Spinal muscular atrophy Health Dictionary

Spinal Muscular Atrophy: From 1 Different Sources


(SMA) a hereditary condition in which cells of the spinal cord die and the muscles in the arms and legs become progressively weaker. Eventually the respiratory muscles are affected and death usually results from respiratory infection. Most affected individuals are wheelchair-bound by the age of 20 and few survive beyond the age of 30. The gene responsible has been located: in affected children it is inherited as a double *recessive. There are three forms of the disease, based on severity of the symptoms and the age at which they appear. Type 1 (infantile spinal muscular atrophy) is the most acute and aggressive form of the condition (see Werdnig–Hoffmann disease). Type 2 develops between the ages of 6 months and 2 years and type 3 (Kugelberg–Welander disease), the least severe form, appears between 2 and 17 years of age.
Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Atrophy

Wasting of a tissue or organ... atrophy

Muscular Dystrophy

See MUSCLES, DISORDERS OF – Myopathy.... muscular dystrophy

Optic Atrophy

A deterioration in the ?bres of the optic nerve (see EYE) resulting in partial or complete loss of vision. It may be caused by damage to the nerve from in?ammation or injury, or the atrophy may be secondary to disease in the eye.... optic atrophy

Spinal Cord

This is the lower portion of the CENTRAL NERVOUS SYSTEM which is situated within the SPINAL COLUMN. Above, it forms the direct continuation of the medulla oblongata, this part of the BRAIN changing its name to spinal cord at the foramen magnum, the large opening in the base of the skull through which it passes into the spinal canal. Below, the spinal cord extends to about the upper border of the second lumbar vertebra, where it tapers o? into a ?ne thread, known as the ?lum terminale, that is attached to the coccyx at the lower end of the spine. The spinal cord is thus considerably shorter than the spinal column, being only 37– 45 cm (15–18 inches) in length, and weighing around 30 grams.

In its course from the base of the skull to the lumbar region, the cord gives o? 31 nerves on each side, each of which arises by an anterior and a posterior root that join before the nerve emerges from the spinal canal. The openings for the nerves formed by notches on the ring of each vertebra have been mentioned under the entry for spinal column. To reach these openings, the upper nerves pass almost directly outwards, whilst lower down their obliquity increases, until below the point where the cord ends there is a sheaf of nerves, known as the cauda equina, running downwards to leave the spinal canal at their appropriate openings.

The cord is a cylinder, about the thickness of the little ?nger. It has two slightly enlarged portions, one in the lower part of the neck, the other at the last dorsal vertebra; and from these thickenings arise the nerves that pass to the upper and lower limbs. The upper four cervical nerves unite to produce the cervical plexus. From this the muscles and skin of the neck are mainly supplied, and the phrenic nerve, which runs down through the lower part of the neck and the chest to innervate the diaphragm, is given o?. The brachial plexus is formed by the union of the lower four cervical and ?rst dorsal nerves. In addition to nerves to some of the muscles in the shoulder region, and others to the skin about the shoulder and inner side of the arm, the plexus gives o? large nerves that proceed down the arm.

The thoracic or dorsal nerves, with the exception of the ?rst, do not form a plexus, but each runs around the chest along the lower margin of the rib to which it corresponds, whilst the lower six extend on to the abdomen.

The lumbar plexus is formed by the upper four lumbar nerves, and its branches are distributed to the lower part of the abdomen, and front and inner side of the thigh.

The sacral plexus is formed by parts of the fourth and ?fth lumbar nerves, and the upper three and part of the fourth sacral nerves. Much of the plexus is collected into the sciatic nerves, the largest in the body, which go to the legs.

The sympathetic system is joined by a pair of small branches given o? from each spinal nerve, close to the spine. This system consists of two parts, ?rst, a pair of cords running down on the side and front of the spine, and containing on each side three ganglia in the neck, and beneath this a ganglion opposite each vertebra. From these two ganglionated cords numerous branches are given o?, and these unite to form the second part – namely, plexuses connected with various internal organs, and provided with numerous large and irregularly placed ganglia. The chief of these plexuses are the cardiac plexus, the solar or epigastric plexus, the diaphragmatic, suprarenal, renal, spermatic, or ovarian, aortic, hypogastric and pelvic plexuses.

The spinal cord, like the brain, is surrounded by three membranes: the dura mater, arachnoid mater, and pia mater, from without inwards. The arrangement of the dura and arachnoid is much looser in the case of the cord than their application to the brain. The dura especially forms a wide tube which is separated from the cord by ?uid and from the vertebral canal by blood vessels and fat, this arrangement protecting the cord from pressure in any ordinary movements of the spine.

