Human System: Nervous System

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. The nervous system is divided into two main systems, the central nervous system (CNS) and the peripheral nervous system. The spinal cord and the brain make up the CNS. Its main job is to get the information from the body and send out instructions. The peripheral nervous system is made up of all of the nerves and the wiring. This system sends the messages from the brain to the rest of the body.

Human System: Skeleton System

The human skeleton system consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart. The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight, and half of this weight is water.

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: there are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.

If you are interested to find out more about the individual bones and their functions, click here.

Human System: Muscular System

So what do muscles do? 

Muscles move cows, snakes, worms and humans. Muscles move you! Without muscles you couldn't open your mouth, speak, shake hands, walk, talk, or move your food through your digestive system. There would be no smiling, blinking, breathing. You couldn't move anything inside or outside you. The fact is, without muscles, you wouldn't be alive for very long! 

Do I have lots of muscles? 

Indeed. On average, probably 40% of your body weight is in muscles. You have over 630 muscles that move you. Muscles can't push. They pull. You may ask yourself, if muscles can't push how can you wiggle your fingers in both directions, back and forth, back and forth? The answer? Muscles often work in pairs so that they can pull in different or opposite directions. 

How do muscles move? 

The cells that make up muscles contract and then relax back to original size. Tiny microscopic fibers in these cells compress by sliding in past each other like a sliding glass door being opened and then shut again. The cells of your muscles use chemical energy from the food you eat to do this. Without food, and particular kinds of nutrients, your muscles wouldn't be able to make the energy to contract! 

Some muscles are known as "voluntary" -- that is, they only work when you specifically tell them to. Do you want to say something? Or swing a bat? Or clap your hands? These are voluntary movements. Others, like the muscular contracting of your heart, the movement of your diaphragm so that you can breathe, or blinking your eyes are automatic. They're called involuntary movements. And how do any of these muscles move? Through signals from your nerves, and, in some cases, your brain, as well. 

Can you hurt muscles? 

Yup. If you hear someone say that they "pulled" a muscle, they have, in fact, torn a muscle in the same way that you can tear a ligament or break a bone. And, like these other living body parts, with a little help, they generally mend themselves. 

Factoids:

• You have over 30 facial muscles which create looks like surprise, happiness, sadness, and frowning.
• Eye muscles are the busiest muscles in the body. Scientists estimate they may move more than 100,000 times a day!
• The largest muscle in the body is the gluteus maximus muscle in the buttocks.

Human System: Respiratory System

Our cells need oxygen to survive. One of the waste products produced by cells is another gas called carbon dioxide. The respiratory system takes up oxygen from the air we breathe and expels the unwanted carbon dioxide. The main organ of the respiratory system is the lungs.

The nose and trachea
Breathing in through the nose humidifies the air. Nose hairs help to trap any particles of dust. The warmed air enters the lungs through the windpipe, or trachea. The trachea is a hollow tube bolstered by rings of cartilage to prevent it from collapsing.

The lungs
The lungs are inside the chest, protected by the ribcage and wrapped in a membrane called the pleura. The lungs look like giant sponges, since they are filled with thousands of tubes, branching smaller and smaller. The smallest components of all are the air sacs, called 'alveoli'. Each one has a fine mesh of capillaries. This is where the exchange of oxygen and carbon dioxide takes place.

The breathing muscles
To stay inflated, the lungs rely on a vacuum inside the chest. The diaphragm is a sheet of muscle slung underneath the lungs. When we breathe, the diaphragm contracts and relaxes. This change in air pressure means that air is ‘sucked’ into the lungs on inhalation and ‘pushed’ out of the lungs on exhalation. The intercostal muscles between the ribs help to change the internal pressure by lifting and relaxing the ribcage in rhythm with the diaphragm.

The exchange of gas
The blood containing carbon dioxide enters the capillaries lining the alveoli. The gas moves from the blood across a thin film of moisture and into the air sac. The carbon dioxide is then breathed out. On inhalation, oxygen is drawn down into the alveoli where it passes into the blood using the same film of moisture.



Summary

The main organ of the respiratory system is the lungs. Our lungs breathe in oxygen and breathe out carbon dioxide. This exchange of gases is vital to life. Breathing depends on the diaphragm, a sheet of muscle slung beneath the lungs inside the ribcage. Common problems of the respiratory system include asthma, bronchitis, emphysema, hayfever, influenza, laryngitis and pneumonia.

For more information on the respiratory system, click here.

Human System: Circulatory System

The circulatory system (also called the cardiovascular system) is made up of group of organs that transport blood and the substances it carries (oxygen, nutrients, etc) to and from all parts of the body. The organs of circulatory system consist of vessels that carry the blood and a muscular pump, the heart, that drives the blood.

Of the vessels, the arteries carry blood away from the heart; the main arterial vessel, the aorta, branches into smaller arteries, which in turn branch repeatedly into still smaller vessels and reach all parts of the body. Within the body tissues, the vessels are microscopic capillaries through which gas and nutrient exchange occurs (see respiration). Blood leaving the tissue capillaries enters converging vessels, the veins, to return to the heart and lungs. The human heart is a four-chambered organ with a dividing wall, or septum, that separates it into a right heart for pumping blood from the returning veins into the lungs and a left heart for pumping blood from the lungs to the body via the aorta.