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Chapter 1 Chapter 1 Musculoskeletal Musculoskeletal Tissue Tissue

Chapter 1 Musculoskeletal Tissue

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Chapter 1 Musculoskeletal Tissue. Tissues of the body. Epithelial Nervous Connective Muscle. Epithelial tissue. Two forms Membranous Forms such structures as the outer layer of the skin, the inner lining of the body cavities and lumina, and the covering of visceral organs Glandular - PowerPoint PPT Presentation

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Page 1: Chapter 1  Musculoskeletal Tissue

Chapter 1 Chapter 1 Musculoskeletal Musculoskeletal TissueTissue

Page 2: Chapter 1  Musculoskeletal Tissue

Tissues of the body Tissues of the body

EpithelialEpithelial NervousNervous ConnectiveConnective MuscleMuscle

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Epithelial tissue Epithelial tissue

Two formsTwo forms– MembranousMembranous

Forms such structures as the outer layer Forms such structures as the outer layer of the skin, the inner lining of the body of the skin, the inner lining of the body cavities and lumina, and the covering of cavities and lumina, and the covering of visceral organs visceral organs

– GlandularGlandular Specialized tissue that forms the Specialized tissue that forms the

secretory portion of glandssecretory portion of glands

Page 4: Chapter 1  Musculoskeletal Tissue

Nervous tissueNervous tissue

Helps coordinate movements via Helps coordinate movements via a complex motor control system a complex motor control system of pre-structured motor programs of pre-structured motor programs and a distributed network of and a distributed network of reflex pathways mediated reflex pathways mediated throughout the CNSthroughout the CNS

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Connective tissueConnective tissue

Found throughout the body Found throughout the body Divided into subtypes according Divided into subtypes according

to the matrix that binds the cellsto the matrix that binds the cells Includes bone, cartilage, tendons, Includes bone, cartilage, tendons,

ligaments, and blood tissue ligaments, and blood tissue

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Muscle tissueMuscle tissue

Responsible for the movement of Responsible for the movement of materials through the body, the materials through the body, the movement of one part of the body with movement of one part of the body with respect to another, and locomotionrespect to another, and locomotion

Three types: Three types: – SmoothSmooth– CardiacCardiac– SkeletalSkeletal

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Connective TissueConnective Tissue

The primary types of connective The primary types of connective tissue cells are:tissue cells are:– Macrophages, which function as Macrophages, which function as

phagocytes to clean up debrisphagocytes to clean up debris– Mast cells, which release chemicals Mast cells, which release chemicals

associated with inflammationassociated with inflammation– Fibroblasts, which are the principal Fibroblasts, which are the principal

cells of connective tissuecells of connective tissue

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Connective Tissue Connective Tissue ProperProper 1.1.        Loose connective tissueLoose connective tissue 2.2.        Dense regular connective tissueDense regular connective tissue 3.3.        Dense irregular connective Dense irregular connective

tissuetissue 4.4.        Elastic connective tissueElastic connective tissue 5.5.        Reticular connective tissueReticular connective tissue 6.6. Adipose connective tissue Adipose connective tissue

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Cartilage and bone Cartilage and bone tissuetissue 1.1.        Hyaline cartilageHyaline cartilage 2.2.        FibrocartilageFibrocartilage 3. Elastic cartilage3. Elastic cartilage

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Collagen and ElastinCollagen and Elastin

Collagen and elastin are vital Collagen and elastin are vital constituents of the musculoskeletal constituents of the musculoskeletal systemsystem

CollagenCollagen– Maintains the structural integrity of various Maintains the structural integrity of various

tissuestissues– Provides tensile strength to tissuesProvides tensile strength to tissues

ElastinElastin– Provides the tissues in which it is situated Provides the tissues in which it is situated

with elastic propertieswith elastic properties

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Collagen and ElastinCollagen and Elastin

Collagenous and elastic fibers are Collagenous and elastic fibers are sparse and irregularly arranged in sparse and irregularly arranged in loose connective tissue, but are loose connective tissue, but are tightly packed in dense connective tightly packed in dense connective tissuetissue– Fascia is an example of loose Fascia is an example of loose

connective tissueconnective tissue – Tendons and ligaments are examples of Tendons and ligaments are examples of

dense regular connective tissuedense regular connective tissue

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TendonsTendons

Cordlike structures that function Cordlike structures that function to attach muscle to bone and to to attach muscle to bone and to transmit the forces generated by transmit the forces generated by muscles to bone in order to muscles to bone in order to achieve movement or stability of achieve movement or stability of the body in spacethe body in space

