Sleep and sleeping sickness

Sleep and sleeping sickness

In animals, sleep is a naturally recurring state characterized by altered consciousness (relative to waking), relatively inhibited sensory activity, and inhibition of nearly all voluntary muscles. It is distinguished from wakefulness by a decreased ability to react to stimuli, and it is more easily reversible than being in hibernation or a coma.

Humans may suffer from a number of sleep disorders. These include such dyssomnias as insomnia, hypersomnia, and sleep apnea; such parasomnias as sleepwalking and REM behavior disorder; and the circadian rhythm sleep disorders.

Sleeping sickness (African trypanosomiasis) is infection with germs 

carried by certain flies. It results in swelling of the brain.

Sleep is a period of rest during which the sleeper loses awareness of his or her surroundings. Sleep, unlike a coma, is easily ended. A sleeping person or animal can be awakened quickly by, for example, a loud noise or a bright flash of light. All human beings and many kinds of animals must have a certain amount of daily sleep at regular intervals.

What happens during sleep. When a person falls asleep, all activity decreases and the muscles relax. The heartbeat and breathing rate slow down. The person slowly becomes less aware of what may be happening all around.

A sleeping person changes the position of the entire body at least a dozen times during about eight hours of slumber. The head, arms, or legs are moved even more often.

Scientists study sleep with an instrument called an electroencephalograph (see Electroencephalograph). Whether a person is awake or asleep, the brain gives off electrical waves. An electroencephalograph measures and records these waves. The brain of an awake, relaxed person gives off about 10 small waves a second.

As a person falls deeply into sleep, the brain sends out slower but larger and larger waves. The slowest, largest waves occur during the first two or three hours of a period of sleep. During slow-wave sleep, mental ac­tivity slows down but does not stop. People awakened from slow-wave sleep can often recall unclear thoughts that they had while asleep.

Periods of small fast waves, similar to those of an awake person, occur at intervals during sleep. During these periods of fast brain wave activity, the sleeper's eyes move rapidly as though they were watching the events of a dream. A sleeper who is awakened during such a period probably will recall dreaming and re­member details of the dream. Sleep during these peri­ods is called dreaming sleep or REM (Rapid Eye Move­ment) sleep. An eight-hour period of sleep includes from three to five periods of dreaming sleep. The dreaming sleep periods last from 5 to 30 minutes each and occur every 90 to 100 minutes. The later dream peri­ods last longer than the earlier ones.

Human sleep patterns. Most adults sleep from 7 to 8 hours every night. Some people, especially those who work at night, sleep during the daytime. Some adults may need as little as 6 hours sleep a night—or even less. But others may require 9 hours sleep—or even more. Most people tend to need slightly less sleeps as they grow older. A person who slept 8 hours a night at 30 years of age may need only 7 hours of sleep at the age of 60.

A person's sleeping patterns develop gradually. New born babies sleep for brief periods throughout the day and night. Their sleep periods include dreaming sleep. By the age of 2 or 3 months, babies have learned to sleep through the night, though they nap for periods during the daytime. By the age of 6, most children have given up daytime naps. Four-year-olds average from 10 to 14 hours of sleep a day, and 10-year-olds average from 9 to 12 hours.

Sleep among animals. Scientists study sleeping animals by the same methods that they study sleeping human beings. Among the vertebrates (animals with backbones), only reptiles, birds, and mammals experi­ence true sleep, with changes in brain wave patterns. Most kinds of reptiles do not have dreaming sleep periods, and most kinds of birds have only very brief ones. All mammals have periods of dreaming sleep and also periods of slow-wave sleep.

Different species of reptiles, birds, and mammals have different sleep patterns. Some sleep for many short periods every day, but others sleep for one long period. Animals that are nocturnal (active at night) sleep during the daytime. Some mammals, such as cattle, can sleep standing up. But they dream only while lying down.

The other two groups of vertebrates—fish and amphibians—have periods of what might be called sleep. During these periods, they become less aware than at other times of what is happening around them. But scientists have found no evidence of brain wave changes that suggest sleep among such animals.

Insects, spiders, and other invertebrates (animals without backbones) have daily periods of reduced activity. But invertebrates do not show a sudden decrease in response to their surroundings. No brain changes have been found to occur during their rest periods.

