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acetylcholine (ACh)
The neurotransmitter responsible for motor control at the junction between nerves and muscles; it is also involved in mental processes such as learning, memory, sleeping, and dreaming. (page 78)
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action potential
The electrical signal that passes along the axon and subsequently causes the release of chemicals from the terminal buttons. (page 72)
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all-or-none principle
The principle that when a neuron fires, it fires with the same potency each time; a neuron either fires or not—it cannot partially fire, although the frequency of firing can vary. (page 75)
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amygdala
A brain structure that serves a vital role in learning to associate things with emotional responses and in processing emotional information. (page 86)
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autonomic nervous system (ANS)
A component of the peripheral nervous system; it transmits sensory signals and motor signals between the central nervous system and the body's glands and internal organs. (page 98)
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axon
A long, narrow outgrowth of a neuron by which information is conducted from the cell body to the terminal buttons. (page 71)
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basal ganglia
A system of subcortical structures that are important for the planning and production of movement. (page 87)
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brain stem
An extension of the spinal cord; it houses structures that control functions associated with survival, such as heart rate, breathing, swallowing, vomiting, urination, and orgasm. (page 84)
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Broca's area
A small portion of the left frontal region of the brain, crucial for the production of language. (page 82)
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cell body
The site in the neuron where information from thousands of other neurons is collected and integrated. (page 71)
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central nervous system (CNS)
The brain and the spinal cord. (page 70)
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cerebellum
A large, convoluted protuberance at the back of the brain stem; it is essential for coordinated movement and balance. (page 84)
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cerebral cortex
The outer layer of brain tissue, which forms the convoluted surface of the brain; the site of all thoughts, perceptions, and complex behaviors. (page 87)
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chromosomes
Structures within the cell body that are made up of DNA, segments of which comprise individual genes. (page 106)
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corpus callosum
A massive bridge of millions of axons that connects the hemispheres and allows information to flow between them. (page 87)
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dendrites
Branchlike extensions of the neuron that detect information from other neurons. (page 71)
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dizygotic twins
Also called fraternal twins; twin siblings that result from two separately fertilized eggs and therefore are no more similar genetically than non-twin siblings. (page 111)
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dominant gene
A gene that is expressed in the offspring whenever it is present. (page 108)
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dopamine
A monoamine neurotransmitter involved in motivation, reward, and motor control over voluntary movement. (page 79)
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electroencephalograph (EEG)
A device that measures electrical activity in the brain. (page 82)
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endocrine system
A communication system that uses hormones to influence thoughts, behaviors, and actions. (page 99)
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endorphins
Neurotransmitters involved in natural pain reduction and reward. (page 80)
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frontal lobes
Regions of the cerebral cortex—at the front of the brain—important for movement and higher-level psychological processes associated with the prefrontal cortex. (page 84)
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functional magnetic resonance imaging (fMRI)
An imaging technique used to examine changes in the activity of the working human brain by measuring changes in the blood's oxygen levels. (page 84)
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GABA
Gamma-aminobutyric acid; the primary inhibitory transmitter in the nervous system. (page 80)
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gene expression
Whether a particular gene is turned on or off. (page 106)
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genes
The units of heredity that help determine the characteristics of an organism. (page 106)
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genotype
The genetic constitution of an organism, determined at the moment of conception. (page 108)
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glutamate
The primary excitatory transmitter in the nervous system. (page 80)
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gonads
The main endocrine glands involved in sexual behavior: in males, the testes; in females, the ovaries. (page 100)
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heredity
Transmission of characteristics from parents to offspring through genes. (page 113)
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heritability
A statistical estimate of the extent to which variation in a trait within a population is due to genetics. (page 113)
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hippocampus
A brain structure that is associated with the formation of memories. (page 86)
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hormones
Chemical substances, released from endocrine glands, that travel through the bloodstream to targeted tissues; the tissues are subsequently influenced by the hormones. (page 99)
