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Chapter 6 – part 2
Skeletal Muscles of the Body
Basic Principles
 600 + muscles in the human body (you are
required to learn 45, lucky kids)!
 Skeletal Muscles pull on bones
 Origin of a muscle = point of attachment
on a stationary bone
 Insertion of a muscle = point of
attachment on the bone that is moving
Figure 6.12 Muscle attachments (origin and insertion).
Muscle
contracting
Origin
Brachialis
Tendon
Insertion
Types of Body Movements
 Flexion
 Decreases the angle of the joint
 Brings two bones closer together
 Typical of bending hinge joints (e.g., knee and elbow) or ball-
and-socket joints (e.g., the hip)
 Extension
 Opposite of flexion
 Increases angle between two bones
 Typical of straightening the elbow or knee
 Extension beyond 180° is hyperextension
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Figure 6.13a Body movements.
Flexion
Hyperextension
Extension
Flexion
Extension
(a) Flexion, extension, and hyperextension of the shoulder and knee
Figure 6.13b Body movements.
Hyperextension
Extension
Flexion
(b) Flexion, extension,
and hyperextension
Types of Body Movements
 Rotation
 Movement of a bone around its longitudinal axis
 Common in ball-and-socket joints
 Example: moving the atlas around the dens of axis (i.e.,
shaking your head ―no‖)
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Figure 6.13c Body movements.
Rotation
Lateral
rotation
Medial
rotation
(c) Rotation
Types of Body Movements
 Abduction
 Movement of a limb away from the midline
 Adduction
 Opposite of abduction
 Movement of a limb toward the midline
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Figure 6.13d Body movements.
Abduction
Adduction
Circumduction
(d) Abduction, adduction,
and circumduction
Types of Body Movements
 Circumduction
 Combination of flexion, extension, abduction, and adduction
 Common in ball-and-socket joints
 Proximal end of bone is stationary, and distal end moves in a
circle
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Figure 6.13d Body movements.
Abduction
Adduction
Circumduction
(d) Abduction, adduction,
and circumduction
Special Movements
 Dorsiflexion
 Lifting the foot so that the superior surface approaches the shin
(toward the dorsum)
 Plantar flexion
 Depressing the foot (pointing the toes)
 ―Planting‖ the foot toward the sole
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Figure 6.13e Body movements.
Dorsiflexion
Plantar flexion
(e) Dorsiflexion and plantar flexion
Special Movements
 Inversion
 Turning sole of foot medially
 Eversion
 Turning sole of foot laterally
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Figure 6.13f Body movements.
Inversion
(f) Inversion and eversion
Eversion
Special Movements
 Supination
 Forearm rotates laterally so palm faces anteriorly
 Radius and ulna are parallel
 Pronation
 Forearm rotates medially so palm faces posteriorly
 Radius and ulna cross each other like an X
© 2015 Pearson Education, Inc.
Figure 6.13g Body movements.
Pronation
(radius rotates
over ulna)
Supination
(radius and ulna
are parallel)
S P
(g) Supination (S) and pronation (P)
Special Movements
 Opposition
 Moving the thumb to touch the tips of other fingers on the same
hand
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Figure 6.13h Body movements.
Opposition
(h) Opposition
Interactions of Skeletal Muscles in the
Body
 In general, groups of muscles that produce opposite actions
lie on opposite sides of a joint
© 2015 Pearson Education, Inc.
Figure 6.14a Muscle action.
(a) A muscle that crosses on the anterior side of a joint produces flexion*
Example:
Pectoralis major
(anterior view)
* These generalities do not apply to the knee and ankle because the lower limb is rotated during development.
The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.
Figure 6.14b Muscle action.
(b) A muscle that crosses on the posterior side of a joint produces extension*
Example: Latissimus
dorsi (posterior view)
The latissimus dorsi
is the antagonist of
the pectoralis major.
* These generalities do not apply to the knee and ankle because the lower limb is rotated during development.
The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.
Figure 6.14c Muscle action.
(c) A muscle that crosses on the lateral side of a joint produces abduction
Example: Deltoid
middle fibers
(anterolateral
view)
Figure 6.14d Muscle action.
(d) A muscle that crosses on the medial side of a joint produces adduction
Example:
Teres major
(posterolateral view)
The teres major is
the antagonist of
the deltoid.
Types of Muscles
 Prime mover—muscle with the major responsibility for a
certain movement
 Antagonist—muscle that opposes or reverses a prime mover
 Synergist—muscle that aids a prime mover in a movement
and helps prevent rotation
 Fixator—stabilizes the origin of a prime mover
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There are 7 different ways that
muscles have been named…
Naming of muscles
Relative Size of the muscle
 Example = gluteus maximus
gluteus minimus
Naming muscles
Direction the muscle fibers run
 Example = rectus (straight) abdominis
Naming muscles
Location of the muscle in the body
 Example = frontalis
lies over the frontal bone
(anatomical terms)
Naming of muscles
Number of origins
 Example = triceps (three heads)
Naming muscles
 Location of Origin and insertion
 Example = sternocleidomastoid
 Attaches to the
sternum, clavicle
and the mastoid process
of the temporal bone
Naming muscles
Shape of the muscle
 Example = deltoid (triangle)
Naming of muscles
Action the muscle makes
 Example – extensor carpi extends
flexor carpi flexes