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

extensionflexion

flexion

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