B Spot Brain Glossary
ACETYLCHOLINE A neurotransmitter active both in the brain,
where it regulates memory, and in the peripheral nervous system,
where it controls the actions of skeletal and smooth muscle.
ACTION POTENTIAL An electrical charge that travels along the
axon to the neuron’s terminal, where it triggers the release of a
neurotransmitter. This occurs when a neuron is activated and temporarily
reverses the electrical state of its interior membrane from
negative to positive.
ADRENAL CORTEX An endocrine organ that secretes steroid hormones
for metabolic functions; for example, in response to stress.
ADRENAL MEDULLA An endocrine organ that secretes epinephrine
and norepinephrine in concert with the activation of the
sympathetic nervous system; for example, in response to stress.
AGONIST 1.) A neurotransmitter, drug, or other molecule that
stimulates receptors to produce a desired reaction. 2.) A muscle
that moves a joint in an intended direction.
ALZHEIMER’S DISEASE A major cause of dementia in the elderly,
this neurodegenerative disorder is characterized by the death of neurons
in the hippocampus, cerebral cortex, and other brain regions.
AMINO ACID TRANSMITTERS The most prevalent neurotransmitters
in the brain, these include glutamate and aspartate, which have
excitatory actions on nerve cells, and glycine and gamma-amino
butyric acid (GABA), which have inhibitory actions on nerve cells.
AMYGDALA A structure in the forebrain that is an important component
of the limbic system and plays a central role in emotional
learning, particularly within the context of fear.
ANDROGENS Sex steroid hormones, including testosterone, found
in higher levels in males than females. They are responsible for
male sexual maturation.
ANTAGONIST 1.) A drug or other molecule that blocks receptors.
Antagonists inhibit the effects of agonists. 2.) A muscle that moves
a joint in opposition to an intended direction.
APHASIA Disturbance in language comprehension or production,
often as a result of a stroke.
APOPTOSIS Programmed cell death induced by specialized biochemical
pathways, often serving a specific purpose in the development
of the animal.
AUDITORY NERVE A bundle of nerve fibers extending from the
cochlea of the ear to the brain that contains two branches: the cochlear
nerve, which transmits sound information, and the vestibular
nerve, which relays information related to balance.
AUTONOMIC NERVOUS SYSTEM A part of the peripheral nervous
system responsible for regulating the activity of internal organs.
It includes the sympathetic and parasympathetic nervous systems.
AXON The fiberlike extension of a neuron by which it sends information
to target cells.
BASAL GANGLIA Structures located deep in the brain that play
an important role in the initiation of movements. These clusters of
neurons include the caudate nucleus, putamen, globus pallidus, and
substantia nigra. Cell death in the substantia nigra contributes to
BRAINSTEM The major route by which the forebrain sends
information to and receives information from the spinal cord and
peripheral nerves. The brainstem controls, among other things,
respiration and the regulation of heart rhythms.
BROCA’S AREA The brain region located in the frontal lobe of the
left hemisphere that is important for the production of speech.
CATECHOLAMINES The neurotransmitters dopamine, epinephrine,
and norepinephrine, which are active in both the brain and
the peripheral sympathetic nervous system. These three molecules
have certain structural similarities and are part of a larger class of
neurotransmitters known as monoamines.
CEREBELLUM A large structure located at the roof of the hindbrain
that helps control the coordination of movement by making connections
to the pons, medulla, spinal cord, and thalamus. It also
may be involved in aspects of motor learning.
CEREBRAL CORTEX The outermost layer of the cerebral hemispheres
of the brain. It is largely responsible for all forms of conscious
experience, including perception, emotion, thought, and planning.
CEREBRAL HEMISPHERES The two specialized halves of the brain.
For example, in right-handed people, the left hemisphere is specialized
for speech, writing, language, and calculation; the right hemisphere
is specialized for spatial abilities, visual face recognition, and
some aspects of music perception and production.
CEREBROSPINAL FLUID A liquid found within the ventricles of
the brain and the central canal of the spinal cord.
CIRCADIAN RHYTHM A cycle of behavior or physiological change
lasting approximately 24 hours.
CLASSICAL CONDITIONING Learning in which a stimulus that
naturally produces a specific response (unconditioned stimulus) is
repeatedly paired with a neutral stimulus (conditioned stimulus).
As a result, the conditioned stimulus can come to evoke a response
similar to that of the unconditioned stimulus.
COCHLEA A snail-shaped, fluid-filled organ of the inner ear responsible
for converting sound into electrical potentials to produce
an auditory sensation.
