Med. Term - Chapter 15, The Nervous System

lethargy

Abnormal inactivity or lack of response to normal stimuli

coma

Abnormally deep unconsciousness with an absence of voluntary response to stimuli

hydrocephalus

Accumulation of fluid in the ventricles of the brain, causing increased intracranial pressure (ICP), thinning of brain tissue, and separation of cranial bones. The two forms of hydrocephalus are acquired hydrocephalus, which occurs after birth, and congenital hydrocephalus, which occurs during fetal development and is found at birth

neurilemma

Additional external myelin sheath that is formed by Schwann cells and found only on axons in the peripheral nervous system. Because the neurilemma does not disintegrate after injury to the axon, its enclosed hollow tube provides an avenue for regeneration of injured axons.

convulsion

Any sudden and violent contraction of one or more voluntary muscles that is commonly associated with such brain disorders as epilepsy

myelin sheath

Axons possess a white, lipoid covering called a myelin sheath. This covering acts as an electrical insulator that reduces the possibility of an impulse stimulating adjacent nerves. It also accelerates impulse transmission through the axon.

Autonomic Nervous System

Because the individual cannot control autonomic nervous system activities, a specialized system consisting of the sympathetic and parasympathetic divisions acts as the regulator of the autonomic nervous system. In general, the sympathetic division and the parasympathetic division bring about opposite effects on the activity of the same organs. In other words, the sympathetic and parasympathetic divisions act as "increase" and "decrease" switches for controlling the actions of the autonomic nervous system. Ordinarily, what one division stimulates, the other inhibits. The sympathetic division regulates body activities when an immediate action is required in stressful or threatening situations. It increases heart rate, depth of breathing, and muscle strength, preparing the body for a "fight-or-flight" response. Conversely, the parasympathetic division decreases the rate and intensity of these processes and exerts its influence when stressful or threatening situations resolve. It causes a decrease in heart rate, dilation of visceral blood vessels, and an increase in the activity of the digestive tract, preparing the body for "rest-and-digest" responses.

dementia

Broad term that refers to cognitive deficit, including memory impairment

Huntington chorea

CNS disorder characterized by quick, involuntary movements, speech disturbances, and mental deterioration; also called neurodegenerative genetic disorder. Onset of Huntington chorea commonly occurs between ages 30 and 50

discography

CT scan of the lumbar region after injection of a contrast medium to detect problems with the spine and spinal nerve roots

efferent

Carry or move away from a central structure. In the nervous system, efferent impulses travel away from the central nervous system.

afferent

Carry or move inward or toward a central structure. In the nervous system, afferent impulses travel toward the central nervous system.

Alzheimer disease (AD)

Cerebral Degeneration; Type of age-associated dementia caused by small lesions called plaques that develop in the cerebral cortex and interrupt the passage of electrochemical signals between cells. Clinical manifestations include memory loss, emotional and behavioral changes, and a decline in cognitive and social skills eventually leading to death. There is no specific treatment, but medications may provide moderate relief.

myasthenia gravis (MG)

Chronic, progressive disorder in which a loss of neurotransmitter receptors produces increasingly severe muscle weakness

limbic system

Complex neural system located beneath the cerebrum that controls basic emotions and drives and plays an important role in memory. The limbic system is primarily related to survival and includes such emotions as fear, anger, and pleasure (food and sexual behavior).

positron emission tomography (PET)

Computed tomography that records the positrons (positively charged particles) emitted from a radiopharmaceutical and produces a cross-sectional image of metabolic activity of body tissues to determine the presence of disease. PET is particularly useful in scanning the brain and nervous system to diagnose disorders that involve abnormal tissue metabolism, such as schizophrenia, brain tumors, epilepsy, stroke, and Alzheimer disease, in addition to cardiac and pulmonary disorders.

anencephaly

Congenital deformity in which some or all of the fetal brain is missing. In anencephaly, the infant is usually stillborn or dies shortly after birth. This deformity can be detected through amniocentesis or ultrasonography early in pregnancy

Effects of the Parasympathetic Nervous System

Decreases or increases the diameter of the pupils in response to changing levels of light; Increases the flow of saliva; Constricts the bronchi; Decreases heart rate, blood pressure, and metabolic rate; Increases digestive activities; Dilates visceral blood vessels

