Anatomy and Physiology: Muscular System

• The muscular system consists of all the muscles of the body. These make up approximately 42% of total body weight, and are composed of long, slender cells known as fibers. The fibers are different lengths and vary in color from white to deep red.
• Each muscle consists of a group of fibers held together by connective tissue, and enclosed in a fibrous sheath or fascia (FASH ee ah).
• Skeletal muscles are elastic and work in pairs - one flexing while the other is extending. They are striated, with horizontal markings, and are stimulated to contract by electrical impulses from the nervous system.
• Skeletal muscles: Fast, white muscle fibers contract rapidly, have poor blood supply, operate without oxygen, and tire quickly. Slow, red muscle fibers contract more slowly, have better blood supplies, operate with oxygen, and do not tire as easily. They are used in ongoing movements, such as maintaining posture.
• Smooth muscle lines most hollow organs of the body, such as the intestines, stomach, and uterus. They help move substances through tubular areas such as blood vessels and the small intestines,  contracting automatically and rhythmically.
• Smooth muscles contract slower than skeletal muscles, but can remain contracted longer, and are not as dependent on oxygen. They are stimulated by electrical impulses or hormones, and use carbohydrates for energy.
• The cardiac muscle or myocardium are striated like skeletal muscles, but are smaller and shorter.
• They are stimulated to contract by electrical impulses sent out from small clumps of specialized tissue in the heart… the sinoatrial    (sī-nō-Ā-trē-ul) and atrioventricular nodes   (ā-trē-ō-ven-trik-y ə-lər) nodes.
• parts of muscle 

  Body – the main portion

   

  Origin – the fixed attachment

   

  Insertion - the point of attachment to the part of the body moved by this muscle
• the origin of the muscle is the scapula attachment;  a tendon provides the insertion on the ulna and radius bones.
• A tendon is a means of attachment, connecting the muscle to the bone. They vary in length, from less than an inch to more than a foot.
• A wide sheet-like tendon is called an aponeurosis 
• Muscles are continually working to maintain posture. This passive muscle contraction known as residual muscle tension is called tonicity.
• With aging, muscles decrease in strength, endurance, range of motion, coordination, and elasticity. Exercising the muscles can help prevent a loss of strength