COGNITION The process or processes by which an organism gains
knowledge or becomes aware of events or objects in its environment
and uses that knowledge for comprehension and problem-solving.
CONE A primary receptor cell for vision located in the retina. It is
sensitive to color and is used primarily for daytime vision.
CORPUS CALLOSUM The large bundle of nerve fibers linking the
left and right cerebral hemispheres.
CORTISOL A hormone manufactured by the adrenal cortex. In
humans, cortisol is secreted in the greatest quantities before dawn,
readying the body for the activities of the coming day.
CRANIAL NERVE A nerve that carries sensory input and motor
output for the head and neck region. There are 12 cranial nerves.
DEPRESSION A mental disorder characterized by sadness, hopelessness,
pessimism, loss of interest in life, reduced emotional wellbeing,
and abnormalities in sleep, appetite, and energy level.
DENDRITE A treelike extension of the neuron cell body. The dendrite
is the primary site for receiving and integrating information
from other neurons.
DOPAM INE A catecholamine neurotransmitter known to have
varied functions depending on where it acts. Dopamine-containing
neurons in the substantia nigra of the brainstem project to the caudate
nucleus and are destroyed in Parkinson’s victims. Dopamine
is thought to regulate key emotional responses and plays a role in
schizophrenia and drug abuse.
DORSAL HORN An area of the spinal cord where many nerve
fibers from peripheral sensory receptors meet other ascending and
descending nerve fibers.
DRUG ADDICTION Loss of control over drug intake or compulsive
seeking and taking of drugs, despite adverse consequences.
ENDOCRINE ORGAN An organ that secretes a hormone directly
into the bloodstream to regulate cellular activity of certain
ENDORPHINS Neurotransmitters produced in the brain that generate
cellular and behavioral effects like those of morphine.
EPILEPSY A disorder characterized by repeated seizures, which are
caused by abnormal excitation of large groups of neurons in various
brain regions. Epilepsy can be treated with many types of anticonvulsant
EPINEPHRINE A hormone, released by the adrenal medulla and
specialized sites in the brain, that acts with norepinephrine to affect
the sympathetic division of the autonomic nervous system. Sometimes
ESTROGENS A group of sex hormones found more abundantly in
females than males. They are responsible for female sexual maturation
and other functions.
EVOKED POTENTIAL A measure of the brain’s electrical activity in
response to sensory stimuli. This is obtained by placing electrodes
on the surface of the scalp (or more rarely, inside the head), repeatedly
administering a stimulus, and then using a computer to average
EXCITATION A change in the electrical state of a neuron that is
associated with an enhanced probability of action potentials.
FOLLICLE-STIMULATING HORMONE A hormone released
by the pituitary gland that stimulates the production of sperm in
the male and growth of the follicle (which produces the egg) in
FOREBRAIN The largest part of the brain, which includes the
cerebral cortex and basal ganglia. The forebrain is credited with the
highest intellectual functions.
FOVEA The centermost part of the eye located in the center of the
retina and that contains only cone photoreceptors.
FRONTAL LOBE One of the four subdivisions of the cerebral cortex.
The frontal lobe has a role in controlling movement and in the
planning and coordinating of behavior.
GAMMA-AMINO BUTYRIC ACID (GABA) An amino acid transmitter
in the brain whose primary function is to inhibit the firing of
GLIA Specialized cells that nourish and support neurons.
GLUTAMATE An amino acid neurotransmitter that acts to excite
neurons. Glutamate stimulates N-methyl-d-aspartate (NMDA)
and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid
(AMPA). AMPA receptors have been implicated in activities ranging
from learning and memory to development and specification
of nerve contacts in developing animals. Stimulation of NMDA
receptors may promote beneficial changes, whereas overstimulation
may be a cause of nerve cell damage or death in neurological
trauma and stroke.
GONAD Primary sex gland: testis in the male and ovary in
GROWTH CONE A distinctive structure at the growing end of
most axons. It is the site where new material is added to the axon.
HAIR CELLS Sensory receptors in the cochlea that convert mechanical
vibration to an electrical signal; they in turn excite
the 30,000 fibers of the auditory nerve that carry the signals to
HIPPOCAMPUS A seahorse-shaped structure located within the
brain and considered an important part of the limbic system. One
of the most studied areas of the brain, it functions in learning,
memory, and emotion.
HOMEOSTASIS The normal equilibrium of body function.
