Skeletal Muscle Action

Origin and insertion The immovable fixed end of a muscle connects to a bone at the origin. The movable end of a muscle connects at the insertion. With contraction, insertion pulls toward the origin Can have more than one of each.

Use and Disuse of Skeletal Muscles Muscles increase with use = hypertrophy Muscles decrease with disuse = atrophy (cast)

Fast Twitch vs. Slow Twitch Muscle Fibers Aerobic exercise uses slow twitch fibers –Ex. Swimming long distance, cross country skiing- raises amount of ATP and blood flow to muscles. –Red fibers

Fast twitch vs. Slow twitch muscle fibers Anaerobic exercise uses fast twitch fibers. –Ex. Weightlifting, and sprinting - diameter of muscle increases by producing more actin and myosin fibers. –White fibers

Muscle Action of Head Facial expression - sadness, surprise, fear, disgust. –Zygomaticus - mouth –Frontalis - eyebrow –Occipitalus - eyebrow

Muscle Action of Head Mastication - chewing –Masseter –Temporalis Closes jaw

Muscle Action of Head Movement of Head Sternocleidomastoid - prayer position

Muscle Action of the Pectoral Girdle (chest and shoulders) Associated with muscles that move arm Move scapula up, down, forward, and backward –Trapezius –Serratus anterior –Pectoralis minor

Muscle action of the pectoral girdle (chest and shoulders) Associated with muscles that move arm Move scapula up, down, forward, and backward –Trapezius –Serratus anterior –Pectoralis minor

Muscles that Move the Arm Flexion - bending a joint to decrease the angle between bones. Extension - movement increasing angles between parts in a joint Abduction - movement of a body part away from the midline. Rotation - movement turning a body part along its longitudinal axis.

Muscles that move arm –Upper arm Pectoralis major - flexor Latissimus dorsi - extensor Deltoid - abductor Teres minor - rotator

Muscles that move arm flexor extensor abductor rotator

Lower Arm Biceps brachii - flexion Brachialis - flexion Brachioradialis - flexion Triceps brachii - extension extension flexion

Muscle Action in Abdominal Wall (Six Pack) Connect the rib cage to the pelvic girdle –External oblique –Internal oblique –Rectus abdominus Hernia –A hole in the abdominal muscles. –Intestines protrude outward to form a lump. –Repaired by surgery

Muscle Action in Thigh Divided into anterior/posterior sections –Anterior sections create flexion –Posterior sections create extension, abduction, and rotation. Gluteus maximus Gluteus medius Tensor Fasciae Latae Adductors of the thigh

Muscle Action in Thigh Cont… Adduction - movement of a body part toward the midline. –Adductor longus –Gracilus

Muscles that Move the Leg (Lower Leg) Divided into two groups –Hamstring group are the flexors Biceps femoris Semitendenosus Semimembranosus Satorius – longest muscle in the body

Muscles that Move the Leg (Lower Leg) Divided into two groups –Quadriceps Group Rectus femoris - middle of the thigh Vastus lateralis - outside of thigh Vastus medialis - midline of thigh

Longest Muscle in the Human Body Sartorius