In section the spinal cord consists partly of grey, but mainly of white, matter. It di?ers from the upper parts of the brain in that the white matter (largely) in the cord is arranged on the surface, surrounding a mass of grey matter (largely neurons – see NEURON(E)), while in the brain the grey matter is super?cial. The arrangement of grey matter, as seen in a section across the cord, resembles the letter H. Each half of the cord possesses an anterior and a posterior horn, the masses of the two sides being joined by a wide posterior grey commissure. In the middle of this commissure lies the central canal of the cord, a small tube which is the continuation of the ventricles in the brain. The horns of grey matter reach almost to the surface of the cord, and from their ends arise the roots of the nerves that leave the cord. The white matter is divided almost completely into two halves by a posterior septum and anterior ?ssure and is further split into anterior, lateral and posterior columns.

Functions The cord is, in part, a receiver and originator of nerve impulses, and in part a conductor of such impulses along ?bres which pass through it to and from the brain. The cord contains centres able to receive sensory impressions and initiate motor instructions. These control blood-vessel diameters, eye-pupil size, sweating and breathing. The brain exerts an overall controlling in?uence and, before any incoming sensation can affect consciousness, it is usually ‘?ltered’ through the brain.

Many of these centres act autonomously. Other cells of the cord are capable of originating movements in response to impulses brought direct to them through sensory nerves, such activity being known as REFLEX ACTION. (For a fuller description of the activities of the spinal cord, see NEURON(E) – Re?ex action.)

The posterior column of the cord consists of the fasciculus gracilis and the fasciculus cuneatus, both conveying sensory impressions upwards. The lateral column contains the ventral and the dorsal spino-cerebellar tracts passing to the cerebellum, the crossed pyramidal tract of motor ?bres carrying outgoing impulses downwards together with the rubro-spinal, the spino-thalamic, the spino-tectal, and the postero-lateral tracts. And, ?nally, the anterior column contains the direct pyramidal tract of motor ?bres and an anterior mixed zone. The pyramidal tracts have the best-known course. Starting from cells near the central sulcus on the brain, the motor nerve-?bres run down through the internal capsule, pons, and medulla, in the lower part of which many of those coming from the right side of the brain cross to the left side of the spinal cord, and vice versa. Thence the ?bres run down in the crossed pyramidal tract to end beside nerve-cells in the anterior horn of the cord. From these nerve-cells other ?bres pass outwards to form the nerves that go direct to the muscles. Thus the motor nerve path from brain to muscle is divided into two sections of neurons, of which the upper exerts a controlling in?uence upon the lower, while the lower is concerned in maintaining the muscle in a state of health and good nutrition, and in directly calling it into action. (See also NERVE; NERVOUS SYSTEM.)... spinal cord

Duchenne Muscular Dystrophy

An X-linked recessive disorder (that is, the abnormal gene is carried on the X chromosome). This means that the disease occurs almost exclusively in males, as its presence in a female is counteracted by the normal gene likely to be in her other X chromosome. The disorder is characterised by progressive muscular weakness and wasting. It is the most common form of muscular dystrophy, ocurring in 30 per 100,000 live male births, often – but not always – in families with other members having the disorder.

The disease usually appears within the ?rst three years of life, beginning in the pelvic girdle and lower limbs and later spreading to the shoulder girdle. The calf muscles become bulky (pseudohypertrophy). The weakness gives rise to a characteristic waddling gait and, when rising from the supine position, the child rolls on to his face and then uses his arms to push himself up. Death usually occurs by the middle of the second decade from respiratory infections. Prenatal screening of female carriers using gene probes is increasingly available. (See DYSTROPHY; MUSCLES, DISORDERS OF – Myopathy.)... duchenne muscular dystrophy

Spinal Anaesthesia

See under ANAESTHESIA.... spinal anaesthesia

Spinal Nerves

A set of 31 pairs of nerves that connect to the spinal cord. Spinal nerves emerge in 2 rows from either side of the spinal cord and leave the spine through gaps between adjacent vertebrae. The nerves then branch out to supply all parts of the trunk, arms, and legs with sensory and motor nerve fibres.