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TendonsTendons

The fascicles of tendons are held The fascicles of tendons are held together by loose connective tissue together by loose connective tissue called called endotenonendotenon – Endotenon contains blood vessels, lymphatics Endotenon contains blood vessels, lymphatics

and nerves, and permits longitudinal and nerves, and permits longitudinal movements of individual fascicles when movements of individual fascicles when tensile forces are applied to the structure tensile forces are applied to the structure

The connective tissue surrounding groups The connective tissue surrounding groups of fascicles and/or the entire structure is of fascicles and/or the entire structure is called the called the epitenonepitenon

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Myotendinous junction Myotendinous junction (MTJ). (MTJ). The site where the muscle and tendon The site where the muscle and tendon

meetmeet Very vulnerable to tensile failure, especially Very vulnerable to tensile failure, especially

biceps and triceps brachii, the rotator cuff biceps and triceps brachii, the rotator cuff muscles, the flexor pollicis longus, the muscles, the flexor pollicis longus, the peroneus longus, the medial head of the peroneus longus, the medial head of the gastrocnemius, the rectus femoris, the gastrocnemius, the rectus femoris, the adductor longus, the iliopsoas, the adductor longus, the iliopsoas, the pectoralis major, the semimembranosus, pectoralis major, the semimembranosus, and the whole hamstrings group and the whole hamstrings group

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Skeletal ligamentsSkeletal ligaments

Skeletal ligaments are fibrous Skeletal ligaments are fibrous bands of dense connective tissue bands of dense connective tissue that connect bones across jointsthat connect bones across joints– Contribute to the stability of joint Contribute to the stability of joint

function by preventing excessive function by preventing excessive motionmotion

– Act as guides to direct motionAct as guides to direct motion– Provide proprioceptive information for Provide proprioceptive information for

joint functionjoint function

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Ligament pathologyLigament pathology

Ligament injuries are graded Ligament injuries are graded according to severityaccording to severity

– First-degree (mild)First-degree (mild)– Second-degree (moderate)Second-degree (moderate)– Third degree (complete)Third degree (complete)

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Ligament pathologyLigament pathology

First-degree sprainFirst-degree sprain– Minimal loss of structural integrityMinimal loss of structural integrity– Little or no swellingLittle or no swelling– Minimal bruisingMinimal bruising– Minimal functional lossMinimal functional loss– Early return to trainingEarly return to training

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Ligament pathologyLigament pathology

Second-degree sprainSecond-degree sprain– Significant structural weakeningSignificant structural weakening– Some abnormal motionSome abnormal motion– More bruising and swellingMore bruising and swelling– Tendency for recurrenceTendency for recurrence– Need protection from risk of further Need protection from risk of further

injuryinjury– May need modified immobilizationMay need modified immobilization

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Ligament pathologyLigament pathology

Third-degree sprainThird-degree sprain– Loss of structural integrityLoss of structural integrity– Marked abnormal motionMarked abnormal motion– Significant bruisingSignificant bruising– Needs prolonged protectionNeeds prolonged protection– Surgery may be consideredSurgery may be considered– Permanent functional instability a Permanent functional instability a

possibilitypossibility

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BoneBone

A highly-vascular form of connective A highly-vascular form of connective tissuetissue

Composed of collagen, calcium Composed of collagen, calcium phosphate, water, amorphous phosphate, water, amorphous proteins, and cellsproteins, and cells

The collagen of bone is produced in The collagen of bone is produced in the same manner as that of ligament the same manner as that of ligament and tendon, but by a different cell, the and tendon, but by a different cell, the osteoblastosteoblast

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BoneBone

There are 206 bones in the There are 206 bones in the human skeletonhuman skeleton– 177 of these bones are involved in 177 of these bones are involved in

voluntary movementvoluntary movement– 29 of these bones are immobile29 of these bones are immobile

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BoneBone

The function of bone is to:The function of bone is to:– Provide supportProvide support– Enhance leverageEnhance leverage– Protect vital structuresProtect vital structures– Provide attachments for both Provide attachments for both

tendons and ligamentstendons and ligaments– Store minerals, particularly calcium. Store minerals, particularly calcium.

