The central nervous system (CNS) consists of the brain and spinal cord.
Description
Comprised of the brain and spinal cord, the CNS is central to the body as opposed to peripheral. It is responsible for unconscious and conscious body functions as well as intellectual functions that allow humans to think. The neuron is the basic nerve cell of the nervous system, however, the nervous system contains many types of cells other than nerve cells. The nerve cell consists of a nucleus in a cell body, dendrites, and axons. The CNS is heavily guarded with protective features, however, this does not make it immune to disease and disorder. The CNS is cushioned with cerebrospinal fluid (CFS), protected by three layers of meninges, and protected from the body by the blood-brain barrier. The blood-brain barrier prevents harmful substances and disease-causing organisms from contaminating the bloodstream entering the CNS.
The skull (cranium) encloses the brain. Three main areas of the brain, the cerebrum, cerebellum, and brain-stem, contain myelinated nerve fibers and white matter, in contrast to the cortex of the brain, the layer of gray matter. The cerebrum, the largest part of the brain containing the left and right hemispheres, controls conscious activities like motor functions. The cerebellum, located above the brainstem, communicates with other regions of the brain and spinal cord to control balance and coordination. The brainstem, the lowest part of the brain extending to the spinal cord, controls unconscious activities necessary for survival like breathing and blood pressure. The spinal cord is protected by the vertebral column from the cervical area to the sacrum. The spinal cord nerves relay sensory information to the brain and motor information to the body.
Function
The central nervous system (CNS) is a processing center that integrates sensory and motor activities via the brain and spinal cord. Nerves are like an electrical wire with an insulating sheath, called myelin, that facilitates the smooth, high-speed transmission of messages. Information in the nervous system is carried by brief electrical impulses that are conducted away from the body of the nerve cell along the axons. When impulses reach the tips of axons, information is transmitted to the next nerve cell in line, or to a muscle or organ. At the point of contact, or synapse, the information is carried across the gap between cells by neurotransmitters. The CNS has two-way communication. Nerve fibers either relay messages to the brain to communicate sensory stimuli, or they relay messages away from the brain to the body's tissues and organs. It is through the spinal cord that messages are sent back and forth to the brain. Spinal nerves in the spinal cord connect the message relay system to rest of the body
Role in human health
Many health care providers, neurologists, neurosurgeons, physiatrists, neuropsychologists, nurses, occupational therapists, speech language pathologists, physical
therapists, and vocational rehabilitation counselors play a role on the health care team and share in the responsibility of the neurologic patient. A combination of methods for assessing patients with neurologic diseases and disorders enables health care professionals to make informed treatment recommendations. These include neurologic and physical examination, laboratory tests such as lumbar puncture, brain-imaging scans such as MRI, neuropsychological testing, and nuclear medicine tests. Treating neurologic diseases and disorders requires active patient participation along with education and support from health care professionals. While patient education may be time-consuming, it is extremely important to the process of maintaining health and preventing disease.
Alzheimer's disease (AD), a progressive, neurodegenerative disease, is the most common cause of dementia in later life. The course of the disease varies from person to person. Although the cause of AD is not yet known, researchers have found a familial tendency for AD. They have also implicated several possibilities including genetics, environmental factors, and biochemical changes in the brain caused by low levels of certain neurotransmitters. AD usually begins after age 65, however, it may have an early onset as early as age 40.
SYMPTOMS. The severity and progression of symptoms vary from person to person. Some of the early symptoms of AD, such as forgetfulness or loss of concentration, can easily be overlooked because they resemble signs of aging or could result from fatigue, depression, or the use of certain medications. Symptoms of AD include:
There is no specific test to confirm a diagnosis of AD. A combination of tools including brain imaging technologies, patient and family history, physical and neurological examination, and neuropsychological testing are utilized to definitively diagnose AD. There is no cure for AD and no clinically proven way to slow the progression of the disease. For some patients, medication may alleviate some of the symptoms. Treatments are intended to make the patient more comfortable.
Stroke
Stroke, also called cerebral vascular accident (CVA), occurs when the blood flow to part of the brain is disrupted. There are primarily two categories of stroke, ischemic and hemorrhagic. The most frequent cause of stroke is a blockage (ischemic) of a blood vessel in the brain. The blockage can have several causes but all with the same result, brain cell damage or death. Brain cells cannot survive without a blood supply of oxygen and nutrients. Blockage of blood flow in the brain can be caused by a clot in a blood vessel (thrombosis) of the brain, the movement of a clot from another part of the body (embolism) to the brain, or a severe narrowing of an artery in the brain (stenosis). In a hemorrhagic stroke, a blood vessel in the brain bursts, bleeding into the brain (intracerebral hemorrhage) or into the spaces surrounding the brain.
SYMPTOMS. The signs and symptoms of stroke depend on the areas of the brain affected and the functions they control. The right cerebral hemisphere controls the left side of the body and the left cerebral hemisphere controls the right side of the body. The symptoms of stroke may be:
sudden numbness or weakness, especially on one side of the body
sudden confusion, difficulty speaking, or understanding speech
sudden difficulty seeing in one or both eyes
sudden trouble walking
sudden dizziness, loss of balance or coordination
sudden severe headache
paralysis, pain
Risk factors for stroke are either changeable or not. For example, a person cannot change their age or family history, but they can change behaviors, like smoking, that put them at risk for a stroke. Risk factors for stroke include:
According to the National Center for Health Statistics, stroke is the third leading cause of death in the United States. In order to improve this statistic, patients need prompt interventions. The public education campaign, "Know Stroke: Know the Signs. Act in Time," promoted by the National Institute of Neurological Disorders and Stroke (NINDS) teaches people how to recognize the signs and symptoms of stroke and the importance of prompt medical treatment to improve recovery. Tissue plasminogen activator (t-PA), the first Food and Drug Administration (FDA) approved acute ischemic stroke treatment, needs to be given within a three-hour window of the onset of symptoms to dissolve the clot. Stroke is diagnosed by a neurological examination, blood tests, brain imaging scans, Doppler ultra-sound, or arteriography.