Signs and risk factors for stroke

Depending on the area of the brain affected by the stroke, signs and symptoms include weakness or paralysis in one-half of the body (hemiparesis, hemiplegia), speech difficulty (dysphasia), lack of muscle coordination (ataxia), confusion, and loss of consciousness. A "mini stroke," also called a transient ischemic attack (TIA), is a type of stroke in which symptoms resolve within 24 hours and do not cause permanent damage. TIAs require immediate medical attention because they are often a precursor to a full-blown stroke. Risk factors for stroke include family history, obesity, smoking, and excessive alcohol use. Because high blood pressure is a risk factor for strokes, antihypertensive medications are important in prevention. Computed tomography (CT) helps determine the type of stroke and treatment options. For ischemic strokes, "clot-buster" (thrombolytic) medications administered within 3 hours of symptom onset can usually prevent permanent disability. Treatment for disabilities caused by stroke involves speech, physical, and occupational therapy and various medications, depending on the type of stroke.

autism

Developmental disorder characterized by extreme withdrawal and an abnormal absorption in fantasy, usually accompanied by an inability to communicate even on a basic level. A person with autism may engage in repetitive behavior, such as rocking or repeating words

Effects of the Sympathetic Nervous System

Dilates the pupils to increase the amount of light entering the eye to optimize vision; Decreases the flow of saliva; Dilates the bronchi; Increases heart rate and metabolic rate; Decreases digestive activities; Constricts visceral blood vessels;

attention deficit-hyperactivity disorder (ADHD)

Disorder affecting children and adults and characterized by impulsiveness, overactivity, and the inability to remain focused on a task. Behavioral modification with or without medical management is commonly used in the treatment of ADHD.

anorexia nervosa

Eating disorder characterized by a refusal to maintain adequate weight for age and height and an all-consuming desire to remain thin

bulimia nervosa

Eating disorder characterized by binging (overeating) and purging (vomiting or use of laxatives)

plasmapheresis

Extracorporeal procedure to treat patients with autoimmune diseases by removing their plasma containing the offending antibodies and replacing it with donor plasma or plasma substitutes. Plasmapheresis helps treat such autoimmune diseases as multiple sclerosis, Guillain-Barré syndrome, and myasthenia gravis

Bell's palsy

Facial nerve palsy; Facial paralysis caused by a functional disorder of the seventh cranial nerve. Bell palsy is commonly associated with herpes virus, but other viruses may be implicated. It is self-limiting and usually resolves spontaneously in 3-5 weeks

occulta

Form of spina bifida in which one or more vertebrae are malformed, and the spinal cord is covered with a layer of skin

meningocele

Form of spina bifida in which the spinal cord develops properly but the meninges protrude through the spine

Sclerosing

Hardening

Brain

In addition to being one of the largest organs of the body, the brain is highly complex in structure and function. (See Fig. 15-3.) It integrates almost every physical and mental activity of the body and is the center for memory, emotion, thought, judgment, reasoning, and consciousness. The four major structures of the brain are the Cerebrum, Cerebellum, Diencephalon, and the Brainstem

agnosia

Inability to comprehend auditory, visual, spatial, olfactory, or other sensations, even though the sensory sphere is intact. The type of agnosia is usually identified by the sense or senses affected, such as visual agnosia. Agnosia is common in parietal lobe tumors.

dyslexia

Inability to learn and process written language, despite adequate intelligence, sensory ability, and exposure

Poliomyelitis

Inflammation of the gray matter of the spinal cord caused by a virus, commonly resulting in spinal and muscle deformity and paralysis. Polio is preventable with standard vaccinations administered to children.

closed head trauma

Injury to the head in which the dura mater remains intact and brain tissue is not exposed. In closed head trauma, the injury site may occur at the impact site, where the brain hits the inside of the skull (coup), or at the rebound site, where the opposite side of the brain strikes the skull (contrecoup)

Oncology

Intracranial tumors that originate directly in brain tissue are called primary intracranial tumors. They are commonly classified according to histological type and include those that originate in neurons and those that develop in glial tissue. A major symptom of intracranial tumors is headache, especially upon arising in the morning, during coughing episodes, and upon bending or sudden movement. Occasionally, papilledema will occur because of increased intracranial pressure. Personality changes are common and include depression, anxiety, and irritability. Intracranial tumors can arise from any structure within the cranial cavity, including the pituitary and pineal glands, cranial nerves, and the leptomeninges. In addition, all of these tissues may be the sites of metastatic spread from primary malignancies that occur outside the nervous system. Metastatic tumors of the cranial cavity tend to exhibit growth characteristics similar to those of the primary malignancy but tend to grow more slowly than the parent tumor. Metastatic tumors of the cranial cavity are usually easier to remove than primary intracranial tumors. Computed tomography (CT) scans and magnetic resonance imaging (MRI) help establish a diagnosis but are not definitive. Surgical removal relieves pressure and confirms or rules out malignancy. Even after surgery, most intracranial tumors require radiation therapy as a second line of treatment. Chemotherapy combined with radiation therapy usually provides the best chance for survival and quality of life.

