The heart is a muscle, which through rhythmical contractions, enables blood circulation to every other organ of the human body. It is one of the first organs that develops during human embryo phase. The heart weights approx. 500gr and is composed of two parts: the right side though which blood flows towards the lungs (small circulation), and the left side, where the blood flow begins (big circulation). The heart is located in the center of the chest, though it leans a bit on the left (rarely also on the right). Heart valves should be fully functional in order for the body to be properly supplied with blood. Thus the heart fulfills its role as a blood pumping organ.
The brain is the part of the body which lets us, and other animals, make sense of things. It gets input from sense organs, and changes behaviour in response to this information. In humans, the brain also controls our use of language, and is capable of abstract thought. The brain is the control centre of the whole body. The brain is made up of a special type of cells. They are connected with each other and with the nerves in our body. In all animals the delicate brain is protected in some way. In ourselves, and all vertebrates, it is protected by the bones of the skull.
A skeleton is the hard structure that supports the body of a living thing. Skeletons can be inside the body or outside the body. In mammals, which include humans, the skeleton is made of bones. All the bones, when they are joined together, make the "skeletal system" of a body. The skeletal system or "skeleton" is under the skin, the muscle and the tissue of the body. The skeleton supports the skin, muscle and tissue, and all the organs that are inside the body. The skeleton protects important internal organs like the brain, heart and lungs. If humans did not have a skeleton then the body would be flat as the skeleton gives the body its frame. The important parts of a human body are the head, the spine, the chest, the abdomen, the arms and hands, and the legs and feet.
The muscular system is one of the major systems in our body. Its main purpose is to produce movement. Muscle is a tissue in animal bodies. Muscles help us to move our body parts. The skeleton and the muscles which move it are known as the musculoskeletal system. Muscles are made of many muscle cells. The cells contract together to make the muscle get shorter. The muscle cells know to do this together because many of them get information sent to them by nerves. Then cells that get the message from nerves tell other cells that are near them. They tell the other cells by sending an electrical current. Muscle cells are filled with proteins called actin and myosin. These are the proteins that make the muscle contract (get shorter).
The circulatory system is the body system that moves blood around the body. The heart and all blood vessels make up the circulatory system. Blood vessels that take blood away from the heart are arteries. Arteries get smaller as they go away from the heart. The smaller arteries that connect to the capillaries, are called arterioles. Blood vessels that take blood towards the heart are veins. Veins get bigger as they go towards the heart. The smallest veins are called venules. Capillaries go between arteries and veins. Capillaries are quite thin, hence the name which comes from the Latin “capillus” meaning "hair." There are two different circulations in the circulatory system. The systemic circulation is how blood goes to most of the body. The pulmonary circulation is how blood goes through the lungs. (Pulmonary means ¨about the lungs¨). This is how it works in mammals, including humans.
The nervous system is a system in the body which sends signals around the body. It lets people respond to what is around them. The central nervous system is the brain, the spinal cord, and nerves. It is there to coordinate movement, to process the input of the senses, and to make the humans act a certain way. It is made up of neurons and cells called glia, among other things. Glial cells keep the neurons safe and healthy. The structure of the system includes the brain and spinal cord, which together are called the central nervous system. The brain has billions of nerve cells to help think, walk, and breathe. The nervous system can react in 1/100 of a second to a stimulus, like a pain signal.
Spinal disc herniation, also known as a slipped disc, is a medical condition affecting the spine in which a tear in the outer, fibrous ring of an intervertebral disc allows the soft, central portion to bulge out beyond the damaged outer rings. Disc herniation is usually due to age-related degeneration of the outer ring, known as the anulus fibrosus, although trauma, lifting injuries, or straining have been implicated as well. Tears are almost always postero-lateral (on the back of the sides) owing to the presence of the posterior longitudinal ligament in the spinal canal. This tear in the disc ring may result in the release of chemicals causing inflammation, which may directly cause severe pain even in the absence of nerve root compression.
An acute myocardial infarction, also called a heart attack, happens when a blood vessel in the heart suddenly becomes blocked. Blood vessels carry blood and oxygen. When a blood vessel in the heart gets blocked, blood cannot get to part of the heart. This part of the heart does not get enough oxygen. This is called ischemia. When the heart muscle becomes ischemic (does not get enough blood and oxygen), the ischemia often causes chest pain. This is called angina pectoris. If the ischemia lasts long enough, the heart muscle that is not getting enough oxygen dies. This is called an infarction. "Myocardial infarction" means "infarction (muscle death) in the heart muscle."
Cardiac arrhythmia (commonly called irregular heartbeat) is the name for a number of conditions, where the heartbeat is not normal. It may be too fast (tachycardia); too slow (bradycardia); or the heart may not beat in its regular rhythm.
Epilepsy is a chronic condition of the brain. It is characterized by seizures that do not seem to have an obvious cause. To the outside viewer, these seizures show as episodes of heavy shaking. Depending on the seizure, the shaking may be short and difficult to detect or it may be longer. People with epilepsy are sometimes called epileptic, but it is the fit or seizure that is "epileptic". Many people have died from seizures.