paralysis implies motor weakness, and can be partial or complete. It can result from dysfunction at any point in the motor system, and the level at which this occurs determines the characteristics of the paralysis.

Movement is initiated by specialized motor nerve cells, the upper motor neurons (sometimes called pyramidal cells, because of their shape). These cells are situated in a special part of the cerebral hemispheres, the motor cortex, and are arranged in a ‘somatotopic’ manner — which means that motor neurons subserving a particular part of the body are clustered together, and are always found in that same place. Upper motor- neurones destined to serve movements of the leg, for example, are located nearer the midline than those destined for the arms. On each side of the brain, the axons from these motor neurons converge as they leave the cerebral cortex, and pass down the brain stem as separate tracts. Just before they reach the spinal cord, most of the fibres from one side cross to the opposite side. This means that upper motor neurons on one side of the cerebral cortex control movements principally on the other side of the body. In the spinal cord they descend as a tract in the outer side part of the cord, and fibres leave the tract progressively to reach and to act on lower motor neurons (anterior horn cells), either directly or via intermediary neurons. Those destined to activate arm muscles, for example, synapse with lower motor neurons in the cervical part of the cord. From there, axons of the lower motor neurons form the motor component of the peripheral nerves, finally reaching the muscle for which they are destined. In the muscle, each nerve fibre divides into a large number of branches. A single branch innervates an individual muscle fibre at a specialized structure, the neuromuscular junction. The signal is finally passed from the nerve to the muscle by the release of a chemical substance, acetylcholine, which diffuses across the narrow gap between nerve and muscle and reacts with specialized acetylcholine receptors on the muscle fibres. This reaction leads to a local electrical potential that triggers muscle contraction.

Upper motor neuron paralysis

is characterized by stiffness of the affected muscles (spasticity); weakness of the muscles that extend the arm and of the muscles that flex the leg; drooping of the lower part of the face; increased tendon reflexes (the response that muscles make when their tendons are briefly tapped); and a positive Babinski (extensor plantar) reflex response, in which the toes move upwards when the side or sole of the foot is stroked. A common cause of an upper motor neuron paralysis is a ‘stroke’, in which either infarction (loss of blood supply) or haemorrhage in one cerebral hemisphere disrupts the motor neurons destined for the opposite half of the body. Hemiplegia is the term for such one-sided paralysis. Other causes include head injury, cerebral tumours, cerebral abscess, and also cerebral palsy in which damage occurs around the time of birth. The extent of the weakness can range from a slight interference with walking, to a paralysis so profound that the patient is chair-bound.

Upper motor neuron fibres can be damaged in their course between the brain and their lower ends by spinal cord injury: a broken neck may cause paralysis of all four limbs as well as the muscles of the torso; or a broken back, paralysis of the legs. Paraplegia is the term for such paralysis on both sides.

Lower motor neuron paralysis

has a different set of characteristics, comprising muscle wasting and weakness, loss of muscle tone, and depressed tendon reflexes. The cause can be damage to the anterior horn cells themselves (as in poliomyelitis); spinal injury in the lower back, where the motor nerve roots run down inside the vertebral column after leaving the spinal cord; or damage to the motor fibres in the nerves running from the spine to the muscles. Weakness can be due also to a disorder at the neuromuscular junction. In this instance it has a characteristic ‘fatiguable’ quality, in which the more the muscle is used the weaker it becomes. The muscles are not wasted. The commonest disease causing a neuromuscular transmission disorder is myasthenia gravis, in which the immune system makes antibodies to the acetylcholine receptors on the muscle fibres. The toxins of certain snakes (e.g. the banded krait) and of bacteria (e.g. botulinum toxin) also block neuromuscular transmission and paralyse their victim. Curare and the contemporary drugs developed from it cause paralysis by acting at this site: originally an arrow poison, but now a feature used to good effect (and of course reversibly) in anaesthetic practice Paralysis can also be due to muscle disease (myopathy). The weakness here usually principally affects the shoulder girdle muscles (making it difficult for the patient to elevate their arms) and the muscles of the pelvis (thereby interfering with walking). Rising from a chair or climbing stairs can be particularly difficult. Muscular dystrophies are genetic disorders, usually progressive, which can lead to profound paralysis. Other causes include inflammatory disorders (e.g. polymyositis), metabolic conditions, and toxic substances.

