Skeletal Muscles of the Body
Chapter 6 – part 2
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
Flexion
Extension
Extension
Hyperextension
(a) Flexion, extension, and hyperextension of the shoulder and knee
Figure 6.13b Body movements.
(b) Flexion, extension,
and hyperextension
Extension
Flexion
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.
(c) Rotation
Rotation
Lateral
rotation
Medial
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.
(e) Dorsiflexion and plantar flexion
Dorsiflexion
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.
(f) Inversion and eversion
Inversion 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
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Figure 6.13g Body movements.
S
(g) Supination (S) and pronation (P)
Supination
(radius and ulna
are parallel)
Pronation
(radius rotates
over ulna)
S P 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.
(h) Opposition
Opposition
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Interactions of Skeletal Muscles in the
Body
In general, groups of muscles that produce opposite actions
lie on opposite sides of a joint
Figure 6.14a Muscle action.
Example:
Pectoralis major
(anterior view)
(a) A muscle that crosses on the anterior side of a joint produces flexion*
* 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.
Example: Latissimus
dorsi (posterior view)
The latissimus dorsi
is the antagonist of
the pectoralis major.
(b) A muscle that crosses on the posterior side of a joint produces extension*
* 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.
Example: Deltoid
middle fibers
(anterolateral
view)
(c) A muscle that crosses on the lateral side of a joint produces abduction
Figure 6.14d Muscle action.
Example:
Teres major
(posterolateral view)
The teres major is
the antagonist of
the deltoid.
(d) A muscle that crosses on the medial side of a joint produces adduction
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