The ?ne web of tissue and branching cells which supports the nerve-?bres and cells of the nervous system. (See NERVE.)
– the corpus callosum. Other clefts or ?ssures (sulci) make deep impressions, dividing the cerebrum into lobes. The lobes of the cerebrum are the frontal lobe in the forehead region, the parietal lobe on the side and upper part of the brain, the occipital lobe to the back, and the temporal lobe lying just above the region of the ear. The outer 3 mm of the cerebrum is called the cortex, which consists of grey matter with the nerve cells arranged in six layers. This region is concerned with conscious thought, sensation and movement, operating in a similar manner to the more primitive areas of the brain except that incoming information is subject to much greater analysis.
Numbers of shallower infoldings of the surface, called furrows or sulci, separate raised areas called convolutions or gyri. In the deeper part, the white matter consists of nerve ?bres connecting di?erent parts of the surface and passing down to the lower parts of the brain. Among the white matter lie several rounded masses of grey matter, the lentiform and caudate nuclei. In the centre of each cerebral hemisphere is an irregular cavity, the lateral ventricle, each of which communicates with that on the other side and behind with the third ventricle through a small opening, the inter-ventricular foramen, or foramen of Monro.
BASAL NUCLEI Two large masses of grey matter embedded in the base of the cerebral hemispheres in humans, but forming the chief part of the brain in many animals. Between these masses lies the third ventricle, from which the infundibulum, a funnel-shaped process, projects downwards into the pituitary body, and above lies the PINEAL GLAND. This region includes the important HYPOTHALAMUS.
MID-BRAIN or mesencephalon: a stalk about 20 mm long connecting the cerebrum with the hind-brain. Down its centre lies a tube, the cerebral aqueduct, or aqueduct of Sylvius, connecting the third and fourth ventricles. Above this aqueduct lie the corpora quadrigemina, and beneath it are the crura cerebri, strong bands of white matter in which important nerve ?bres pass downwards from the cerebrum. The pineal gland is sited on the upper part of the midbrain.
PONS A mass of nerve ?bres, some of which run crosswise and others are the continuation of the crura cerebri downwards.
CEREBELLUM This lies towards the back, underneath the occipital lobes of the cerebrum.
MEDULLA OBLONGATA The lowest part of the brain, in structure resembling the spinal cord, with white matter on the surface and grey matter in its interior. This is continuous through the large opening in the skull, the foramen magnum, with the spinal cord. Between the medulla, pons, and cerebellum lies the fourth ventricle of the brain.
Structure The grey matter consists mainly of billions of neurones (see NEURON(E)) in which all the activities of the brain begin. These cells vary considerably in size and shape in di?erent parts of the brain, though all give o? a number of processes, some of which form nerve ?bres. The cells in the cortex of the cerebral hemispheres, for example, are very numerous, being set in layers ?ve or six deep. In shape these cells are pyramidal, giving o? processes from the apex, from the centre of the base, and from various projections elsewhere on the cell. The grey matter is everywhere penetrated by a rich supply of blood vessels, and the nerve cells and blood vessels are supported in a ?ne network of ?bres known as neuroglia.
The white matter consists of nerve ?bres, each of which is attached, at one end, to a cell in the grey matter, while at the other end it splits up into a tree-like structure around another cell in another part of the grey matter in the brain or spinal cord. The ?bres have insulating sheaths of a fatty material which, in the mass, gives the white matter its colour; they convey messages from one part of the brain to the other (association ?bres), or, grouped into bundles, leave the brain as nerves, or pass down into the spinal cord where they end near, and exert a control upon, cells from which in turn spring the nerves to the body.
Both grey and white matter are bound together by a network of cells called GLIA which make up 60 per cent of the brain’s weight. These have traditionally been seen as simple structures whose main function was to glue the constituents of the brain together. Recent research, however, suggests that glia are vital for growing synapses between the neurons as they trigger these cells to communicate with each other. So they probably participate in the task of laying down memories, for which synapses are an essential key. The research points to the likelihood that glial cells are as complex as neurons, functioning biochemically in a similar way. Glial cells also absorb potassium pumped out by active neurons and prevent levels of GLUTAMATE – the most common chemical messenger in the brain – from becoming too high.
The general arrangement of ?bres can be best understood by describing the course of a motor nerve-?bre. Arising in a cell on the surface in front of the central sulcus, such a ?bre passes inwards towards the centre of the cerebral hemisphere, the collected mass of ?bres as they lie between the lentiform nucleus and optic thalamus being known as the internal capsule. Hence the ?bre passes down through the crus cerebri, giving o? various small connecting ?bres as it passes downwards. After passing through the pons it reaches the medulla, and at this point crosses to the opposite side (decussation of the pyramids). Entering the spinal cord, it passes downwards to end ?nally in a series of branches (arborisation) which meet and touch (synapse) similar branches from one or more of the cells in the grey matter of the cord (see SPINAL CORD).
