1. Muscles of the Body
Chapter 11

2. Interactions of Skeletal Muscles
The arrangement of body muscles permits them to work either together or in opposition to achieve a movement
As muscle contract they can only pull on the skeleton; they can never push
If you are pushing an object it is the contraction of some group of muscles in the body that will accomplish it
Generally muscles are grouped to “undo” an action done by another group
Quadriceps / Hamstrings

3. Working out with Muscles
Muscle contraction causes shortening, not lengthening of a muscle
Concentric / shortening against resistance
Eccentric / lengthening against resistance
Typically as a muscle contracts it moves its insertion toward its origin
Lat. bar pull down / Latissimus dorsi
However, some muscles can contract and move its origin toward its insertion
Pull ups / Latissiums dorsi

4. Functional Muscle Groups
Muscles can be classified into four functional groups
Prime movers
Antagonists
Synergists
Fixators

5. Prime Movers
A muscle that provides the major force for producing a specific movement is called a prime mover or agonist
The biceps brachii is the prime mover of elbow flexion
Origin of
Biceps Brachii
Coracoid
Process

6. Antagonist
Muscles that oppose a particular movement are called antagonist
When a prime mover is active, the antagonist muscles are often stretched and may be in a relaxed state
Antagonists also regulate the action of prime mover

7. Synergist
Synergists aid agonists by promoting the same movement and by reducing extraneous movements that may be produced when the prime mover acts
In two joint muscles synergists stabilize a joint as the muscle acts on the other
Synergist can also restrict rotary
movement at a joint so the muscle’s
full effort be applied to the desired
movement

8. Fixator
When a synergist immobilize a muscle’s origin they are called fixators
Their action serves to stabilize the bone upon which a prime mover acts
Serratus anterior holds the scapula against the thorax while a prime mover acts upon the arm

9. Naming Skeletal Muscles
Location of the muscle
Intercostal, Temporalis
Shape of the muscle
Deltoid; Trapezius
Relative size of the muscle
Maximus; medius; minimus; brevis; longus
Direction of muscle fibers
Rectus (straight) fibers run parallel to line of pull
Transverse; fibers run perpendicular to line
Oblique; fibers are oblique to the line

10. Naming of Muscles Number of origins
Biceps; triceps; quadriceps
Location of muscle origin and/or insertion
Sterno (sternum); cleido (clavicle); mastoid (mastoid process of temporal bone)
Action of the muscle
Flexor; extensor; adductor, supinator

11. Arrangement of Fascicles
Arrangement of fascicles within a muscle vary
Arrangements result in differing shapes and capabilities
Common forms are
Parallel
fusiform
Pennate
Uni-, bi-, multi-
Convergent
Circular or sphincteral

13. Parallel Arrangement of Fascicles
In parallel arrange- ment the long axis of the fascicles run parallel to the long axis of the muscle
Form long straplike muscles that have greatest potential for shortening
Act over a long excursion
Not very powerful

14. Pennate Arrangement of Fascicles
Pennate fascicles are short and they attach obliquely to a central tendon
Occur as pennate, bipennate and multipennate forms
Pennate muscles with the highest concentration of fibers, shorten little, but are very powerful
A) Pennate / Ext. digitorum longus
B) Bipennate / Rectus Femoris
C) Multipennate / Deltoid

15. Convergent Arrangement of Fascicle
A convergent muscle has a broad origin and its fascicles converge toward a single tendon
Muscle has a broad triangular shape
Muscle can act upon the joint from a variety of positions
Pectoralis major

16. Circular Arrangement of Fascicles
Fascicular pattern is arranged in concentric rings
Muscles with this arrangement surround external body openings which they close by contracting
This type of muscles are called sphincters which literally means squeezers

17. Lever Systems
The operation of most skeletal muscles involves the use of levers and lever systems
Lever
A rigid bar that moves on a fixed point
Fulcrum
A fixed point of leverage
Effort
The forced applied to move a resistance
Load
The resistance to me moved

18. Lever Systems In the human body . . . Levers Fulcrums Effort Load
The bones of the skeleton
Fulcrums
The joints of the body
Effort
Applied by the muscles of the body
Load
Bone, overlying tissue, and other objects to which your body applies force

19. Lever Systems
A lever allows a given effort to move a heavier load or to move a load farther or faster that it otherwise could
A small difference in the site of a muscle’s insertion can translate into large differences in the amount of force must generate to move a given load