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Two Components of the Two Components of the SkeletonSkeleton

Axial Axial SkeletonSkeleton

SkullSkull Spinal Spinal

ColumnColumn SternumSternum RibsRibs

Appendicular Appendicular SkeletonSkeleton

Upper ExtremityUpper Extremity Lower ExtremityLower Extremity

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Major Bone TypesMajor Bone Types

1.1. LongLong

2.2. ShortShort

3.3. FlatFlat

4.4. IrregularIrregular

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Long BonesLong Bones

CharacteristicsCharacteristics– Possess a cylindrical shaft and Possess a cylindrical shaft and

medullary canalmedullary canal– Relatively broad endsRelatively broad ends– Thick walled shaftThick walled shaft

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Long Bones of Long Bones of SkeletonSkeleton

Upper ExtremityUpper Extremity

1.1. ClavicleClavicle

2.2. HumerusHumerus

3.3. UlnaUlna

4.4. RadiusRadius

5.5. MetacarpalsMetacarpals

6.6. PhalangesPhalanges

Lower ExtremityLower Extremity

1.1. FemurFemur

2.2. TibiaTibia

3.3. FibulaFibula

4.4. MetatarsalsMetatarsals

5.5. PhalangesPhalanges

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Short BonesShort Bones

Relatively short, compact and Relatively short, compact and solid structuressolid structures

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Short Bones of Short Bones of SkeletonSkeleton

Upper ExtremityUpper Extremity

Carpals Carpals (wrist)(wrist)

Lower ExtremityLower Extremity

Tarsals Tarsals (ankle)(ankle)

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Flat BonesFlat Bones

Examples:Examples: SternumSternum ScapulaeScapulae RibsRibs Pelvic bonesPelvic bones PatellasPatellas

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Irregular BonesIrregular Bones

Examples:Examples: Bones of Spinal ColumnBones of Spinal Column

– The 24 vertebraeThe 24 vertebrae– SacrumSacrum– CoccyxCoccyx

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Characteristics of BoneCharacteristics of Bone

EpiphysesEpiphyses– Each bone has two epiphysis, which are Each bone has two epiphysis, which are

layers of cartilage at the ends of the layers of cartilage at the ends of the bonesbones

– The presence of an epiphysis indicates The presence of an epiphysis indicates incomplete bone growthincomplete bone growth

ArticulationArticulation– Connection point of bones (joint)Connection point of bones (joint)– Type of articulation helps determine the Type of articulation helps determine the

type and amount of motion possibletype and amount of motion possible

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Pathology of bonePathology of bone

OsteoporosisOsteoporosis– Maybe primary or secondaryMaybe primary or secondary

OsteomalaciaOsteomalacia– Characterized by incomplete mineralization of Characterized by incomplete mineralization of

normal osteoid tissuenormal osteoid tissue OsteomyelitisOsteomyelitis

– An acute or chronic inflammatory process of An acute or chronic inflammatory process of the bone and its marrow secondary to infectionthe bone and its marrow secondary to infection

Paget’s disease (osteitis deformans)Paget’s disease (osteitis deformans)– An osteometabolic disorderAn osteometabolic disorder

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Cartilage TissueCartilage Tissue

Cartilage tissue consists of cartilage Cartilage tissue consists of cartilage cells called chondrocytescells called chondrocytes– Chondrocytes are specialized cells that are Chondrocytes are specialized cells that are

responsible for the development of responsible for the development of cartilage, and the maintenance of the cartilage, and the maintenance of the extracellular matrixextracellular matrix

Cartilage tissue exists in three forms:Cartilage tissue exists in three forms:– HyalineHyaline– ElasticElastic– FibrocartilageFibrocartilage

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Hyaline cartilageHyaline cartilage

Covers the ends of long bones Covers the ends of long bones and, along with the synovial fluid and, along with the synovial fluid that bathes it, provides a smooth that bathes it, provides a smooth and almost frictionless and almost frictionless articulating surfacearticulating surface