BLOOD VESSELS Four vessels carry blood to the brain: two internal carotid arteries in front, and two vertebral arteries behind. These communicate to form a circle (circle of Willis) inside the skull, so that if one is blocked, the others, by dilating, take its place. The chief branch of the internal carotid artery on each side is the middle cerebral, and this gives o? a small but very important branch which pierces the base of the brain and supplies the region of the internal capsule with blood. The chief importance of this vessel lies in the fact that the blood in it is under especially high pressure, owing to its close connection with the carotid artery, so that haemorrhage from it is liable to occur and thus give rise to stroke. Two veins, the internal cerebral veins, bring the blood away from the interior of the brain, but most of the small veins come to the surface and open into large venous sinuses, which run in grooves in the skull, and ?nally pass their blood into the internal jugular vein that accompanies the carotid artery on each side of the neck.
MEMBRANES The brain is separated from the skull by three membranes: the dura mater, a thick ?brous membrane; the arachnoid mater, a more delicate structure; and the pia mater, adhering to the surface of the brain and containing the blood vessels which nourish it. Between each pair is a space containing ?uid on which the brain ?oats as on a water-bed. The ?uid beneath the arachnoid membrane mixes with that inside the ventricles through a small opening in the fourth ventricle, called the median aperture, or foramen of Magendie.
These ?uid arrangements have a great in?uence in preserving the brain from injury.... divisions
Cause Although this is one of the most common diseases of the central nervous system in Europe – there are around 50,000 affected individuals in Britain alone – the cause is still not known. The disease comes on in young people (onset being rare after the age of 40), apparently without previous illness. The ratio of women-to-men victims is 3:2. It is more common in ?rst and second children than in those later in birth order, and in small rather than big families. There may be a hereditary factor for MS, which could be an autoimmune disorder: the body’s defence system attacks the myelin in the central nervous system as if it were a ‘foreign’ tissue.
Symptoms These depend greatly upon the part of the brain and cord affected by the sclerotic patches. Temporary paralysis of a limb, or of an eye muscle, causing double vision, and tremors upon exertion, ?rst in the affected parts, and later in all parts of the body, are early symptoms. Sti?ness of the lower limbs causing the toes to catch on small irregularities in the ground and trip the person in walking, is often an annoying symptom and one of the ?rst to be noticed. Great activity is shown in the re?ex movements obtained by striking the tendons and by stroking the soles of the feet. The latter re?ex shows a characteristic sign (Babinski sign) in which the great toe bends upwards and the other toes spread apart as the sole is stroked, instead of the toes collectively bending downwards as in the normal person. Tremor of the eye movements (nystagmus) is usually found. Trembling handwriting, interference with the functions of the bladder, giddiness, and a peculiar ‘staccato’ or ‘scanning’ speech are common symptoms at a later stage. Numbness and tingling in the extremities occur commonly, particularly in the early stages of the disease. As the disease progresses, the paralyses, which were transitory at ?rst, now become con?rmed, often with great rigidity in the limbs. In many patients the disease progresses very slowly.
People with multiple sclerosis, and their relatives, can obtain help and guidance from the Multiple Sclerosis Society. Another helpful organisation is the Multiple Sclerosis Resources Centre. Those with sexual or marital problems arising out of the illness can obtain information from SPOD (Association to Aid the Sexual and Personal Relationships of People with a Disability). (See APPENDIX 2: ADDRESSES: SOURCES OF INFORMATION, ADVICE, SUPPORT AND SELFHELP.)
Treatment is di?cult, because the most that can be done is to lead a life as free from strain as possible, to check the progress of the disease. The use of INTERFERON beta seems to slow the progress of MS and this drug is licensed for use in the UK for patients with relapsing, remitting MS over two years, provided they can walk unaided – a controversial restriction on this (expensive) treatment. CORTICOSTEROIDS may be of help to some patients.
The NATIONAL INSTITUTE FOR CLINICAL EXCELLENCE (NICE) ruled in 2001 that the use of the drugs interferon beta and glatiramer acetate for patients with multiple sclerosis was not cost-e?ective but recommended that the Department of Health, the National Assembly for Wales and the drug manufacturers should consider ways of making the drugs available in a cost-e?ective way. Subsequently the government said that it would consider funding a ‘risk-sharing’ scheme in which supply of drugs to patients would be funded only if treatment trials in individuals with MS showed that they were e?ective.
The Department of Health has asked NICE to assess two CANNABIS derivatives as possible treatments for multiple sclerosis and the relief of post-operative pain. Trials of an under-thetongue spray and a tablet could, if successsful, lead to the two drugs being available around 2005.
It is important to keep the nerves and muscles functioning, and therefore the patient should remain at work as long as he or she is capable of doing it, and in any case should exercise regularly.... multiple sclerosis (ms)
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