20. Mechanical Advantage
A small effort applied over a relatively long distance can be used to move a large load over a small distance
Such a lever operates at a mechanical advantage and is commonly called a power lever because it can lift heavy loads

21. Mechanical Disadvantage
When the load is far from the fulcrum and the force is applied near the fulcrum, the force exerted by the muscle must be greater than the load moved
These levers are useful because they allow the load to move rapidly through a large distance and are called speed levers

22. Lever Systems
Regardless of type, all levers follow the same basic principle:
Effort farther than load from fulcrum = mechanical advantage
Effort nearer than load to fulcrum = mechanical disadvantage
Depending on the relative position of the three elements (effort, fulcrum, load) a lever is classified as either a first, second, or third class lever

23. First Class Levers
In first class levers the effort is applied at one end of the lever and the load is at the other end with the fulcrum in between them (LFE)
Extension/flexion of the head, other exist but usually operate at a mechanical disadvantage

24. Second Class Levers
In second class levers the effort is applied at one end, the fulcrum is at the other, with the load somewhere in between (FLE)
Plantar flexion of the foot

25. Third Class Levers
In third class levers, the effort is applied at a point between the load and the fulcrum (LEF)
These levers operate with great speed and always at a mechanical disadvantage
Most levers of the body are third class levers which permit an insertion close to the joint and allow rapid movement with little shortening of the muscle

26. Which Lever is it? Fulcrum in the middle? 1st Class
Load in the middle? 2nd Class
Effort in the middle? 3rd Class

27. Lever Summary
Difference in the positioning of the three elements modify muscle activity with respect to
Speed on contraction
Range of movement
Weight of the load that can be lifted
Speed levers act at a mechanical disadvantage
Force is lost, but speed is gained
Power levers act at a mechanical advantage
Force is gained, but speed is lost

28. Major Skeletal Muscles
There are over 600 muscles in the body
Approximately 125 are presented in text
There will be 55 assigned to you to learn
As you learn these muscles try to relate to its attachments and position and what joint(s) it acts across
The best way to learn muscle actions is to act them out in your body

31. Muscle of Head: Facial Expression
Table 10.1

32. Muscles of Head: Facial Expression
Promote facial expression and non-verbal expression
Highly variable in shape and strength
Unusual in that they insert into skin or other muscles and not bone
Innervated by Cranial nerve VII (facial)

33. Muscles of Head: Mastication

34. Muscles of Head: Mastication
Four pairs of muscles are involved with mastication
Chewing and biting
Masseter
Temporalis
Grinding movements
Pterygoid
Buccinator
Trigeminal and Facial nerves

35. Muscles of Head: Tongue Movement
Table 10.2

36. Muscles of Head: Tongue Movement
The extrinsic muscles of the tongue serve to anchor and move the tongue
These muscles serve to protrude, depress, and retract the tongue
Innervated by the hypoglossal nerve

37. Muscle that Promote Swallowing
Table 10.8

38. Muscles that Promote Swallowing
Lateral view of the constrictor muscles of the pharynx
These muscles are shown in their proper anatomical relationship

39. Muscles of Anterior Neck & Throat
Table 10.3

40. Muscles of Anterior Neck & Throat
Most of these muscles are involved with the coordinated action of swallowing which have the following sequence
Widening the pharynx and closing the larynx
Closing the superior nasal cavity
Propulsion of food through the pharynx into the esophagus
Return of musculature to normal positioning

41. Muscles of Neck Sternocleidomastoid is a head flexor
Scalenes contribute to lateral flexion of the neck
Splenius is a head extensor

42. Muscles of Neck
The head is moved by muscles originating from the axial skeleton which include
Sternocleidomastoid / head flexors
Scalenes / lateral head flexion
Splenius / head extension

43. Muscles of Vertebral Column

44. Muscle of the Vertebral Column
Trunk extension is effected by the deep muscles of the back
The erector spinae is the largest of the group and consists of three bands
Iliocostalis
Longissimus
Spinalis
Other muscles of the vertebral column include
Semispinalis / extends head
Quadratus lumborum / Lateral flexion

45. Muscle of the Thorax: Breathing

46. External Intercostals
O - Inferior border of rib above
I - Superior border of rib below
A - Pulls ribs upward to aid in respiration

47. Internal intercostals
O - Superior border of rib below
I - Inferior border of rib above
Draws ribs together; aids in expiration