J. Newsom-Davis

paralysis or palsy , complete loss or impairment of the ability to use voluntary muscles, usually as the result of a disorder of the nervous system. The nervous tissue that is injured may be in the brain, the spinal cord, or in the muscles themselves. Accordingly there may be general paralysis, involvement of only one side (hemiplegia), paralysis on both sides at one level ( paraplegia or quadriplegia), or localized paralysis in a small group of nerves or muscles.

The cause of paralysis may be any injury that tears or compresses the nerves; it may be hemorrhage, tumor, infection, or substances toxic to nerve tissue. One of the most frequent causes of paralysis is stroke , in which hemorrhage, thrombosis, or obstruction of a cerebral vessel interferes with nerve function. Another disorder in which a resting tremor is one of the main symptoms, accompanied by slowness and poverty of movement, muscular rigidity, and postural instability is Parkinson's disease . Cerebral palsy is due to an injury to the brain motor tissue before or during birth. However, this disorder is nonprogressive. Partial or complete paralysis often accompanies multiple sclerosis .

Paralysis

Sang Lan’s Story

What Is Paralysis?

How Does a Person Become Paralyzed?

Signs and Symptoms

Diagnosis

Is Paralysis Treatable?

Living with Paralysis

Will There Ever Be a Cure?

Resources

Paralysis (pa-RAL-i-sis) is the inability to consciously control the movement of the muscles.

KEYWORDS

for searching the Internet and other reference sources

Muscular system

Nervous system

Spinal cord injury

Sang Lan’s Story

As she was warming up for her routine at the July 1998 Goodwill Games, 17-year-old Chinese gymnast Sang Lan prepared to jump over the vaulting horse, a move she had performed thousands of times. But Sang flung herself too forcefully into the vault and landed on her head instead of her feet. The impact snapped the sixth and seventh vertebrae (VER-te-bray) in her neck, damaging her spinal cord and leaving her unable to move from the chest down. Sang s disability is probably permanent. This type of injury is one of the causes of the condition called paralysis.

What Is Paralysis?

Muscle is a special kind of tissue that enables our bodies to move. It is under the control of the nervous system, which processes messages to and from all parts of the body. Sometimes the nerve cells, or neurons, that control the muscles become diseased or injured. When that happens, a person loses the ability to move the muscles voluntarily, and we say that the person is paralyzed.

Paralysis of the muscles of the face, arm, and leg on one side of the body is called hemiplegia (“hemi” means “half”) and usually results from damage to the opposite side of the brain. Damage to the nerves of the spinal cord affects different parts of the body, depending on the amount of damage and where it occurred. Paralysis of both lower limbs is called paraplegia, and paralysis of both arms and both legs is called quadriplegia. Paralysis may be temporary or permanent, depending on the disease or injury. Because paralysis can affect any muscle in the body, a person may lose not only the ability to move but also the ability to talk or to breathe unaided.

How Does a Person Become Paralyzed?

Physical injury—for example, sports or car accidents—poisoning, infection, blocked blood vessels, and tumors can all cause paralysis. Defects in the developing brain of the fetus or brain injury during birth can cause a paralytic condition known as cerebral palsy. In diseases such as multiple sclerosis, inflammation scars the nerves, interrupting communication between the brain and the muscles. Sometimes the muscle tissue itself is affected. In muscular dystrophy, deterioration of the muscle tissue of the arms and legs causes increasing weakness.

Guillain-Barré (gee-YAN ba-RAY) syndrome is an autoimmune disorder in which the body’s own cells attack the insulation and core of the nerve fibers, beginning in the hands and feet. In myasthenia gravis (my-es-THEE-nee-a GRA-vis), another autoimmune disorder, a chemical malfunction disrupts the communication needed for muscles to contract.

In rare cases, no physical cause for paralysis can be found. Psychologists call this condition a conversion disorder—that is, a person converts his or her psychological anxiety into physical symptoms of paralysis, but nerve and muscle function are still intact.

Signs and Symptoms

The signs and symptoms of paralysis vary. When the spinal cord is crushed, as in Sang Lan’s injury, a person is immediately paralyzed and loses feeling in the affected limbs. When damage to the muscles or central nervous system is caused by a progressive disease or disorder, such as muscular dystrophy or multiple sclerosis, symptoms are gradual and often start with muscle fatigue and weakness. With poliomyelitis (PO-le-o-my-e-LY-tis) and stroke, paralysis comes on suddenly, with little or no warning.

Diagnosis

Information about symptoms and their onset helps the doctor pinpoint the cause of paralysis. With certain genetic diseases that are inherited, such as muscular dystrophy, family medical history provides important clues.

Is Paralysis Treatable?

