musculoskeletal development · 63 musculoskeletal development in this chapter you will begin to...

63

Musculoskeletal DevelopmentIn this chapter you will begin to study musculoskeletal morphogenesis. The skeleton not only serves as an important framework and site for muscle deployment, but also provides protection for many other important organ systems. Additionally, it is an important site for calcium storage, an important metaboilte. The muscles are the motor machines of the body that stabilize the skeleton, move it, and are important heat generating organs. Prior to the lecture you should be able to:

• Describe all the bones of the axial and appendicular skeleton.• Describe the muscle patterns of the body and outline the muscle groups

within the skeletlal muscular system.After this lecture you should be able to:

• Explain the developmental emergence of the the somite and the associated cell movements during somitic morphogenesis related to musculoskeletal development.

• Describe the stages involved in the formation of the vertebral column and rib cage.

• Explain the morphogenesis of the appendicular skeleton and its continued growth.

• Describe the differences and similarities in endochondral and intramembranous bone formation.

• Describe the development of skeletal muscle.• Outline the morphogenesis and patterns of muscle development in the

trunk and limbs.• Outline all the key steps and features in the development of the skull

and the formation of the head musculature.

What can be more curious than that the hand of man, formed for grasping, that of a mole for digging, the leg of a horse, the paddle of the porpoise, and the wing of the bat should all be constructed on the same pattern and should include similar bones, and in the same relative position?

Charles Darwin, 1859

E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n

64

Anatomy ReviewReview the basics of the musculoskeletal system

Skeletal ReviewYou should understand the basic anatomy of the following:Bones and joints of the skeletal system

Bones and joints of the skull

Bones and joints of the postcranial axial skeleton

Bones and joints of the appendicular skeleton

Anatomy of the synovial joint

Anatomy of a typical long bone

Muscle ReviewDesign of skeletal musclesYou should understand the relations of connective tissue and muscles cells within the design of a muscle.Muscle groups of the headYou should understand the basic layout of the muscles in the body.

Somitic musclesExtraocular muscles

Tongue muscles

Branchial arch musclesMuscle of the first branchial arch

Muscle of the second branchial arch

Muscles of the third branchial arch

Muscles of the fourth and sixth branchial arch

Muscles of the caudal branchial arch

Muscle groups of the trunk wallEpaxial muscles

Superficial muscles

Deep muscles

Hypaxial musclesSubvertebral muscles

Four-layered lateral wall muscles

Ventral muscles

Limb musclesMuscles annexed from the body wall

Ventral muscles

Dorsal muscles

65

M u s c u l o s k e l e t a l D e v e l o p m e n t

Development of the Paraxial MesodermParaxial mesoderm after gastrulation

Emergence of somitomeres

Differentiation of the somitesEpithelial somites

Segmental mesenchymal sclerotomes

Segmental dermamyotome epithelial plate

Sclerotome Migration and DifferentiationMigration of the sclerotomeRole of differential growth


66

ResegmentationLoose cranial half

Dense caudal half

Relations to dermamyotome and spinal nerve

Mesenchymal (blastemal) costovertebral elementDevelopment during the 4th and 5th embryonic weeks

Ventral to developing neural tube

Dorsal to the neural tube

In the body wall

Cartilaginous costovertebral skeletonSixth to eighth weeks of embryonic development

Body centers

Neural arch centers

Costal centers

Fusion of cartilage centers

67


Bony stage of costovertebral developmentEighth embryonic week to 25 years

Primary ossification centersCentrum

Vertebral arch

Costal elements

JointsNeurocentral joints

Costovertebral joints

Secondary ossification centersSpinous process

Transverse processes

Annular epiphyses

Development of associated structuresIntervertebral discs

Periosteum and ligaments

Segmental variation


68

Development of the SternumMesenchymal condensations of lateral somatic mesodermPaired sternal bars

Chondrification and fusion

Ossification centersManubrium

Sternebrae

Xiphoid process

Morphogenesis of the MyotomeTerminology

Role of body mesenchyme in muscle differentiation

Muscle cell formationMyoblast

Myotube

Myofiber

69


Trunk muscle patternsEpaxial muscles

Layers

Hypaxial musclesSubvertebral muscle

Four-layered lateral muscle wall

Ventral muscle


70

Postnatal trunk musclesRecall that the embryonic patterns that arises from the somites is found in the adult trunk. There are epaxial muscles with deep, intermediate, and superficial layers, and hypaxial muscles with ventral, four-layered lateral, and subvertebral muscle components.

71


Development of Limb Skeleton - OverviewBasic featuresLimb bud

Lateral (somatic) mesodermMesenchymal (blastemal) stage

Cartilaginous stage

Endochondral bone formation

Limb FieldConcept of a morphogenetic field

A group of cells whose position and fate are specified with respect to the same set of boundaries. A particular field of cells will give rise to its particular organ when transplanted to a different part of the embryo, and the cells of the field can regulate their fates to make up for missing cells in the field.

