Muscles Of The Body
Understanding Muscles

Muscles Of The Body

Contents

• Facts About Muscles
• What Is A Muscle?
• What Muscles Do
• What Do Muscles Look Like?
• How Do Muscles Work?
• How Does A Muscle Know When To Contract?
• Different Stages Of Contraction
• Diseases And Disorders Of Muscles

Interesting Facts About Muscles

Unlike some other mammals human babies are not born knowing how to control the voluntary muscles that help us stand and move. When they start to grow they learn to control and co-ordinate muscles in the following order: first the head, then the neck, the shoulders and arms, and only then the lower parts of the body. When a baby finally learns to stand and walk, it has mastered all the muscles of movement because the last ones in the learning process are the pelvis and legs.

Shivering: When you are cold your body starts producing body heat by making muscles contract and relax quicker than usual. This is the sensation known as shivering.

Muscles account for 23 percent of a woman's body weight and about 40 percent of a man's.

Every additional pound of muscle weight you gain by exercising means you will naturally burn an additional 50 calories a day (the muscle consumes energy).

The smallest muscle is in your body is called the stapedius and it is inside the ear, and is the size of this letter : I

The body's longest muscle is the satorius found on the inner thigh. The biggest muscle is the gluteus maximus (found in your bottom - when you bend forward it is the muscle you use to stand upright again).

What Is A Muscle?

A muscle is a group of elastic tissues.

Structure: Muscle tissue is bound together in bundles and contained in a sheath (sometimes called a fascia), the end of which extends to form a tendon that attaches the muscle to other parts of the body (like a bone). Muscle is 75 percent water, 20 percent proteins and 5 percent fats, mineral salts and glycogen.

What does it do? A muscle's role is to bring about movement of the body (like walking) or to start an involuntary function (like breathing or a heartbeat). When the muscle contracts, it starts a movement in the surrounding structures (the tendons, ligaments and eventually bones). The muscle contracts in response to a 'message' (nerve stimulus) sent by the brain through a motor nerve.

What Muscles Do

1. Contract (squeeze) and thereby cause the movement of different parts of the body. For example, they move joints and bones so we can do things like raise our arm and walk. Muscles move food along our digestive system, open and close our eyes, circulate blood through our body. Different types of muscles carry out different actions.
2. Keep joints (like the hip joint) stable and in place.
3. Maintain good posture - when our back muscles are strong for example, we stand straighter and are less likely to suffer back pain.
4. Help temperature control e.g. shivering and dilation of capillaries (see how the skin works).

What Do Muscles Look Like?

There are 3 different types of muscles, each with a different structure.

1. Skeletal Muscle

Function: These are the muscles that we consciously control e.g. our arms and legs. If we want to walk we do so.

Structure: Skeletal muscle has cylindrical cells which make up fibers. Each fiber has several nuclei (multi-nucleated cells) and is surrounded by a sheath (sarcolemma). The muscle will be made from hundreds or thousands of these fibers. The muscle fibers form bundles and they all run in the same direction. Under a microscope voluntary muscle looks stripy. When the muscle contracts the actin filaments slide between the myosin filaments which causes a shortening and thickening of the fibers.

2. Smooth Muscle

Function: These are the muscles we do not consciously control e.g. those that are found in the walls of blood and lymphatic vessels, in respiratory, digestive and urinary systems. These muscles work automatically whether we want them to or not!

Structure: Smooth muscles have spindle-shaped cells with no distinct membrane and only one nucleus. Bundles of the fibers form the muscle we see with the naked eye.

3. Cardiac Muscle

Function: To power the pump action of the heart.

Structure: Cardiac muscle only exists in the heart; it is involuntary muscle tissue but its fibers are striated and each cell has one nucleus so, in structure, it resembles skeletal muscle. Each cell or fiber has a nucleus.

How Do Muscles Work?