48. Muscles of the Thorax: Breathing

49. Diaphragm
O - Inferior border of rib cage, costal cartilages of last 6 ribs, and lumber vertabrae
I - Central tendon
A - Inspiration

50. Muscles of the Abdominal Wall

51. Muscles of Abdominal Wall
The anterior and lateral abdominal wall has no bony reinforcement
It is composed of four paired muscles, their investing fasciae and their aponeuroses
The muscles of the abdominal wall include
Rectus abdominis
External oblique
Internal oblique
Transverse abdominis

52. Muscles of the Abdominal Wall

53. Muscles of the Abdominal Wall
Illustration of how the aponeuroses of the lateral abdominal muscles contribute to the rectus abdominis sheath
Enclosure of the Rectus abdominis within the aponeuroses prevents anterior protrusion or bowstringing of the muscle
The Linea alba represents the central fusion of the aponeurses along the midline

54. Rectus abdominis O - Pubic crest and symphasis
I - xiphoid process and costal cartilages of ribs 5 - 7
A - Flex and rotate lumbar region of the vertebral column

55. External oblique O - by fleshy strips from outer surfaces of ribs 5-7
I - Linea alba; pubic crest and tubercle via aponeurosis
A - flexing vertebral column

56. Internal oblique
O -Lumbodorsal fasica, iliac crest and inguinal ligament
I - Linea alba, pubic crest and last 3 ribs
A - Flex vertebral column

57. Transverse abdominis
O - inguinal ligament, lumbo- dorsal fascia, cartilages of last 6 ribs, iliac crest
I - Linea alba, pubic crest
A - compresses abdominal contents

58. Muscles of the Pelvic Floor

59. Muscles of the Pelvic Floor
Stretching between the two sides of the pelvic arch is the urogenital diaphram
The Sphinter urethrae surrounds the urethra and allow voluntary urination

60. Muscles of the Pelvic Floor
Superficial space contains muscles (Ischocavernosus, Bulbospongiosus) that help maintain erection of the penis and clitoris
The external anal sphinter encircles the anus and allows for voluntary control of defectation

61. Muscles of the Anterior Thorax

62. Pectoralis minor O - anterior surfaces of ribs 3-5
I - coracoid process of scapula
A - ribs fixed draws scapula forward and downward

63. Serratus anterior O - ribs 1-9
I - entire anterior surface of vertebral border of scapula
A - Protract the scapula; rotates scapula

64. Muscles of the Posterior Thorax

65. Trapezius
O - Occipital bone, ligamentum nuchae, spines of C7 & all thoracic vert.
I - Acromium and spine of scapula and lateral 1/3 of clavicle
A - elevate and rotate scapula

66. Levator scapulae O - transverse processes of C1 - C4
I - superior angle of scapula
A - elevates and adducts scapula

67. Rhomboid major O - spinous processes of T2 - T5
I - medial border of scapula
A - retract; rotate; and stabilize scapula

68. Rhomboid minor O - spinous processes of C7 and T1
I - medial border of scapula
A - retract; rotate; and stabilize scapula

69. Muscles Crossing the Shoulder Joint
A total of nine muscles cross the shoulder joint to insert on the humerus
The three prime movers of the shoulder joint are
Pectoralis major
Lastissimus dorsi
Deltoid
The remaining six muscles are synergists and fixators
Four of these six are muscles of the rotator cuff

70. Muscles Crossing the Shoulder Joint

71. Pectoralismajor O - clavicle, sternum, and cartilages of ribs 1 - 6
I - greater tubercle of humerus
A - arm flexion, medial arm rotation, arm adduction

72. Latissimus dorsi O - spines of T6 - T12 and L1 - L5 etc
I - Inter- tubicular groove of humerus
A - arm extension, adduction and med. rotation

73. Deltoid O - Lateral 1/3 of clavicle, acromium, and spine of scapula
I - Deltoid tuberosity of humerus
A - arm abduction; flex/ ext. arm; med./ lat. rotate arm

74. Subscapularis O - subscapular fossa of scapula
I - lesser tubercle of humerus
A - medial rotator of arm

75. Supraspinatus O - supra spinatus fossa of scapula
I - superior part of greater tubercle of humerus
A - holds head of humerus in glenoid fossa to stabilize shoulder joint

76. Infraspinatus O - infra spinatus fossa of scapula
I - greater tubercle of humerus
A - laterally rotates scapula

77. Teres minor O - lateral border of dorsal scapular surface
I - greater tubercle of humerus
A - laterally rotates scapula

