narcolepsy

Pathophysiology of narcolepsy

Narcolepsy is a disabling sleep disorder characterized by excessive daytime somnolence (EDS), cataplexy and REM sleep-related abnormalities. It is a frequently-occurring but under-diagnosed disorder that affects 0.03 to 0.16% of the general population in various countries. Although most cases occur sporadically, familial clustering may be observed. The disease is tightly associated with the specific Human Leukocyte Antigen (HLA) allele, DQB1*0602/DQA1*0102 [most often in combination with HLA-DR2 (DRB1*15)]. Genetic transmission is, however, likely to be polygenic in most cases, and genetic factors other than HLA-DQ are also likely to be implicated. In addition, environmental factors are involved in disease predisposition. Human narcolepsy is currently treated with central nervous system (CNS) stimulants for EDS and antidepres-sants for cataplexy and abnormal REM sleep. These treatments are purely symptomatic and induce numerous side effects. These compounds disturb nocturnal sleep in many patients, and tolerance may develop as a result of continuous treatment. Narcolepsy was reported to exist in canines in the early 1970s. Both sporadic and familial cases are also observed in this animal species. A highly-penetrant single autosomal recessive canine narcolepsy gene (canarc-1) is involved in the transmission of narcolepsy in Doberman pinschers and Labrador retrievers. The canine model is an invaluable resource for studying the pharmacological and physiological control of EDS and cataplexy. Experiments using canine narcolepsy have demonstrated that increased cholinergic and decreased monoaminergic transmission are likely to underlie the pathophysiology of the disorder. Pharmacological studies have shown that blockade of noradrenergic uptake mediates the anticataplectic effect of currently-prescribed antidepressants, while blockade of dopaminergic uptake and/or stimulation of dopamine release mediates the wake-promoting effect of CNS stimulants.... (author abst.)

Medications
The types, number, and severity of the symptoms determine which drugs are used to treat the narcolepsy.
Severe daytime sleepiness may require treatment with high doses of stimulant medication, and sometimes a combination of stimulants may be needed.
Rare or infrequent cataplexy and other associated symptoms may not require any drug treatment, or treatment on an "as needed” regimen may be adequate.
Insomnia and depression may also require treatment.
Therapy should be catered to the individual needs of the patient. For example, improved alertness may be critical throughout the day for most students and working adults, but may be critical only at certain times of the day (for example, driving times) for other people.
Alerting medications are used for the treatment of excessive daytime sleepiness.
Amphetamines [for example, dextroamphetamine (Dexedrine), methamphetamine hydrochloride (Desoxyn), dextroamphetamine (Dextrostat), amphetamine and dextroamphetamine (Adderall)] and methylphenidate (Ritalin) are generalized central nervous system stimulants. These medications are used in narcolepsy to decrease sleepiness and improve alertness. However, they can also produce undesirable side effects including elevation of blood pressure, nervousness, irritability, and rarely, paranoid reactions. Alerting medications can also lead to drug dependency due to the feeling of euphoria they can cause. However, drug dependency has rarely been described in individuals with narcolepsy.
Pemoline (Cylert) is used as an alerting medication but it is less effective than traditional stimulants. This drug has the potential risk of toxic side effects on the liver and liver blood tests need to be monitored frequently.
Modafinil (Provigil), approved by the Food and Drug Administration (FDA) in 1999, has alerting effects similar to those of the traditional stimulant. Modafinil is not a general CNS stimulant like amphetamines, but the precise way it works is unknown. This drug has a much lower risk for high blood pressure and mental side effects because it acts in a different way than classic stimulants. It does not have significant effects on the sympathetic nervous system and does not cause mood changes, euphoria, or dependence. Furthermore, modafinil does not become ineffective with prolonged use. Headache and nausea are the most commonly reported side effects, and they are usually mild and temporary. These side effects can be reduced by a slow increase from a low initial dose up to the desired dose. This medication does not affect cataplexy and other REM sleep symptoms.
Modafinil is usually used in a single daily dose. Switching patients from amphetamines to modafinil may cause the reappearance of cataplexy in patients previously well controlled. Increasing the dose or adding an anti-cataplectic medication usually solves this problem.
Monoamine oxidase inhibitors (MAOIs): A class of antidepressants called monoamine oxidase inhibitors (MAOIs) can also be used for treatment of excessive daytime sleepiness. This includes phenelzine (Nardil) and selegiline (Eldepryl).
Anticataplectic medication is the general name for drugs that are used to treat cataplexy. These drugs may also be used for the other REM related symptoms, such as hypnagogic hallucinations and sleep paralysis. Tricyclic antidepressants (TCAs), used in lower than antidepressant doses, are often effective in controlling cataplexy. These medications act on neurotransmitter systems to produce suppression of REM sleep and consequently improve the symptoms of cataplexy.
