| acetylcholine | A neurotransmitter used by somatic neurons that contract the body's large muscles and by neurons in the brain that apparently regulate wakefulness and dream sleep.
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| action potential | A brief electrical signal that travels the length of the axon.
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| adrenal glands | Two glands on the kidneys, which are involved in physical and emotional arousal.
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| afferent neurons | Neurons that transmit messages from sense organs to the central nervous system.
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| all-or-none principle | The law that states that, once a neural action potential is produced, its magnitude is always the same.
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| amygdala | The part of the limbic system that plays a role in emotional arousal.
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| aphasia | An impairment of the ability to understand or use language.
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| association areas | Areas within each lobe of the cerebral cortex believed to play general rather than specific roles.
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| autonomic nervous system | The division of the peripheral nervous system that controls the involuntary actions of internal body organs, such as heartbeat and breathing, and is important in the experience of emotion.
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| axons | Neuron branches that transmit messages to other neurons.
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| brain | The complex mass of neural cells and related cells encased in the skull.
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| Broca's area | An area of the frontal lobe of the left cerebral hemisphere that plays a role in speaking language.
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| cell body | The central part of the neuron that includes the nucleus.
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| cell membrane | The covering of a neuron or another cell.
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| central nervous system | The brain and the nerve fibers that make up the spinal cord.
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| cerebellum | Two rounded structures behind the pons involved in the coordination of muscle movements, learning, and memory.
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| cerebral cortex | The largest structure in the forebrain, controlling conscious experience and intelligence and being involved with the somatic nervous system.
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| cerebral hemispheres | The two main parts of the cerebral cortex, divided into left and right hemispheres.
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| chromosomes | The strips in cell nuclei that contain genes.
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| cingulate cortex | A part of the limbic system lying in the cerebral cortex that processes cognitive information in emotion.
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| corpus callosum | The link between the cerebral hemispheres.
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| cortisol | A hormone produced by the adrenal glands.
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| cretinism | A type of mental retardation in children caused by a deficiency of thyroxin.
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| dendrites | Extensions of the cell body that receive messages from other neurons.
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| deoxyribonucleic acid (DNA) | The complex molecule containing the genetic code.
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| depolarization | The process during which positively charged ions flow into the axon, making it less negatively charged inside.
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| dizygotic twins | Twins formed from the fertilization of two ova by two sperm.
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| dominant gene | The gene that produces a trait in an individual even when paired with a recessive gene.
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| dopamine | A neurotransmitter substance used by neurons in the brain that control large muscle movements and by neurons in pleasure and reward systems in the brain.
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| efferent neurons | Neurons that transmit messages from the central nervous system to organs and muscles.
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| electroencephalogram (EEG) | A recording of the electrical activity of the brain obtained through electrodes placed on the scalp.
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| endocrine system | The system of glands that secretes hormones.
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| epinephrine | A hormone produced by the adrenal glands.
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| estrogen | A female sex hormone.
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| fertilization | The uniting of sperm and ovum, which produces a zygote.
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| forebrain | The parts of the brain, including the thalamus, hypothalamus, and cerebral cortex, that cover the hindbrain and midbrain and fill much of the skull.
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| frontal lobes | The part of the cerebral cortex in the front of the skull involved in planning, organization, voluntary motor movements, and speech.
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| functional MRI | A type of MRI that measures the activity of parts of the brain by measuring the use of oxygen by groups of neurons.
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| gamete | A sex cell, which contains 23 chromosomes instead of the normal 46.
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| ganglia | Clusters of cell bodies of neurons outside of the central nervous system.
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| genes | The hereditary units made up of deoxyribonucleic acid.
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| glands | Structures in the body that secrete substances.
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| glucagon | A hormone produced by the islets of Langerhans that causes the liver to release sugar into the bloodstream.
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| gonads | The glands that produce sex cells and hormones important in sexual arousal and that contribute to the development of secondary sex characteristics.
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| hindbrain | The lowest part of the brain, located at the base of the skull.
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| hippocampus | The part of the limbic system that plays a role in emotional arousal and memory.
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| hormones | Chemical substances, produced by endocrine glands, that influence internal organs.
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| hypothalamus | The small part of the forebrain involved with motives, emotions, and the functions of the autonomic nervous system.
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| insulin | A hormone produced by the islets of Langerhans that reduces the amount of sugar in the bloodstream.
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| interneuron | Neurons in the central nervous system that connect other neurons.
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| ions | Electrically charged particles.
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| islets of Langerhans | Endocrine cells in the pancreas that regulate the level of sugar in the blood.