cerebrospinal fluid (CSF) analysis

Laboratory test to examine a sample of the fluid surrounding the brain and spinal cord that helps diagnose disorders of the central nervous system, including viral and bacterial infections, tumors, and hemorrhage

paralysis

Loss of voluntary motion in one or more muscle groups with or without loss of sensation. Strokes and spinal cord injuries are the most common causes of paralysis. Strokes usually affect only one side of the body. Spinal cord injuries result in paralysis below the site of the injury

psychosis

Major emotional disorder in which contact with reality is lost to the point that the individual is incapable of meeting the challenges of daily life

bipolar disorder

Mental disorder that causes unusual shifts in mood, emotion, energy, and the ability to function; also called manic-depressive illness

depression

Mood disorder associated with sadness, despair, discouragement and, commonly, feelings of low self-esteem, guilt, and withdrawal

mania

Mood disorder characterized by mental and physical hyperactivity, disorganized behavior, and excessively elevated mood

myelomeningocele

Most severe form of spina bifida in which the spinal cord and meninges protrude through the spine

spina bifida

Neural tube defect; Congenital deformity of the neural tube (embryonic structure that becomes the fetal brain and spinal cord), which fails to close during fetal development. The most common forms of spina bifida are meningocele, meningomyelocele, and occulta.

neurosis

Nonpsychotic mental illness that triggers feelings of distress and anxiety and impairs normal behavior. A child who has consistently been warned of "germs" by an overprotective parent may later develop an irrational fear of such things as using public restrooms and touching doorknobs or phones.

Schwann cell

On nerves in the peripheral nervous system, the myelin sheath is formed by a neuroglial cell called a Schwann cell that wraps tightly around the axon. Its exterior surface forms a thin tube called the neurilemma, or neurolemma. The neurilemma acts as a protective coat for peripheral neurons. If the neurilemma covering remains intact after an injury to the nerve, it forms a tube that provides a pathway for possible neuron regeneration after injury.

Neurons

One of the two cell types of the nervous system. Neurons transmit impulses. Depending on the direction in which they transmit information, neurons and nerves are classified as afferent (when the impulse moves toward the brain or spinal cord) or efferent (when the impulse moves away from the brain or spinal cord). The three major structures of the neuron are the cell body, axon, and dendrites. The cell body is the enlarged structure of the neuron that contains the nucleus of the cell and various organelles. Its branching cytoplasmic projections are dendrites that carry impulses to the cell body and axons that carry impulses from the cell body. Dendrites resemble tiny branches on a tree, providing additional surface area for receiving impulses from other neurons. Axons are threadlike extensions of nerve cells that transmit impulses to dendrites of other neurons and to muscles and glands.

ventricle

Organ chamber or cavity that receives or holds fluid. In the nervous system, cerebrospinal fluid flows through the ventricles of the brain into the spinal cavity and then returns to the brain, where it is absorbed into the blood.

palsy

Paralysis, usually partial, and commonly characterized by weakness and shaking or uncontrolled tremor

thalamotomy

Partial destruction of the thalamus to treat intractable pain; involuntary movements, including tremors in Parkinson disease; or emotional disturbances. Thalamotomy produces few neurological deficits or changes in personality

stereotactic radiosurgery (SRS)

Procedure that uses three-dimensional imaging (stereotactic) along with high doses of highly focused radiation to destroy tumors and other abnormal growths in the brain, spinal column, and other body sites with minimal exposure to surrounding healthy tissue. Because of its accuracy and precision, the principles used in SRS are now being applied to treat various body tumors with a procedure called stereotactic body radiotherapy (SBRT)

blood-brain barrier

Protective mechanism that blocks specific substances found in the bloodstream from entering delicate brain tissue

anxiety

Psychological "worry" disorder characterized by excessive pondering or thinking "what if..." Feelings of worry, dread, lack of energy, and a loss of interest in life are common signs associated with anxiety.

affective disorder

Psychological disorder in which the major characteristic is an abnormal mood, usually mania or depression

myelography

Radiographic examination to detect pathology of the spinal cord, including the location of a spinal cord injury, cysts, and tumors following injection of a contrast medium

computed tomography angiography (CTA, CT angiography)

