| action potential | The term used to describe the brief wave of electrical charge that sweeps down the axon during the transmission of a nerve impulse. p. 49
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| adrenal glands | Important endocrine glands that are instrumental in regulating moods, energy level, and the ability to cope with stress. p. 63
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| association cortex | Region of the cerebral cortex in which the highest intellectual functions, including thinking and problem solving, occur (also called association areas). p. 60
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| autonomic nervous system | Division of the PNS that communicates with the body's internal organs. It consists of the sympathetic and parasympathetic nervous systems. p. 46
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| axon | The part of the neuron that carries information away from the cell body to other cells; each neuron has only one axon. p. 48
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| brain stem | The region of the brain that includes most of the hindbrain (excluding the cerebellum) and the midbrain. p. 54
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| cell body | Part of the neuron that contains the nucleus, which directs the manufacture of substances that the neuron needs for growth and maintenance. p. 48
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| central nervous system (CNS) | The brain and spinal cord. p. 46
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| cerebral cortex | Highest level of the forebrain, where the highest mental functions, such as thinking and planning, take place. p. 57
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| chromosomes | Threadlike structures that contain genes and DNA. Humans have 23 chromosome pairs in the nucleus of every cell. Each parent contributes one chromosome to each pair. p. 67
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| corpus callosum | A large bundle of axons that connect the brain's two hemispheres. p. 60
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| dendrites | Branches of a neuron that receive and orient information toward the cell body; most neurons have numerous dendrites. p. 48
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| deoxyribonucleic acid (DNA) | A complex molecule that contains genetic information; makes up chromosomes. p. 67
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| endocrine system | A set of glands that regulate the activities of certain organs by releasing hormones into the bloodstream. p. 64
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| forebrain | The highest level of the brain. Key structures in the forebrain are the limbic system, thalamus, basal ganglia, hypothalamus, and cerebral cortex. p. 55
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| frontal lobe | The part of the cerebral cortex just behind the forehead that is involved in the control of voluntary muscles, intelligence, and personality. p. 59
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| glial cells | Provide support and nutritional benefits in the nervous system. p. 48
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| hindbrain | The lowest level of the brain, consisting of the medulla, cerebellum, and pons. p. 54
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| hormones | Chemical messengers manufactured by the endocrine glands. p. 64
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| hypothalamus | Forebrain structure involved in regulating eating, drinking, and sex; directing the endocrine system through the pituitary gland; and monitoring emotion, stress, and reward. p. 56
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| Limbic system | Loosely connected network of structures–including the amygdala and hippocampus–that play important roles in memory and emotion. p. 55
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| midbrain | Located between the hindbrain and forebrain, a region in which many nerve-fiber systems ascend and descend to connect the higher and lower portions of the brain. p. 54
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| motor cortex | Area of the cerebral cortex that processes information about voluntary movement. p. 59
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| myelin sheath | A layer of fat cells that encases and insulates most axons. The myelin sheath speeds up the transmission of nerve impulses. p. 48
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| nervous system | The body's electrochemical communication circuitry, made up of billions of neurons. p. 44
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| neural networks | Clusters of neurons that are interconnected to process information. p. 46
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| neuron | Nerve cell that is specialized for processing information. Neurons are the basic units of the nervous system. p. 48
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| neurotransmitters | Chemicals that carry information across the synaptic gap from one neuron to the next. p. 49
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| occipital lobe | The part of the cerebral cortex at the back of the head that is involved in vision. p. 59
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| parasympathetic nervous system | The division of the autonomic nervous system that calms the body. p. 46
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| parietal lobe | Area of the cerebral cortex at the top of the head that is involved in registering spatial location, attention, and motor control. p. 59
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| peripheral nervous system (PNS) | The network of nerves that connects the brain and spinal cord to other parts of the body. It is divided into the somatic nervous system and the autonomic nervous system. p. 46
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| pituitary gland | An important endocrine gland at the base of the skull that controls growth and regulates other glands. p. 64
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| plasticity | The brain's special capacity for modification and change. p. 45
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| Reticular formation | A midbrain system that consists of a diffuse collection of neurons involved in stereotypical behaviors such as walking, sleeping, or turning to attend to a sudden noise. p. 54
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| sensory cortex | Area of the cerebral cortex that processes information about body sensations. p. 59
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| somatic nervous system | Division of the PNS consisting of sensory nerves, whose function is to convey information to the CNS, and motor nerves, whose function is to transmit information to the muscles. p. 46
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| sympathetic nervous system | The division of the autonomic nervous system that arouses the body. p. 46
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| synapses | Tiny junctions between two neurons, generally where the axon of one neuron meets the dendrites or cell body of another neuron. p. 49
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| temporal lobe | The portion of the cerebral cortex just above the ears that is involved in hearing, language processing, and memory. p. 59
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| thalamus | Forebrain structure that functions as a relay station to sort input and direct it to different areas of the cerebral cortex. It also has ties to the reticular formation. p. 56
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