The Muscular System Myology – the study of muscles Orthopedics – branch of medical science that is concerned with the prevention or correction of disorders of the muscular system Muscular tissue makes up about 40 – 50% of the total body weight and is composed of highly specialized cells

Skeletal Muscle Attaches to the bones and moves the skeleton Striated – alternating light and dark bands that contract and relax by conscious control….they are Voluntary muscles

Smooth muscle Located in walls of hollow internal structures such as blood vessels, airways, the stomach and the intestines Non striated and are involuntary

Cardiac muscle Found only in the heart It is striated It is involuntary

Functions of Muscular tissue Producing body movements – walking, running, etc Stabilizing body positions – maintain body postures such as sitting, standing, holding your head up Regulating organ volume – holding your urine, storage of food in stomach Moving substances within the body – cardiac muscle moving blood through the body, smooth muscle moving food through the digestive system Producing heat – shivering, maintaining homeostasis

Skeletal Muscle Several connective tissue coverings are associated with skeletal muscle. The entire muscle is wrapped in epimysium Perimysium surrounds bundles of muscle fibers called fascicles Endomysium wraps each muscle fiber

Skeletal Muscle Tendon – is a cord of dense connective tissue that attaches a muscle to a bone. Example: Achilles tendon- attaches the calcaneus to the gastrocnemius muscle.

Look at Figure 8.1 on page 174 Sarcolemma – membrane that covers each muscle fiber Sarcoplasm – contains mitochondria that produces A LOT of ATP during muscle contraction Sarcoplasmic reticulum – stores calcium ions required for muscle contraction Myoglobin – reddish pigment, stores oxygen until needed by mitochondria to make ATP

Look at Figure 8.1 on page 174 Sarcomeres – basic functional units of striated muscle Muscular hypertrophy – an increase in muscle fiber diameter due to the production of more myofibrils, mitochondria, sarcoplasmic reticulum, etc. It results from forceful, repetitive muscular activity, such as strength training.

Misc. Read blue box pg 179 (Botox) and 180 (rigor mortis) and blue box pg 182 (creatine supplementation) Muscle tone – to sustain muscle tone, small groups of motor units are alternately active and inactive in a constantly shifting pattern. Muscle tone keeps skeletal muscles firm, but it does not result in a contraction strong enough to produce movement. Example: tone muscles in your neck keeps the head upright.

Physiology of contraction Both Calcium and energy in the form of ATP are needed for muscle contraction! ATP present in muscle fibers is enough to power a contraction for only a few seconds. ATP production has 3 sources Creatine phosphate (small amino acid synthesized in the liver) Anaerobic cellular respiration Aerobic cellular respiration

Misc. Muscle fatigue – inability of a muscle to contract forcefully after prolonged activity. There is lowered release of calcium ions from the sarcoplasmic reticulum, resulting in a decline of calcium. There is insufficient oxygen and other nutrients and a buildup of lactic acid.

Cardiac muscle Cardiac muscle fibers interconnect with one another by irregular transverse thickenings of the sarcolemma called intercalated discs. The discs hold the fibers together and contain junctions that allow muscle action potentials to spread quickly from one fiber to another.

Aging Beginning at age 30 humans undergo a slow, progressive loss of skeletal muscle mass that is replaced by fibrous tissue and adipose tissue (fat).

Skeletal movement Skeletal muscle as an organ are composed of several different types of tissues: muscle tissue, vascular tissue (blood and blood vessels), nervous tissue and connective tissues. Skeletal muscle is NOT attached directly to the bone. Movement is produced by pulling on tendons, which in turn pull on bones. Most cross at least on joint and are attached to the articulating bones that form the joint. When the muscle contracts it draws one bone toward the other

Skeletal movement The two bones do not move equally. One is held nearly in its original position. The attachment of a muscle (by means of tendon) to the stationary bone is called the origin. The other end of the muscle is attached by means of a tendon to the movable bone at the insertion. Analogy – a spring on a door. The part of the spring attached to the door represents the insertion, the part attached to the frame is the origin.

Misc. Muscles and function Levator – produces upward movement Sphincter – decreases size of opening (digestive system) Triceps – three origins Masseter – moves the mandible Trapezius – moves pectoral girdle Gracilis – rotates thigh at hip joint; flexes leg at knee joint Tibialis anterior – moves the foot

Disorders Neuromuscular disease – disease or disorder of the skeletal muscle tissue itself Muscular dystrophy – inherited muscle destroying diseases that cause progressive degeneration of skeletal muscle fibers Duchenne muscular dystrophy is the most common form. Fibromyalgia – painful disorder tha tusually appears between the ages of 25 and 50

Medical terminology Myalgia – pain in or associated with muscles Myositis – inflammation of muscle fibers