muscles of the body chapter 11. interactions of skeletal muscles the arrangement of body muscles...

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


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, lumbodorsal fascia, cartilages of last 6 ribs, iliac crest

I - Linea alba, pubic crest

A - compresses abdominal contents

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


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


A - laterally rotates scapula

Teres minor

O - lateral border of dorsal scapular surface


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


I - base of second and third metacarpals

A - powerful wrist flexor;

Palmaris longus


I - palmer aponeurosis

A - weak wrist flexor; tenses palmer aponeurosis

Flexor carpi ulnaris


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


A - extends knee

Vastus medialis

O - linea aspera, intertrochanteric line


A - extends knee

Vastus intermedius

O - anterior and lateral surfaces of proximal shaft of femur


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

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

muscles of the body chapter 11. interactions of skeletal muscles the arrangement of body muscles...

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