Absence seizure—form
of seizure consisting of momentary clouding of consciousness and awareness of
the person’s surroundings. These include petit
mal seizures in children
Acetylcholine—neurotransmitter
chemical released at the end of nerve cells
Akinetic—pertaining
to, characterized by, or causing akinesia
Alzheimer disease—brain
disorder marked by gradual and progressive mental deterioration (dementia),
personality changes, and impairment of daily function. Characteristics are
speech disturbance, restlessness, anxiety, depression. Genetic factors may be a
cause. A mutation on chromosomes 14 has been linked familial cases
Amyloid—a
protein. Deposit of amyloid occur in neruofibrillary tangles, senile plaque and
blood vessels in Alzheimer’s disease
Amyotrophic lateral
sclerosis—Lou Gehrig disease. Degenerative disorder of motor neurons in the
spinal cord and brainstem. Signs are weakness and atrophy muscles in hands,
forearms and legs; difficulty in swallowing and talking, dyspnea develop and
respiratory muscles become affected
Analgesia--
absence of sensibility to pain
Anencephaly—a
congenital brain malformation
Anesthesia—lack
of normal sensation such as absence of touch or pain. Two common types of anesthesia
are spinal and epidural block
Anesthetics—agents
that reduce or eliminate sensation. General and local
Aneurysm—enlarged,
weakened area in an arterial wall, which may rupture, leading to hemorrhages
and CVA (stroke)
Aphasia—difficult
with speech
Apraxia—movements
and behavior are not purposeful.
Arachnoid membrane—the
second layer of the meninges surrounding the brain and spinal cord. This spider
like membrane is loosely attached to the other meninges by web like fiber, so
there is a space for fluid between the fibers and the third membrane
Astrocytes cells—star
like in appearance and transport water and salts between capillaries and
neurons
Astrocytoma—malignant
tumor of astrocytes (glial brain cells)
Ataxia—condition
of decreased coordination. Persistent unsteadiness on the feet can be caused by
a disorder involving the cerebellum. Lack of muscular coordination
Aura—peculiar
sensation experienced by the affected person before onset of a seizure.
Dizziness, numbness and visual or olfactory disturbance are examples of aura.
Peculiar sensations that precede the onset of illness occurring before the
onset of an attack of migraine or epileptic seizure
Autonomic nervous
system—The peripheral nervous system also functions involuntarily and
automatically, without conscious control. This system of nerve fibers carries
impulses away from the central nervous system to the glands, heart, blood
vessels and involuntary muscles found in the walls of tubes like the intestines
and hollow organs such as stomach and urinary bladder. Some autonomic nerves
are sympathetic nerves and others are parasympathetic nerves.
Axon—extending
from the cell body, long process of a nerve fiber that generally conducts
impulses away/ along from the body of the nerve cell.
Basal ganglia—group
of cells that regulate intentional movements of the body
Bell palsy—paralysis
on one side of the face. The likely cause is a viral infection
Blood brain barrier—They
associates with blood vessels and regulate the passage of potentially harmful substances
from the blood into the nerve cells of the brain, consists of special lining
(endothelial) cells, which along with actrocytes separates capillaries from
nerve cells. Blood brain barrier blocks drug access to brain tissue in
chemotherapeutic drugs to treat brain tumors
Bradykinesia—abnormal
slowness of movement
Brain tumor—neoplastic
disorder, abnormal growth of brain tissue and meninges, most primary tumors
arise from glial cell (gliomas) or the meninges. Types of gliomas include
astrocytoma, oligodendroglioma and ependymoma. Tumor can cause swelling and
hydrocephalus
Brain—controls
body activities.
Brainstem—the
pons and medulla are part of the brainstem. Posterior portion of brain that
connects the cerebrum with the spinal cord
Cardiac center—slows
the heart rate when the heart is beating too rapidly
Cauda equine—below
the end of spinal cord, a fan of nerve fibers or collection of spinal nerves.
Bundle of spinal nerves below the end of the spinal cord.