The most abundant cartilage The most abundant cartilage within the body within the body

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Elastic cartilageElastic cartilage

A very specialized connective A very specialized connective tissue, primarily found in tissue, primarily found in locations such as the outer ear, locations such as the outer ear, and portions of the larynxand portions of the larynx

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FibrocartilageFibrocartilage

Fibrocartilage functions as a Fibrocartilage functions as a shock absorber in both weight shock absorber in both weight bearing, and non-weight bearing bearing, and non-weight bearing jointsjoints

Examples include the symphysis Examples include the symphysis pubis, the intervertebral disc, and pubis, the intervertebral disc, and the menisci of the kneethe menisci of the knee

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Pathology of cartilagePathology of cartilage

OsteoarthritisOsteoarthritis– Can be primary or secondaryCan be primary or secondary

Osteochondritis dissecansOsteochondritis dissecans– And osteochondral fractureAnd osteochondral fracture

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JointsJoints

Joints are regions where bones are Joints are regions where bones are capped and surrounded by connective capped and surrounded by connective tissues that hold the bones together tissues that hold the bones together and determine the type and degree of and determine the type and degree of movement between themmovement between them

Joints may be classified as Joints may be classified as diarthrosisdiarthrosis, , which permit free bone movement and which permit free bone movement and synarthrosissynarthrosis, in which very limited or , in which very limited or no motion occursno motion occurs

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Joint ClassificationsJoint Classifications

Synarthrodial Synarthrodial (immovable)(immovable) Amphiarthrodial Amphiarthrodial (slightly movable)(slightly movable)

– SyndesmosisSyndesmosis– Synchondrosis Synchondrosis

Diarthrodial Diarthrodial (freely movable)(freely movable)

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DiarthrosisDiarthrosis

This type of joint generally unites This type of joint generally unites long bones and has great long bones and has great mobility. Examples include but mobility. Examples include but are not limited to the hip, knee are not limited to the hip, knee and shoulder and elbow jointsand shoulder and elbow joints

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Diarthrodial Joint Diarthrodial Joint CharacteristicsCharacteristics

1.1. Articular cavity presentArticular cavity present

2.2. Joint encased within ligamentous Joint encased within ligamentous capsulecapsule

3.3. Capsule lined with synovial membraneCapsule lined with synovial membrane

4.4. Secretion of synovial fluid, which Secretion of synovial fluid, which lubricates the jointlubricates the joint

5.5. Smooth articular surfaces, which are Smooth articular surfaces, which are covered with cartilagecovered with cartilage

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Diarthrodial Joint Diarthrodial Joint ClassificationsClassifications1.1. Ball and socket Ball and socket (spheroidal; (spheroidal;

enthrodial)enthrodial)

2.2. Hinge Hinge (ginglymoid)(ginglymoid)

3.3. Pivot Pivot (trochoid)(trochoid)

4.4. Condyloid Condyloid (ellipsoidal)(ellipsoidal)

5.5. Irregular Irregular (arthrodial: plane) (arthrodial: plane)

6.6. SellarSellar (saddle) (saddle)

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Ball-and-Socket JointBall-and-Socket Joint

Surface:Surface:– Spherical head fits intoSpherical head fits into– Cup cavity of other boneCup cavity of other bone

Motion: TriaxialMotion: Triaxial– Flexion/ExtensionFlexion/Extension– Abduction/AdductionAbduction/Adduction– CircumductionCircumduction

Example:Example:– HipHip– ShoulderShoulder

Page 44: Chapter 1  Musculoskeletal Tissue

Hinge Hinge (ginglymus)(ginglymus) Joint Joint

Surface:Surface:– 1 surface spool-like1 surface spool-like– 1 surface is concave 1 surface is concave

and fits over spooland fits over spool Motion: UniaxialMotion: Uniaxial

– Concave surface glides Concave surface glides partially around the partially around the spool-like processspool-like process

Example: humero-ulnar jointExample: humero-ulnar joint

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Pivot Pivot (trochoid)(trochoid) Joint Joint

SurfaceSurface– Peg-like pivotPeg-like pivot

Motion: UniaxialMotion: Uniaxial– Rotation onlyRotation only

Example:Example:– Atlanto-axialAtlanto-axial– RadioulnarRadioulnar

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Condyloid JointCondyloid Joint

