Your Muscles— How They Function

By Martinez - October 12, 2017

Muscles—Masterpieces of Design

LIFE is sustained through movement. For example, your chest rises and falls with each breath, and your heart beats rhythmically, keeping you alive. What causes these movements? Muscles!
Muscles are tough, elastic tissues that enable your body parts to function and to express your thoughts and feelings in actions. Whether the action is smiling, laughing, crying, talking, walking, running, working, playing, reading, or eating, muscles are involved. It is hard to think of anything you do that does not involve a muscle.
There are about 650 muscles in your body. The smallest are attached to the tiniest bones, found in the ear. The largest are the gluteus muscles in the buttocks, which move the legs. Making up about one half of a man's body weight and about one third of a woman's, muscles are designed for work. 

Human muscles

They are considered "biological engines, or muscle cars by some," and they 'transform more energy into motion each day than all man-made engines combined, including the automobile,' observed Gerald H. Pollack, a professor of bioengineering.

Even when you are resting, your muscles remain in a state of readiness—ready to be called into action. At any given time, some fibers in each muscle are contracted. Without this slight contraction, your jaw would hang open and your body's internal organs would have little support. Even while you are standing or sitting, your muscles make slight adjustments to help maintain your posture or to keep you from falling off your chair.

The Marvel Of Muscle Contraction

A muscle's action may appear simple. But the mechanism of contraction is awesome. Professor Gerald H. Pollack says: "I have come to stand in awe of the esthetic in nature's design. The conversion of chemical energy into mechanical energy is accomplished so adroitly—it is tempting to say so intelligently—that one is drawn to marvel."
Let us use an electron microscope to look at the intricate operation of muscle contraction and learn more about this masterpiece of our Creator's design.
Each muscle cell, or fiber which is another term for it, is actually a bundle of smaller fibers called myofibrils that are organized in parallel form. Each myofibril contains thousands of thinner myofilaments. Some myofilaments are thicker, some thinner. The thicker contain myosin, and the thinner contain actin, proteins that help the muscle cell contract.
On the surface of each muscle fiber is a hollow. The nerve fiber, branching off from the spine, ends there and fits into the hollow. Our muscles swing into motion when the brain gives the command and the message, fired across millions of nerve cells of the central nervous system, reaches the nerve ending. As each nerve ending is stimulated, more than 100 tiny sacs burst open, spilling a chemical that amplifies the nerve's impulse as it comes in contact with the membrane of the muscle cell. This sets off a wave of electrical activity that excites the whole muscle cell, causing the cell's membrane to release electrically charged calcium ions, which spark the mechanical process of contraction.
Calcium ions now spread through the whole muscle fiber via a network of fine tubes and come into contact with various proteins. Somehow the calcium's action on these proteins causes protected protein sites along the thin actin filament shaft to be uncovered or exposed.
At the same time, pairs of rounded buds, crowned with a high-energy compound called ATP, projecting from the thicker myosin filaments, move into action. One of the buds of the myosin filament head latches onto one of the now-exposed active sites on the actin filament, forming a cross bridge. The other bud splits the ATP and releases enough energy for the cross bridge to pull or slide the actin filament alongside or over the myosin filament. Like a team working hand over hand to pull a rope, the myosin heads release their grip and reattach themselves farther along the actin shaft, all the while propelling the actin filament toward the center of the myosin filament. This action is repeated until the contraction is complete. The entire chain reaction takes place in just a few thousandths of a second!
With the contraction completed, the calcium returns to its source in the muscle cell's membrane, the exposed sites along the actin filament shaft are once again covered up, and the muscle fiber relaxes until it receives stimuli again.

