Summary Chapter 7 Muscular System I Seeley's Essentials of Anatomy and Physiology, 9th Edition I Johmel De Ocampo

Chapter key points: Muscle fibers are organized into fasciculi, and fasciculi are organized into muscles by associated connective tissue. Each skeletal muscle fiber is a single cell containing numerous myofibrils. Myofibrils are composed of actin and myosin myofilaments. Sarcomeres are joined end-to-end to form myofibrils. Cell membranes have a negative charge on the inside relative to a positive charge outside. This is called the resting membrane potential. Action potentials are a brief reversal of the membrane charge. They are carried rapidly along the cell membrane. Sodium ions (Na+) move into cells during depolarization, and K+ moves out of cells during repolarization. Small contraction forces are generated when small numbers of motor units are recruited, and greater contraction forces are generated when large numbers of motor units are recruited. Energy is produced by aerobic (with oxygen) and anaerobic (without oxygen) respiration. Muscles contract either isometrically (tension increases, but muscle length stays the same) or isotonically (tension remains the same, but muscle length decreases). Muscles of facial expression are associated primarily with the mouth and eyes. Four pairs of muscles are involved in mastication. Tongue movements involve intrinsic and extrinsic muscles. Swallowing involves the suprahyoid and infrahyoid muscles, plus muscles of the soft palate, pharynx, and larynx. Neck muscles move the head. The erector spinae muscles hold the body erect. Intercostal muscles and the diaphragm are involved in breathing. Muscles of the abdominal wall flex and rotate the vertebral column, compress the abdominal cavity, and hold in and protect the abdominal organs. Muscles form the floor of the pelvis. The upper limb is attached to the body primarily by muscles. Arm movements are accomplished by pectoral, rotator cuff, and deltoid muscles. The elbow is flexed and extended by anterior and posterior arm muscles, respectively. Supination and pronation of the forearm are accomplished by supinators and pronators in the forearm. Movements of the wrist and fingers are accomplished by most of the twenty forearm muscles.