Muscles of the Body
Chapter 11
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
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
Functional Muscle Groups Muscles can be classified into four
functional groups– Prime movers– Antagonists– Synergists– Fixators
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
CoracoidProcess
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
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 rotarymovement at a joint so the muscle’sfull effort be applied to the desired movement
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
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
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
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
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
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 longusB) Bipennate / Rectus FemorisC) Multipennate / Deltoid
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
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
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
Lever Systems In the human body . . . Levers
– 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
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
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
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
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
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
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
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
Which Lever is it? Fulcrum in the middle? 1st Class
Load in the middle? 2nd Class
Effort in the middle? 3rd Class
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
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
Muscle of Head: Facial ExpressionTable 10.1
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)
Muscles of Head: Mastication
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
Muscles of Head: Tongue MovementTable 10.2
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
Muscle that Promote SwallowingTable 10.8
Muscles that Promote Swallowing Lateral view of the constrictor muscles of
the pharynx These muscles are shown in their proper
anatomical relationship
Muscles of Anterior Neck & ThroatTable 10.3
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
Muscles of Neck
Sternocleidomastoid is a head flexor Scalenes contribute to lateral flexion of the neck Splenius is a head extensor
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
Muscles of Vertebral Column
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
Muscle of the Thorax: Breathing
External Intercostals
O - Inferior border of rib above
I - Superior border of rib below
A - Pulls ribs upward to aid in respiration
Internal intercostals
O - Superior border of rib below
I - Inferior border of rib above
Draws ribs together; aids in expiration
Muscles of the Thorax: Breathing
Diaphragm
O - Inferior border of rib cage, costal cartilages of last 6 ribs, and lumber vertabrae
I - Central tendon
A - Inspiration
Muscles of the Abdominal Wall
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
Muscles of the Abdominal Wall
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
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
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
Internaloblique
O -Lumbodorsal fasica, iliac crest and inguinal ligament
I - Linea alba, pubic crest and last 3 ribs
A - Flex vertebral column
Transverse abdominis
O - inguinal ligament, lumbo- dorsal fascia, cartilages of last 6 ribs, iliac crest
I - Linea alba, pubic crest
A - compresses abdominal contents
Muscles of the Pelvic Floor
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
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
Muscles of the Anterior Thorax
Pectoralisminor
O - anterior surfaces of ribs 3-5
I - coracoid process of scapula
A - ribs fixed draws scapula forward and downward
Serratusanterior
O - ribs 1-9 I - entire
anterior surface of vertebral border of scapula
A - Protract the scapula; rotates scapula
Muscles of the Posterior Thorax
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
Levator scapulae O - transverse
processes of C1 - C4
I - superior angle of scapula
A - elevates and adducts scapula
Rhomboid major O - spinous
processes of T2 - T5
I - medial border of scapula
A - retract; rotate; and stabilize scapula
Rhomboid minor O - spinous
processes of C7 and T1
I - medial border of scapula
A - retract; rotate; and stabilize scapula
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
Muscles Crossing the Shoulder Joint
Pectoralismajor O - clavicle,
sternum, and cartilages of ribs 1 - 6
I - greater tubercle of humerus
A - arm flexion, medial arm rotation, arm adduction
Latissimus dorsi O - spines of
T6 - T12 and L1 - L5 etc
I - Inter- tubicular groove of humerus
A - arm extension, adduction and med. rotation
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
Subscapularis
O - subscapular fossa of scapula
I - lesser tubercle of humerus
A - medial rotator of arm
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
Infraspinatus
O - infra spinatus fossa of scapula
I - greater tubercle of humerus
A - laterally rotates scapula
Teres minor
O - lateral border of dorsal scapular surface
I - greater tubercle of humerus
A - laterally rotates scapula
Teres major
O - posterior surface of scapula at inferior angle
I - lesser tubercle of humerus
A - extends, medially rotates and adducts humerus
Coraco- brachialis O - coracoid
process of scapula
I - medial surface of shaft of humerus
