A disability can be the result of a disease, an accident, or of genetics, which means that it is a condition that a person is born with.
A lot of times disabled people can learn new ways to do things or use special machines or specially trained animals to help them work around their disability.
Scientists do not know exactly why people need sleep, but studies show that sleep is necessary for survival. Sleep appears to be necessary for the nervous system to work properly. While too little sleep one night may leave us feeling drowsy and unable to concentrate the next day, a long period of too little sleep leads to poor memory and physical performance.
Hallucinations (seeing things that aren’t really there), vision problems, and mood swings may develop if sleep deprivation continues.
“Dog days” are the hot, humid days of summer that usually take place in the Northern Hemisphere in July and August typically between July 3 and August 11. The days get their name from the dog star Sirius of the constellation Canis Major.
At this time of year, Sirius, the brightest visible star, rises in the east at the same time as the Sun in the northern hemisphere. Ancient Egyptians believed that the heat of this brilliant star added to the Sun’s heat to create this hot weather and they blamed the star for everything from withering droughts to sickness.
Technically, no. While it is responsible for receiving and transmitting all messages of pain for the whole body, the brain itself does not have pain receptors.
That means that, if you could somehow gain access to another person’s brain, you could poke it or pinch it and that person would not feel the pain.
Dams, which are structures that hold back water, have been built since ancient times. They are usually made of earth, rock, brick, or concrete—or a combination of these things. They are constructed to control the flow of water in a river, and they are built for a number of reasons. One reason is to prevent flooding. Heavy rains in high country may cause water levels in a river to rise. As the river flows downhill, it may overflow its banks, flooding communities located downstream. A dam can prevent this by stopping or slowing rushing water, allowing it to be released at a controlled rate. Dams are also frequently used to store water for general use and farming. When a river’s flow is restricted by a dam, water often spreads out behind the dam to form a lake or reservoir in the river valley. That water can then be used as needed, preventing water shortages and crop damage during long periods of dry weather.
A great number of dams today are used to make electricity. Such hydroelectric dams are built very tall, to create a great difference in the height of the water level behind and in front of it. High water behind a dam passes through gates in the dam wall that allow it to fall to the river far below. As the water falls, it flows past huge blades called turbines; the turbines run generators that make electricity. One of the world’s largest and most productive hydroelectric dams is the Hoover Dam, located on the Colorado River between Nevada and Arizona. Built in the 1930s, it is 726 feet (221 meters) high and 1,244 feet (379 meters) long. Its reservoir (Lake Mead)—the world’s largest— supplies water to several states, allowing huge regions of naturally dry terrain in southern California, Arizona, and Mexico to flourish. Many modern dams are used for all three purposes: flood control, water storage, and hydroelectric power.
Dust mites are microscopic organisms that live in dust. These unwelcome visitors invade your nose and can irritate your mucous membranes, triggering nerve cells that signal the lungs to fill with air. When the air passages close and pressure builds up, your nose tingles and twitches, and you sneeze—forcing mucus (the slimy, moisturizing substance), dust, pollen, and mites out of your nose at speeds of up to 525 feet (160 meters) per second!
Sneezing is one of the body’s reflexes, an automatic way it rids itself of harmful substances like bacteria and germs. It also keeps the tubes that carry the air from your nose to your lungs healthy.
A fruit is the part of the plant that nourishes and protects new seeds as they grow. The plant’s ovaries develop into fruit once the eggs inside have been fertilized by pollen. Some plants produce juicy fruit, such as peaches, pears, apples, lemons, and oranges.
Others produce dry fruit, such as nuts and pea pods. If an animal doesn’t eat the fruit, or a human doesn’t pick it off, it falls to the ground and decays and fertilizes the soil where a new seed will grow.
The ribs are thin, flat, curved bones in your upper body that form a protective “cage” around the heart and lungs. The ribs are comprised of 24 bones arranged in 12 pairs that form a kind of cage that encloses the upper body and gives the chest its familiar shape. The ribs serve several important functions.
They protect the heart and lungs from injuries and shocks that might damage them. Ribs also protect parts of the stomach, spleen, and kidneys. The ribs help you to breathe. As you inhale, the muscles in between the ribs lift the rib cage up, allowing the lungs to expand. When you exhale, the rib cage moves down again, squeezing the air out of your lungs.
Muscles are attached to bones by tendons, the longest and strongest of which is called the Achilles tendon in your heel. This thick band of tissue attaches the muscles of the calf to the heel bone and is the key to the foot’s ability to flex.
The Achilles tendon allows you to push off of your foot when walking or running. In ancient Greek myth, the hero Achilles died from a wound to his heel, so the popular expression “Achilles heel” often refers to a physical weakness or limitation.
Yes and no. Bones are hard connective tissue, made up of bone cells, fat cells, and blood vessels, as well as nonliving materials, including water and minerals. Some bones have a very hard, heavy outer layer made out of compact bone. Under this layer is a lighter layer called spongy bone, which is located inside the end, or head, of a long bone.
Spongy bone is tough and hard, but light, because it has lots of irregularly-shaped sheets and spikes of bone (called trabeculae) that make it porous (full of tiny holes). The soft, jelly-like inner core of bone is called the bone marrow. It is where red blood cells, certain white blood cells, and blood platelets are formed. The jawbone is the hardest bone in your body. Although bones are hard, they are not the hardest substance in the human body: the enamel on your teeth is harder.