Surface:Surface:– Oval or egg-shaped Oval or egg-shaped

convex surfaceconvex surface– Fits into a reciprocally Fits into a reciprocally

shaped concave surfaceshaped concave surface Motion: BiaxialMotion: Biaxial

– Forward/backwardForward/backward– Side to SideSide to Side

Example:Example:– wristwrist

Page 47: Chapter 1  Musculoskeletal Tissue

Irregular JointIrregular Joint

SurfaceSurface– Irregularly shaped, Irregularly shaped, – usually flat or slightly usually flat or slightly

curved.curved. Motion:Motion:

– Gliding (non-axial)Gliding (non-axial) Examples: some intercarpal jointsExamples: some intercarpal joints

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Saddle JointSaddle Joint

Surface:Surface:– Ends of both bones are convexEnds of both bones are convex– Like western saddleLike western saddle

Motion: biaxialMotion: biaxial– Flexion/ExtensionFlexion/Extension– Abduction/AdductionAbduction/Adduction

Example:Example:– CarpometacarpalCarpometacarpal

joint of thumbjoint of thumb

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Diarthrodial Joint Diarthrodial Joint Classifications and AxesClassifications and Axes

Number of Number of AxesAxes

00

NonaxiaNonaxiall

11

UniaxiUniaxialal

22

BiaxialBiaxial33

TriaxiaTriaxiall

ClassificatiClassificationon

IrregulaIrregularr

Hinge/Hinge/

PivotPivotCondyloiCondyloi

d/d/

SaddleSaddle

Ball Ball

& & SocketSocket

Page 50: Chapter 1  Musculoskeletal Tissue

Synovial jointsSynovial joints

The bones that articulate in a The bones that articulate in a synovial joint are capped with a synovial joint are capped with a smooth layer of hyaline cartilage smooth layer of hyaline cartilage called called articular cartilagearticular cartilage. .

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SynarthrosisSynarthrosis

There are three major types of There are three major types of synarthroses based on the type of tissue synarthroses based on the type of tissue uniting the bone surfacesuniting the bone surfaces::– Synostosis joints: united by bone tissue. Synostosis joints: united by bone tissue.

Examples include sutures and gomphosesExamples include sutures and gomphoses – Synchondrosis joints: joined by either hyaline or Synchondrosis joints: joined by either hyaline or

fibrocartilage. Examples include the epiphyseal fibrocartilage. Examples include the epiphyseal plates of growing bones and the articulations plates of growing bones and the articulations between the first rib and the sternumbetween the first rib and the sternum

– Syndesmosis joints: joined together by an Syndesmosis joints: joined together by an interosseous membrane. Examples include interosseous membrane. Examples include joints such as the symphysis pubisjoints such as the symphysis pubis

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Synarthrodial Joint Synarthrodial Joint CharacteristicsCharacteristics

Surface:Surface:– Bones are united by fibrous tissue Bones are united by fibrous tissue

continuous with periosteumcontinuous with periosteum Motion: Motion:

– None permittedNone permitted Example:Example:

– Sutures of the SkullSutures of the Skull

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Amphiarthrodial - Amphiarthrodial - Syndesmosis Joint Syndesmosis Joint CharacteristicsCharacteristics

Surface:Surface:– Ligamentous connection between Ligamentous connection between

bones bones Motion:Motion:

– Minimal movement between bonesMinimal movement between bones Examples:Examples:

– Inferior tibiofibular jointInferior tibiofibular joint

Page 54: Chapter 1  Musculoskeletal Tissue

Amphiarthrodial - Amphiarthrodial - Synchondrosis Joint Synchondrosis Joint CharacteristicsCharacteristics

SurfaceSurface::– bones are united by bones are united by

fibrocartilage fibrocartilage MotionMotion: :

– Bend &TwistBend &Twist ExampleExample::

– Articulations between Articulations between bodies of vertebraebodies of vertebrae Symphysis pubisSymphysis pubis Costochondral joints of the ribs w/ sternumCostochondral joints of the ribs w/ sternum

