| Acetylcholine | A neurotransmitter that, among its functions, triggers muscle contraction. |
| Action Potential | A neural impulse; a brief electrical charge that travels down an axon. It is generated by the movement of positively charged atoms in and out of channels in the axon's membrane. |
| Adrenal Glands | A pair of endocrine glands just above the kidneys. They secrete the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which help to arouse the body in times of stress. |
| Agonist | A chemical that mimics the action of a neurotransmitter. |
| All or None Law | Either the neuron fires or it doesn't, and its action potentials are all the same size. That is, weaker stimuli do not produce smaller action potentials. |
| Amygdala | Two almond-shaped neural clusters that are components of the limbic system and are linked to emotion, especially fear and aggression. |
| Antagonist | A chemical that opposes the action of a neurotransmitter. |
| Aphasia | Impairment of language, usually caused by left hemisphere damage either to Broca's area (impairing speaking) or to Wernicke's area (impairing understanding). |
| Association Areas | Areas of the cerebral cortex that are not involved in primary motor or sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking, and speaking. |
| Autonomic Nervous System | The part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasympathetic division calms. |
| Axon | The extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands. |
| Basilar Membrane | Runs the length of the spiraled cochlea, holds the auditory receptors. |
| Behavioral Genetics | The study of the relative power and limits of genetic and environmental influences on behavior. |
| Biological Psychology | A branch of psychology concerned with the links between biology and behavior. |
| Brainstem | The oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; it is responsible for automatic survival functions. |
| Broca's Area | Controls language expression - an area of the frontal lobe, usually in the left hemisphere, that directs the muscle movements involved in speech. |
| Cell Body | The soma contains the cell nucleus and much of the chemical machinery common to most cells. (soma is Greek for "body") |
| Central Nervous System | The brain and the spinal cord. |
| Cerebellum | The "little brain" attached to the rear of the brainstem; it helps coordinate voluntary movement and balance. |
| Cerebral Cortex | The intricate fabric of interconnected neural cells that covers the cerebral hemispheres; the body's ultimate control and information-processing center. |
| Chromosomes | Threadlike structures made of DNA molecules that contain the genes. |
| Corpus Callosum | The large band of neural fibers connecting the two brain hemispheres and carrying messages between them. |
| CT Scan | (computed tomography) - A series of x-ray photographs taken from different angles and combined by computer into a composite representation of a slice through the body. Also called CAT scan. |
| Dendrite | The bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body. |
| DNA | (deoxyribonucleic acid) - A complex molecule containing the genetic information that makes up the chromosomes. (A molecule has two strands - forming a "double helix" - held together by bonds between pairs of nucleotides.) |
| Dopamine | Contributes to control of voluntary movement, pleasurable emotions. Decreased levels associated with Parkinson's Disease. Over activity associated with Schizophrenia. |
| Eardrum | The thin, semitransparent, oval-shaped membrane that separates the middle ear from the external ear. |
| Electroencephalogram | (EEG) - An amplified recording of the waves of electrical activity that sweep across the brain's surface. These waves are measured by electrodes placed on the scalp. |
| Endocrine System | The body's "slow" chemical communication system; a set of glands that secrete hormones into the bloodstream. |
| Endorphins | "Morphine within" - Natural, opiate-like neurotransmitters linked to pain control and to pleasure. |
| Environment | Every nongenetic influence, from prenatal nutrition to the people and things around us. |
| Evolutionary Psychology | The study of behavior and the mind using principles of natural selection. Natural selection has favored genes that designed both behavioral tendencies and information-processing systems that solved adaptive problems faced by our ancestors, thus contributing to the survival and spread of their genes. |
| Excitatory PSP | A positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials. |
| fMRI | (functional magnetic resonance imagining) - Consists of several new variations on MRI technology that monitor blood and oxygen flow in the brain to identify areas of high activity. |
| Forebrain | The largest and most complex region of the brain, encompassing a variety of structures, including the thalamus, hypothalamus, limbic system, and cerebrum. |
| Fraternal Twins | Twins who develop from separate eggs. They are genetically no closer than brothers and sisters, but they share a fetal environment. |
| Frontal Lobes | The portion of the cerebral cortex lying just behind the forehead; involved in speaking and muscle movements and in making plans and judgments. |
| GABA | (gamma aminobutyric acid) - Serves as a widely distributed inhibitory transmitter. Valium and similar antianxiety drugs work at its synapses. |
| Gender | In psychology, the characteristics, whether biologically or socially influenced, by which people define male or female. |
| Gene | The biochemical units of heredity that make up the chromosomes; a segment of DNA capable of synthesizing a protein. |
| Genome | The complete instructions for making an organism, consisting of all the genetic material in its chromosomes. |
| Genotype | Refers to a person's genetic makeup. |
| Glial Cells | Cells in the nervous system that support, nourish, and protect neurons. |
| Heritability | The proportion of variation among individuals that we can attribute to genes. |
| Hindbrain | Includes the cerebellum and two structures found in the lower part of the brainstem; the medulla and the pons. |
| Hippocampus | A neural center located in the limbic system that helps process explicit memories for storage. Damage may result in the lose of ability to store new facts. |
| Homeostasis | A tendency to maintain a balanced or constant internal state; the regulation of any aspect of body chemistry, such as blood glucose, around a particular level. |
| Hormones | Chemical messengers, mostly those manufactured by the endocrine glands, that are produced in one tissue and affect another. |