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| limbic system | A complex brain system, composed of the amygdala, hippocampus, septal area, and cingulate cortex, that works with the hypothalamus in emotional arousal.
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| magnetic resonance imaging (MRI) | An imaging technique using magnetic resonance to obtain detailed views of brain structure and function.
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| medulla | The swelling at the top of the spinal cord responsible for controlling breathing and a variety of reflexes.
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| metabolism | The process through which the body uses energy.
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| midbrain | The small area at the top of the hindbrain that serves primarily as a reflex center for orienting the eyes and ears.
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| monozygotic twins | Twins formed from a single ovum; they are identical in appearance because they have the same genetic structure.
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| myelin sheath | The insulating fatty covering wrapped around part of the neuron.
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| nerve | A bundle of long neurons outside the brain and spinal cord.
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| neuron | An individual nerve cell.
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| neurotransmitters | Chemical substances, produced by axons, that transmit messages across the synapse.
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| norepinephrine | A hormone produced by the adrenal glands.
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| occipital lobes | The part of the cerebral cortex, located at the base of the back of the head, that plays an essential role in the processing of sensory information from the eyes.
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| ovaries | Female endocrine glands that secrete sex-related hormones and produce ova, or eggs.
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| pancreas | The organ near the stomach that contains the islets of Langerhans.
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| parasympathetic division | The division of the autonomic nervous system that generally "calms" internal organs.
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| parathormone | A hormone that regulates ion levels in neurons and controls excitability of the nervous system.
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| parathyroid glands | Four glands embedded in the thyroid that produce parathormone.
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| parietal lobes | The part of the cerebral cortex located behind the frontal lobes at the top of the skull containing the somatosensory area.
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| peripheral nervous system | pùe-rif« er-al) The network of nerves that branches from the brain and spinal cord to all parts of the body.
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| pineal gland | The endocrine gland that is largely responsible for the regulation of biological rhythms.
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| pituitary gland | The body's master gland, located near the bottom of the brain, whose secretions help regulate the activity of the other glands in the endocrine system.
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| polarized | The resting state of a neuron, when mostly negative ions are inside and mostly positive ions are outside the cell membrane.
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| pons | The part of the hindbrain that is involved in balance, hearing, and some parasympathetic functions.
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| receptor sites | Sites on the dendrite that receive the neurotransmitter substance.
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| recessive gene | The gene that produces a trait in an individual only when the same recessive gene has been inherited from both parents.
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| semipermeable | sem««e-pe«r-møe-ah-b«l) A surface that allows some, but not all, particles to pass through.
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| septal area | A part of the limbic system that processes cognitive information in emotion.
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| serotonin | A neurotransmitter used by systems of neurons believed to regulate sleep, dreaming, appetite, anxiety, depression, and the inhibition of violence.
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| somatic nervous system | The division of the peripheral nervous system that carries messages from the sense organs, muscles, joints, and skin to the central nervous system and from the central nervous system to the skeletal muscles.
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| somatosensory area | The strip of parietal cortex running parallel to the motor area of the frontal lobes that plays a role in body senses.
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| spinal cord | The nerve fibers in the spinal column.
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| stroke | A rupture of a blood vessel in the brain that often results in the destruction of a part of the brain.
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| sympathetic division | The division of the autonomic nervous system that generally activates internal organs during emotional arousal or when physical demands are placed on the body.
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| synapse | The space between the axon of one neuron and the dendrite of another.
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| synaptic gap | The small space between two neurons at a synapse.
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| synaptic knobs | The knoblike tops of axons.
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| synaptic vesicles | Tiny vessels containing stored quantities of the neurotransmitter substance held in the synaptic knobs of the axon.
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| temporal lobes | The part of the cerebral cortex that extends back from the area of the temples beneath the frontal and parietal lobes and that contains areas involved in the sense of hearing and understanding language.
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| testes | Male endocrine glands that secrete sex-related hormones and produce sperm cells.
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| testosterone | A male sex hormone.
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| thalamus | The part of the forebrain that primarily routes sensory messages to appropriate parts of the brain.
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| thyroid gland | The gland below the voice box that regulates metabolism.
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| thyroxin | A hormone produced by the thyroid that is necessary for proper mental development in children and helps determine weight and level of activity in adults.
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| Wernicke's aphasia | A form of aphasia in which persons can speak normally but cannot make sense out of language spoken to them by others.
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| Wernicke's area | The language area of the cortex that plays an essential role in understanding spoken language.
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| zygote | The stable cell resulting from fertilization; in humans, it has 46 chromosomes-23 from the sperm and 23 from the ovum.
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2002 McGraw-Hill Higher Education