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neuron
a nerve cell; the basic building block of the nervous system.
dendrites
a neuron's often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body.
axon
the neuron extension that passes messages through its branches to other neurons or to muscles or glands.
myelin sheath
a fatty tissue layer segmentally encasing the axons of some neurons; enables vastly greater transmission speed as neural impulses hop from one node to the next.
action potential
a neural impulse; a brief electrical charge that travels down an axon.
refractory period
in neural processing, a brief resting pause that occurs after a neuron has fired; subsequent action potentials cannot occur until the axon returns to its resting state.
threshold
the level of stimulation required to trigger a neural impulse.
all-or-none response
a neuron's reaction of either firing (with a full-strength response) or not firing.
synapse
the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft.
neurotransmitters
chemical messengers that cross the synaptic gaps between neurons.
reuptake
a neurotransmitter's reabsorption by the sending neuron.
endorphins
"morphine within"—natural, opiate-like neurotransmitters linked to pain control and to pleasure.
agonist
a molecule that increases a neurotransmitter's action.
antagonist
a molecule that inhibits or blocks a neurotransmitter's action.
nervous system
the body's speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.
central nervous system (CNS)
the brain and spinal cord.
peripheral nervous system (PNS)
the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.
nerves
bundled axons that form neural cables connecting the central nervous system with muscles, glands, and sense organs.
sensory (afferent) neurons
neurons that carry incoming information from the sensory receptors to the brain and spinal cord.
motor (efferent) neurons
neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.
interneurons
neurons within the brain and spinal cord; they communicate internally and process information between the sensory inputs and motor outputs.
somatic nervous system
the division of the peripheral nervous system that controls the body's skeletal muscles. Also called the skeletal nervous system.
autonomic nervous system (ANS)
the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart).
sympathetic nervous system
the division of the autonomic nervous system that arouses the body, mobilizing its energy.
parasympathetic nervous system
the division of the autonomic nervous system that calms the body, conserving its energy.
reflex
a simple, automatic response to a sensory stimulus, such as the knee-jerk response.
endocrine system
the body's "slow" chemical communication system; a set of glands that secrete hormones into the bloodstream.
hormones
chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.
adrenal glands
a pair of endocrine glands that sit just above the kidneys and secrete hormones (epinephrine and norepinephrine) that help arouse the body in times of stress.
pituitary gland
the endocrine system's most influential gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.
lesion
tissue destruction. A brain lesion is a naturally or experimentally caused destruction of brain tissue.
EEG (electroencephalogram)
an amplified recording of the waves of electrical activity sweeping across the brain's surface. These waves are measured by electrodes placed on the scalp.
CT (computed tomography) scan
a series of X-ray photographs taken from different angles and combined by computer into a composite representation of a slice of the brain's structure. (Also called CAT scan.)
PET (positron emission tomography) scan
a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task.
MRI (magnetic resonance imaging)
a technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. MRI scans show brain anatomy.
fMRI (functional MRI)
a technique for revealing bloodflow and, therefore, brain activity by comparing successive MRI scans. fMRI scans show brain function as well as its structure.
brainstem
the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.
medulla
the base of the brainstem; controls heartbeat and breathing.
thalamus
the brain's sensory control center, 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.
reticular formation
a nerve network that travels through the brainstem and thalamus and plays an important role in controlling arousal.
cerebellum
the "little brain" at the rear of the brainstem; functions include processing sensory input, coordinating movement output and balance, and enabling nonverbal learning and memory.
limbic system
neural system (including the amygdala, hypothalamus, and hippocampus) located below the cerebral hemispheres; associated with emotions and drives.
amygdala
two lima-bean-sized neural clusters in the limbic system; linked to emotion.
hypothalamus
a neural structure lying below the thalamus; it directs several maintenance activities, helps govern the endocrine system via the pituitary gland, and is linked to emotion and reward.
cerebral cortex
the intricate fabric of interconnected neural cells covering the cerebral hemispheres; the body's ultimate control and information-processing center.
glial cells (glia)
cells in the nervous system that support, nourish, and protect neurons; they also play a role in learning, thinking, and memory.