Disc prolapse may lead to pressure on a spinal nerve, causing pain. Injury to a nerve may lead to loss of sensation or movement in the area supplied by the nerve. (See also nerve injury; neuropathy.)... spinal nerves

Spinal Column

Also known as the spine, this forms an important part of the skeleton, acting both as the rigid pillar which supports the upper parts of the body and as a protection to the SPINAL CORD and nerves arising from it. The spinal column is built up of a number of bones placed one upon another, which, in consequence of having a slight degree of turning-movement, are known as the vertebrae. The possession of a spinal cord supported by a vertebral column distinguishes the higher animals from the lower types, and is why they are called vertebrates. Of the vertebrates, humans alone stand absolutely erect, and this erect carriage of the body gives to the skull and vertebral column certain distinctive characters.

The human backbone is about 70 cm (28

inches) in length, and varies little in full-grown people; di?erences in height depend mainly upon the length of the lower limbs. The number of vertebrae is 33 in children, although in adult life ?ve of these fuse together to form the sacrum, and the lowest four unite in the coccyx, so that the number of separate bones is reduced to 26. Of these there are seven in the neck, known as cervical vertebrae; 12 with ribs attached, in the region of the thorax known as thoracic or dorsal vertebrae; ?ve in the loins, called lumbar vertebrae; ?ve fused to form the sacrum; and four joined in the coccyx. These numbers are expressed in a formula thus: C7, D12, L5, S5, Coc4=33.

Although the vertebrae in each of these regions have distinguishing features, all the vertebrae are constructed on the same general plan. Each has a thick, rounded, bony part in front, known as the body, and these bodies form the main thickness of the column. Behind the body of each is a ring of bone, the neural ring, these rings placed one above another forming the bony canal which lodges the spinal cord. From each side of the ring a short process of bone known as the transverse process stands out, and from the back of the ring a larger process, the spinous process, projects. These processes give attachment to the strong ligaments and muscles which unite, support, and bend the column. The spines can be seen or felt beneath the skin of the back lying in the centre of a groove between the muscular masses of the two sides, and they give to the column its name of the spinal column. One of these spines, that of the seventh cervical vertebra, is especially large and forms a distinct bony prominence, where the neck joins the back. Between the bodies of the vertebrae lies a series of thick discs of ?brocartilage known as intervertebral discs. Each disc consists of an outer portion, known as the annulus ?brosus, and an inner core, known as the nucleus pulposus. These 23 discs provide the upper part of the spine with pliability and resilience.

The ?rst and second cervical vertebrae are specially modi?ed. The ?rst vertebra, known as the atlas, is devoid of a body, but has a specially large and strong ring with two hollows upon which the skull rests, thus allowing forward and backward movements (nodding). The second vertebra, known as the axis, has a pivot on its body which ?ts into the ?rst vertebra and thus allows free rotation of the head from side to side. The spinal column has four natural curves (see diagram) which help to cushion the shocks of walking and running.

The neural rings of the vertebrae form a canal, which is wide in the neck, smaller and almost round in the dorsal region, and wide again in the lumbar vertebrae. Down the canal runs the spinal cord, and the nerves leaving the cord do so through openings between the vertebrae which are produced by notches on the upper and lower margins of each ring. The intervertebral foramina formed by these notches are so large in comparison with the nerves passing through them that there is no chance of pressure upon the latter, except in very serious injuries which dislocate and fracture the spine.... spinal column

Disuse Atrophy

The wasting of muscles after prolonged immobility. This can be seen after lengthy immobilisation in a plaster cast, and is particularly severe following paralysis of a limb through nerve injury. (See ATROPHY.)... disuse atrophy

Pseudohypertrophic Muscular Dystrophy

A condition in which certain muscles enlarge owing to a fatty and ?brous degeneration, giving a false appearance of increased strength.

Pseudomonas Aeruginosa

A pathogenic bacterium of the genus pseudomonas – rod-like, motile gram-negative bacteria (see GRAM’S STAIN) – that occurs in pus from wounds and is associated with urinary tract infections. The bacteria mostly live in soil and decomposing organic matter and help to recycle nitrogen in nature. Most of the bacteria in this genus are harmless to humans.... pseudohypertrophic muscular dystrophy

Sudek’s Atrophy

Osteoporosis (see under BONE, DISORDERS OF) in the hand or foot which develops quickly as a result of injury, infection or malignant growth.... sudek’s atrophy

Liver – Acute Yellow Atrophy

Necrosis. Fatal disease in which the substance of the liver is destroyed. Incidence is rare since the public has been alerted to the dangers of certain chemical toxins, fumes from synthetic glues, solvents, and poisonous fungi.

