Category Human Body

How do I breathe?

When you breathe, you draw air in through the nose and mouth and into the lungs. Air consists of 79 percent nitrogen and about 21 percent oxygen, with small amounts of carbon dioxide and other, rare gases. Air travels down a tube called the trachea that forks into other tubes called bronchi, which lead into the lungs. From here the air passes into a series of smaller air passages and eventually into tiny air sacs, or bladders, called alveoli. Oxygen is absorbed through the thin walls of the alveoli into the blood, and waste carbon dioxide is released to be breathed out as a waste product.

How big are the alveoli?

Each alveolus is about 0.2 mm across. The walls of the alveoli are very thin — only one cell thick — so oxygen and carbon dioxide can easily pass through. There are probably 300 million alveoli in the lungs.

Why do many of my muscles work in pairs?

                A muscle can only pull in one direction. It needs another muscle to pull in the opposite direction in order to return a bone to its original position.

                When you lift your forearm, the biceps muscle shortens to lift the bone. When you straighten your arm, the triceps muscle pulls it back again and the biceps relaxes. The same action takes place in your legs when you walk and run, and when you move your fingers and toes.

What causes muscle cramp?

                      Cramp is caused by the build-up of a waste substance called lactic acid. When a muscle works harder than usual, it starts to break down stored food without using oxygen. This process is called anaerobic respiration. It produces lactic acid as a waste product. As the lactic acid builds up it interferes with muscle action, making the muscle feel tired, until the acid is flushed away by the blood. If too much lactic acid builds up, it makes the muscle contract very sharply and painfully, causing a cramp.

How does regular exercise help the muscles?

                 Muscles are able to adapt gradually to the amount of work they have to do, so regular exercise can build them up and make them healthier. Exercise strengthens the muscles and improves muscle tone. It can also improve your body shape and posture, as well as strengthening your heart and improving your blood flow. It will generally make you feel much better and help you to sleep soundly.

How do muscle fibres shorten?

Muscle fibres contain tiny rod-like structures that overlap. When the fibre receives a nerve signal that tells it to contract, these rods slide over one another, making the fibre shorter. As the fibres shorten, the whole muscle contracts. All the fibres do not contract together. The harder the muscle needs to pull, the greater the number of fibres that will contract at the same time.

Can I make my muscles grow?

Muscles react to frequent exercise by growing more muscle cells, or fibres, making the muscle thicker and more bulky. The more fibres there are in a muscle, the stronger it will be. This explains why athletes who take constant exercise develop very large muscles.

How many muscles do I have?

You have about 650 muscles in your body. There are more than 50 muscles in your face alone.

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Which are the strongest muscles?

                            Although it is not very big, the strongest muscle in the body, for its weight, is the masseter muscle in the jaw. It allows you to have a powerful biting action. The largest muscle of all is the gluteus maximus (a Latin name, like many medical terms). It runs from the buttocks down the back of the thigh. The longest muscle is the sartorius, which runs from the hip bone, or pelvis, right down to just below the knee.

What is muscle tone?

Muscles need constant work to keep them strong and healthy. When two muscles work against each other, they will always be slightly contracted and under tension. This is called muscle tone. The fitter you are, more strongly these muscles will pull against one another, even while you are relaxed.

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What job do muscles do?

                      Muscles are needed for all body movements. Muscles move the bones, pulling them into position as they move about their joints. Some muscles just move soft parts of the body, for example, the face muscles that allow you to smile.

                      You can control many of your movements by using voluntary muscles. Other muscles, called involuntary muscles, work automatically to maintain the body. The heart, for instance, beats without your being aware of it. The muscles that squeeze your food along inside the intestines also work automatically.

How are muscles joined to bone?

                     Muscles are attached to bone by long ropy strands called tendons, which are made of collagen. You can feel these tendons on the inside of your wrist when you flex your hand and fingers.

How are muscles constructed?

                    Muscles are built up from millions of thread-like cells called muscle fibres. These fibres are gathered into bunches. Nerves instruct the muscle fibres when to shorten, or contract, causing the whole muscle to become shorter in length. The shortened muscle then pulls on the tendon and the bone to which it is joined.

Can joints wear out?

                  Joints can become diseased or wear out after a lifetime of use. When this happens, the cartilage or the fluid inside the joint gradually disappears. The joint becomes hard to move and may be very painful.

How many joints do I have?

                      The human body has more than 100 joints. Some joints move like a simple hinge, such as those in the elbows and knees. Other joints move in all directions, such as the shoulder joint or the base of the thumb. Joints in the spine allow only a small amount of movement between the vertebrae that protect the spinal cord. Joints such as the bones of the skull and those joining the two sides of the pelvis are locked firmly together so they do not move at all.

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