A - flexion and adduction of humerus
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
Muscles Crossing the Elbow Joint
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
Biceps brachii
O - short head/ coracoid process of scapula; long head / supra glendoid tubercle
I - radial tuberosity
A - flexes arm and forearm; supinates
Brachialis O - anterior,
distal humerus I - coracoid
process of ulna A - forearm
flexor
Brachio radialis
O - lateral supracondylar ridge
I - styloid process of radius
A - forearm flexion; a semi pronated position gives it its best mechanical advantage
Muscles of Forearm
Muscles of the forearm are divided equally into flexors and extensors– Flexors on the
medial epicondyle
– Extensors on the lateral epicondyle
Pronator teres
O - medial epicondyle of humerus
I - lateral radius at midshaft
A - pronates forearm; weak elbow flexor
Flexor carpi radialis
O - medial epicondyle of humerus
I - base of second and third metacarpals
A - powerful wrist flexor;
Palmaris longus
O - medial epicondyle of humerus
I - palmer aponeurosis
A - weak wrist flexor; tenses palmer aponeurosis
Flexor carpi ulnaris
O - medial epicondyle of humerus
I - pisiform bone and base of 5th metacarpal
A - flexor of wrist
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)
Muscles Crossing the Hip
and Knee
Iliacus O - iliac fossa I - lesser
trochanter of femur
A - hip flexion
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
Psoas minor O - Transverse
processes and bodies of T12 and L1
I - Rim of acetabulum
A - flexes lumbar vertebrae
Sartorius O - anterior
superior iliac spine
I - medial aspect of proximal tibia
A - Flexes and laterally rotates thigh; flexes knee
Adductors Adductors
– Adductor magnus
– Adductor longus
– Adductor brevis
– Pectineus
– Gracilis
Adductor magnus
O - ischial and pubic rami and ischial tuberosity
I - linea aspera and adductor tubercle
A - adducts and laterally rotates thigh
Adductor longus
O - pubis near pubic symphysis
I - linea aspera A - adducts,
flexes and laterally rotates thigh
Adductor brevis
O - body and inferior ramus of pubis
I - linea aspera A - adducts and
laterally rotates thigh
Pectineus
O - pectineal line of pubis
I - lesser trochanter of femur
A - adducts, flexes, and laterally rotates thigh
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
Quadriceps femoris Muscles include
– Rectus femoris
– Vastus lateralis
– Vastus medialis
– Vastus intermedius
Rectus femoris
O - anterior inferior iliac spine
I - patella and tibial tuberosity
A - extends knee and flexes thigh at hip
Vastus lateralis
O - greater trochanter, intertrochanteric line
I - patella and tibial tuberosity
A - extends knee
Vastus medialis
O - linea aspera, intertrochanteric line
I - patella and tibial tuberosity
A - extends knee
Vastus intermedius
O - anterior and lateral surfaces of proximal shaft of femur
I - patella and tibial tuberosity
A - extend knee
Tensor fascia latae
O - anterior aspect of iliac crest
I - iliotibial tract A - flexes and
abducts thigh
Gluteal Muscles
Gluteus maximus
O - dorsal ilium, sacrum and coccyx
I - gluteal tuberosity of femur
A - thigh extension
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
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
Lateral rotators
In this view cutting the gluteal muscles reveals the lateral rotators of the thigh
Lateral rotators
In this view cutting the gluteal muscles reveals the lateral rotators of the thigh
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
Semi- tendinosus
O - ischial tuberosity
I - medial aspect of upper tibial shaft
A - extends thigh at hip; flexes knee, medially rotates leg
Semi- membranosus O - ischial
tuberosity I - medial
condyle of tibia A - extends thigh
and flexes knee, medially rotates leg
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
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
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
Peroneus tertius O - distal surface
of fibula and interosseous membrane
I - dorsum of fifth metatarsal
A - dorsiflexes and everts foot
Extensor hallucis O - anteriomedial
fibula shaft and interosseous membrane
I - distal phalanx of great toe
A - extends great toe, dorsiflexes foot
Muscles - Lateral Compartment Muscles of the
lateral compartment are primarily plantar flex and evert the foot– Peroneus
longus
– Peroneus brevis
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
Peroneus brevis O - distal shaft
of fibula I - proximal end
of the 5th metatarsal
A - Plantar flexes and everts foot
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
Gastrocnemius
O - from medial and lateral condyles of femur
I - calcaneus via calcaneal tendon
A - plantar flexes foot, flexes knee
Soleus
O - superior tibia, fibula and interosseus membrane
I - calcaneus via calcaneal tendon
A - plantar flexes ankle
Plantaris
O - posterior femur above lateral condyle
I - calcaneus A - plantar
flexion, knee flexion
Popliteus
O - lateral condyle of femur
I - proximal tibia A - flexes and
rotates knee medially to unlock knee from full extension
Flexor digitorum longus O - posterior
tibia I - distal
phalanges of toes 2-5
A - plantar flexes and flexes toes
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
Tibialis posterior O - superior
tibia and fibula and interosseous membrane
I - tarsals and metatarsals 2-4
A - inversion, plantar flexion
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
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
Intrinsic Muscles of the Foot
Intrinsic Muscles of the Foot
Intrinsic Muscles of the Foot
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