Radiographic image of the interior of a vessel in combination with a CT scan to produce high-resolution, three-dimensional images of blood vessels. CTA identifies blocked blood vessels, aneurysms, and buildup of plaque in a blood vessel. It also aids in differentiating hemorrhagic stroke and ischemic stroke

electroencephalography (EEG)

Recording of electrical activity in the brain, whose cells emit distinct patterns of rhythmic electrical impulses. Different wave patterns in the EEG are associated with normal and abnormal waking and sleeping states. They help diagnose such conditions as tumors and infections and help locate seizure focus or areas of inactivity.

electromyography (EMG)

Recording of electrical signals (action potentials) that occur in a muscle when it is at rest and during contraction to assess muscular disease or nerve damage. In an EMG, an electrode inserted into a muscle transmits electrical activity of the muscle and displays it on a monitor to assess the health of the muscle and the motor neurons that control it

ventriculoperitoneal shunting

Relieves intracranial pressure due to hydrocephalus by diverting (shunting) excess cerebrospinal fluid from the ventricles into the peritoneal or thoracic cavity

paresthesia

Sensation of numbness, prickling, tingling, or heightened sensitivity. Paresthesia can be caused by disorders affecting the central nervous system, such as stroke, transient ischemic attack, multiple sclerosis, transverse myelitis, and encephalitis

lumbar puncture (LP)

Spinal puncture or spinal tap; Needle puncture of the spinal cavity to extract spinal fluid for diagnostic purposes, introduce anesthetic agents into the spinal canal, or remove fluid to allow other fluids (such as radiopaque substances) to be injected

panic attack

Sudden, intense feeling of fear that comes without warning and is not attributable to any immediate danger. A key symptom of a panic attack is the fear of its recurrence

trephination

Technique that cuts a circular opening into the skull to reveal brain tissue and decrease intracranial pressure

cryosurgery

Technique that exposes abnormal tissue to extreme cold to destroy it. Cryosurgery is sometimes used to destroy malignant tumors of the brain

nerve conduction velocity (NCV)

Test that measures the speed at which impulses travel through a nerve. In NCV, one electrode stimulates a nerve while other electrodes placed over different areas of the nerve record an electrical signal (action potential) as it travels through the nerve. This test helps diagnose muscular dystrophy and neurological disorders that destroy myelin

Cranial Nerves

The 12 pairs of cranial nerves originate in the brain and emerge through canals or openings in the base of the skull. Each cranial nerve is designated by name or number. Cranial nerves may be sensory, motor, or a mixture of both types of neurons. Sensory (afferent) nerves receive impulses from the sense organs, the environment, and the visceral organs and transmit them to the CNS. Motor (efferent) nerves conduct impulses from the CNS to muscles and glands. Mixed nerves are composed of sensory (afferent) and motor (efferent) neurons. An example of a mixed nerve is the facial nerve. It acts in a motor capacity by transmitting impulses to the facial muscles for smiling or frowning. However, it also acts in a sensory capacity by transmitting taste impulses from the tongue to the brain.

Meninges

The brain and spinal cord receive limited protection from three coverings called meninges (singular, meninx). These coverings are the dura mater, arachnoid, and pia mater. The dura mater is the outermost covering of the brain and spinal cord. It is tough, fibrous, and dense and composed primarily of connective tissue. Because of its thickness, this membrane is also called the pachymeninges. Beneath the dura mater is a cavity called the subdural space, which is filled with serous fluid. The arachnoid is the middle covering and, as its name suggests, has a spider-web appearance. It fits loosely over the underlying structures. A subarachnoid space contains cerebrospinal fluid, a colorless fluid that contains proteins, glucose, urea, salts, and some white blood cells. This fluid circulates around the spinal cord and brain and through ventricles located within the inner portion of the brain. It provides nutritive substances to the central nervous system and adds additional protection for the brain and spinal cord by acting as a shock absorber. Normally, cerebrospinal fluid is absorbed as rapidly as it is formed, maintaining a constant fluid volume. Any interference with its absorption results in a collection of fluid in the brain, a condition called hydrocephalus. The pia mater is the innermost meninx. This membrane directly adheres to the brain and spinal cord. As it passes over the brain, it follows the contours of the gyri and sulci. It contains numerous blood vessels and lymphatics that nourish the underlying tissues. Because of the thinness and delicacy of the arachnoid and pia mater, these two meninges are collectively called the leptomeninges.

synapse

The functional connection between two neurons or between a neuron and its effector organ (muscle or gland) is a gap or space. Impulses must travel from the axon terminal of one neuron to the dendrite of the next neuron or to its effector organ by crossing this synapse. The impulse within the transmitting axon causes a chemical substance called a neurotransmitter to be released at the end of its axon. The neurotransmitter diffuses across the synapse and attaches to the receiving neuron at specialized receptor sites. When sufficient receptor sites are occupied, it signals an acceptance "message" and the impulse passes to the receiving neuron. The receiving neuron immediately inactivates the neurotransmitter and prepares the site to receive another impulse.