78. Teres major O - posterior surface of scapula at inferior angle
I - lesser tubercle of humerus
A - extends, medially rotates and adducts humerus

79. Coraco- brachialis O - coracoid process of scapula
I - medial surface of shaft of humerus
A - flexion and adduction of humerus

80. Muscles Crossing the Elbow Joint
Since the elbow is a hinge joint the movement promoted by these muscles are limited almost to flexion and extension of the forearm
There are three muscles anteriorly
Biceps brachii
Brachialis
Brachioradialis
There is one muscle posteriorly
Triceps brachii

81. Muscles Crossing the Elbow Joint

82. Triceps brachii
O - long head/ infraglenoid tubercle; lat. and medial heads / posterior humerus;
I - Olecranon process of ulna
A - forearm extensor; long head assist in adduction

83. Biceps brachii
O - short head/ coracoid process of scapula; long head / supra glendoid tubercle
I - radial tuberosity
A - flexes arm and forearm; supinates

84. Brachialis O - anterior, distal humerus I - coracoid process of ulna
A - forearm flexor

85. Brachio radialis O - lateral supracondylar ridge
I - styloid process of radius
A - forearm flexion; a semi pronated position gives it its best mechanical advantage

86. Muscles of Forearm
Muscles of the forearm are divided equally into flexors and extensors
Flexors on the medial epicondyle
Extensors on the lateral epicondyle

87. Pronator teres O - medial epicondyle of humerus
I - lateral radius at midshaft
A - pronates forearm; weak elbow flexor

88. Flexor carpi radialis O - medial epicondyle of humerus
I - base of second and third metacarpals
A - powerful wrist flexor;

89. Palmaris longus O - medial epicondyle of humerus
I - palmer aponeurosis
A - weak wrist flexor; tenses palmer aponeurosis

90. Flexor carpi ulnaris O - medial epicondyle of humerus
I - pisiform bone and base of 5th metacarpal
A - flexor of wrist

91. Muscles Crossing the Hip and Knee
Muscles crossing the hip and knee can be grouped into
Hip flexors (4)
Gluteal muscles (3)
Medial compartment (5 adductors)
Anterior compartment (4 knee extensors)
Posterior compartment (3 knee flexors)
Lateral rotators (5)

92. Muscles Crossing the Hip and Knee

93. Iliacus
O - iliac fossa
I - lesser trochanter of femur
A - hip flexion

94. Psoas major
O - transverse processes and bodies of T12 and all lumbar vertebrae
I - lesser trochanter of femur
A - hip flexion and lateral hip flexion

95. Psoas minor O - Transverse processes and bodies of T12 and L1
I - Rim of acetabulum
A - flexes lumbar vertebrae

96. Sartorius O - anterior superior iliac spine
I - medial aspect of proximal tibia
A - Flexes and laterally rotates thigh; flexes knee

97. Adductors Adductors Adductor magnus Adductor longus Adductor brevis
Pectineus
Gracilis

98. Adductor magnus O - ischial and pubic rami and ischial tuberosity
I - linea aspera and adductor tubercle
A - adducts and laterally rotates thigh

99. Adductor longus O - pubis near pubic symphysis I - linea aspera
A - adducts, flexes and laterally rotates thigh

100. Adductor brevis O - body and inferior ramus of pubis I - linea aspera
A - adducts and laterally rotates thigh

101. Pectineus O - pectineal line of pubis I - lesser trochanter of femur
A - adducts, flexes, and laterally rotates thigh

102. Gracilis O - inferior ramus and body of pubis
I - medial surface of tibia just inferior to media condyle
A - adducts thigh, flexes and medially rotates thigh

103. Quadriceps femoris Muscles include Rectus femoris Vastus lateralis
Vastus medialis
Vastus intermedius

104. Rectus femoris O - anterior inferior iliac spine
I - patella and tibial tuberosity
A - extends knee and flexes thigh at hip

105. Vastus lateralis O - greater trochanter, intertrochanteric line
I - patella and tibial tuberosity
A - extends knee

106. Vastus medialis O - linea aspera, intertrochanteric line
I - patella and tibial tuberosity
A - extends knee

107. Vastus intermedius
O - anterior and lateral surfaces of proximal shaft of femur
I - patella and tibial tuberosity
A - extend knee