Multiple sclerosis
Multiple sclerosis (MS) is a common neurological disease that occurs mainly in young adults. The course of the disease varies from person to person and is categorized by type. Relapsing-remitting MS (RRMS) has a course of acute attacks with full or partial recovery during remissions. Secondary progressive MS (SPMS) is initially relapsing-remitting and then becomes progressive. Primary progressive MS (PPMS) has a progressive course from the beginning of the disease with no remissions. Progressive-relapsing MS (PRMS) has a progressive
course from the beginning with acute relapses, with or without full recovery.
MS is believed to be an autoimmune disease, where the immune system targets the myelin in the central nervous system. MS is the most common demyelinating disease. During an attack (exacerbation), inflammation occurs in the white matter of the central nervous system. This process is followed by destruction of myelin causing areas called plaques. Not only is the myelin damaged, but the attack may also damage or sever the nerve fibers underneath the myelin. The nerve cannot conduct or send a signal properly without the myelin sheath.
MS can be difficult to diagnose because there are other diseases with similar symptoms, and there is no specific test to confirm the diagnosis. A process of elimination may be done along with a combination of imaging technologies such as MRI, CSF analysis, evoked potentials (EVP), medical history, and clinical examination.
SYMPTOMS. The symptoms of MS are unpredictable, can vary greatly from person to person, and come and go. The neurological symptoms of MS are the result of demyelination. Symptoms include:
blurred, double vision, and blind spots
numbness, tingling, and paresthesias (pins and needles)
fatigue, dizziness, and vertigo
difficulties with memory loss, concentration, and attention
difficulty with coordination, balance, and gait
muscle and nerve pain, muscle weakness, and tremors
bladder and bowel problems
There are many conventional and alternative treatment therapies to alleviate the symptoms of MS, but there is no cure. However, four medications have been shown to slow down disease progression. The FDA approved Interferon beta 1b (Betaseron) in 1993, Interferon beta 1a (Avonex) in 1996, and glatirameracetate (Copaxone) in 1996 for the treatment of RRMS. They were clinically shown to decrease the frequency and severity or attacks by approximately 30%. Mitoxantrone (Novantrone), a chemotherapy agent that suppresses immune function, was FDA approved in 2000 for the treatment of worsening RRMS and SPMS.
Research
Research in neuroscience and the development of new research techniques and technologies offer hope to the millions of patients and families affected by neurological diseases and disorders. Research into new treatments doesn't solve the problem, therefore, scientists are researching areas such as neurogenetics to discover how to prevent certain disorders. New treatment options and the possibility of cures can bring a sense of optimism to patients. However, the research process takes years before a treatment is available to the public. Only controlled clinical trials with human participants can determine if a treatment is safe and effective for patients.
KEY TERMS
Antigen—A substance that stimulates the immune system to produce antibodies.
Autoimmune—The immune system sees self as a foreign antigen and attacks a part of the body.
Cerebrospinal fluid—Fluid surrounding and cushioning the brain and spinal cord.
Cognitive—Information processing functions carried out by the brain that include comprehension, memory, attention, planning, problem-solving, etc.
Dura mater—The outermost layer of meninges.
Exacerbation—The appearance of new symptoms or the aggravation of old symptoms.
Gene—Basic units of heredity in every cell that tell the cell how to put together different proteins.
Interferon—A naturally occuring immune system protein.
Lumbar puncture—A diagnostic procedure that uses a hollow needle to penetrate the spinal canal between the vertebrae to remove cerebrospinal fluid for analysis.
Meninges—Three layers of protective connective tissue covering the brain and spinal consisting of the pia mater, arachnoid, and dura mater.
Myelin—A protective coating made of fat and protein that insulates the nerve and enhances efficient nerve fiber conduction.
Neurotransmitter—A chemical that transmits a nerve impulse at the synapse.
BOOKS
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision: DSM-IV-TR. Washington, DC: American Psychiatric Association, 2000.
Burks, J. S., and K. P. Johnson. Multiple Sclerosis: Diagnosis, Medical Management and Rehabilitation. New York: Demos, 2000.
Caplan, L.R. Caplan's Stroke: A Clinical Approach. Boston: Butterworth-Heinenmann, 2000.
PERIODICALS
"Recommendations for the Establishment of Stroke Centers: A Consensus Statement from the Brain Attack Coalition." Journal of American Medical Association (June 21, 2000): 3102-3109.
Stroke Council of the American Heart Association. "Primary Prevention of Ischemic Stroke." Circulation (Jan. 2,2001): 163-182.
ORGANIZATIONS
Alzheimer's Association. 919 N. Michigan Ave., Ste. 1100, Chicago IL 60611-1676. (800) 272-3900. <http://www.alz.org>.
Alzheimer's Disease Education and Referral Center. PO Box 8250. Silver Spring, MD 20907-8250. (800) 438-4380. <http://www.alzheimers.org>.
American Academy of Neurology. 1080 Montreal Ave., St. Paul, MN 55116. (651) 695-1940.
American Neurological Association. 5841 Cedar Lake Rd., Ste. 204, Minneapolis, MN 55416. <http://www.ana.org>.