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BursaBursa

Flattened sac-like structuresFlattened sac-like structures Closely associated with some Closely associated with some

synovial joints synovial joints Produce small amounts of fluid Produce small amounts of fluid

allowing for smooth and almost allowing for smooth and almost frictionless motion between frictionless motion between contiguous muscles, tendons, contiguous muscles, tendons, bones, ligaments, and skin bones, ligaments, and skin

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Skeletal MuscleSkeletal Muscle

A single muscle cell is called a A single muscle cell is called a muscle muscle fiberfiber or or myofibermyofiber – Individual muscle fibers are wrapped in a Individual muscle fibers are wrapped in a

connective tissue envelope called connective tissue envelope called endomysiumendomysium

– Bundles of myofibers which form a whole Bundles of myofibers which form a whole muscle (fasiciculus) are encased in the muscle (fasiciculus) are encased in the perimysiumperimysium. The perimysium is continuous . The perimysium is continuous with the deep fasciawith the deep fascia

– Groups of fasiciculus are surrounded by a Groups of fasiciculus are surrounded by a connective sheath called the connective sheath called the epimysiumepimysium

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Machinery of Machinery of movementmovement Each myofibril contains many Each myofibril contains many

fibers called fibers called myofilamentsmyofilaments, which , which run parallel to the myofibril axis run parallel to the myofibril axis – The myofilaments are comprised of The myofilaments are comprised of

two protein filaments: actin (thin) two protein filaments: actin (thin) and myosin (thick)and myosin (thick)

– The A bands are composed of The A bands are composed of mmyosinyosin filaments, while the I bands filaments, while the I bands are composed of are composed of actinactin filaments filaments

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Machinery of Machinery of movementmovement The actin filaments of the I band The actin filaments of the I band

overlap into the A band, giving the overlap into the A band, giving the edges of the A band a darker edges of the A band a darker appearance than the central region appearance than the central region (H band), which only contains myosin(H band), which only contains myosin

At the center of each I band is a thin At the center of each I band is a thin dark Z line. A dark Z line. A sarcomeresarcomere represents represents the distance between each Z linethe distance between each Z line

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Machinery of Machinery of movementmovement When a muscle contracts isotonically:When a muscle contracts isotonically:

– The distance between the Z lines decreasesThe distance between the Z lines decreases– The I band and H bands disappearThe I band and H bands disappear– The width of the A band remains unchangedThe width of the A band remains unchanged

This shortening of the sarcomeres is not This shortening of the sarcomeres is not produced by a shortening of the actin produced by a shortening of the actin and myosin filaments, but by a sliding of and myosin filaments, but by a sliding of actin filaments over the actin filaments, actin filaments over the actin filaments, which pulls the Z lines togetherwhich pulls the Z lines together

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Machinery of Machinery of movementmovement Cross-bridgesCross-bridges

– Structures that Structures that serve to connect the actin and serve to connect the actin and myosin filamentsmyosin filaments

– The myosin filaments contain two flexible The myosin filaments contain two flexible hinge-like regions, which allow the cross-hinge-like regions, which allow the cross-bridges to attach and detach from the actin bridges to attach and detach from the actin filamentfilament

– During contraction, the cross-bridges attach During contraction, the cross-bridges attach and undergo power strokes, which provide the and undergo power strokes, which provide the contractile forcecontractile force

– During relaxation, the cross-bridges detach During relaxation, the cross-bridges detach

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Machinery of Machinery of movementmovement The regulation of cross-bridge The regulation of cross-bridge

attachment and detachment is a attachment and detachment is a function of two proteins found in the function of two proteins found in the actin filaments: tropomyosin and actin filaments: tropomyosin and troponintroponin– Tropomyosin attaches directly to the actin Tropomyosin attaches directly to the actin

filamentfilament– Troponin attaches to the tropomyosin, Troponin attaches to the tropomyosin,

rather than directly to the actin filamentrather than directly to the actin filament For contraction to take place, the For contraction to take place, the

tropomyosin must be movedtropomyosin must be moved

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The energy for The energy for movementmovement The energy required to power The energy required to power

muscular activity is derived from muscular activity is derived from the hydrolysis of ATP to ADP and the hydrolysis of ATP to ADP and inorganic phosphate.inorganic phosphate.