In some cases, the side effects may limit the use of TCAs, although in most cases the side effects are temporary. The most frequent side effects are called "anticholinergic side effects," including dry mouth, dry eyes, blurred vision, urine retention, constipation, impotence, increased appetite, drowsiness, nervousness, confusion, restlessness, and headache. Some of the TCAs may increase periodic limb movements in sleep, which could further disrupt already disturbed nighttime sleep in narcoleptic patients. If TCAs are abruptly discontinued, a significant worsening of the cataplexy and other REM related symptoms could occur. This "rebound phenomenon" may appear in 72 hours after discontinuation of the medication and peak in approximately 10 days from the withdrawal.
The most frequently used TCAs for the treatment of cataplexy and other REM related symptoms are protriptyline (Vivactil), imipramine (Tofranil), clomipramine (Anafranil), desipramine (Norpramine), and amitriptyline (Elavil). Sedating TCAs such as clomipramine, amitriptyline, and imipramine, are usually prescribed for evening use, whereas the alerting ones (protriptyline and desipramine) are recommended for use during the day.
Selective serotonin reuptake inhibitors (SSRIs) are also useful in treating cataplexy at doses that are comparable to those used to treat depression. The most frequently used SSRIs for treatment of cataplexy and REM related symptoms are fluoxetine (Prozac), paroxetine (Paxil), sertraline (Zoloft), citalopram (Celexa), and venlafaxine (Effexor). The SSRIs may not be as effective as the TCAs, but they have fewer side effects. The most frequently reported side effects are dizziness, lightheadedness, nausea, and mild tremor. Rarely, mild constipation or diarrhea may occur. Fluoxetine (Prozac) given late in the day may cause insomnia.
Sodium oxybate (Xyrem), also known as gamma-hydroxybutyrate or GHB, was approved by the FDA in 2002 to treat cataplexy, and in 2005 was also approved to treat excessive daytime sleepiness (EDS). This drug is usually administered in two doses; the first is given at bedtime and the second four hours later. It unifies sleep and improves the disturbed nighttime sleep characteristic of narcolepsy. This nighttime benefit may help decrease daytime drowsiness and cataplexy. Sodium oxybate is unrelated to drugs that are known to be sleep-inducing (hypnotic) and is not used for insomnia. It can cause drowsiness and should only be taken at night.
Non-drug treatments
Non-drug treatments include education of the patient and family members and modification of behavior patterns. Understanding the symptoms of narcolepsy may help relieve some of the frustrations, fears, anger, depression, and resentment of patients and family members. Emotional reactions are responses to both the unusual nature of the symptoms and society's ignorance of this disease. National organizations and local narcolepsy support groups are additional sources of information and assistance. (See "For more information" below.)
Behavioral approaches include establishing a regular, structured sleep-wake schedule. Planned naps of 15 to 30 minutes or longer may be beneficial in reducing daytime sleepiness. Certain dietary restrictions should be observed (for example, avoidance of large meals and alcohol). Regular exercise and exposure to bright light can improve alertness. Occupational, marriage, and family counseling may help improve the patient's quality of life.
Special considerations may be needed for school schedules and working conditions. Occupations that require working in shifts, changing the work schedule, or driving should be avoided. The dangers of driving while sleepy and/or experiencing cataplexy need to be addressed and the patients should be advised to avoid driving with these symptoms. However, many patients with narcolepsy are able to drive for short distances at certain times of the day and after taking their stimulant medications. Reporting requirements to the Department of Motor Vehicles (DMV) differ from state to state. Some states require that individuals who have any lapses of consciousness or sleepiness be reported to the DMV.
What is the outcome (prognosis) for patients with narcolepsy?
Narcolepsy is a life-long disease. The symptoms may vary in severity during the patient's lifespan, but they never disappear completely. Symptoms usually gradually worsen over time, and then tend to become stable. Even then, the excessive daytime sleepiness may become more pronounced and require additional medication. At other times, cataplexy or the other symptoms may decrease or even disappear for a time.
Different factors contribute to changes in a patient's symptoms, including an irregular sleep/wake schedule, the use of substances or drugs that affect the central nervous system, infections of the brain, and the development of additional sleep disorders, such as sleep apnea syndrome (SAS), periodic limb movements in sleep syndrome (PLMS), or others. Regular doctor check-ups and adherence to the drug plan and behavioral treatment may diminish these fluctuations and improve the patient's symptoms and quality of life.
A primary care physician, usually in collaboration with a sleep medicine specialist, can recognize the symptoms of narcolepsy, initiate the proper evaluation, and manage the treatment that is recommended by the specialist.
What's in the future for narcolepsy?
