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Skeletal Muscle Action
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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.
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Use and Disuse of Skeletal Muscles
• Muscles increase with use = hypertrophy
• Muscles decrease with disuse = atrophy (cast)
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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
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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
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Muscle Action of Head
• Facial expression - sadness, surprise, fear, disgust.
– Zygomaticus - mouth
– Frontalis - eyebrow
– Occipitalus - eyebrow
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Muscle Action of Head
• Mastication - chewing
– Masseter– Temporalis
Closes jaw
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Muscle Action of Head
Movement of Head
• Sternocleidomastoid - prayer position
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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
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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
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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.
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Muscles that move arm
– Upper arm• Pectoralis major - flexor• Latissimus dorsi -
extensor• Deltoid - abductor• Teres minor - rotator
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Muscles that move arm
flexor
extensor
abductor
rotator
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Lower Arm
• Biceps brachii - flexion• Brachialis - flexion• Brachioradialis - flexion• Triceps brachii -
extension
extensionflexion
flexion
flexion
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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
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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
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Muscle Action in Thigh Cont…
• Adduction - movement of a body part toward the midline.
– Adductor longus– Gracilus
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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
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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
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Longest Muscle in the Human Body
• Sartorius