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The energy for The energy for movementmovement Three major energy systems:Three major energy systems:

– Phosphagen system (anaerobic)Phosphagen system (anaerobic)– Glycolysis system (anaerobic)Glycolysis system (anaerobic)– Oxidative system (aerobic)Oxidative system (aerobic)

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Neuromuscular Neuromuscular JunctionJunction Each muscle fiber is innervated by a Each muscle fiber is innervated by a

somatic motor neuronsomatic motor neuron One neuron and the muscle fibers it One neuron and the muscle fibers it

innervates constitute a motor unit, or innervates constitute a motor unit, or functional unit of the musclefunctional unit of the muscle

Each motor neuron branches as it enters Each motor neuron branches as it enters the muscle to innervate a number of the muscle to innervate a number of muscle fibersmuscle fibers

The area of contact between a nerve and a The area of contact between a nerve and a muscle fiber is known as the motor muscle fiber is known as the motor endplate, or neuromuscular junctionendplate, or neuromuscular junction

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Muscle contractionMuscle contraction Release of a chemical acetycholine from the axon Release of a chemical acetycholine from the axon

terminals at the neuromuscular junctionsterminals at the neuromuscular junctions Electrical activation of the skeletal muscle fibers Electrical activation of the skeletal muscle fibers Release of CaRelease of Ca2+2+ from the terminal cisternae from the terminal cisternae The released CaThe released Ca2+2+ diffuses into the sarcomeres, diffuses into the sarcomeres,

binds to troponin, displaces the tropomyosin, and binds to troponin, displaces the tropomyosin, and allows the actin to bind with the myosin cross-allows the actin to bind with the myosin cross-bridgesbridges

At the end of the contraction, the sarcoplasmic At the end of the contraction, the sarcoplasmic reticulum actively accumulates Careticulum actively accumulates Ca22 which requires which requires the degradation of adenosine triphosphate (ATP) the degradation of adenosine triphosphate (ATP) to adenosine diphosphate. (ADP)to adenosine diphosphate. (ADP)

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Muscle Fiber TypesMuscle Fiber Types

Four different types of muscle Four different types of muscle fibers have been recognized fibers have been recognized within skeletal muscle:within skeletal muscle:– Type I (slow twitch red oxidative)Type I (slow twitch red oxidative)– Type IIa (fast twitch red oxidative)Type IIa (fast twitch red oxidative)– Type IIb (fast twitch white glycolytic)Type IIb (fast twitch white glycolytic)– Type IIc (fast twitch intermediate)Type IIc (fast twitch intermediate)

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Slow twitch FibersSlow twitch Fibers

Slow twitch fibers are richly Slow twitch fibers are richly endowed with mitochondria and endowed with mitochondria and have a high capacity for oxygen have a high capacity for oxygen uptakeuptake– Suitable for activities of long Suitable for activities of long

duration or endurance, including duration or endurance, including postureposture

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Fast Twitch FibersFast Twitch Fibers

Fast twitch fibers can be separated Fast twitch fibers can be separated into those that have a high into those that have a high complement of mitochondria (Type complement of mitochondria (Type IIa), those that are mitochondria IIa), those that are mitochondria poor (Type IIb) and those that poor (Type IIb) and those that display a mixture of characteristics display a mixture of characteristics (Type IIc)(Type IIc)– Fast twitch fibers are suited to quick, Fast twitch fibers are suited to quick,

explosive actions, including such explosive actions, including such activities as sprinting activities as sprinting

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Pathology of musclePathology of muscle

Muscle strains may be classified Muscle strains may be classified according to their severity:according to their severity:– Mild (first degree): involves a tear of a Mild (first degree): involves a tear of a

few muscle fibers with minus swelling and few muscle fibers with minus swelling and discomfortdiscomfort

– Moderate (second degree): involves Moderate (second degree): involves greater damage to the muscle and clear greater damage to the muscle and clear loss of strengthloss of strength

– Severe (third degree): involves a tear Severe (third degree): involves a tear extending across the whole muscle bellyextending across the whole muscle belly

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Pathology of musclePathology of muscle

Myositis ossificans: is an aberrant Myositis ossificans: is an aberrant reparative process that causes reparative process that causes benign heterotopic ossification in benign heterotopic ossification in soft tissuesoft tissue