Causalgia—intense
burning pain following injury to a sensory nerve
Cell body—contains
the cell nucleus, the part of a neuron containing the nucleus but not
incorporating the axon and dendrites. Also called soma
Central nervous
system—consists of brain and spinal cord
Cephalgia—headaches
may result from vasodilation of blood vessels in tissue surrounding the brain
or from tension in neck and scalp muscles
Cerebellar—Involving
the part of the brain (cerebellum), which controls walking, balance, and
coordination
Cerebellopontine—Referring
to the cerebellum and pons
Cerebellum, pons and
medulla oblongata—structure within the brain lie in the back and below the
cerebrum and connect the cerebrum with the spinal cord
Cerebellum—functions
to coordinate voluntary movements and to maintain balance and posture
Cerebra contusion—
type of traumatic disorder, bruising of brain tissue as a result of direct
trauma to the head. It is usually associated with a fracture of the skull, as
well as with edema and an increase in intracranial pressure.
Cerebral angiography—x
ray imaging of the arterial blood vessels in the brain after injection contrast
material. Diagnose vascular disease such as aneurysm, occlusion in the brain
Cerebral concussion—type
of traumatic brain injury caused by a blow to the head.
Cerebral cortex—
A thin mantle of gray matter about the size of a formal dinner napkin covering
the surface of each cerebral hemisphere. The cerebral cortex is crumpled and
folded, forming numerous convolutions (gyri) and crevices (sulci)
Cerebral edema—swelling
Cerebral hemispheres—the
brain is divided in half, a right side and left side, each hemisphere is
subdivided into four major lobes named for the cranial bones that overlie them.
These lobes are frontal, parietal, Occipital and temporal, as well as gryi and
sulci
Cerebral palsy—partial
paralysis and or lack of muscular coordination caused by loss of oxygen or
blood flow to the cerebrum during pregnancy
Cerebrospinal fluid
(CSF)—circulates throughout the brain and spinal cord
Cerebrospinal fluid
analysis—samples of CSF are examined. It measure protein, glucose, and red
and white blood cells. CSF can also detect tumor cell, bacteria and viruses.
These studies are used to diagnose infection, tumors or multiple sclerosis
Cerebrovascular
accident—vascular disorder, disruption in the normal blood supply to the
brain; stroke. This condition is also known as cerebral infarction, is the
result of impaired oxygen supply to the brain. There are three types of stroke;
thrombotic, embolic and hemorrhagic. The major risk of stroke is hypertension,
diabetes, smoking and heart disease
Cerebrum—largest
part of the brain, “thinking area”. on the surface of cerebrum, nerve cells lie
in sheath which make up cerebral cortex. Thought, judgment, memory, association
and discrimination are functions of cerebrum
Chorea—dance-like
Comatose—a coma
is state of unconsciousness from which the patient cannot be aroused.
Complex partial
seizure—common type, these patients have seizures that caused them to pause
in whatever they are doing and have memory problems
Computed tomography
of the brain—computerized x ray technique that generates multiple images of
the brain and spinal. It is useful for fracture, visualizing blood and bone,
bleeding and brain injury
Corpus callosum—lies
in the center of the brain and connects the two hemispheres
Cranial nerves—12
pairs of nerves that carry impulses between the brain and the head and neck.
The one exception is the 10th cranial nerve, called vagus nerve.
Cranial nerves carry motor impulses from the cerebrum to muscles and glands and
these produce movement and activity
Dementia—mental
decline and deterorization
Demyelination—loss
of myelin insulating the nerve fiber and characteristic of multiple sclerosis,
an acquired illness affecting the central nervous system. Destruction of myelin
on axons of neurons
Demyelination—loss
of myelin insulation, prevents the conduction of nerve impulses through the
axon and causes paresthesias, muscle weakness, unsteady gait and paralysis
Dendrites—are the
branched fiber/projection of a neuron that is the first part to receive the
nervous impulse and act to propagate the electrochemical stimulation received
from other neural cells to the cell body, or soma, of the neuron from which the
dendrites project. Electrical stimulation is transmitted onto dendrites by
upstream neurons (usually their axons) via synapses which are located at
various points throughout the dendritic tree. Dendrites play a critical role in
integrating these synaptic inputs and in determining the extent to which action
potentials are produced by the neuron.
Dopamine—CNS
neurotransmitter made by cells in the basal ganglia. Deficiency in patient with
Parkinson disease
Doppler ultrasound
studies—sound waves detect blood flow in the carotid and intracranial
arteries.
Dura mater—outermost
and toughest membrane of the meninges, this thick, rough membrane contains
channels (Dural sinuses) that contain blood. Subdural space, is below the Dural membrane
Dyskinesia—condition
marked by involuntary, spasmodic movements.