By squeezing (contraction): The fibers become shorter and thicker and the bits attached to the fibers (bones, tendons and fascia) are pulled by the contraction and move. When a muscle fiber contracts it follows the 'all or nothing' law i.e. it contracts completely or not at all. Varying forces (strengths) of contraction are produced depending upon the number of fibers recruited. The greater the number of fibers that contract, the greater the force produced. Smooth muscle and cardiac muscle contract independently of our conscious will. Skeletal muscles, however, move because we want them to. There are two types of contraction:

• Isometric: as the muscle contracts, its length remains the same whilst the tension increases in an attempt to overcome the opposing force, e.g. pushing against an object that is too heavy to move (such as a wall) or holding a glass of water still in front of you.
• Isotonic: as the muscle contracts, its length changes whilst the tension remains constant or develops to overcome the opposing force, pushing an object over or lifting a glass of water to your mouth and lowering it back to the table.

How Do We Move?

In skeletal muscle (those attached to bones) a muscle needs to pass over a joint to create movement. Muscle contraction pulls one bone towards another and thus moves the limb. Muscles never work alone: all movement results from the combined actions of several muscles. In general, muscles work in pairs. Each pair contains an agonist (the contracting muscle) and an antagonist (the opposing, relaxing muscle). The agonist and the antagonist must contract and relax equally to ensure a smooth and not jerky movement.

How Does A Muscle Know When To Contract?

The stimulus (instruction) to contract comes from the nervous system through the nerves. Motor nerves enter the muscles and break into many nerve endings, each one stimulating a single muscle fiber. Sometimes we make a conscious decision to move a muscle (like an arm) - and this 'message' is conveyed to the muscles through the nervous system. The nervous system however is also continually sending messages to smooth muscle and the cardiac muscle to contract without our 'knowledge'.

Different Stages of Contraction

Tone: slight degree of contraction by some fibers as others are relaxing. In normal healthy muscles there will always be a few muscle fibers contracting at any one time, even during sleep. This action gives normal posture to the body.

Relaxation: a lessening of tension, so a reduction in the number of fiber contracting at any one time. Muscle tension can be affected by conscious effort and thought and relaxation can be taught.

Problems with Over-Contraction

Muscle tension: Normally stress induced, this is where the person constantly squeezes the same muscle - perhaps clenching their jaw or balling their fist. Usually the person becomes so used to the action, they stop noticing.

Muscle fatigue: When stimulated a muscle needs oxygen and fuel for its energy. This fuel is mainly glucose, stored in the muscle as glycogen and fats and transported by the blood. The muscle burns the glucose and fats by combining them with oxygen from the blood. If a muscle continues to contract without enough rest (e.g. if someone does too much exercise without breaks), the muscle will run out of oxygen and a by-product of this deficiency, lactic acid, will build up. This acid causes a burning sensation in the muscle, the muscle begins to quiver and soon stops contracting. The exerciser will feel stiffness and pain in the affected muscle.

Where Do Muscles Get Their Energy?

In order for contraction (and therefore movement) to take place, there must be an adequate blood supply to provide oxygen and nutrients and to remove carbon dioxide and waste products from energy production. Muscles receive their nutrients and oxygen from the arterial capillaries. This is converted into energy by chemical changes. The nutrients and oxygen are used up by the muscle and the waste product, lactic acid, is then excreted into the venous blood stream.

A muscle's ability to contract is affected by the following factors:
• energy available
• strength of the stimulus from the nerve
• time muscle has been contracting
• adequate blood supply bringing enough oxygen and nutrients
• temperature of muscle (warmth increases response)
• presence of waste products like lactic acid.

Primary Muscles Of The Body

Diseases And Disorders Of The Muscles

Atony
A medical condition where the muscle has lost strength. It is associated with seizures and other conditions.

Atrophy
Partial or complete wasting away of a muscle. It can be caused by nerve damage, poor diet, poor circulation or reduced hormone circulation.

Achilles bursitis
Common sports injury foot pain in athletes. It is the inflammation of one or more bursae (small sacs) of synovial fluid in and around the Achilles.

Adhesions
Fibrous bands that form between tissues and organs, often as a result of injury.

