Muscles Of The Body
• Facts About 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).
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
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.
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:
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.
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'.
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.
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:
|Primary Muscles Of The Body
Frozen shoulder (adhesive capsulitis)
Tennis elbow (lateral epicondylitis)
Golfer's elbow (medial epicondylitis)
Repetitive Strain injury/syndrome
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.
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