Dyslexia—developmental
reading disorder occurring when the brain does not properly recognize, process,
and interpret language
Electroencephlography—recording
of the electrical of the brain
Embolic—an
embolus travels to the cerebral arteries and occludes a small vessel. It occurs
very suddenly.
Embolus—clot of
material that travels through the bloodstream and suddenly block the vessel
Encephalitis—Encephalitis
is an inflammation of the brain, usually caused by a direct viral infection or
a hyper-sensitivity reaction to a virus or foreign protein. Brain inflammation
caused by a bacterial infection is sometimes called cerebritis.
Encephalopathy—any
degenerative disease of the brain.
Ependymal cells—(Greek
ependyma) line membranes within the brain and spinal cord where CSF is produced
and circulates (helps from CSF)
Epidural hematomas—An
accumulation of blood between the skull and the Dura mater
Epilepsies—Greek
word meaning a laying hold of
Epilepsy—chronic
brain disorder characterized by recurrent seizure activity. A Sudden discharge
of electrical activity within the brain. Seizures are often symptoms of
underlying brain pathologic conditions such as tumor, meningitis, vascular
disease or a scar tissue from a head injury
Femoral nerve—lumbar
nerve leading to and from the thigh (femur)
Gait—manner of
walking
Gangilia—singular
(gangilion) small collection of nerve cell bodies outside the brain and spinal
cord
Glial (neuroglial)
cells—make up its supportive, protective and connective tissues framework
of central nervous system and help it ward off infection. It does not transmit
impulses, far numerous than neurons and can reproduce. Types of
glial—astrocytes cells, microglial cell, oligodendroglial cells and ependymal
cells
Glioblastoma
multiforme—most malignant form of astrocytoma
Glioblastoma—highly
malignant tumor, gliomas are tumors of glial cells
Gyrus—plural
gyri. Sheet of nerve cells that produces a rounded ridge on the surface of the
cerebral cortex; convolution
Hemiparesis—affects
either left or right side of the body.
Hemiplegia—results
from brain injury or stroke, affecting left or right side of the body
Hemorrhages—a
blood vessel, such as the cerebral artery, breaks and bleeding atherosclerosis,
or high blood pressure
Herniated disk—common
cause leading to pain, weakness or numbness down the leg
Herpes zoster
(shingles)—infectious disorders, viral infection affecting peripheral
nerves. Blister and pain spread along peripheral nerves caused by herpes virus,
the same virus that cause chickenpox.
Human immunodeficiency
virus (HIV) encephalopathy—infectious disorders, brain disease and dementia
occurring with AIDS
Huntington disease
(Huntington chorea)—hereditary disorder marked by degenerative changes in
the cerebrum leading to abrupt involuntary movements and mental deterioration.
It results in personality changes, along with choreic movements or the arms,
legs and facial grimpacing; this disease is located on chromosome 4
Hydrocephalus—a
congenital disorder in which abnormal accumulation of fluid in the brain. It can
occurs in adults as a result of tumors and infection.
Hypalgesia—diminished
sensation to pain
Hyperalgesia—increased
sensitivity to pain
Hyperesthesia—a
light touch with a pin ma provoke increased sensation.
Hyperkinesias—Pathologically
increased muscular movement. Hyperactivity, especially in children.
Amphetamines (CNS stimulants) are used to treat in children
Hypesthesia—diminished
sensitivity to pain
Hypothalamus—blow the thalamus is also an important part of
the brain. Contains neurons that control body temperature, sleep, appetite,
sexual desire and emotion of fear and pleasure. It regulates the release of
hormones from the pituitary glands at the base of the brain and integrates the
activities of the sympathetic and parasympathetic nervous system
Ictal event—Latin—ictus,
meaning blow or a stroke. Pertaining to a sudden, onset as with the convulsion
of an epileptic seizure
Intrathecal injection—chemicals,
such as chemotherapeutic drugs, can be delivered into the subarachnoid space
Irreversible coma (brain
death)—complete unresponsitivity to stimuli and a flat electroencephalogram
tracing
Leptomeningeal—the
pia and arachnoid membranes are known as the leptomeninges because of thin and
delicate structure. Pertaining to leptomeninges
Lumbar puncture—CSF
is withdrawn from between two lumbar vertebrae for analysis. Informal name
“spinal tap”
Lumbar puncture—spinal
fluid can be withdrawn for diagnosis or relief of pressure on brain. A hollow
needle is inserted into the lumbar region of the spinal column blow the region
where the nervous tissue of the spinal cord ends
Lymphatic plexus—an
interconnecting network of lymph vessels
Magnetic resonance
angiography—produces images of blood vessels
Magnetic resonance
imaging—magnetic field and pulses of radio wave energy create images of the
brain and spinal cord. It useful to diagnose stroke and detect bleeding problem
and head injury
Medulla oblongata—connects
the spinal cord with the brain. Nerve tracts cross from right to left and left
to right in the medulla oblongata. It contains three vital centers that
regulate internal activities of the body; respiratory center, cardiac center
and vasomotor center. A Part of the brain just below the spinal cord. Controls
breathing, heartbeat and the size of blood vessels
Meningeal—pertaining
to the meninges, the three layers of membranes covering the brain and spinal
cord.