108. Tensor fascia latae O - anterior aspect of iliac crest
I - iliotibial tract
A - flexes and abducts thigh

109. Gluteal Muscles

110. Gluteus maximus O - dorsal ilium, sacrum and coccyx
I - gluteal tuberosity of femur
A - thigh extension

111. Gluteus medius
O - between anterior and posterior gluteal lines on lateral surface of ilium
I - greater trochanter of femur
A - abducts and medially rotates thigh

112. Gluteus minimus
O - between anterior and inferior gluteal lines on external surface of femur
I - greater trochanter of femur
A - abducts and medially rotates thigh

113. Lateral rotators
In this view cutting the gluteal muscles reveals the lateral rotators of the thigh

114. Lateral rotators
In this view cutting the gluteal muscles reveals the lateral rotators of the thigh

115. Biceps femoris O - (long) ischial tuberosity, (short) linea aspera
I - head of fibula and lateral condyle of tibia
A - extends thigh and flexes knee, laterally rotates leg

116. Semi- tendinosus O - ischial tuberosity
I - medial aspect of upper tibial shaft
A - extends thigh at hip; flexes knee, medially rotates leg

117. Semi- membranosus O - ischial tuberosity I - medial condyle of tibia
A - extends thigh and flexes knee, medially rotates leg

118. Muscles -Anterior Compartment
Muscles of the anterior compartment are primarily toes extensors and dorsiflexors
Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
Peroneus tertius
Important in walking during the recovery phase of gait

119. Tibialis anterior O - lateral condyle and upper 2/3 of tibia
I - inferior medial surface of medial cuneiform and 1st metatarsal bone
A - dorsiflexion, inverts foot

120. Extensor digitorum longus
O - lateral condyle of tibia, proximal 3/4 of fibula
I - 2nd & 3rd phalanges of toes 2-5 via extensor expansion
A - Dorsiflexion, toe extension

121. Peroneus tertius
O - distal surface of fibula and interosseous membrane
I - dorsum of fifth metatarsal
A - dorsiflexes and everts foot

122. Extensor hallucis
O - anteriomedial fibula shaft and interosseous membrane
I - distal phalanx of great toe
A - extends great toe, dorsiflexes foot

123. Muscles - Lateral Compartment
Muscles of the lateral compartment are primarily plantar flex and evert the foot
Peroneus longus
Peroneus brevis

124. Peroneus longus O - head and upper portion of fibula
I - under the foot to first metatarsal and medial cuneiform
A - plantar flexes and everts foot

125. Peroneus brevis O - distal shaft of fibula
I - proximal end of the 5th metatarsal
A - Plantar flexes and everts foot

126. Muscles of Posterior Compartment
Muscles of the posterior compartment are primarily plantar flexors and flex the toes
Gastrocnemius
Soleus
Tibialis posterior
Flexor digitorum longus
Flexor hallucis longus

127. Gastrocnemius O - from medial and lateral condyles of femur
I - calcaneus via calcaneal tendon
A - plantar flexes foot, flexes knee

128. Soleus O - superior tibia, fibula and interosseus membrane
I - calcaneus via calcaneal tendon
A - plantar flexes ankle

129. Plantaris O - posterior femur above lateral condyle I - calcaneus
A - plantar flexion, knee flexion

130. Popliteus O - lateral condyle of femur I - proximal tibia
A - flexes and rotates knee medially to unlock knee from full extension

131. Flexor digitorum longus
O - posterior tibia
I - distal phalanges of toes 2-5
A - plantar flexes and flexes toes

132. Flexor hallicus longus
O - medial part of shaft of fibula, interosseous membrane
I - distal phalanx of great toe
A - plantar flexes and inverts foot, flexes great toe

133. Tibialis posterior
O - superior tibia and fibula and interosseous membrane
I - tarsals and metatarsals 2-4
A - inversion, plantar flexion

134. Intrinsic Muscles of the Foot
The intrinsic muscles of the foot help to flex, extend, abduct, and adduct the toes
Collectively the muscles support the arches of the foot assisted by some tendons of leg muscles
The muscles occur in four layers from superficial to deep

135. Intrinsic Muscles of the Foot
Muscles of the second layer flex, adduct, and abduct the toes
Muscles include
Flexor digitorum brevis
Abductor hallucis
Abductor digiti minimi

136. Intrinsic Muscles of the Foot

137. Intrinsic Muscles of the Foot

138. Intrinsic Muscles of the Foot