The brain, central nervous system (CNS), and autonomic nervous system control most body functions. The skin is the body’s largest sensory organ and is supplied with local pain and temperature receptors as well as parasympathetic fibers to hair follicles, sweat glands, and blood vessels.
The brain and spinal cord
In order to function, the brain must be supplied with blood. If this supply ceases because of a blood clot (thrombus) blocking a vessel, a stroke occurs. The symptoms may include partial paralysis, numbness, or loss of speech. After a stroke, these usually diminish gradually as other areas of the brain take over some functions of the damaged part. Factors that increase the likelihood of a stroke are constriction in a blood vessel (atheroma), high blood pressure, heart disease, and shock.
Evaluation of the extent of brain injury is essential after a stroke. Modern technology utilizes angiograms, magnetic resonance imaging (MRI), and computerized axial tomography (CAT scans, involving computer-enhanced X-ray photography); treatment varies according to the diagnosis. Where muscles and coordination are affected, physiotherapy is helpful in restoring function.
Symptoms resembling those of a stroke may be caused by accidents to the head, particularly if there is any bleeding in or around the brain. The most obvious symptom is loss of consciousness, though whether this occurs or not, more profound symptoms loss of memory, disorientation, fainting attacks, and speech or motor defects may occur later, even after apparent recovery.
The second most common neurological disease is epilepsy, caused by abnormal electrical activity in the brain. Symptoms vary in character and severity and can include twitching, hallucinations, unconsciousness, and con vulsions. Seizures can be controlled with med ication.
Spinal nerves are susceptible to damage if the bone or cartilage surrounding them shifts awkwardly. This occurs in a herniated disk, in which a damaged intervertebral cartilage disk presses on a spinal nerve. If the sciatic nerve is so trapped, this causes sciatica.
Infections of the brain or spinal cord, such as meningitis or encephalitis, which affect the protective covering membranes (meninges) or the brain itself, are extremely dangerous. Treatment is with antibiotics and must be both rapid and vigorous, as both conditions can cause long-term damage and may be fatal. Poliomyelitis is a virus infection that affects the gray matter of the spinal cord and can cause paralysis. Children are now immunized against the disease, and it is now rare.
Injury to the brain in an accident may cause concussion, or symptoms similar to those of a stroke. Spinal cord damage usually results in paralysis of parts of the body supplied by nerves originating below the point of injury. Peripheral nerves can be cut or crushed, but can grow again. New microsurgical techniques endeavor to join severed nerve sheaths to help this regeneration.
Degeneration of the nervous system
Like other parts of the body, the brain degenerates with increasing age. Ultimately, this may cause senile dementia, which is marked particularly by deterioration in intellectual functions. One form of dementia, called Alzheimer’s disease, can occur in middle-aged people as well as in the elderly.
Multiple sclerosis is a degenerative disease of the white matter of the brain and spinal cord. The cause is not known. Symptoms vary according to the parts of the CNS that are affected, but are characterized by various forms of uncoordination. There is no specific treatment, although steroids and ACTH (adrenocorticotropic hormone) may sometimes help.
Infections of the skin
Skin is exposed to a wide variety of damaging agents, including viruses, bacteria, parasites, carcinogens, and even the sun.
Viral infections of the skin include warts and cold sores and are extremely common. Treatment concentrates on alleviating the symptoms, though some antiviral drugs are available. Boils and impetigo, caused by bacteria, are treated with antibiotics. Fungal infections include ringworm, thrush (moniliasis), and athlete’s foot, treated with antifungal drugs. The skin may also be attacked by scabies mites, fleas, or lice.
Other skin conditions
Eczema is a type of allergic reaction in which the skin is itchy and inflamed and may flake at the affected patch. Treatment is with soothing creams or, in more serious cases, with ointments containing steroids. Dermatitis is a similar condition, generally caused by a substance such as a metal or a chemical compound, for example, soap that has been in contact with the skin.
The cause of acne remains unknown, although hormonal factors appear to be important. In most cases, the condition improves spontaneously. Recently, high doses of vitamin A have been found to be effective in prevention or treatment. Exposure to sunlight may also help.
Psoriasis produces red, scaly lesions, especially over the elbows and knees. Treatment involves the use of ointments that improve the skin’s ability to absorb sunlight.
Sunlight has beneficial effects on the skin, notably the production of vitamin D and the reduction of acne. But sunlight is potentially harmful, too. It damages the underlying connective tissue, reducing elasticity, and is a potential cause of all types of skin cancer.