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hypothalamus
A brain structure that is involved in the regulation of bodily functions, including body temperature, body rhythms, blood pressure, and blood glucose levels; it also influences our basic motivated behaviors. (page 86)
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magnetic resonance imaging (MRI)
A method of brain imaging that uses a powerful magnetic field to produce high-quality images of the brain. (page 83)
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monozygotic twins
Also called identical twins; twin siblings that result from one zygote splitting in two and therefore share the same genes. (page 111)
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myelin sheath
A fatty material, made up of glial cells, that insulates some axons to allow for faster movement of electrical impulses along the axon. (page 74)
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neurons
The basic units of the nervous system; cells that receive, integrate, and transmit information in the nervous system. They operate through electrical impulses, communicate with other neurons through chemical signals, and form neural networks. (page 70)
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neurotransmitters
Chemical substances that transmit signals from one neuron to another. (page 75)
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nodes of Ranvier
Small gaps of exposed axon, between the segments of myelin sheath, where action potentials take place. (page 74)
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norepinephrine
A monoamine neurotransmitter involved in states of arousal and attention. (page 79)
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occipital lobes
Regions of the cerebral cortex—at the back of the brain—important for vision. (page 88)
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parasympathetic division
A division of the autonomic nervous system; it returns the body to its resting state. (page 99)
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parietal lobes
Regions of the cerebral cortex—in front of the occipital lobes and behind the frontal lobes—important for the sense of touch and for attention to the environment. (page 88)
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peripheral nervous system (PNS)
All nerve cells in the body that are not part of the central nervous system. The peripheral nervous system includes the somatic and autonomic nervous systems. (page 70)
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phenotype
Observable physical characteristics, which result from both genetic and environmental influences. (page 108)
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pituitary gland
A gland located at the base of the hypothalamus; it sends hormonal signals to other endocrine glands, controlling their release of hormones. (page 99)
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plasticity
A property of the brain that allows it to change as a result of experience or injury. (page 101)
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positron emission tomography (PET)
A method of brain imaging that assesses metabolic activity by using a radioactive substance injected into the bloodstream. (page 83)
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prefrontal cortex
The frontmost portion of the frontal lobes, especially prominent in humans; important for attention, working memory, decision making, appropriate social behavior, and personality. (page 90)
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receptors
In neurons, specialized protein molecules on the postsynaptic membrane; neurotransmitters bind to these molecules after passing across the synapse. (page 76)
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recessive gene
A gene that is expressed only when it is matched with a similar gene from the other parent. (page 108)
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resting membrane potential
The electrical charge of a neuron when it is not active. (page 72)
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reuptake
The process whereby a neurotransmitter is taken back into the presynaptic terminal buttons, thereby stopping its activity. (page 77)
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serotonin
A monoamine neurotransmitter important for a wide range of psychological activity, including emotional states, impulse control, and dreaming. (page 79)
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somatic nervous system (SNS)
A component of the peripheral nervous system; it transmits sensory signals and motor signals between the central nervous system and the skin, muscles, and joints. (page 97)
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split brain
A condition that occurs when the corpus callosum is surgically cut and the two hemispheres of the brain do not receive information directly from each other. (page 92)
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sympathetic division
A division of the autonomic nervous system; it prepares the body for action. (page 98)
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synapse
The gap between the terminal buttons of a "sending" neuron and the dendrites of a "receiving" neuron; the site at which chemical communication occurs between neurons. (page 72)
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temporal lobes
Regions of the cerebral cortex—below the parietal lobes and in front of the occipital lobes—important for processing auditory information, for memory, and for object and face perception. (page 90)
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terminal buttons
At the ends of axons, small nodules that release chemical signals from the neuron into the synapse. (page 72)
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thalamus
The gateway to the brain; it receives almost all incoming sensory information before that information reaches the cortex. (page 86)
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transcranial magnetic stimulation (TMS)
The use of strong magnets to briefly interrupt normal brain activity as a way to study brain regions. (page 84)
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