The discovery that a lack of hypocretins in the cerebrospinal fluid (CSF) may be related to the cause of narcolepsy could lead to the development of tests to determine the level of hypocretins in the CSF. Such tests could help in the diagnosis of narcolepsy. The expectation is that these tests will be simple (drawing blood), and will reflect the level of hypocretins in the CSF. In addition, the discovery of the role of hypocretins in the development of narcolepsy may lead to the development of new drugs for the treatment of narcolepsy.
Narcolepsy At A Glance
Narcolepsy is a chronic disease of the central nervous system. The symptoms include excessive daytime sleepiness (EDS), loss of muscle tone (cataplexy), distorted perceptions (hypnagogic hallucinations), inability to move or talk (sleep paralysis), disturbed nocturnal sleep, and automatic behavior.
Narcolepsy usually begins in teenagers or young adults and affects both sexes equally.
The prevalence of narcolepsy is similar to that of Parkinson's disease and multiple sclerosis. Approximately 125,000 to 200,000 Americans are estimated to suffer from narcolepsy, but only fewer than 50,000 are actually properly diagnosed.
Abnormalities in the structure and function of a particular group of nerve cells in the brain called hypocretin neurons are thought to play a role in the development of narcolepsy.
The diagnosis of narcolepsy is based on a clinical evaluation, specific questionnaires, sleep logs or diaries, and the results of sleep laboratory tests (polysomnography and multiple sleep latency test).
Treatment options for narcolepsy include drug and behavioral modification therapies and disease-specific education of the patient and family members. The treatment should be individualized, depending on the types and severity of the symptoms, the life conditions of the patients, and the specific goals of therapy.
Optimal management usually takes weeks to months to achieve and requires continued communication among the physician, patient, family members, and others.
Alerting medications are used for the treatment of excessive daytime sleepiness. Amphetamines and methylphenidate (Ritalin) are general CNS stimulants that decrease sleepiness and improve alertness. Modafinil (Provigil) has alerting effects similar to those of the traditional stimulants but has less undesirable side effects.
Anticataplectic medications are used to treat cataplexy, hypnagogic hallucinations, and sleep paralysis. Tricyclic antidepressants (TCAs) are often effective in controlling cataplexy, but also frequently produce side effects that could limit their use.
Selective serotonin reuptake inhibitors (SSRIs) are also useful in the treatment of cataplexy and their side effects are milder. Sodium oxybate (Xyrem) is a medication with anticataplectic effects that also improves disturbed nocturnal sleep.
Behavioral approaches to treating narcolepsy include establishing a structured sleep-wake cycle and planned naps, and involve diet, exercise, and occupational, marriage, and family counseling.
Abnormal: Not normal. Deviating from the usual structure, position, condition, or behavior. In referring to a growth, abnormal may mean that it is cancerous or premalignant (likely to become cancer ). See the entire definition of Abnormal
Amitriptyline: An antidepressant medication. In some patients with depression, abnormal levels of brain chemicals called neurotransmitters may relate to the depression. Amitriptyline elevates mood by raising the level of neurotransmitters in brain tissue. Amitriptyline is also a sedative that is useful for depressed patients with insomnia, restlessness, and nervousness. It is sometimes used to treat fibromyalgia and symptoms related to chronic pain. Brand names are Elavil and Endep. A generic version is available.
Amphetamine: A drug with a stimulant effect on the central nervous system that can be both physically and psychologically addictive when overused. This drug has been much abused recreationally. The street term "speed" refers to stimulant drugs such as amphetamine.
Ankylosing: Undergoing ankylosis (stiffening or fusion of a joint).
Ankylosing spondylitis: A type of arthritis that causes chronic inflammation of the spine and the sacroiliac joints. Chronic inflammation in these areas causes pain and stiffness in and around the spine. Over time, chronic spinal inflammation (spondylitis) can lead to a complete cementing together (fusion) of the vertebrae, a process called ankylosis. Ankylosis causes total loss of mobility of the spine. See the entire definition of Ankylosing spondylitis
Anticholinergic: The action of certain medications that inhibit the transmission of parasympathetic nerve impulses and thereby reduce spasms of smooth muscle (such as that, for example, in the bladder).
Antidepressant: Anything, and especially a drug, used to prevent or treat depression. See the entire definition of Antidepressant
Antigen: A substance that is capable of causing the production of an antibody . See the entire definition of Antigen
Apnea: An apnea is a period of time during which breathing stops or is markedly reduced. There are two types of apneas, the more common obstructive sleep apnea and the less common central sleep apnea. See the entire definition of Apnea
Arms: An appendage in anatomy and in clinical trials. See: Arm.