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.
parietal lobes
the portion of the cerebral cortex lying at the top of the head and toward the rear; receives sensory input for touch and body position.
occipital lobes
the portion of the cerebral cortex lying at the back of the head; includes areas that receive information from the visual fields.
temporal lobes
the portion of the cerebral cortex lying roughly above the ears; includes the auditory areas, each receiving information primarily from the opposite ear.
motor cortex
an area at the rear of the frontal lobes that controls voluntary movements.
somatosensory cortex
an area at the front of the parietal lobes that registers and processes body touch and movement sensations.
association areas
areas of the cerebral cortex that are not involved in primary motor or sensory functions.
plasticity
the brain's ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience.
neurogenesis
the formation of new neurons.
corpus callosum
the large band of neural fibers connecting the two brain hemispheres and carrying messages between them.
split brain
a condition resulting from surgery that isolates the brain's two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them.
consciousness
our subjective awareness of ourselves and our environment.
cognitive neuroscience
the interdisciplinary study of the brain activity linked with cognition (including perception, thinking, memory, and language).
dual processing
the principle that information is often simultaneously processed on separate conscious and unconscious tracks.
behavior genetics
the study of the relative power and limits of genetic and environmental influences on behavior.
environment
every nongenetic influence, from prenatal nutrition to the people and things around us.
chromosomes
threadlike structures made of DNA molecules that contain the genes.
DNA (deoxyribonucleic acid)
a complex molecule containing the genetic information that makes up the chromosomes.
genes
the biochemical units of heredity that make up the chromosomes; segments of DNA capable of synthesizing proteins.
genome
the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes.
identical (monozygotic) twins
develop from a single fertilized egg that splits in two, creating two genetically identical organisms.
fraternal twins (dizygotic twins)
develop from separate fertilized eggs. They are genetically no closer than ordinary brothers and sisters, but they share a prenatal environment.
molecular genetics
the subfield of biology that studies the molecular structure and function of genes.
heritability
the proportion of variation among individuals that we can attribute to genes. The heritability of a trait may vary, depending on the range of populations and environments studied.
interaction
the interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity).
epigenetics
"above" or "in addition to" (epi) genetics; the study of environmental influences on gene expression that occur without a DNA change.
evolutionary psychology
the study of the evolution of behavior and mind, using principles of natural selection.
natural selection
the principle that inherited traits that better enable an organism to survive and reproduce in a particular environment will most likely be passed on to succeeding generations.
mutation
a random error in gene replication that leads to a change.
cell body
the part of a neuron that contains the nucleus; the cell's life support center.
hippocampus
a neural center located in the limbic system; helps process for storage explicit (conscious) memories of facts and events.
MEG (magnetoencephalography)
a brain imaging technique that measures magnetic fields from the brain's natural electrical activity.
blindsight
a condition in which a person can respond to a visual stimulus without consciously experiencing it
parallel processing
processing many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions.
sequential processing
processing one aspect of a problem at a time; generally used to process new information or to solve difficult problems.
heredity
the genetic transfer of characteristics from parents to offspring.
molecular behavior genetics
the study of how the structure and function of genes interact with our environment to influence behavior.
social script
a culturally modeled guide for how to act in various situations.
consciousness
our subjective awareness of ourselves and our environment.
hypnosis
a social interaction in which one person (the hypnotist) suggests to another (the subject) that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur.
posthypnotic suggestion
a suggestion, made during a hypnosis session, to be carried out after the subject is no longer hypnotized; used by some clinicians to help control undesired symptoms and behaviors.
dissociation
a split in consciousness, which allows some thoughts and behaviors to occur simultaneously with others.
circadian rhythm
the biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occur on a 24-hour cycle.
REM sleep
rapid eye movement sleep; a recurring sleep stage during which vivid dreams commonly occur.
alpha waves
the relatively slow brain waves of a relaxed, awake state.
sleep
a periodic, natural loss of consciousness—as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation.
hallucinations
false sensory experiences, such as seeing something in the absence of an external visual stimulus.
delta waves
the large, slow brain waves associated with the deep sleep of NREM-3.
NREM sleep
non-rapid eye movement sleep; encompasses all sleep stages except for REM sleep.
suprachiasmatic nucleus (SCN)
a pair of cell clusters in the hypothalamus that controls circadian rhythm.
insomnia
recurring problems in falling or staying asleep.
narcolepsy
a sleep disorder characterized by uncontrollable sleep attacks. The sufferer may lapse directly into REM sleep, often at inopportune times.
sleep apnea
a sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings.
night terrors
a sleep disorder characterized by high arousal and an appearance of being terrified.
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