Meninges—three
layers of connective tissue membranes that surrounds the brain and spinal cord
Meningioma—slowly
growing benign tumor
Meningitis—infectious
disorders, inflammation of the meninges; leptomeningitis—caused by bacteria
(pyogenic meningitis) or virus (aseptic or viral meningitis). Fever and
meningeal irritation, such as headache and a stiff neck
Meningocele—the
meninges protrude to the outside of the body
Microglial cell—small
cells with many branching processes, as phagocytes they protect neurons in
response to inflammation. Remove waste products from the CNS
Migraine—severe,
recurring, unilateral, vascular headache. Symptoms are known as aura. Sensitivity
to sound and light and temporary visual and sensory disturbance.
Motor (efferent)
nerves)—travel from the spinal cord and brain to muscles of the body,
telling them
Motor aphasia—is
present when the patient knows what he or she wants to say but cannot pronounce
it.
Motor apraxia—the
inability to carry out planned movements or to handle small objects, although
cognizant of the proper use of the object.
Multiple sclerosis—destruction
of the myelin sheath on neurons in the CNS and its replacement by plaques of
sclerotic tissue. It is a chronic disease often marked by long periods of
stability and worsening. Can be seen on MRI. Probably involves an autoimmune
disease of lymphocytes reacting against myelin
Myasthenia gravis—autoimmune
neuromuscular disorder characterized by weakness of voluntary muscles.
Antibodies block the ability of acetylcholine to transmit the nervous impulse
from nerve to muscle cell. Onset of symptom usually is gradual, double vision
(diplopia) and facial weakness
Myelin sheath—covering
of white fatty tissue that surrounds and insulate the axon and speed
transmission of the electrical impulse. It gives white appearance to the nerve
fiber.
Myelin—a fatty
tissue that can cover the axons
Myelomenngocele—spinal
cord and meninges protrude
Myelopathy—the
viral disease affects the gray matter of the spinal cord. Leading to paralysis
of muscles that rely on the damaged neurons.
Myemeningocele—neural
tube defect caused by failure of the neural tube to close during embryonic
development. This occurs in infants born with spina bifida
Myoneural—pertaining
to nerve terminations in muscles
Narcolepsy—sudden,
uncontrollable compulsion to sleep. Amphetamines and stimulants drugs are
prescribed to prevent attacks.
Nerve—macroscopic,
cord like collection of fibers that carry electrical impulses, able to be seen
with a naked eye. Consists of a bundle of dendrites and axons that travel
together like strands of rope.
Nervous system—most
complex system of human body and classified into two divisions. Central nervous
system and peripheral nervous system
Neuralgia—trigeminal
neuralgia involves flashes of pain radiating along the course of the trigeminal
nerve
Neurasthenia—nervous
exhaustion and fatique, often following depression or lack of nerve strength
Neurofibrillary
tangles—bundles of fibrils in the cytoplasm of a neuron in the cerebral
cortex
Neuron—an
individual nerve cell, a microscopic structure, impulses pass along the parts
of a nerve cell in a definite manner and direction. Functional cell of the
nervous system
Neuropathy—a
functional disturbance or pathological change in the peripheral nervous system,
sometimes limited to noninflammatory lesions as opposed to those of neuritis
Neurotransmitter—chemical
substance/messenger by neuron on which the transfer of the impulse across the
synapse depends. It stimulates another cell, which can be a nerve cell, muscle
cell or gland cell. Examples are acetycholine, norepinephrine, epinephrine
(adrenaline), dopamine, serotonin and endorphine
Occlusion--blockage
Oligodendroglial
cells—have few dendrites; these form the myelin sheath in the central
nervous system. Also called oligodendrocyte
Palliative—relieving
symptoms but not curing them
Palsy—paralysis
complete or partial loss of motor function
Paraplegia—originally,
a stroke on one side. The term means paralysis both legs and lower part of the
body caused by injury or disease of the spinal cord or cauda equine
Parasympathetic
nerves—normally acts as a balance for the sympathetic nerves. It also slows
down heart rate, lower blood pressure and stimulates intestinal contractions to
clear rectum.