Aside from poliomyelitis (which can be prevented by vaccination) and brain and spinal cord injuries (which in some cases can be prevented by using appropriate safety measures), it is usually not possible to prevent the conditions that cause paralysis, and most of the time there is no specific treatment. Steroid medications are sometimes given at the time of spinal cord injury to reduce inflammation in an attempt to limit the amount of damage to the spinal nerves. For people with paralysis who must use wheelchairs, treatment emphasizes exercises and special care to avoid infections and pressure sores. Patients with myasthenia gravis may be offered a drug that helps their muscles contract. Most people with Guillain-Barré syndrome recover on their own. Conversion disorder can be difficult to treat; the underlying psychological problem must be addressed.

Living with Paralysis

Many people with paralysis have normal lifespans, even when the condition is the result of progressive disease. People who are confined to wheelchairs can still drive, swim, fly planes, and even ski. But being paralyzed requires major adjustments to daily living, because the muscles a person usually relies on to do certain things no longer work. For example, for people with severe paralysis, ordinary body functions like urinating and having bowel movements may be difficult tasks. In extreme cases, a person may not even be able to breathe without assistance. Help is available to cope with most cases of paralysis, and people with this condition can often hold jobs, raise families, and participate in life’s activities.

Will There Ever Be a Cure?

Ten years ago, no one would have imagined that badly injured nerves could heal. But in the future, people may be able to regain the function they have lost through injury to their motor nerves. For example, experiments with rats and cats have shown that it is possible to repair damaged nerves and that severed spinal cord tissue can be made to grow back. Of course, many questions need to be answered before these approaches can be applied to humans.

“Like a Mind in a Jar”

Jean-Dominique Bauby, editor of the magazine Elle, was 43 and had a wife and two young children when he suffered a stroke that left him with a condition called locked-in syndrome. Bauby was able to think, but he could not speak or move a single muscle in his body except for his left eye. He began to communicate by blinking his eye in a kind of code that a friend painstakingly transcribed letter by letter, first into words and then into sentences. The sentences became a book titled The Diving Bell and the Butterfly. The book was an instant best-seller in France and later inspired readers worldwide.

See also

Bedsores (Pressure Sores)

Cerebral Palsy

Incontinence

Multiple Sclerosis

Muscular Dystrophy

Spina Bifida

Stroke

Resources

Book

Reeve, Christopher. Still Me. New York: Random House, 1996. A book by the actor, now paralyzed, who once played Superman.

Magazine

WE Magazine. A lifestyle magazine for people with disabilities.
http://www.wemagazine.com

Organizations

National Institute of Neurological Disorders and Stroke, Office of Communications and Public Liaison, P.O. Box 5801, Bethesda, MD 20824. A U.S. government agency that is a major source of information regarding neurological disorders and stroke.
http://www.ninds.nih.gov

National Spinal Cord Injury Association (NSCIA), 8300 Colesville Road, Suite 551, Silver Spring, MD 20910.
http://www.erols.com/nscia/resource

Tutorial

”Paralysis Analysis.” An informative tutorial on spinal-cord injuries and an update on current advances in research.
http://whyfiles.news.wisc.edu/023spinal_cord/index.htm

pa·ral·y·sis / pəˈraləsis/ • n. (pl. -ses / -sēz/ ) the loss of the ability to move (and sometimes to feel anything) in part or most of the body, typically as a result of illness, poison, or injury. ∎  inability to act or function in a person, organization, or place: the paralysis gripping the country.

paralysis Weakness or loss of muscle power; it can vary from a mild condition to complete loss of function and sensation in the affected part. It can be associated with almost any disorder of the nervous system, including brain or spinal cord injury, infection, stroke, poisoning, or progressive conditions such as a tumour or motor neurone disease. Paralysis is very rarely total.

paralysis (pă-ral-i-sis) n. muscle weakness that varies in its extent, its severity, and the degree of spasticity or flaccidity according to the nature of the underlying disease and its distribution in the brain, spinal cord, peripheral nerves, or muscles. See also diplegia, hemiplegia, paraplegia, poliomyelitis.
—paralytic (pa-ră-lit-ik) adj.

paralysis XVI. — L. — Gr. parálusis, f. paralúesthai be ‘loosened’ or disabled at the side, pass. of paralúein, f. PARA-1 + lúein loosen.
So paralyse, U.S. paralyze XIX. — F. paralyser. paralytic XIV. — (O)F. — L. — Gr.

paralysis The usual modern translation of the AV palsy (Acts 8: 7).

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