Frozen shoulder (adhesive capsulitis)
Stiffness in the shoulder which worsens over time. The connective tissue surrounding the shoulder becomes inflamed and stiff, and grows together with abnormal bands of tissue greatly restricting motion and causing chronic pain.

Achilles tendonitis
Is an injury to the achilles tendon generally caused by overuse of the affected limb and is more common among athletes training under less than ideal conditions.

Bursitis
Inflammation of one or more bursae (small sacs) of synovial fluid, usually found around the joints where the muscles slide over the bones. When inflamed they can cause pain on movement.

Cramp
Is an unpleasant, often painful sensation caused by contraction or over-shortening of muscles. Cramps can be caused by cold, vigorous exercise and over-exertion; also extreme heat and dehydration.

Fibromyalgia
People with fibromyalgia experience widespread muscle pain and fatigue. The pain is not constant but can come and go. It is characterized by tender points on the body which are highly sensitive to pain at the slightest pressure. See symptoms of fibromyalgia.

Lumbago
Backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis.

Myositis
Inflammation of a muscle, usually caused by injury or autoimmune disease.

Housemaid's knee
When the kneecap (small sac on the kneecap called a bursa) becomes inflamed, it swells up, forming a large egg like protrusion over the knee cap. It's called housemaid's knee because it was a common complaint of maids who kneeled down to scrub floors.

Tennis elbow (lateral epicondylitis)
Painful inflammation of the tendon at the outer border of the elbow resulting from overuse of lower arm muscles (a motion caused by playing tennis).

Golfer's elbow (medial epicondylitis)
Inflammatory condition of the elbow which in some ways is similar to tennis elbow.

Microtrauma
General term given to small injuries to the body.

Muscle Fatigue
Is a direct term for the inability to exert force with one's muscles to the degree that would be expected given the individual's general physical fitness.

Repetitive Strain injury/syndrome
Pain with associated loss of function in a limb resulting from its repeated movement.

Tendonitis
Is an inflammation in or around tendons (bands of strong fibrous tissue that hold muscle to bone). See also bone and joint problems.

Spasm
A more than usual number of muscle fibers in sustained contraction, usually in response to pain. Fibers contract for much longer than is usually necessary.

Spasticity
Stiff or rigid muscles, or muscles spasm involuntarily.

Sprain
Sudden twist or wrench of the joint's ligaments. The most commonly sprained joint is the ankle (often called a 'twisted ankle'). A sprained ankle is usually caused by the joint 'going over', thus putting all the body weight on the ankle.

Strain
An injury to a muscle or its tendon; may occasionally involve rupture (tearing) of muscle fibers, muscle sheath or tendon. Cause: overexertion, over-stretching, over-use; failure to warm up before strenuous activity, especially sport.

Muscular dystrophy
Any of several hereditary diseases of the muscular system characterized by weakness and wasting of skeletal muscles.

Rupture
A forcible tearing or disruption of a tissue.

Shin splints
A painful inflammation of the muscles around the shins; frequent among runners.

Tetanus
An acute and serious infection of the central nervous system caused by bacterial infection of open wounds.

The Muscle Symptoms Link To:

Nervous system: relies upon nerve impulses to produce a contraction in the muscle. Without nerve stimulus movement would not be possible.

Skeletal system: muscles always cross a joint and thus rely on the skeletal system for leverage and movement.

Digestive system: nutrition/energy in the form of glucose is received from the digestive system. If it is not immediately used it is converted to glycogen and stored in the muscle fibres for energy production later.

Circulatory system: muscles receive oxygen from the vascular and respiratory system.

Other Useful Guides

Recommended screenings for women: What tests should you have?
Main causes of death in women: Interesting statistics
Dangers of stress: What it does to the body.
Effects of depression: Understanding the condition.
How menopause affects the body: Hormones and other effects.
Effects of estrogen: The impact of too little or too much.
Head and face condition: Diseases and disorders.
Hospital departments explained: How to find your way around a hospital.
Female reproduction system: How this system works.
Back problems: A to Z on conditions.

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