Autoimmune: Pertaining to autoimmunity, a misdirected immune response that occurs when the immune system goes awry and attacks the body itself. See the entire definition of Autoimmune
Autoimmune disease: An illness that occurs when the body tissues are attacked by its own immune system . The immune system is a complex organization within the body that is designed normally to "seek and destroy" invaders of the body, including infectious agents. Patients with autoimmune diseases frequently have unusual antibodies circulating in their blood that target their own body tissues. See the entire definition of Autoimmune disease
Automatic behavior: A behavior that is performed without conscious knowledge and that does not appear to be under conscious control. See the entire definition of Automatic behavior
Blood pressure: The blood pressure is the pressure of the blood within the arteries. It is produced primarily by the contraction of the heart muscle. It's measurement is recorded by two numbers. The first (systolic pressure) is measured after the heart contracts and is highest. The second (diastolic pressure) is measured before the heart contracts and lowest. A blood pressure cuff is used to measure the pressure. Elevation of blood pressure is called "hypertension".
Blurred vision: Lack of sharpness of vision with, as a result, the inability to see fine detail. Blurred vision can occur when a person who wears corrective lens is without them. Blurred vision can also be an important clue to eye disease.

Brain: That part of the central nervous system that is located within the cranium ( skull ). The brain functions as the primary receiver, organizer and distributor of information for the body. It has two (right and left) halves called "hemispheres." See the entire definition of Brain
Breathing: The process of respiration, during which air is inhaled into the lungs through the mouth or nose due to muscle contraction, and then exhaled due to muscle relaxation.
Cataplexy: A debilitating medical condition in which a person suddenly feels weak and collapses at moments of strong emotion such as laughter, anger, fear or surprise. In so collapsing, people with cataplexy may injure themselves. See the entire definition of Cataplexy
Cerebrospinal fluid: CSF. A watery fluid, continuously produced and absorbed, which flows in the ventricles (cavities) within the brain and around the surface of the brain and spinal cord. See the entire definition of Cerebrospinal fluid
Chronic: This important term in medicine comes from the Greek chronos, time and means lasting a long time. See the entire definition of Chronic
Chronic disease: A disease that persists for a long time. A chronic disease is one lasting 3 months or more, by the definition of the U.S. National Center for Health Statistics. Chronic diseases generally cannot be prevented by vaccines or cured by medication, nor do they just disappear. Eighty-eight percent of Americans over 65 years of age have at least one chronic health condition (as of 1998). Health damaging behaviors - particularly tobacco use, lack of physical activity, and poor eating habits - are major contributors to the leading chronic diseases. See the entire definition of Chronic disease
Constipation: Infrequent (and frequently incomplete) bowel movements. The opposite of diarrhea, constipation is commonly caused by irritable bowel syndrome, diverticulosis, and medications (constipation can paradoxically be caused by overuse of laxatives). Colon cancer can narrow the colon and thereby cause constipation. The large bowel (colon) can be visualized by barium enema x-rays, sigmoidoscopy, and colonoscopy. Barring a condition such as cancer, high-fiber diets can frequently relieve the constipation.
Contrast: Short for "contrast media." Contrast media are X-ray dyes used to provide contrast, for example, between blood vessels and other tissue.
Depression : An illness that involves the body, mood, and thoughts, that affects the way a person eats and sleeps, the way one feels about oneself, and the way one thinks about things. A depressive disorder is not the same as a passing blue mood. It is not a sign of personal weakness or a condition that can be wished away. People with a depressive disease cannot merely "pull themselves together" and get better. Without treatment, symptoms can last for weeks, months, or years. Appropriate treatment, however, can help most people with depression. See the entire definition of Depression
Diagnosis: 1 The nature of a disease ; the identification of an illness. 2 A conclusion or decision reached by diagnosis. The diagnosis is rabies . 3 The identification of any problem. The diagnosis was a plugged IV. See the entire definition of Diagnosis
Diarrhea : A familiar phenomenon with unusually frequent or unusually liquid bowel movements, excessive watery evacuations of fecal material. The opposite of constipation . The word "diarrhea" with its odd spelling is a near steal from the Greek "diarrhoia" meaning "a flowing through." Plato and Aristotle may have had diarrhoia while today we have diarrhea. There are myriad infectious and noninfectious causes of diarrhea. See the entire definition of Diarrhea
Dizziness : Painless head discomfort with many possible causes including disturbances of vision, the brain, balance (vestibular) system of the inner ear, and gastrointestinal system. Dizziness is a medically indistinct term which laypersons use to describe a variety of conditions ranging from lightheadedness, unsteadiness to vertigo. See the entire definition of Dizziness
Dry mouth: The condition of not having enough saliva to keep the mouth wet. This is due to inadequate function of the salivary glands. Everyone has dry mouth once in a while when they are nervous, upset or under stress. But if someone has a dry mouth most all of the time, it can be uncomfortable and lead to serious health problems. See the entire definition of Dry mouth
Elavil: See: Amitriptyline.