Parenchyma—essential
distinguishing tissue of an organ or system. Neurons and nerves are the
parenchyma of the nervous system. In the brain and spinal cord, neurons, which
conduct electrical impulse, are the parenchyma tissue.
Paresis—partial
paralysis or weakness in muscles
Paresthesia—tingling,
burning, and “pins and needles” sensations
Parkinson disease
(parkinsonism)—degeneration of neurons in the basal ganglia, occurring in
later life and leading to tremors, weakness of muscles, and slowness of
movement. It is caused by a deficiency of dopamine. Typical “pill-rolling” tremor
of hands and characteristics mask-like lack of facial expression
Peripheral nervous
system—cranial nerves and spinal nerves, plexuses, peripheral nerves
throughout the body. The cranial and spinal nerves who functions voluntary,
helps the body respond to the changes outside world, they include sense
receptors for eye sight, hearing and balance, smell and touch and sensory
nerves. Nerves outside the brain and spinal cord
Pia mater—containing
CSF, closest to the brain and spinal cord. It contains delicate/thin connective
tissue with a rich supply of blood vessels
Pia-arachnoid—most
physician refer to the pia and arachnoid together
Plexus—large
network intersecting blood vessels and lymphatic vessels of nerves in the
peripheral nervous system. The cervical, branchial and lumbaosacral plexuses
are the examples that include cervical, lumbar and sacral nerves.
Polio—gray matter
Polyneuritis—inflammation
of several peripheral nerves simultaneously.
Pons—part of
brainstem that literally means bridge. Contains nerve fiber tracts that connect
the cerebellum and cerebrum with the rest of the brain. Connection of Nerves to eyes and face
Positron emission
tomography scan—radioactive glucose is injected and then detected in the
brain to image the metabolic activity of the cell
Postictal events—neurologic
symptoms such as weakness in epileptic patients after seizures
Quadriplegia—all
four extremities limbs are paralyzed or are affected. Injury is at the cervical
level of the spinal cord.
Radiculitis—inflammation
of the spinal nerve roots
Radiculopathy—sciatica
is a radiculopathy affecting the sciatic nerve root in the back.
Receptor—organ
that receives a nervous stimulus and passes it on to afferent nerves. The skin,
ear, eyes and taste buds are receptors
Rectal plexus—plexus
of veins in the rectal region
Respiratory center---controls
muscles of respiration in response to chemical
Sciatic nerve—beginning
in a region of the hip. Nerve extending from the base of the spine down the
thigh, lower leg and foot.
Sciatica—pain or
inflammation along the course of the nerve
Semicomatose—refers
to a stupor (unresponsiveness) from which a patient can be aroused
Senile plaques—Abnormal
structures, composed of parts of nerve cells surrounding protein deposits,
found in the brains of people with Alzheimer's disease
Sensory (afferent)
nerves—carry messages related to changes in the environment toward the
spinal cord and brain through receptor
Sensory aphasia—difficulty
understanding language and many pronounce words easily but use them
inappropriate
Spina bifida cystica—is
more severe form with cyst-like protrusions
Spina bifida occulta—the
vertebral defect is covered with the skin and evident only on x ray or other
imaging examination. A neural tube defect
Spina bifida—congenital
defects in the lumbar spinal column caused by imperfect union of vertebral
parts.