What happens without sleep. People deprived of sleep lose energy and become quick-tempered. After two days without sleep, a person finds that lengthy concentration becomes difficult. Through pure determina­tion, a person may perform tasks well for short periods but is easily distracted. Many mistakes are made, espe­cially in routine tasks, and attention slips at times. Even "sleepless" person experiences periods of dozing off for a few seconds or more. The person falls completely asleep unless kept active continuously.

People who go without sleep for more than three days have great difficulty thinking, seeing, and hearing clearly. Some have periods of hallucinations, during which they see things that do not really exist. They also confuse daydreams with real life and often lose track of their thoughts in the middle of a sentence while speak­ing to someone.

Human beings have gone without sleep for up to 11 days. But people who have stayed awake so long lose contact with reality. They become suspicious and fearful

of others. For example, they may believe that a doctor is an undertaker who has come to bury them, or that the food they are eating has been poisoned.

The need for sleep. Sleep restores energy to the body, particularly to the brain and nervous system. Peo­ple require both slow-wave sleep and dreaming sleep. Extra sleep of either kind does not make up for a lack of the other. Slow-wave sleep may help especially in build­ing protein and restoring the control of the brain and nervous system over the muscles, glands, and other body systems. Dreaming sleep may be especially impor­tant for maintaining such mental activities as learning, reasoning, and emotional adjustment.

Scientists are still seeking answers to many questions about the need for sleep. They do not know, for exam­ple, why human beings cannot simply rest, as insects do. Nor have they discovered exactly how sleep restores vigour to the body. Related articles: Baby (Sleeping         conditions), Hibernation, Nightmare, Insomnia, Sleepwalking, Dream, Narcolepsy, and Snoring.

Sleeping sickness is a disease that attacks the nerv­ous system and often results in a prolonged sleep. It af­fects human beings and other vertebrates (animals with backbones) and is usually fatal if untreated. Sleeping sickness occurs only in Africa and is a serious health problem there for both humans and animals. Its effect makes livestock rearing impossible in some areas of the continent. The disease is also referred to as African sleeping sickness or African trypanosomiasis.

Cause. Sleeping sickness is caused by several spe­cies of single-celled parasites called trypanosomes. These organisms have a wormlike shape and a whiplike extension, called a flagellum, at one end. The flageilum also extends along one side of the body to form a struc­ture called an undulating membrane. A trypanosome moves by waving or whipping the membrane.

The trypanosomes that cause sleeping sickness in hu­mans have the scientific names T. rhodesiense and T. gambiense. (The T. stands for Trypanosoma.) The trypa­nosomes are transmitted by the tsetse fly, an insect that lives along lake shores and riverbanks in Africa. The fly becomes infected with trypanosomes while feeding on the blood of an already infected human or animal. The trypanosomes multiply in the insect's stomach, then pass to the salivary glands. A person becomes in­fected when bitten by an infected fly.

Sleeping sickness in livestock results from in­fection by other trypano­somes, including T. brucei and T. congolense. The trypanosomes are gener­ally transmitted by tsetse flies or other biting insects. One species is transmitted by an infected animal during mating.

Symptoms and diagnosis. The speed at which sleeping sickness develops in people varies with the type of trypanosome involved. In general, T. rhode­siense produces symptoms that progress more rapidly than those caused by T. gambiense. Most cases of sleep­ing sickness begin with fever, headache, and chills. These symptoms are followed by swelling of the lymph nodes, skin rash, and weakness. In severe cases, the trypanosomes infect the central nervous system, result­ing in uncontrollable sleep, coma, and death.

Doctors diagnose sleeping sickness by examining a sample of the patient's blood, spinal fluid, or lymph. In patients who have the disease, the sample contains tryp­anosomes, which can be seen under a microscope. Early diagnosis of sleeping sickness is important because prompt treatment can eliminate the parasites and pre­vent permanent damage to nerve tissues.

Treatment and prevention. Doctors use a variety of drugs to control sleeping sickness in people. The drug suramin is commonly given in the early stages of the disease. If treatment starts before the central nervous system becomes infected, the chances for recovery are excellent. Treatment of sleeping sickness in its later stages is less successful. In addition, trypanosomes tend to develop resistance to the drugs used.

Scientists have done much work on finding methods to control sleeping sickness and its carriers. In some parts of Africa, insecticide sprays have proved effective in eliminating tsetse fly populations. Other control ef­forts include the use of radiation to make male tsetse flies sterile and therefore unable to reproduce. See Tsetse fly and Insomnia.