Euphoria: Elevated mood. Euphoria is a desirable and natural occurrence when it results from happy or exciting events. An excessive degree of euphoria that is not linked to events is characteristic of hypomania or mania, abnormal mood states associated with bipolar disorders. See the entire definition of Euphoria
Excessive daytime sleepiness: A neurological disorder in which there is a sudden recurrent uncontrollable compulsion to sleep. Excessive daytime sleepiness is also known as narcolepsy. See the entire definition of Excessive daytime sleepiness
Fatigue: A condition characterized by a lessened capacity for work and reduced efficiency of accomplishment, usually accompanied by a feeling of weariness and tiredness. Fatigue can be acute and come on suddenly or chronic and persist. See the entire definition of Fatigue
FDA: The Food and Drug Administration, an agency within the U.S. Public Health Service, which is a part of the Department of Health and Human Services. See the entire definition of FDA
Food and Drug Administration: The FDA, an agency within the U.S. Public Health Service, which is a part of the Department of Health and Human Services. See the entire definition of Food and Drug Administration
Gene: The basic biological unit of heredity . A segment of deoxyribonucleic acid (DNA) needed to contribute to a function. See the entire definition of Gene
Genetic: Having to do with genes and genetic information.
Headache : A pain in the head with the pain being above the eyes or the ears, behind the head (occipital), or in the back of the upper neck. Headache, like chest pain or back ache, has many causes. See the entire definition of Headache
Heart: The muscle that pumps blood received from veins into arteries throughout the body. It is positioned in the chest behind the sternum (breastbone; in front of the trachea, esophagus, and aorta; and above the diaphragm muscle that separates the chest and abdominal cavities. The normal heart is about the size of a closed fist, and weighs about 10.5 ounces. It is cone-shaped, with the point of the cone pointing down to the left. Two-thirds of the heart lies in the left side of the chest with the balance in the right chest. See the entire definition of Heart
Heredity: Genetic transmission from parent to child.
High blood pressure : Also known as hypertension, high blood pressure is, by definition, a repeatedly elevated blood pressure exceeding 140 over 90 mmHg -- a systolic pressure above 140 with a diastolic pressure above 90. See the entire definition of High blood pressure
HLA: The major human histocompatibility system. HLA-typing is done before transplantation to determine the degree of histocompatibility. HLA is an acronym for Human Leukocyte Antigens. See the entire definition of HLA
Hypnagogic: Concerning the drowsiness one commonly feels before sleep , the transitional state preceding sleep , and also the hallucinations that may occur at that time. See the entire definition of Hypnagogic
Hypothalamus: The area of the brain that controls body temperature, hunger, and thirst.
Immune: Protected against infection. The Latin immunis means free, exempt.
Immune system: A complex system that is responsible for distinguishing us from everything foreign to us, and for protecting us against infections and foreign substances. The immune system works to seek and kill invaders. See the entire definition of Immune system
Impotence : A common problem among men characterized by the consistent inability to sustain an erection sufficient for sexual intercourse or the inability to achieve ejaculation , or both. Impotence can vary. It can involve a total inability to achieve an erection or ejaculation, an inconsistent ability to do so, or a tendency to sustain only very brief erections. See the entire definition of Impotence
Indicate: In medicine, to make a treatment or procedure advisable because of a particular condition or circumstance. For example, certain medications are indicated for the treatment of hypertension during pregnancy while others are contraindicated.
Infection: The growth of a parasitic organism within the body. (A parasitic organism is one that lives on or in another organism and draws its nourishment therefrom.) A person with an infection has another organism (a "germ") growing within him, drawing its nourishment from the person. See the entire definition of Infection
Injury: Harm or hurt. The term "injury" may be applied in medicine to damage inflicted upon oneself as in a hamstring injury or by an external agent on as in a cold injury. The injury may be accidental or deliberate, as with a needlestick injury. The term "injury" may be synonymous (depending on the context) with a wound or with trauma.
Insomnia: The perception or complaint of inadequate or poor-quality sleep because of one or more of the following: difficulty falling asleep; waking up frequently during the night with difficulty returning to sleep; waking up too early in the morning; or unrefreshing sleep. Insomnia is not defined by the number of hours of sleep a person gets or how long it takes to fall asleep. Individuals vary normally in their need for, and their satisfaction with, sleep. Insomnia may cause problems during the day, such as tiredness, a lack of energy, difficulty concentrating, and irritability. See the entire definition of Insomnia
Jaw: The bones below the mouth (the mandible) and the bone above the mouth just above the mouth (the maxilla). The word jaw comes from the Anglo-Saxon ceowan meaning to chew. See the entire definition of Jaw
Laboratory: A place for doing tests and research procedures and preparing chemicals, etc. Although "laboratory" looks very like the Latin "laboratorium" (a place to labor, a work place), the word "laboratory" came from the Latin "elaborare" (to work out, as a problem, and with great pains), as evidenced by the Old English spelling "elaboratory" designating "a place where learned effort was applied to the solution of scientific problems." See the entire definition of Laboratory
Lightheadedness: A feeling you are "going to faint." Lightheadedness is medically distinct from dizziness, unsteadiness, and vertigo. See: Dizziness, Unsteadiness, and Vertigo.
