producing, storing, and releasing neurotransmitters.basilar membrane:one of two parallel membranes that comprise the organ of Corti in the inner ear. Hair cells are attached to the basilar membrane.bipolar cells:specialized sensory nerve cells located in the retina that are stimulated by either rods or cones. Cones mostly have a one-to-one ratio with bipolar cells, whereas several rod cells may communicate with one bipolar cell.