| action potential | The brief wave of electrical charge that sweeps down the axon during the transmission of a nerve impulse.
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| adrenal glands | Important endocrine glands that are instrumental in regulating moods, energy level, and the ability to cope with stress.
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| afferent nerves | Sensory nerves that transport information to the brain.
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| agonist | A drug that mimics or increases a neurotransmitter's effects.
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| all-or-none principle | Once an electrical impulse reaches a certain level of intensity, it fires and moves all the way down the axon without losing any of its intensity.
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| antagonist | A drug that blocks a neurotransmitter's effects.
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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.
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| autonomic nervous system | The division of the PNS that communicates with the body’s internal organs. It consists of the sympathetic and parasympathetic nervous systems.
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| axon | The part of the neuron that carries information away from the cell body to other cells.
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| basal ganglia | Large clusters of neurons, located above the thalamus and under the cerebral cortex, that work with the cerebellum and the cerebral cortex to control and coordinate voluntary movements.
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| brain stem | The region of the brain that includes most of the hindbrain (excluding the cerebellum) and the midbrain.
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| cell body | The part of the neuron that contains the nucleus, which directs the manufacture of substances that the neuron needs for growth and maintenance.
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| central nervous system (CNS) | The brain and spinal cord.
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| cerebral cortex | Highest level of the forebrain, where the highest mental functions, such as thinking and planning, take place.
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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.
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| corpus callosum | The large bundle of axons that connects the brain’s two hemispheres.
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| dendrites | Branches of a neuron that receive and orient information toward the cell body; most neurons have numerous dendrites.
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| deoxyribonucleic acid (DNA) | A complex molecule that contains genetic information; makes up chromosomes.
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| dominant-recessive genes principle | principle The principle that, if one gene of a pair governing a given characteristic (such as eye color) is dominant and one is recessive, the dominant gene overrides the recessive gene. A recessive gene exerts its influence only if both genes in a pair are recessive.
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| efferent nerves | Motor nerves that carry the brain's output.
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| endocrine system | A set of glands that regulate the activities of certain organs by releasing their chemical products (hormones) into the bloodstream.
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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.
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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.
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| genes | The units of hereditary information. They are short segments of chromosomes, composed of DNA.
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| genotype | An individual's genetic heritage; his or her actual genetic material.
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| glial cells | Cells that provide support and nutritional benefits in the nervous system.
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| hindbrain | The lowest portion of the brain, consisting of the medulla, cerebellum, and pons.
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| Hormones | Chemical messengers manufactured by the endocrine glands.
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| hypothalamus | Small forebrain structure involved in regulating eating, drinking, and sex; directing the endocrine system; and monitoring emotion, stress, and reward.
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| limbic system | Loosely connected network of structures—including the amygdala and hippocampus—that play important roles in memory and emotion.
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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.
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| motor cortex | Area of the cerebral cortex that processes information about voluntary movement.
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| myelin sheath | The layer of fat cells that encases and insulates most axons. The myelin sheath speeds up the transmission of nerve impulses.
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| nervous system | The body's electrochemical communication circuitry, made up of billions of neurons.
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| neural networks | Networks of nerve cells that integrate sensory input and motor output.
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| neurons | Nerve cells that are specialized for processing information. Neurons are the basic units of the nervous system.
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| neurotransmitters | Chemicals that carry information across the synaptic gap from one neuron to the next.
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| occipital lobe | The part of the cerebral cortex at the back of the head that is involved in vision.
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| parasympathetic nervous system | The division of the autonomic nervous system that calms the body.
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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.
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| peripheral nervous system | 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.
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| phenotype | The expression of an individual’s genotype in observable, measurable characteristics.
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| pituitary gland | An important endocrine gland at the base of the skull that controls growth and regulates other glands.
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| plasticity | The brain's special capacity for modification and change.
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| resting potential | The stable, negative charge of an inactive neuron.
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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.
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| somatic nervous system | The 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.
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| somatosensory cortex | Area of the cerebral cortex that processes information about body sensations.
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| stress | The response of individuals to changes in circumstances and events that threaten their coping abilities.
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| stressors | Circumstances and events that threaten individuals and tax their coping abilities
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| sympathetic nervous system | The division of the autonomic nervous system that arouses the body.
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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.
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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.
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| thalamus | Forebrain structure that functions as a relay station to sort information and send it to appropriate areas in the forebrain for further integration and interpretation.
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