Muscular System 7.5 Over 600 muscles make up the muscular system Muscles are made of bundles of muscle fibers that are held together by connective tissue

Properties or Characteristics Excitability- ability to respond to a stimulus such as a nerve impulse Contractibility- when muscle fibers are stimulated by nerves, they contract, or become short and thick, this causes movement Extensibility- ability to be stretched Elasticity- allows the muscle to return to its original shape after it has contracted or stretched

3 kinds of muscle Cardiac- forms the walls of the heart, contracts to circulate blood, involuntary because it functions without conscious thought or control Visceral or smooth- found in the internal organs of the body such as the digestive, respiratory, blood vessels, and eyes; contracts to cause movement in these systems, involuntary because it functions without conscious thought or control Skeletal- attached to bone, causes movement, voluntary because person has control over their actions

Functions Attach to bone to provide voluntary movement Produce heat and energy Help maintain posture by holding the body erect Protects internal organs

Methods of Attachment Tendons; strong, tough, fibrous connective tissue, examples are Achilles tendon which attaches the gastrocnemium muscle on the calf of the leg to the heel bone Fascia-tough, sheet like membrane that covers and protects the tissue, example lumbodorsal fascia which surround the deep muscles of the trunk and back

When muscles attach to bones, one end becomes the origin and end becomes the insertion Origin- end that does not move Insertion- end that moves when muscle contracts Example: origin of shoulder muscle, called the deltoid, is by the clavicle and scapula, insertion is on the humerus. When the deltoid contracts the area by the scapula remains stationary but the area by the humerus moves and abducts arm away from the body

Actions of 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 Extension- increasing the angle between two bones or straightening a body part Rotation- turning a body part around its own axis, turning the head from side to side Circumduction- moving in a circle at a joint, moving one end of a body part in a circle while the other stays stationary, swinging the arm in a circle

Main Muscles Trapezius- upper back and neck Deltoid- shoulder Biceps brachii- upper arm Triceps brachii- upper arm Pectoralis major- upper chest Rectus abdominus- ribs to pubis Latissimus dorsi- spine around to chest Gluteus maximus- buttocks

Diseases Fibromyalgia- chronic widespead pain in specific muscle sites Symptoms include stiffness, numbness or tingling in the arms or legs, fatigue, headaches, depression Etiology unknown but stress, weather, and poor physical fitness affect condition Medication to relax muscle and control pain

Muscular dystrophy Group of inherited diseases Lead to chronic progressive muscle atrophy (muscles shrink in size and lose strength) Appears in early childhood Most types end in total disability and early death

Spasm or cramp are sudden painful involuntary contraction of muscle that usually occur in leg or foot May result from overextension, low electrolyte levels, poor circulation Use gentle pressure and stretching to relieve spasm Strain from overstretching or injury to muscle or tendon frequently occur in the back, arms, and legs; prolonged or sudden muscle exertion is usually the cause, rest and elevation, muscle relaxant medication, heat/cold