Types of Muscles

There are three types of muscles in your body. Each performs a different job. One is the cardiac muscle, which pumps the heart. The heart muscle rests half its life, for after each contraction the muscle relaxes until the next contraction.
Cardiac muscle

Another type of muscle is smooth muscle. These muscles wrap themselves around most of your internal organs, including blood vessels. Like heart muscle, whose action is involuntary, smooth muscles are not consciously controlled. They perform such vital functions as moving fluids through your kidneys and bladder, pushing food through your digestive tract, regulating the flow of blood through your vessels, shaping your eye lenses, and dilating the light aperture of your pupils.
Most of your 650 muscles are skeletal muscles. These carry out your voluntary movements. You learn to control these muscles from birth. A baby, for example, learns to move its arms and legs so that it can walk and balance. Because muscles can only contract, skeletal muscles work in pairs. When one muscle contracts, the other relaxes. Without this joint effort, every time you use your hand to scratch your head, you would have to let gravity pull your arm down. Instead, your triceps, the muscle that is the partner of your biceps, contracts, enabling you to straighten out your arm quickly.
Muscles vary in size and shape. Some are long and slim, for example, the hamstring muscles of the legs. Others are heavy and thick, such as the gluteus muscles in the buttocks. All are designed to allow you to move. The rib cage would be rigid if it were not for muscles that fill the gaps between the ribs. These enables the chest wall to move like an accordion, helping you to breathe. Much like the layers in plywood, abdomen muscles are arranged in sheets at different angles, to prevent your abdominal organs from falling out.

Muscle and Tendon Cooperation

Muscles that pull on your bones are attached to them by tough, white cordlike tissues called tendons. Tendons extend far inside muscles and link up with connective tissue that surrounds muscle fiber. Connective tissue enables the forces generated inside your muscles to tug on the tendon and move your bones. The most powerful tendon, the Achilles tendon, is attached to one of the strongest muscles of your body, in your calf. Calf muscles act as the body's shock absorbers. When you walk, run, or jump, they withstand pressures of more than a ton.
The versatility of your hand is another example of muscle and tendon cooperation. Twenty pairs of muscles found in your forearm latch onto your multijointed hand and finger bones by long tendons that pass under a fibrous wristband. These together with 20 more muscles that line your palm and fingers give your hand the amazing dexterity needed to assemble the delicate inner workings of a fine watch or to grasp an ax handle to chop wood.

Muscles Of Facial Expression

Over 30 facial muscles
More than any other feature of your body, the face expresses your personality. To accommodate a huge variety of facial expressions, your body has alarge concentration of muscles in your face—over 30 in all. Why, it takes 14 muscles just to make you smile!

Facial muscles

Some facial muscles are powerful, such as those attached to your jaw, which can exert 200 pounds [75 kg] of force to chew your food. Others are delicate yet durable, such as the muscles that control your eyelids when you blink, bathing your eyes with fluid that washes off dirt and germs more than 20,000 times a day.

Amazing Design

Each muscle is designed to contract smoothly. Skeletal muscles must have their contractions tailored so that the same amount of strength is not used when picking up a feather as when lifting a 20-pound [10 kg] weight. How is this achieved? Let us see.
All muscles are made up of individual cells. Because muscle cells are stretched out, they are referred to as fibers. Some fibers are lighter in color, others darker. The lighter ones are fast-contracting, or fast-twitch, fibers. These are utilized when you need short bursts of energy, such as when picking up a heavy load or running a 100-yard dash. Fast-twitch muscle fibers are powerful, and glycogen, a sugar, is the energy source that fuels them. However, they tire quickly and may even cramp or ache because of an accumulation of lactic acid.
The darker muscle fibers are slow-contracting, or slow-twitch, fibers, and they are driven by oxygen metabolism. Since these fibers have a richer blood supply and have more aerobic energy than fast-contracting fibers, slow-twitch fibers "are the cords of endurance."
Another type of fiber is slightly darker than the pale fast-contracting fibers. This fiber is similar to them but is resistant to fatigue. Because this type utilizes well both sugar and oxygen as fuel, it is likely involved when you do prolonged, intense work.
There is a mixture of these types of fibers in each individual and within different muscles. Long-distance runners, for example, may average 80 percent slow-twitch fibers in their leg muscles, while sprinters can average better than 75 percent of the fast-twitch kind.