Limb: The arm or leg.
Liver: An organ in the upper abdomen that aids in digestion and removes waste products and worn-out cells from the blood. The liver is the largest solid organ in the body. The liver weighs about three and a half pounds (1.6 kilograms). It measures about 8 inches (20 cm) horizontally (across) and 6.5 inches (17 cm) vertically (down) and is 4.5 inches (12 cm) thick.
See the entire definition of Liver
Medical history: 1. In clinical medicine, the patient's past and present which may contain clues bearing on their health past, present, and future. The medical history, being an account of all medical events and problems a person has experienced, including psychiatric illness, is especially helpful when a differential diagnosis is needed.2. The history of medicine.
Memory: 1. The ability to recover information about past events or knowledge. 2. The process of recovering information about past events or knowledge. 3. Cognitive reconstruction. The brain engages in a remarkable reshuffling process in an attempt to extract what is general and what is particular about each passing moment. See the entire definition of Memory
Modafinil: An oral drug first approved by the FDA in 1998 for the treatment of narcolepsy , a condition in which there is an uncontrollable desire to sleep . Modafinil promotes wakefulness. In 2004 the FDA also approved modafinil for the treatment of obstructive sleep apnea and sleeping problems caused by shift work. See the entire definition of Modafinil
Motor: In medicine, having to do with the movement of a part of the body. Something that produces motion or refers to motion. For example, a motor neuron is a nerve cell that conveys an impulse to a muscle causing it to contract. The term "motor" today is also applied to a nerve that signals a gland to secrete. Motor is as opposed to sensory.
Mouth: 1. The upper opening of the digestive tract, beginning with the lips and containing the teeth, gums, and tongue. Foodstuffs are broken down mechanically in the mouth by chewing and saliva is added as a lubricant. Saliva contains amylase, an enzyme that digests starch. 2. Any opening or aperture in the body. The mouth in both senses of the word is also called the os, the Latin word for an opening, or mouth. The o in os is pronounced as in hope. The genitive form of os is oris from which comes the word oral.

Multiple sclerosis : Abbreviated MS. A disease of the central nervous system (CNS) marked by numbness, weakness, loss of muscle coordination, and problems with vision, speech, and bladder control. MS is an autoimmune disease in which the body's immune system attacks myelin, a key substance that serves as a nerve insulator and helps in the transmission of nerve signals. The progress, severity and specific symptoms in MS are unpredictable. One never knows when attacks will occur, how long they will last, or how severe they will be. Most people with MS are between the ages of 20 and 40 at the time of diagnosis. The term "multiple" refers to the multiple places in the CNS that are affected and to the multiple relapses and remissions characteristic of MS. See the entire definition of Multiple sclerosis
Muscle: Muscle is the tissue of the body which primarily functions as a source of power. There are three types of muscle in the body. Muscle which is responsible for moving extremities and external areas of the body is called "skeletal muscle." Heart muscle is called "cardiac muscle." Muscle that is in the walls of arteries and bowel is called "smooth muscle."
Mutation: A permanent change, a structural alteration, in the DNA or RNA . In humans and many other organisms, mutations occur in DNA. However, in retroviruses like HIV , mutations occur in RNA which is the genetic material of retroviruses. See the entire definition of Mutation
Narcolepsy: A neurological disorder marked by a sudden recurrent uncontrollable compulsion to sleep . Narcolepsy is often associated with cataplexy (a sudden loss of muscle tone and paralysis of voluntary muscles associated with a strong emotion), sleep paralysis (immobility of the body that occurs in the transition from sleep to wakefulness), what are called hypnagogic hallucinations (pre-sleep dreams) and automatic behaviors (such as doing something "automatically" and not remembering afterwards how one did it). See the entire definition of Narcolepsy
Nausea: Nausea, is the urge to vomit. It can be brought by many causes including, systemic illnesses, such as influenza, medications, pain, and inner ear disease. When nausea and/or vomiting are persistent, or when they are accompanied by other severe symptoms such as abdominal pain, jaundice, fever, or bleeding, a physician should be consulted.