| Hypothalamus | A neural structure that directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system via the pituitary gland, and is linked to emotion. |
| Identical Twins | Twins who develop from a single fertilized egg that splits in two, creating two genetically identical organisms. |
| Inhibitory PSP | A negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials. |
| Interaction | The dependence of the effect of one factor (such as environment) on another factor (such as heredity). |
| Interneurons | Central nervous system neurons that internally communicate and intervene between the sensory inputs and motor outputs. |
| Lesion | Tissue destruction. In the brain - is a naturally or experimentally caused destruction of brain tissue. |
| Limbic System | A doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres; associated with emotions such as fear and aggression and drives such as those for food and sex. Includes the hippocampus, amygdala, septum, and hypothalamus. |
| Medulla | The base of the brainstem; controls heartbeat and breathing. |
| Midbrain | The segment of the brainstem that lies between the hindbrain and the forebrain. Running through the hindbrain and the midbrain is the reticular formation. |
| Molecular Genetics | The subfield of biology that studies the molecular structure and function of genes. |
| Motor Cortex | An area at the rear of the frontal lobes that controls voluntary movements. |
| Motor Neurons | Efferent neurons that carry outgoing information from the central nervous system to the muscles and glands. |
| MRI | (magnetic resonance imaging) - A technique that uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of soft tissue; allows us to see structures within the brain. |
| Mutation | A random error in gene replication that leads to a change in the sequence of nucleotides; the source of all genetic diversity. |
| Myelin Sheath | A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next. |
| Natural Selection | The principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations. |
| Nerves | Neural "cables" containing many axons. These bundled axons, which are part of the peripheral nervous system, connect the central nervous system with muscles, glands, and sense organs. |
| Nervous System | The body's speedy, electrochemical communication system, consisting of all the nerve cells of the peripheral and central nervous systems. |
| Neural Networks | Interconnected neural cells. |
| Neuron | A nerve cell; the basic building block of the nervous system. |
| Neurotransmitters | Chemical messengers that traverse the synaptic gaps between neurons. When released by the sending neuron, they travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse. |
| Norepinephrine | Contributes to modulation of mood and arousal. |
| Occipital Lobes | The portion of the cerebral cortex lying at the back of the head; includes the visual areas, which receive visual information from the opposite visual field. |
| Parasympathetic Nervous System | The division of the autonomic nervous system that calms the body, conserving its energy. |
| Parietal Lobes | The portion of the cerebral cortex lying at the top of the head and toward the rear; includes the sensory cortex. |
| Peripheral Nervous System | The sensory and motor neurons that connect the central nervous system to the rest of the body. |
| PET Scan | (positron emission tomography) - A visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task. |
| Phenotype | Refers to the ways in which a person's genotype is manifested in observable characteristics. |
| Pituitary Gland | The endocrine system's most influential gland. Under the influence of the hypothalamus, it regulates growth and controls other endocrine glands. |
| Plasticity | The brain's capacity for modification, as evident in brain reorganization following damage (especially in children) and in experiments on the effects of experience on brain development. |
| Pons | Includes a bridge of fibers that connects the brainstem with the cerebellum. It also contains several clusters of cell bodies involved with sleep and arousal. |
| Receptors | Proteins on a cell membrane that receive chemical signals. |
| Reflex | A simple, automatic, inborn response to a sensory stimulus, such as the knee-jerk response. |
| Refractory Period | The minimum length of time after an action potential during which another action potential cannot begin. (1 or 2 milliseconds) |
| Resting Potential | A neuron's stable, negative charge when the cell is inactive. |
| Reticular Formation | A nerve network in the brainstem that plays an important role in controlling arousal. |
| Sensory Cortex | The area at the front of the parietal lobes that registers and processes body sensations. |
| Sensory Neurons | Afferent neurons that carry incoming information from the sense receptors to the central nervous system. |
| Septum | A part of the limbic system that is involved in pleasure and the restraint of aggression. |
| Serotonin | Involved in regulation of sleep and wakefulness, eating, aggression. Abnormal levels may contribute to depression and obsessive-compulsive disorder. |
| Somatic Nervous System | The division of the peripheral nervous system that controls the body's skeletal muscles. Also called the skeletal nervous system. |
| Somatic Neurons | Afferent nerve fibers that carry information inward to the central nervous system from the periphery of the body. |
| Spinal Cord | Part of the central nervous system that relays signals from peripheral senses to the brain and conveys messages from the brain to the rest of the body. |
| Split Brain | A condition in which the two hemispheres of the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them. |
| Sympathetic Nervous System | The division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations. |
| Synapse | The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. |
| Temperament | A person's characteristic emotional reactivity and intensity. |
| Temporal Lobes | The portion of the cerebral cortex lying roughly above the ears; includes the auditory areas, each of which receives auditory information primarily from the opposite ear. |
| Thalamus | The brain's sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla. |
| Threshold | The level of stimulation required to trigger a neural impulse. |
| Wernicke's Area | Controls language reception - a brain area involved in language comprehension and expression; usually in the left temporal lobe. |
| X Chromosome | The sex chromosome found in both men and women. Females have two; males have one. One from each parent produces a female child. |
| Y Chromosome | The sex chromosome found only in males. When paired with the sex chromosome from the mother, it produces a male child. |