Activated by Nerves
All muscle fibers are activated by nerves. When these send impulses to your muscles, the muscles respond with a twitch, or contraction. Yet, not all muscle fiber in a given muscle contracts at once. Rather, the muscle fiber is arranged into motor units. In a motor unit, a single nerve is attached to and controls many fibers.
Some motor units, such as those in your leg muscles, are composed of more than 2,000 fibers to a single nerve. But the motor units in your eye control only three fibers each. Having a smaller group of fibers in a unit and more units per muscle allows for more coordinated, finer movements, such as those needed for threading a needle or playing the piano.
When you pick up a feather, only some motor units contract. When you lift a heavy object, special sensory organs in your muscle fiber send a message with lightning speed to the brain and call more motor units into action, thus increasing the force you use to lift the load. When you walk slowly, only some motor units are activated; whereas, when you run, many more are stimulated and with greater frequency.
Your heart muscle differs from skeletal muscle in that it contracts in an all-or-nothing fashion. When one cell is stimulated in the heart muscle, the message is spread to all the cells and they all become fired up at once, resulting in the entire muscle contracting and then relaxing, about 72 times a minute.
Smooth muscles act much the way the heart muscle does—once the contraction begins, the entire organ contracts. But smooth muscles can remain contracted without tiring for a longer time than heart muscles. Smooth muscles hardly make their presence known, unless you experience an occasional hunger pain or the forceful contractions of childbirth.

Muscle And Fitness—Keep Your Muscles in Shape
"Exercise helps the whole body, inside and out. . . . Muscles exercised regularly do a better job at everything," states the book Muscles: The Magic of Motion. Exercise produces good muscle tone, which better supports your internal organs and helps your muscles resist fatigue.
Two different types of exercise are beneficial for your muscles. Anaerobic exercise, in which you lift weights a short time each day, strengthens your muscles. Stronger muscles stores more sugar and fatty acids and also can burn these fuels more efficiently, helping your muscles resist fatigue.
Aerobic forms of exercise, such as jogging, swimming, bicycling, or brisk walking, promote overall fitness. This kind of endurance exercise increases blood flow to muscles and increases mitochondria, which create ATP, the energy compound needed to make your muscles contract. Your heart especially benefits from this type of exercise, which may even help prevent a heart attack.
Bending and stretching the muscles before you do strenuous exercise can help prevent sprains or other damage to your muscles. Such warm-up exercises raise the temperature in your muscles, which circulates more blood to them and, in turn, helps enzymes produce more energy, enabling your muscles to contract better. Cooling down with the same exercises you warmed up with helps prevent aches and stiffness by removing the lactic acid buildup.
Muscle exercises

However, it must be noted that you can damage skeletal muscle by exercise that is too vigorous, especially if you are not trained. Also, if you place too much tension on your muscles by repeated lengthening contractions, as you could when lowering a heavy load slowly or running downhill, you may tear muscle fiber. Even a small tear resulting from strain can cause painful muscle spasms and inflammation.
Take care of your muscles. Give them the proper exercise and rest so that they can continue to serve you like a well-designed engine, your body's 'ultimate motor.'

Muscles and Nutrition

Good nutrition is a key factor in maintaining healthy muscles. Foods rich in calcium, such as dairy products, and in potassium, such as avocados, bananas, citrus and dried fruits, deep-yellow vegetables, nuts, and seeds help to regulate muscle contractions. Whole-grain breads and cereals supply iron and B-complex vitamins, especially B1, which is crucial in converting carbohydrates, proteins, and fats into the energy fuel your muscles need. Always drink plenty of water because this helps to maintain your electrolyte balance and also flushes out lactic acid and other waste products that could interfere with muscle function.

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