Neuroglia

The other type of cells in the nervous system. cells that support neurons and bind them to other neurons or other tissues of the body. Although they do not transmit impulses, they provide a variety of activities essential to the proper functioning of neurons. The term neuroglia literally means "nerve glue" because these cells were originally believed to serve only to bind neurons to each other and to other structures. They are now known to supply nutrients and oxygen to neurons and assist in other metabolic activities. They also play an important role when the nervous system suffers injury or infection. The four major types of neuroglia are astrocytes, oligodendrocytes, microglia, and ependyma.

Cerebellum

The second largest structure of the brain, the cerebellum, occupies the posterior portion of the skull. Most functions of the cerebellum involve movement, posture, or balance. When the cerebrum initiates muscular movement, the cerebellum coordinates and refines it.

Somatic Nervous System

The somatic nervous system, the part of the peripheral nervous system associated with voluntary muscle control, is made up of the cranial nerves and the spinal nerves.

Spinal Nerves

The spinal nerves emerge from the intervertebral spaces in the spinal column and extend to various locations of the body. All 31 pairs of spinal nerves are mixed nerves. Each pair is identified according to the vertebra from which it exits. All spinal nerves have two points of attachment to the spinal cord: an anterior (ventral) root and a posterior (dorsal) root. The anterior root contains motor fibers, and the posterior root contains sensory fibers. These two roots unite to form the spinal nerve, which has afferent and efferent qualities.

tractotomy

Transection of a nerve tract in the brainstem or spinal cord. Tractotomy is sometimes used to relieve intractable pain

concussion

Traumatic injury to the brain that causes unconscoiousness and is commonly of a temporary nature. Symptoms of concussion may include headache, dizziness, nausea, vomiting, and blurred vision, but symptoms may not appear for days or weeks after the injury.

intravenous (IV) tissue plasminogen activator (tPA)

Treatment for ischemic stroke using tissue plasminogen activator (tPA), a potent clot-busting drug, injected directly into a vein. IV tPA helps treat ischemic stroke but must be given within 4 hours of symptom onset. Knowing the symptoms of stroke and calling 911 are essential because there is a very narrow window for diagnosing and effectively treating the patient

cerebral palsy (CP)

Type of paralysis that affects movement and muscle coordination and may affect gross and fine motor skills. CP commonly occurs because of trauma to the brain before or during the birthing process

echoencephalography

Ultrasound technique used to study intracranial structures of the brain and diagnose conditions that cause a shift in the midline structures of the brain. Echoencephalography is a bedside procedure that is especially useful in detecting hemorrhage and hydrocephalus in children less than 2 years of age and infants in the neonatal unit but has largely been replaced by CT for older children and adults.

Cerebrovascular disease

a group of disorders affecting the vessels that supply blood to the brain. Denied oxygen, brain tissue begins to die, a medical emergency called stroke, cerebrovascular accident (CVA), or "brain attack." The three major types of stroke are ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage. The causes of an ischemic stroke are similar to that of a heart attack and include emboli, thrombi, and atherosclerosis that limit blood flow to brain tissue. A common cause of ischemic stroke is atherosclerosis of the arteries of the brain or neck (carotid).

Reye syndrome

acute noninflammatory encephalopathy and fatty degenerative liver failure; Potentially fatal syndrome that commonly causes brain swelling and liver damage and is characterized by confusion, hyperventilation, violent behavior, seizures, and possibly coma. Reye syndrome primarily affects children and teenagers recovering from a viral infection, most commonly flu or chickenpox, especially when aspirin products have been used

Multiple Sclerosis

an autoimmune disease that targets the myelin sheath on the nerves of the central nervous system. MS causes inflammation, sclerosing, and, finally, demyelination throughout the spinal cord and brain. Myelin deterioration impedes the transmission of electrical impulses from one neuron to another. In effect, the pathway of nerve impulses develops "short circuits," producing a wide variety of symptoms. Signs and symptoms of MS include tremors, muscle weakness, bradykinesia, and such visual disturbances as blurred vision, poor contrast, double vision, and eye pain. Other symptoms include bowel and bladder disorders, sexual disfunction, balance problems, cognitive difficulties, numbness, tingling, and pain. Many patients require a cane, walker, or wheelchair as the disease progresses. During remissions, symptoms temporarily disappear, but progressive hardening of myelinated areas leads to other attacks. MS generally affects a person's quality of life, rather than longevity. Medications and physical therapy can ease or control symptoms, but currently there is no cure for the disease.