Symptoms: jaundice, delirium and convulsions.

As it is the work of the liver to neutralise incoming poisons it may suffer unfair wear and tear, alcohol and caffeine being common offenders.

Treatment for relief of symptoms only: same as for abscess of the liver.

Treatment by or in liaison with a general medical practitioner. ... liver – acute yellow atrophy

Decompression, Spinal Canal

Surgery to relieve pressure on the spinal cord or a nerve root emerging from it (see microdiscectomy). Pressure may have various causes, including a disc prolapse, a tumour or abscess of the spinal cord, or a tumour, abscess or fracture of the vertebrae. Any of these conditions can cause weakness or paralysis of the limbs and loss of bladder control.

To treat major disc prolapses and tumours, a laminectomy (removal of the bony arches of 1 or more vertebrae) to expose the affected part of the cord or nerve roots may be performed. Recovery after treatment depends on the severity and duration of the pressure, the success of the surgery in relieving the pressure, and whether any damage is sustained by the nerves during the operation.... decompression, spinal canal

Peroneal Muscular Atrophy

A rare, inherited disorder characterized by muscle wasting in the feet and calves and then in the hands and forearms.

The condition, also known as Charcot–Marie– Tooth disease, is caused by degeneration of some peripheral nerves.

It is more common in boys, and usually appears in late childhood or adolescence.

Muscle wasting stops halfway up the arms and legs, making them look like inverted bottles; sensation may be lost.

There is no treatment, but the sufferer rarely becomes totally incapacitated because the disease usually progresses very slowly.

Life expectancy is normal.... peroneal muscular atrophy

Progressive Muscular Atrophy

A type of motor neuron disease in which the muscles of the hands, arms, and legs become weak and wasted and twitch involuntarily. The condition eventually spreads to other muscles.... progressive muscular atrophy

Spinal Tap

See lumbar puncture.... spinal tap

Sudeck’s Atrophy

Swelling and loss of use of a hand or foot after a fracture or other injury.

Treatment includes elevation of the affected hand or foot, gentle exercise, and heat treatment.

Full recovery is usual within about 4 months.... sudeck’s atrophy

Muscular System

The muscles of the body that are attached to the skeleton. These muscles are responsible for voluntary movement, and also support and stabilize the skeleton. In most cases, a muscle attaches to a bone (usually by means of a tendon) and crosses over a joint to attach to another bone. Muscles can produce movement by contracting and shortening to pull on the bone to which they are attached. They can only pull, not push, and are therefore arranged so that the pull of one muscle or group of muscles is opposed to another, enabling a movement to be reversed. Although most actions of the skeletal muscles are under conscious control, reflex movements of certain muscles occur in response to stimuli.

There are more than 600 muscles in the body, classified according to the type of movement they produce.

An extensor opens out a joint, a flexor closes it; an adductor draws a part of the body inwards, an abductor moves it outwards; a levator raises it, a depressor lowers it; and constrictor or sphincter muscles surround and close orifices.... muscular system

Becker Muscular Dystrophy

a *sex-linked (X-linked) disorder in which affected males develop an increase in muscle size followed by weakness and wasting. It usually starts between the ages of 5 and 15, and 25 years after onset most patients are wheelchair-bound. Although most men become severely disabled, life expectancy is close to normal. The disorder is similar to Duchenne *muscular dystrophy but less severe. [P. E. Becker (20th century), German geneticist]... becker muscular dystrophy

Gyrate Atrophy

a rare hereditary condition causing night blindness and constricted visual fields, usually developing in the first decade of life. Clinically it is characterized by a progressive atrophy of the choroid and retina.... gyrate atrophy

Leber’s Optic Atrophy

a rare hereditary disorder, usually affecting young males, that is characterized by loss of central vision due to neuroretinal degeneration. Visual loss in one eye is rapid and usually followed by loss in the second eye. [T. Leber]... leber’s optic atrophy

Multiple System Atrophy

(MSA) a condition that results from degeneration of cells in the *basal ganglia (resulting in *parkinsonism), the *cerebellum (resulting in *ataxia), the *pyramidal system, and the *autonomic nervous system (resulting in symptoms of autonomic failure, such as postural hypotension).... multiple system atrophy

Muscular Rheumatism

any aching pain in the muscles and joints. Commonly the symptoms are due to *fibrositis; wear and tear of the joints (*osteoarthritis); or to inflammation of the muscles associated with abnormal immune reactions (*polymyalgia rheumatica). Generalized muscle pain with specific tender points and fatigue is called *fibromyalgia.... muscular rheumatism