Spinal cord—column
of nervous tissue extending from the medulla oblongata to the second lumbar
vertebra with the vertebral column. It carries all the nerves to ad from the limbs
and lower part of the body and a pathway for impulses going to and from the
brain. A cross section view of the spinal cord reveals an inner region of gray matter and an outer region of white matter
Spinal nerves—thirty
one pairs of nerves arising from the spinal cord carry messages between the
spinal cord and the chest, abdomen and extremities
Stereotactic
radiosurgery—use of specialized instrument to locate and treat targets in
the brain. A gamma knife (high-energy radiation beam) is used to treat deep and
inaccessible intracranial tumors and abnormal blood vessel masses without
surgical incisions proton stereotactic radiosurgery delivers and uniform dose
of proton radiation to a target and spares surrounding normal tissue
Stimulus— A
factor capable of eliciting a response in a nerve,begin as impulse in the
branching fibers of the neuron, which are called dendrites. An agent of change
in the internal and external environment that evoke response
Stroma—of an
organ is the connective and supportive tissue of an organ. Stromal tissue of
the nervous system consists of the glial (neuroglial) cells.
Subarachnoid space—the
space between the arachnoid membranes and the pia mater membranes. It contains
cerebrospinal fluid.
Subdural hematomas—A
subdural hematoma is a collection of blood in the space between the outer layer
(dura) and middle layers of the covering of the brain (the meninges)
Sulcus—plural
sulci. Depression or groove in the surface of the centebral cortex. Fissure
Sympathetic nerves—stimulate
the body in times of stress and crises, they increase heart rate and
forcefulness, dilate airways for more oxygen can increase blood pressure, it
stimulate the adrenal glands to secrete epinephrine(adrenaline), while also
inhibiting intestinal contractions for slow digestion
Synapse—the space
where they nervous impulse jumps from one neuron to another. A space through
which nervous impulses travels between the nerve cells or between the nerve and
muscle or glandular cells
Syncopal—sudden
and temporary loss of consciousness caused by inadequate flow of blood to the
brain
Syncope—fainting
Tardive dyskinesia—irreversible
neurological disorder of involuntary movements may develop in people who
receive certain antipsychotic drugs for extended periods.
Temporal lobe epilepsy—seizure
begins in the temporal lobe of the brain.
Terminal end fiber—the
nervous impulses pass through the axon to leave the cell via the terminal end
fibers of the neuron.
Thalamic—pertaining
to the thalamus
Thalamus—important
part of the brain, acts like a “triage center” and decides what is important
and what is not, processing and relaying sensory information to the cerebral
cortex. It also plays a major role in maintaining levels of awareness and
consciousness. It conducts impulses between the spinal cord an cerebrum
Thrombotic—blood
clot in the arteries leading to the brain, resulting in occlusion of the
vessels. Atherosclerosis leads to this common type of stroke as blood vessels
become blocked over time. Before total occlusion, a patient may experience
symptoms that point to the gradual occlusion of blood vessels known as transient ischemic attacks
Thymectomy—method
of treatment for myasthenia gravis. Removal of thymus gland
TIA—transient
ischemic attack
Tics—an
involuntary, compulsive, rapid, repetitive, stereotyped movement or
vocalization, experienced as irresistible although it can be suppressed for
some length of time (tourette syndrome)
Tonic-clonic seizures
(grand mal or ictal events)—characterized by a sudden loss of
consciousness, falling down and tonic contractions following by clonic
contractions. These convulsion are often preceded by aura.
Tourette syndrome—involuntary,
spasmodic, twitching movements; uncontrollable vocal sounds and inappropriate
words.
Trigeminal nerve—5th
cranial nerve
Vagal—this
cranial nerve has branches to the head and neck, as well as to the chest
Vagus nerve—10th
cranial nerve, branches reach to larynx, trachea, bronchi, lungs, aorta,
esophagus and stomach. Carries messages to and from the neck, chest and
abdomen.
Vasomotor center—affects
the muscle in the walls of blood vessels, thus influencing blood pressure
Ventricles—spaces
or canals in the middle of the cerebrum. They contain watery fluid through the
brain and around the spinal cord. These fluids are cerebrospinal fluid and it
protects the brain and spinal cord from shock by acting like a cushion. It
usually clear and colorless and contains lymphocytes, sugar and proteins. Also
found in heart, they are the two lower chambers of the heart
Vertebral plexus—plexus
of veins related to the backbone
White and gray
matters—the white nervous tissue, constituting the conducting portion of
the brain and spinal cord, composed mostly of myelinated nerve fibers. Gray
matter or substance is the term used to describe the tissues composed of
unmyelinated fibers
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