Seizure disorders

any medical condition characterized by sudden changes in behavior or consciousness caused by uncontrolled electrical activity in the brain. They include epileptic seizures, which have no known cause, are chronic, and occur repeatedly, and nonepileptic seizures, which are triggered by disorders or conditions that irritate the brain. These triggers commonly include brain injury, congenital anomalies, metabolic disorders, brain tumors, fever, vascular disturbances, and genetic disorders. Whether epileptic or nonepileptic, seizures manifest in various forms. The two most common forms are partial seizures and generalized seizures. In partial seizures, only a portion of the brain is involved. There is a short alteration of consciousness of about 10 to 30 seconds with repetitive, unusual movements and confusion. In a generalized seizure, the entire brain is involved. The most common type of generalized seizure is the tonic-clonic (grand mal) seizure. In tonic-clonic seizures, the body alternates between excessive muscle tone and rigidity (tonic) and jerking muscle contractions (clonic) in the extremities. After the seizure, such neurological symptoms as weakness, confusion, headache, and nausea may occur. These symptoms are called a postictal event, which commonly lasts for 5 to 30 minutes but may last longer with a severe seizure. Many patients experience a warning signal (aura) of an imminent seizure. Auras vary considerably and may include sensory phenomena without a precipitating stimulus, such as a strange taste in the mouth, the sound of a ringing bell, or an inability to react properly to usual situations. Auras provide time for preparation, such as lying down, avoiding staircases, and so forth, to minimize injuries should a grand mal seizure occur. Diagnosis and evaluation of epilepsies commonly rely on electroencephalography and magnetic source imaging (MSI) to locate the affected area of the brain. Antiepileptic medications help control seizures.

Astrocytes

as their name suggests, are star-shaped neuroglia. They provide three-dimensional mechanical support for neurons and form tight sheaths around the capillaries of the brain. These sheaths provide an obstruction called the blood-brain barrier that keeps large molecular substances from entering the delicate tissue of the brain. Even so, small molecules, such as water, carbon dioxide, oxygen, and alcohol, readily pass from blood vessels through the barrier and enter the interstitial spaces of the brain. Researchers must consider the blood-brain barrier when developing drugs that treat brain disorders. Astrocytes also perform mildly phagocytic functions in the brain and spinal cord.

myel/o

bone marrow; spinal cord. ex: poli/o/myel/itis

encephal/o

brain. ex: encephal/o/cele (Encephalocele is a condition in which portions of the brain and meninges protrude through a bony midline defect in the skull.)

cerebr/o

cerebrum. ex: cerebr/o/tomy

Ependyma

ciliated cells that line the fluid-filled cavities of the central nervous system, especially the ventricles of the brain. They assist in the circulation of cerebrospinal fluid (CSF).

Peripheral Nervous System

composed of all nervous tissue located outside the spinal column and skull. It consists of sensory neurons, which carry impulses from the body to the CNS (afferent), and motor neurons, which carry impulses from the brain and spinal cord to muscles and glands (efferent). The PNS is divided into the somatic nervous system and the autonomic nervous system. Some motor nerves in the peripheral nervous system innervate muscles under conscious control of the individual. They regulate such actions as walking and talking. The motor nerves that influence voluntary muscles comprise the somatic nervous system. Other motor nerves innervate involuntary muscles (muscles of the digestive or respiratory organs), glands, and cardiac muscles. The motor nerves that influence involuntary muscles, glands, and heart muscle make up the autonomic nervous system.

Brainstem

composed of three structures: the midbrain (also called the mesencephalon), separating the cerebrum from the brainstem; the medulla, which attaches to the spinal cord; and the pons, or "bridge," connecting the midbrain to the medulla. In general, the brainstem is a pathway for impulse conduction between the brain and spinal cord. The brainstem is the origin of 10 of the 12 pairs of cranial nerves and controls respiration, blood pressure, and heart rate. The brainstem is the site that controls the beginning of life (initiation of the heartbeat in a fetus) and the end of life (cessation of respiration and heart activity).

