the position of the umbilical cord when it lies below the presenting part of the fetus in an intact bag of membranes. See also cord prolapse.
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
The term is also used for the symptoms or signs with which a patient ?rst brings to a doctor.... presentation
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
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