HORMONES Chemical messengers secreted by endocrine glands
to regulate the activity of target cells. They play a role in sexual
development, calcium and bone metabolism, growth, and many
HUNTINGTON’S DISEASE A movement disorder caused by the
death of neurons in the basal ganglia and other brain regions. It is
characterized by abnormal movements called chorea — sudden,
jerky movements without purpose.
HYPOTHALAMUS A complex brain structure composed of many
nuclei with various functions, including regulating the activities
of internal organs, monitoring information from the autonomic
nervous system, controlling the pituitary gland, and regulating sleep
INTERNEURON A neuron that exclusively signals another neuron.
INHIBITION A synaptic message that prevents a recipient neuron
IONS Electrically charged atoms or molecules.
LIMBIC SYSTEM A group of brain structures — including the
amygdala, hippocampus, septum, basal ganglia, and others — that
help regulate the expression of emotion and emotional memory.
LONG-TERM MEMORY The final phase of memory, in which
information storage may last from hours to a lifetime.
MANIA A mental disorder characterized by excessive excitement,
exalted feelings, elevated mood, psychomotor overactivity, and
overproduction of ideas. It may be associated with psychosis; for
example, delusions of grandeur.
MEMORY CONSOLIDATION The physical and psychological
changes that take place as the brain organizes and restructures
information to make it a permanent part of memory.
METABOLISM The sum of all physical and chemical changes that
take place within an organism and all energy transformations that
occur within living cells.
MIDBRAIN The most anterior segment of the brainstem. With the
pons and medulla, the midbrain is involved in many functions,
including regulation of heart rate, respiration, pain perception,
MITOCHONDRIA Small cylindrical organelles inside cells that provide
energy for the cell by converting sugar and oxygen into special
energy molecules, called adenosine triphosphate (ATP).
MONOAMINE OXIDASE (MAO) The brain and liver enzyme
that normally breaks down the catecholamines norepinephrine,
dopamine, and epinephrine, as well as other monoamines such
MOTOR NEURON A neuron that carries information from the
central nervous system to muscle.
MYASTHENIA GRAV IS A disease in which acetylcholine receptors
on muscle cells are destroyed so that muscles can no longer respond
to the acetylcholine signal to contract. Symptoms include muscular
weakness and progressively more common bouts of fatigue. The
disease’s cause is unknown but is more common in females than in
males; it usually strikes between the ages of 20 and 50.
MYELIN Compact fatty material that surrounds and insulates the
axons of some neurons.
NMDA RECEPTORS N-methyl-d-aspartate (NMDA) receptors,
one of three major classes of glutamate receptors, which have been
implicated in activities ranging from learning and memory to development
and specification of nerve contacts in a developing animal.
NECROSIS Cell death due to external factors, such as lack of
oxygen or physical damage, that disrupt the normal biochemical
processes in the cell.
NERVE GROWTH FACTOR A substance whose role is to guide
neuronal growth during embryonic development, especially in the
peripheral nervous system. Nerve growth factor also probably helps
sustain neurons in the adult.
NEURON A nerve cell specialized for the transmission of information
and characterized by long, fibrous projections called axons and
shorter, branchlike projections called dendrites.
NEUROPLASTICITY A general term used to describe the adaptive
changes in the structure or function of nerve cells or groups of
nerve cells in response to injuries to the nervous system or alterations
in patterns of their use and disuse.
NEUROTRANSMITTER A chemical released by neurons at a synapse
for the purpose of relaying information to other neurons
NOCICEPTORS In animals, nerve endings that signal the sensation
of pain. In humans, they are called pain receptors.
NOREPINEPHRINE A catecholamine neurotransmitter, produced
both in the brain and in the peripheral nervous system. Norepinephrine
is involved in arousal and in regulation of sleep, mood,
and blood pressure.
OCCIPITAL LOBE One of the four subdivisions of the cerebral cortex.
The occipital lobe plays a role in processing visual information.
OLFACTORY BULB A round, knoblike structure of the brain
responsible for processing the sense of smell. Specialized olfactory
receptor cells are located in a small patch of mucous membrane lining
the roof of the nose. Axons of these sensory cells pass through
perforations in the overlying bone and enter two elongated olfactory
bulbs lying on top of the bone.
ORGANELLES Small structures within a cell that maintain the cell
and do the cell’s work.
PA RASYMPA THETIC NERVOUS SYSTEM A branch of the autonomic
nervous system concerned with the conservation of the
body’s energy and resources during relaxed states.
PA RIETAL LOBE One of the four subdivisions of the cerebral cortex.