Central Nervous System

consists of the brain and spinal cord. Its nervous tissue consists of white matter and gray matter. Bundles of axons and their white lipoid myelin sheaths constitute white matter. Unmyelinated fibers, dendrites, and nerve cell bodies make up the gray matter of the brain and spinal cord.

crani/o

cranium (skull). ex: crani/o/malacia

syncope

fainting; Brief loss of consciousness and posture caused by a temporary decrease of blood flow to the brain. Syncope may be associated with a sudden decrease in blood pressure, a decrease in heart rate, or changes in blood volume or distribution. The person usually regains consciousness and becomes alert right away but may experience a brief period of confusion.

-esthesia

feeling. ex: hyper/esthesia (Hyperesthesia involves a marked sensitivity to touch, pain, or other sensory stimuli.)

Oligodendrocytes

form the myelin sheath that covers the axons in the central nervous system. Oligodendrocytes do not produce neurilemma, and thus injury or damage to neurons located in the central nervous system is irreparable. The short, unmyelinated spaces between adjacent segments of the myelin sheath are called nodes of Ranvier. These nodes help speed the transmission of impulses down the axon.

gangli/o

ganglion (knot or knotlike mass). ex: gangli/ectomy (A ganglion is a mass of nerve cell bodies (gray matter) in the peripheral nervous system.)

gli/o

glue; neuroglial tissue. ex: gli/oma

Guillain-Barré syndrome

infective or idiopathic polyneuritis; Autoimmune condition that causes acute inflammation of the peripheral nerves damaging their myelin sheaths, resulting in decreased nerve impulses, loss of reflex response, and sudden muscle weakness. Guillain-Barré syndrome usually follows a gastrointestinal or respiratory infection. In the acute phase, the patient may temporarily require respiratory support until the inflammation subsides

Diencephalon

interbrain; composed of many smaller structures, including the thalamus and the hypothalamus. The thalamus receives all sensory stimuli except olfactory stimuli and processes and transmits them to the appropriate centers in the cerebral cortex. In addition, the thalamus receives impulses from the cerebrum and relays them to efferent nerves. The hypothalamus regulates involuntary activities, such as heart rate, body temperature, and fluid balance. It also controls many endocrine functions.

magnetic source imaging (MSI)

magnetoencephalography (MEG); Noninvasive neuroimaging technique to pinpoint the specific location where seizure activity originates and enable custom surgical treatment for tumor and epileptic tissue resection. MSI is medically necessary for presurgical evaluation of persons with epilepsy to identify and localize areas of epileptic activity

mening/o

meninges (membranes covering the brain and spinal cord). ex: mening/o/cele

meningi/o

meninges (membranes covering the brain and spinal cord). ex: meningi/oma

kinesi/o

movement. ex: brady/kines/ia

-kinesia

movement. ex: hyper/kinesia

para-

near, beside; beyond. ex: para/plegia

radicul/o

nerve root. ex: radicul/algia

neur/o

nerve. ex: neur/o/lysis (Neurolysis is sometimes performed using cryoablation or radiofrequency techniques to relieve intractable pain as a temporary or permanent measure.)

intracerebral hemorrhage

occurs when there is a sudden rupture of an artery within the brain. After the rupture, released blood compresses brain structures and destroys them. In a subarachnoid hemorrhage, blood is released into the space between the brain and the tissues that surround the brain. This condition is commonly caused by a ruptured aneurysm and is usually fatal.

nervous system

one of the most complicated systems of the body in structure and function. It senses physical and chemical changes in the internal and external environments, processes them, and then responds to maintain homeostasis. The nervous system coordinates, regulates, and integrates voluntary activities, such as walking and talking, and involuntary activities, such as digestion and circulation. The entire neural network of the body relies on the transmission of electrochemical impulses that travel from one area of the body to another. The speed at which this transmission occurs is almost instantaneous, thus providing an immediate response to change.

-taxia

order, coordination. ex: a/taxia (Ataxia refers to poor muscle coordination, especially when voluntary movements are attempted.)

-algesia

pain. ex: an/algesia

-algia

pain. ex: syn/algia (Synalgia, commonly called referred pain, is pain experienced in a part of the body other than the place of pathology. For example, right shoulder pain is commonly associated with gallstones.)