Nerve: A bundle of fibers that uses chemical and electrical signals to transmit sensory and motor information from one body part to another. See: Nervous system.
Neurological: Having to do with the nerves or the nervous system.
Neurotransmitter: A chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or other tissue. A neurotransmitter is a messenger of neurologic information from one cell to another. See the entire definition of Neurotransmitter
Objective: In a microscope, the objective (also called the objective lens) is the lens nearest to the object being examined whereas the lens closest to the eye is termed the ocular (the eyepiece). See the entire definition of Objective
Onset: In medicine, the first appearance of the signs or symptoms of an illness as, for example, the onset of rheumatoid arthritis . There is always an onset to a disease but never to the return to good health. The default setting is good health. See the entire definition of Onset
Paralysis: Loss of voluntary movement (motor function). Paralysis that affects only one muscle or limb is partial paralysis, also known as palsy; paralysis of all muscles is total paralysis, as may occur in cases of botulism.
Parkinson's disease: See: Parkinson disease.
Polysomnography: Continuous recording of specific physiologic variables during sleep . Polysomnography typically records brain wave changes (electroencephalogram), eye movements (electrooculogram), muscle tone ( electromyogram ), respiration, electrocardiogram (EKG), and leg movements. See the entire definition of Polysomnography
Prevalence: The proportion of individuals in a population having a disease. Prevalence is a statistical concept referring to the number of cases of a disease that are present in a particular population at a given time. See the entire definition of Prevalence
Primary care: The "medical home" for a patient, ideally providing continuity and integration of health care. All family physicians and most pediatricians and internists are in primary care. The aims of primary care are to provide the patient with a broad spectrum of care, both preventive and curative, over a period of time and to coordinate all of the care the patient receives. See the entire definition of Primary care
Prognosis: 1. The expected course of a disease .2. The patient's chance of recovery. The prognosis predicts the outcome of a disease and therefore the future for the patient . His prognosis is grim, for example, while hers is good. See the entire definition of Prognosis
Proteins: Large molecules composed of one or more chains of amino acids in a specific order determined by the base sequence of nucleotides in the DNA coding for the protein. See the entire definition of Proteins
Provigil: Brand name of the drug modafinil. See: Modafinil.
Quality of life: An important consideration in medical care, quality of life refers to the patient's ability to enjoy normal life activities. Some medical treatments can seriously impair quality of life without providing appreciable benefit, while others greatly enhance quality of life.
Rebound: Return of the original symptoms when maneuvers or treatment is discontinued.
Receptor: 1. In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance. There are many receptors. There is a receptor for ( insulin ; there is a receptor for low-density lipoproteins ( LDL ); etc. To take an example, the receptor for substance P, a molecule that acts as a messenger for the sensation of pain , is a unique harbor on the cell surface where substance P docks. Without this receptor, substance P cannot dock and cannot deliver its message of pain. Variant forms of nuclear hormone receptors mediate processes such as cholesterol metabolism and fatty acid production. Some hormone receptors are implicated in diseases such as diabetes and certain types of cancer. A receptor called PXR appears to jump-start the body's response to unfamiliar chemicals and may be involved in drug-drug interactions.2. In neurology, a terminal of a sensory nerve that receives and responds to stimuli. See the entire definition of Receptor
Regimen: With the accent on the first syllable (reg as in Reggie Jackson), a regimen is a plan, a regulated course such as a diet, exercise or treatment, designed to give a good result. A low-salt diet is a regimen.
REM sleep : REM sleep is the portion of sleep when there are rapid eye movements (REMs). See the entire definition of REM sleep
Resolution: In genetics , resolution refers to the degree of molecular detail on a physical map of DNA , ranging from low to high. See the entire definition of Resolution
Reuptake: The reabsorption of a secreted substance by the cell that originally produced and secreted it. The process of reuptake, for example, affects serotonin. See the entire definition of Reuptake
Rule out: A term much used in medicine, meaning to eliminate or exclude something from consideration. The ACB (albumin cobalt binding) test helps rule out a heart attack in the differential diagnosis of severe chest pain.
Sclerosis: Localized hardening of skin.
