GLOSSARY - GLOSSARY A1 See primary auditory cortex....

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GLOSSARY A1 See primary auditory cortex. absolute refractory period The period of time, meas- ured from the onset of an action potential, during which another action potential cannot be triggered. accommodation The focusing of light by changing the shape of the eye’s lens. acetylcholine (ACh) An amine that serves as a neurotransmitter at many synapses in the peripheral and central nervous systems, including the neuro- muscular junction. ACh See acetylcholine. ACTH See adrenocorticotropic hormone. actin A cytoskeletal protein in all cells and the major thin filament protein in a skeletal muscle fiber; causes muscle contraction by specific chemical inter- actions with myosin. action potential A brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels; also known as spike, nerve impulse, or discharge. Action potentials sweep like a wave along axons to transfer information from one place to another in the nervous system. activational effect The ability of a hormone to activate reproductive processes or behaviors in the mature organism. active zone A presynaptic membrane differentiation that is the site of neurotransmitter release. adenosine triphosphate (ATP) The molecule that is the cell’s energy source. The hydrolysis of ATP to produce adenosine diphosphate (ADP) releases energy that fuels most of the biochemical reactions of the neuron. ADP is converted back to ATP in the mitochondria. adenylyl cyclase An enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP), a second messenger. adrenal cortex The outer segment of the adrenal gland; releases cortisol when stimulated by the pituitary adrenocorticotropic hormone. adrenal medulla The inner segment of the adrenal gland, innervated by preganglionic sympathetic fibers; releases epinephrine. adrenaline A catecholamine neurotransmitter synthe- sized from norepinephrine; also called epinephrine. adrenocorticotropic hormone (ACTH) A hormone released by the anterior pituitary in response to cor- ticotropin-releasing hormone; stimulates the release of cortisol from the adrenal gland. affective aggression A threatening or defensive form of aggression accompanied by vocalizations and a high level of ANS activity. affective disorder A psychiatric condition character- ized by disordered emotions; also called mood disorder. Examples are major depression and bipolar disorder. affective neuroscience The study of the neural basis of mood and emotion. afferent An axon coursing toward and innervating a given structure. See also efferent. after-hyperpolarization The hyperpolarization that follows strong depolarization of the membrane; the last part of an action potential, also called undershoot. agnosia
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GLOSSARY - GLOSSARY A1 See primary auditory cortex....

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