Parkinson disease

paralysis agitans or shaking palsy; Degenerative disorder in which the progressive loss of brain cells leads to impairment in motor function, including tremors, muscular rigidity, and a slowing of movement

-plegia

paralysis. ex: quadri/plegia

-paresis

partial paralysis. ex: hemi/paresis (When used alone, the term paresis refers to partial paralysis or motor weakness.)

radiculopathy

radiculitis; Disorder affecting one or more nerves at the location where the nerve root exits the spine and commonly the result of a herniated or compressed disk, degenerative changes, arthritis, or bone spurs. The areas most commonly affected are the neck (cervical radiculopathy) and lower back (lumbar radiculopathy or sciatica). Rest and antiinflammatory medications are the usual method of treatment.

-lepsy

seizure. ex: narc/o/lepsy (In narcolepsy, the individual has a sudden and uncontrollable urge to sleep at an inappropriate time, such as when driving.)

thec/o

sheath (usually referring to the meninges) ex: intra/thec/al

herpes zoster

shingles; Acute inflammatory eruption of highly painful vesicles on the trunk of the body or, occasionally, the face that is caused by the same virus that causes chickenpox. Vaccines can reduce the risk of contracting shingles. Early treatment can shorten the infection or reduce the chance of complications

-phasia

speech. ex: a/phasia

sthen/o

strength. ex: hyper/sthen/ia (Hypersthenia is characterized by rigid muscles and muscle tension when resting; also called hypertonia)

narc/o

stupor; numbness; sleep. ex: narc/o/tic (Narcotics depress the central nervous system, thus relieving pain and producing sleep.)

ton/o

tension. ex: dys/ton/ia (Dystonia usually refers to a movement disorder characterized by sustained muscle contractions, resulting in a persistently abnormal posture.)

thalam/o

thalamus. ex: thalam/o/tomy (Thalamotomy is performed to treat intractable pain or psychoses.)

Leptomeninges

the inner two meninges, the arachnoid and the pia mater, between which circulates the cerebrospinal fluid

Cerebrum

the largest, uppermost portion of the brain. It consists of two hemispheres divided by a deep longitudinal fissure, or groove. The fissure does not completely separate the hemispheres. A structure called the corpus callosum joins these hemispheres, permitting communication between the right and left sides of the brain. Each hemisphere consists of five lobes. Four of these lobes are named for the bones that lie directly above them: frontal, parietal, temporal, and occipital. The fifth lobe, the insula, is hidden from view and can be seen only upon dissection. The cerebral surface consists of numerous folds, or convolutions, called gyri. The gyri are separated by furrows, or fissures, called sulci. A thin layer called the cerebral cortex covers the entire cerebrum and is composed of gray matter. Most information processing occurs in the cerebral cortex. The remainder of the cerebrum is primarily composed of white matter (myelinated axons). Major functions of the cerebrum include sensory perception and interpretation, language, voluntary movement, and memory. Beneath the cerebrum is a primitive "emotional brain" called the limbic system. The limbic system is essential for survival and works in conjunction with the "thinking brain." It controls such behaviors as rage, fear, and anger and such emotional aspects as food enjoyment and sexual behavior. Mental and emotional illnesses are commonly the result of an imbalance in brain chemicals or electrical activity in the limbic system.

Microglia

the smallest of the neuroglia, possess phagocytic properties and become very active during times of infection.

pachy-

thick. ex: pachy/mening/itis (The dura mater (pachymeninx) is a thick membrane that provides protection for the brain and spinal cord.)

lept/o

thin, slender. ex: lept/o/mening/o/pathy (The leptomeninges include the pia mater and arachnoid, both of which are thin and delicate in structure, as opposed to the dura mater.)

Spinal Cord

transmits sensory impulses from the body to the brain and motor impulses from the brain to the muscles and organs of the body. The sensory nerve tracts are called ascending tracts because the direction of the impulse is upward. Conversely, motor nerve tracts are called descending tracts because they carry impulses in a downward direction to muscles and organs. A cross-sectional view of the spinal cord reveals an inner area of gray matter composed of cell bodies and dendrites and an outer area of white matter composed of myelinated tissue of the ascending and descending tracts. The entire spinal cord is located within the spinal cavity of the vertebral column, with spinal nerves exiting between the intervertebral spaces throughout almost the entire length of the spinal column. Unlike the cranial nerves, which have specific names, the spinal nerves are identified by the region of the vertebral column from which they exit.

ventricul/o

ventricle (of the heart or brain). ex: ventricul/itis

-asthenia

weakness, debility. ex: my/asthenia

papilledema

when the optic disc in the back of the eyeball swells

lex/o

word, phrase. ex: dys/lex/ia (Dyslexia is a difficulty with reading or an inability to read, including the tendency to reverse letters or words when reading or writing.)