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Anatomy and Physiology 7:5 Muscular System 600+ muscles in the body Bundles of muscle fibers held together with connective tissue Properties of Muscles Properties of muscles Excitability/irritability The ability to respond to a stimulus such as a nerve impulse. Contractibility Muscle fibers that are stimulated by nerves contract, or become short and thick, which causes movement. Extensibility The ability to be stretched. Elasticity Allows the muscle to return to its original shape after it has contracted or stretched. Kinds of Muscles Cardiac—involuntary Visceral or smooth—involuntary Skeletal—voluntary Smooth Muscle • Has narrow, tapered rod-shaped cells. • Has nonstriated, uninucleated fibers • Occurs in walls of internal organs and blood vessels • Is involuntary © 2009 The McGraw-Hill Companies, Inc. All rights reserved Cardiac Muscle • Has striated, tubular, branched, uninucleated fibers • Occurs in walls of heart • Is involuntary © 2009 The McGraw-Hill Companies, Inc. All rights reserved Skeletal Muscle • Has striated, tubular, multinucleated fibers. • Is usually attached to skeleton • Is voluntary © 2009 The McGraw-Hill Companies, Inc. All rights reserved Functions of Muscles Attach to bones to provide movement Produce heat and energy Help maintain posture Protect internal organs Skeletal muscles Smooth muscle Cardiac muscle ◦ Attached to bones by tendons ◦ Connected across joints so when they contract, bones they attach to move ◦ Found on organ walls such as digestive system ◦ Contractions produce movement of organ contents ◦ Produces heart chamber contractions ◦ This pumps blood from the heart into the blood vessels © 2009 The McGraw-Hill Companies, Inc. All rights reserved Hold bones tightly together ◦ Stabilize joints Small muscles hold vertebrae together ◦ Stabilize the spinal column © 2009 The McGraw-Hill Companies, Inc. All rights reserved Sphincters ◦ Valve-like structures formed by muscles ◦ Control movement of substances in and out of passages ◦ Example: A urethral sphincter prevents or allows urination © 2009 The McGraw-Hill Companies, Inc. All rights reserved Heat is released with muscle contraction ◦ Helps the body maintain a normal temperature ◦ Moving your body can make you warmer if you are cold ◦ Shivers is an extreme example of this © 2009 The McGraw-Hill Companies, Inc. All rights reserved Attachments to Bone Tendon Strong, tough, connective-tissue cords. Fascia Tough, sheetlike, membrane that covers and protects the tissue. Origin The end that does not move when the muscle contracts. Insertion The end that moves when the muscle contracts. Actions or Movements of Muscles Adduction Moving a body part toward the midline. Abduction Moving a body part away from the midline. Flexion Decreasing the angle between two bones, or bending a body part. Actions or Movements of Muscles Extension Increasing the angle between two bones, or straightening a body part. Rotation Turning a body part around its own axis (Example: Turning head side to side). Circumduction Moving in a circle at a joint. Muscle Tone Partially contracted at all times Muscle tone allows for state of readiness Loss of muscle tone © 2009 The McGraw-Hill Companies, Inc. All rights reserved Diseases and Abnormal Conditions Fibromyalgia Chronic, wide-spread pain in a specific muscle sites. Muscular dystrophy A group of inherited diseases that lead to chronic, progressive muscle atrophy. Duchenne’s dystrophy Type of muscular dystrophy; caused by a genetic defect. Diseases and Abnormal Conditions Myasthenia gravis Chronic condition where nerve impulses are not properly transmitted to the muscles. Muscle spasms or cramps Painful, sudden, involuntary muscle contractions. Strain Overstretching of or injury to a muscle and/or tendon.