Spine And Spinal Cord, Diseases And Injuries Of

Scoliosis A condition where the spine is curved to one side (the spine is normally straight when seen from behind). The deformity may be mobile and reversible, or ?xed; if ?xed it is accompanied by vertebral rotation and does not disappear with changes in posture. Fixed scoliosis is idiopathic (of unknown cause) in 65–80 per cent of cases. There are three main types: the infantile type occurs in boys under three and in 90 per cent of cases resolves spontaneously; the juvenile type affects 4–9 year olds and tends to be progressive. The most common type is adolescent idiopathic scoliosis; girls are affected in 90 per cent of cases and the incidence is 4 per cent. Treatment may be conservative with a ?xed brace, or surgical fusion may be needed if the curve is greater than 45 degrees. Scoliosis can occur as a congenital condition and in neuromuscular diseases where there is muscle imbalance, such as in FRIEDREICH’S ATAXIA.

Kyphosis is a backward curvature of the spine causing a hump back. It may be postural and reversible in obese people and tall adolescent girls who stoop, but it may also be ?xed. Scheuermann’s disease is the term applied to adolescent kyphosis. It is more common in girls. Senile kyphosis occurs in elderly people who probably have osteoporosis (bone weakening) and vertebral collapse.

Disc degeneration is a normal consequence of AGEING. The disc loses its resiliance and becomes unable to withstand pressure. Rupture (prolapse) of the disc may occur with physical stress. The disc between the fourth and ?fth lumbar vertebrae is most commonly involved. The jelly-like central nucleus pulposus is usually pushed out backwards, forcing the annulus ?brosus to put pressure on the nerves as they leave the spinal canal. (See PROLAPSED INTERVERTEBRAL DISC.)

Ankylosing spondylitis is an arthritic disorder of the spine in young adults, mostly men. It is a familial condition which starts with lumbar pain and sti?ness which progresses to involve the whole spine. The discs and ligaments are replaced by ?brous tissue, making the spine rigid. Treatment is physiotherapy and anti-in?ammatory drugs to try to keep the spine supple for as long as possible.

A National Association for Ankylosing Spondylitis has been formed which is open to those with the disease, their families, friends and doctors.

Spondylosis is a term which covers disc degeneration and joint degeneration in the back. OSTEOARTHRITIS is usually implicated. Pain is commonly felt in the neck and lumbar regions and in these areas the joints may become unstable. This may put pressure on the nerves leaving the spinal canal, and in the lumbar region, pain is generally felt in the distribution of the sciatic nerve – down the back of the leg. In the neck the pain may be felt down the arm. Treatment is physiotherapy; often a neck collar or lumbar support helps. Rarely surgery is needed to remove the pressure from the nerves.

Spondylolisthesis means that the spine is shifted forward. This is nearly always in the lower lumbar region and may be familial, or due to degeneration in the joints. Pressure may be put on the cauda equina. The usual complaint is of pain after exercise. Treatment is bed rest in a bad attack with surgery indicated only if there are worrying signs of cord compression.

Spinal stenosis is due to a narrowing of the spinal canal which means that the nerves become squashed together. This causes numbness with pins and needles (paraesthia) in the legs. COMPUTED TOMOGRAPHY and nuclear magnetic resonance imaging scans can show the amount of cord compression. If improving posture does not help, surgical decompression may be needed.

Whiplash injuries occur to the neck, usually as the result of a car accident when the head and neck are thrown backwards and then forwards rapidly. This causes pain and sti?ness in the neck; the arm and shoulder may feel numb. Often a support collar relieves the pain but recovery commonly takes between 18 months to three years.

Transection of the cord occurs usually as a result of trauma when the vertebral column protecting the spinal cord is fractured and becomes unstable. The cord may be concussed or it may have become sheared by the trauma and not recover (transected). Spinal concussion usually recovers after 12 hours. If the cord is transected the patient remains paralysed. (See PARALYSIS.)... spine and spinal cord, diseases and injuries of

Spinal Accessory Nerve

see accessory nerve.... spinal accessory nerve

Spinal Shock

a state of *shock accompanied by temporary paralysis of the lower extremities that results from injury to the spine and is often associated with *ileus. If the spinal cord is transected, permanent motor paralysis persists below the level of spinal-cord division.... spinal shock

Sudek’s Atrophy

see complex regional pain syndrome. [P. H. M. Sudek (1866–1938), German surgeon]... sudek’s atrophy



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