Skeletal Muscle Action
Origin and insertion
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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
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Muscles increase
with use =
hypertrophy
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Muscles decrease
with disuse =
atrophy (cast)
Fast Twitch vs.
Slow Twitch Muscle Fibers
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Aerobic exercise
uses slow twitch
fibers
– Ex. Swimming long
distance, cross
country skiingraises amount of
ATP and blood
flow to muscles.
– Red fibers
Fast twitch vs. Slow twitch muscle fibers
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Anaerobic exercise
uses fast twitch
fibers.
– Ex.
Weightlifting, and
sprinting diameter of
muscle increases
by producing more
actin and myosin
fibers.
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White fibers
Muscle Action of Head
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Facial expression sadness, surprise,
fear, disgust.
– Zygomaticus mouth
– Frontalis - eyebrow
– Occipitalus eyebrow
Muscle Action of Head
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Mastication chewing
– Masseter
– Temporalis
Closes jaw
Muscle Action of Head
Movement of Head
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Sternocleidomastoid prayer position
Muscle Action of the Pectoral
Girdle (chest and shoulders)
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Associated with
muscles that move
arm
Move scapula up,
down, forward, and
backward
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Trapezius
Serratus anterior
Pectoralis minor
Muscle action of the pectoral girdle
(chest and shoulders)
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Associated with
muscles that move
arm
Move scapula up,
down, forward, and
backward
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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
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Biceps brachii - flexion
Brachialis - flexion
Brachioradialis - flexion
Triceps brachii - extension
flexion
flexion
flexion
extension
Muscle Action in Abdominal Wall
(Six Pack)
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Connect the rib cage
to the pelvic girdle
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External oblique
Internal oblique
Rectus abdominus
Hernia
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A hole in the abdominal
muscles.
Intestines protrude
outward to form a lump.
Repaired by surgery
Muscle Action in Thigh
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Divided into
anterior/posterior
sections
Anterior sections create
flexion
Posterior sections create
extension, abduction, and
rotation.
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Gluteus maximus
Gluteus medius
Tensor Fasciae Latae
Adductors of the thigh
Muscle Action in Thigh Cont…
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Adduction - movement of a
body part toward the
midline.
Adductor longus
Gracilus
Muscles that Move the Leg
(Lower Leg)
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Divided into two
groups
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Hamstring group
are the flexors
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Biceps femoris
Semitendenosus
Semimembranosus
Satorius – longest
muscle in the body
Muscles that Move the Leg
(Lower Leg)
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Divided into two
groups
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Quadriceps Group
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Rectus femoris middle of the thigh
Vastus lateralis outside of thigh
Vastus medialis midline of thigh
Longest Muscle in the
Human Body
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Sartorius