The parietal lobe plays a role in sensory processes, attention, and
PA RKINSON’S DISEASE A movement disorder caused by death of
dopamine neurons in the substantia nigra, located in the midbrain.
Symptoms include tremor, shuffling gait, and general reduction in
PEPTIDES Chains of amino acids that can function as neurotransmitters
PERIPHERAL NERVOUS SYSTEM A division of the nervous system
consisting of all nerves that are not part of the brain or spinal cord.
PHOSPHORYLATION Transfer of a phosphate molecule from adenosine
triphosphate (ATP) to a protein (ion channel, neurotransmitter
receptor, or other regulatory protein), resulting in activation
or inactivation of the protein. Phosphorylation is believed to be
a necessary step in allowing some neurotransmitters to act and is
often the result of second-messenger activity.
PHOTORECEPTOR A nerve ending, cell, or group of cells specialized
to sense or receive light.
PITUITARY GLAND An endocrine organ closely linked with the
hypothalamus. In humans, the pituitary gland is composed of two
lobes and secretes several different hormones that regulate the
activity of other endocrine organs throughout the body.
PONS A part of the hindbrain that, with other brain structures,
controls respiration and regulates heart rhythms. The pons is a major
route by which the forebrain sends information to and receives
information from the spinal cord and peripheral nervous system.
PSYCHOSIS A severe symptom of mental disorders characterized
by an inability to perceive reality. Psychosis can occur in many
conditions, including schizophrenia, mania, depression, and druginduced
RECEPTOR CELL A specialized sensory cell, designed to pick up and
transmit sensory information.
RECEPTOR MOLECULE A specific protein on the surface of or
inside a cell with a characteristic chemical and physical structure.
Many neurotransmitters and hormones exert their effects by binding
to receptors on cells.
RETINA A multilayered sensory tissue that lines the back of the eye
and contains the receptor cells to detect light.
REUPTAKE A process by which released neurotransmitters are
absorbed for later reuse.
ROD A sensory neuron located in the periphery of the retina. The
rod is sensitive to light of low intensity and is specialized for nighttime
SCHIZOPHRENIA A chronic mental disorder characterized by
psychosis (e.g., hallucinations and delusions), flattened emotions,
and impaired cognitive function.
SECOND MESSENGERS Substances that trigger communications
among different parts of a neuron. These chemicals play a role in
the manufacture and release of neurotransmitters, intracellular
movements, carbohydrate metabolism, and processes of growth and
development. The messengers’ direct effects on the genetic material
of cells may lead to long-term alterations of behavior, such as
memory and drug addiction.
SEROTONIN A monoamine neurotransmitter believed to play
many roles, including but not limited to temperature regulation,
sensory perception, and the onset of sleep. Neurons using serotonin
as a transmitter are found in the brain and gut. Several antidepressant
drugs are targeted to brain serotonin systems.
SHORT-TERM MEMORY A phase of memory in which a limited
amount of information may be held for several seconds or minutes.
STEM CELL Unspecialized cells that renew themselves for long
periods through cell division.
STIMULUS An environmental event capable of being detected by
STROKE A block in the brain’s blood supply. A stroke can be
caused by the rupture of a blood vessel, a clot, or pressure on a blood
vessel (as by a tumor). Without oxygen, neurons in the affected
area die and the part of the body controlled by those cells cannot
function. A stroke can result in loss of consciousness and death.
SYMPA THETIC NERVOUS SYSTEM A branch of the autonomic
nervous system responsible for mobilizing the body’s energy and
resources during times of stress and arousal.
SYNAPSE A physical gap between two neurons that functions as
the site of information transfer from one neuron to another.
TASTE BUD A sensory organ found on the tongue.
TEMPORAL LOBE One of the four major subdivisions of each
hemisphere of the cerebral cortex. The temporal lobe functions in
auditory perception, speech, and complex visual perceptions.
THALAMUS A structure consisting of two egg-shaped masses of
nerve tissue, each about the size of a walnut, deep within the brain.
The key relay station for sensory information flowing into the
brain, the thalamus filters out information of particular importance
from the mass of signals entering the brain.
VENTRICLES Comparatively large spaces filled with cerebrospinal
fluid. Of the four ventricles, three are located in the forebrain and
one in the brainstem. The lateral ventricles, the two largest, are
symmetrically placed above the brainstem, one in each hemisphere.
WERNICKE’S AREA A brain region responsible for the comprehension
of language and the production of meaningful speech.
WHITE MATTER The part of the brain that contains myelinated
nerve fibers. The white matter is white because it is the color of
myelin, the insulation covering the nerve fibers.