Sensation: In medicine and physiology , sensation refers to the registration of an incoming ( afferent ) nerve impulse in that part of the brain called the sensorium , which is capable of such perception. Therefore, the awareness of a stimulus as a result of its perception by sensory receptors. (Sensory is here synonymous with sensation.) See the entire definition of Sensation
Serotonin: A hormone , also called 5-hydroxytryptamine , in the pineal gland , blood platelets, the digestive tract, and the brain. Serotonin acts both as a chemical messenger that transmits nerve signals between nerve cells and that causes blood vessels to narrow. See the entire definition of Serotonin
Sleep : The body's rest cycle. See the entire definition of Sleep
Sleep apnea: The temporary stoppage of breathing during sleep , often resulting in daytime sleepiness. Apnea is a Greek word that means "want of breath." See the entire definition of Sleep apnea
Sleep disorders: Any disorder that affects, disrupts, or involves sleep . The most common sleep disorder is probably snoring, although it is usually not medically significant. Insomnia, sleep apnea , restless leg syndrome , and sleepwalking are also sleep disorders. Most large medical centers have diagnostic and treatment facilities dedicated to sleep disorders. See the entire definition of Sleep disorders
Sleep paralysis: A frightening form of paralysis that occurs when a person suddenly finds himself or herself unable to move for a few minutes, most often upon falling asleep or waking up. Sleep paralysis is due to an ill-timed disconnection between the brain and the body. See the entire definition of Sleep paralysis
Sodium: The major positive ion (cation) in fluid outside of cells. The chemical notation for sodium is Na+. When combined with chloride, the resulting substance is table salt. See the entire definition of Sodium
Spinal cord: The major column of nerve tissue that is connected to the brain and lies within the vertebral canal and from which the spinal nerves emerge. Thirty-one pairs of spinal nerves originate in the spinal cord: 8 cervical , 12 thoracic , 5 lumbar, 5 sacral, and 1 coccygeal. The spinal cord and the brain constitute the central nervous system ( CNS ). The spinal cord consists of nerve fibers that transmit impulses to and from the brain. Like the brain, the spinal cord is covered by three connective-tissue envelopes called the meninges . The space between the outer and middle envelopes is filled with cerebrospinal fluid ( CSF ), a clear colorless fluid that cushions the spinal cord against jarring shock. Also known simply as the cord. See the entire definition of Spinal cord
Spondylitis: Inflammation of one or more of the vertebrae of the spine. Diffuse inflammation of the spine is seen in the disease ankylosing spondylitis . Localized spondylitis is seen with infections of a certain area of the spine, such as in Pott's disease. See the entire definition of Spondylitis
Stress: Forces from the outside world impinging on the individual. Stress is a normal part of life that can help us learn and grow. Conversely, stress can cause us significant problems. See the entire definition of Stress
Stroke : The sudden death of some brain cells due to a lack of oxygen when the blood flow to the brain is impaired by blockage or rupture of an artery to the brain. A stroke is also called a cerebrovascular accident or, for short, a CVA. See the entire definition of Stroke
Sympathetic nervous system: A part of the nervous system that serves to accelerate the heart rate, constrict blood vessels, and raise blood pressure. The sympathetic nervous system and the parasympathetic nervous system constitute the autonomic nervous system, the branch of the nervous system that performs involuntary functions.
Symptom: Any subjective evidence of disease. Anxiety, lower back pain, and fatigue are all symptoms. They are sensations only the patient can perceive. In contrast, a sign is objective evidence of disease. A bloody nose is a sign. It is evident to the patient, doctor, nurse and other observers.
Syndrome: A set of signs and symptoms that tend to occur together and which reflect the presence of a particular disease or an increased chance of developing a particular disease. See the entire definition of Syndrome
Therapy: The treatment of disease . See the entire definition of Therapy
Tired: A feeling of a lessened capacity for work and reduced efficiency of accomplishment, usually accompanied by a sense of weariness and fatigue. See the entire definition of Tired
Tiredness: See: Tired.
Trauma: Any injury , whether physically or emotionally inflicted. "Trauma" has both a medical and a psychiatric definition. Medically, "trauma" refers to a serious or critical bodily injury, wound, or shock . This definition is often associated with trauma medicine practiced in emergency rooms and represents a popular view of the term. In psychiatry , "trauma" has assumed a different meaning and refers to an experience that is emotionally painful, distressful, or shocking, which often results in lasting mental and physical effects. See the entire definition of Trauma
Tremor: Any abnormal repetitive shaking movement of the body. Tremors have many causes and can be inherited, be related to illnesses such as thyroid disease, or caused by fever, hypothermia, drugs or fear.
Trigger: Something that either sets off a disease in people who are genetically predisposed to developing the disease, or that causes a certain symptom to occur in a person who has a disease. For example, sunlight can trigger rashes in people with lupus.
Urine: Liquid waste. The urine is a clear, transparent fluid. It normally has an amber color. The average amount of urine excreted in 24 hours is from 40 to 60 ounces (about 1,200 cubic centimeters). Chemically, the urine is mainly an aqueous (watery) solution of salt (sodium chloride) and substances called urea and uric acid. Normally, it contains about 960 parts of water to 40 parts of solid matter. Abnormally, it may contain sugar (in diabetes), albumen (a protein) (as in some forms of kidney disease), bile pigments (as in jaundice), or abnormal quantities of one or another of its normal components.
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