Limbs as morphogenetic fieldsMesodermal cells of the vertebrate limb can be identified by:

1) removing certain groups of cells and observing if a limb develops in their absence;

2) transplanting certain cells to a new location and observe whether they form a limb;

3) marking groups of cells with labels and observing which descendant cells partake in limb development.


72

Factors in Limb Bud DevelopmentMesodermal outgrowthFibroblastic growth factor – the limb bud inducer

Block experiments

FGF soaked bead experiments

Apical ectodermal ridge (AER)What is it?

Role of AER:1) maintain the mesoderm beneath it in a plastic, proliferating phase that enables linear growth of the limb;

2) maintain the expression of those molecules that generate the anterior-posterior (thumb-pinky) axis;

3) interacting with proteins specifying the anterior-posterior and dorsal-ventral axes so that each cell is given instructions on how to differentiate.

Progress zone – the mesodermal componentWhat is it?

Relation to progress zone

Proximodistal growth and differentiationTime in the progress zone

Apoptosis in limb formation

Implications in vertebrate limb diversity

73


AER

AER

AER

AER

RemoveAER 20 hours Humerus

forms

RemoveAER

RemoveAER

RemoveAER

20 hours

20 hours

20 hours24 hours

Add beadwith salinesolution

Add beadcontainingFGF2

Add beadcontainingFGF2

ImplantsecondbeadcontainingFGF2

Bead

Humerusforms

Humerus

Bead

Radius

Ulna

HumerusRadius

Ulna

Carpals

Digits

Secondbead


74

Bone and Joint Formation in the LimbLateral plate mesenchymeMost limb bones

ExceptionsScapular body and spine

Blastemal stageMesenchymal condensation

Chondrification

OssificationProcess of endochondral bone formation

Cartilaginous anlage

Diaphyseal collar

Spread of diaphyseal collar and medullary cavity formation

Epiphyseal centers

Growth plate

Fusion

Cartilage Anlage Primary Ossification Center

Spread of Primary Center Secondary Ossification Center

CrossSections

CrossSections

New bone deposition

New bone deposition

Mitotic cartilage cells

Mitotic cartilage cells

75


Joint formationCondensed mesenchyme

Undifferentiated zoneModifications

Synovial joints

Cartilage joints

Fibrous joints

Muscle Formation in the LimbMyotomal epithelial plate of somiteInduced by lateral plate mesoderm

Migrations of presumptive muscles cellsDorsal muscle masses

Ventral muscle masses


76

Differentiation of muscle massesRelation to bone formation

Annexation of body wall muscles

Growth onto body wall

Limb rotation

Relation of muscle cells and connective tissue

77


Morphogenesis of the Cranial BonesThree developmental anlage give rise to the cranium

Blastemal craniumThree centers to emerge

Chondrocranium or cartilaginous neurocranium

Dermatocranium or membranous neurocranium

Splanchnocranium or viscerocraniumCartilaginous splanchnocranium

Membranous splanchnocranium

Chondrocranium or cartilaginous neurocraniumEndochondral bones

Support for developing brain and special sensory structuresParachordal cartilages or basal plate

Supports brainstem

From occipital scleretomes and first cervical sclerotome

Becomes basi-occipital bone

Hypophysial cartilageSupports pituitary gland

From neural crest

Becomes body of sphenoid bone

Trabeculae cranii or prechordal cartilagesSupports olfactory lobe of brain

From neural crest

Becomes body of the ethmoid bone

Nasal capsuleSupports nasal epithelium

From neural crest

Becomes conchae and perpendicular plate of ethmoid and inferior nasal conchae

Ala orbitalis and ala temporalisSupports developing eye

From neural crest

Becomes lesser wing and part of greater wing of sphenoid bone

Otic capsulesSupports inner ear anatomy

From neural crest

Becomes petrous and mastoid parts of the temporal bone


78

Ossification of the chondrocraniumBone centers

Synostosis

Sutures

Dermatocranium or membranous neurocraniumDermal or intramembranous bones

Formation of calvarium

Fontanelles

Sutures

79


Splanchnocranium or viscerocraniumThis series of skeletal elements arise from the interesting region known as the branchial or pharyngeal arches of the developing embryonic head. (See the following page for branchial arch development.) The middle ear ossicles, the jaw bones, the hyoid bone, and the cartilages of the larynx arise from the skeletal elements of these arches. Some of the bones form endochondrally from the cartilages of the arches, while others form as intramembranous ossifications around cartilage precursors. The skeletal elements are represented in the illustration below. Neural crest origin

Cartilaginous viscerocranium or derivatives of cartilaginous archFirst arch

Malleus, incus, and condyle and mentum of mandible

Second archStapes, styloid process, and lesser horn and superior body of hyoid bone

Third archGreater horn and inferior body of hyoid bone

Fourth and sixth archesThyroid, cricoid, and arytenoid cartilages

Membranous viscerocranium or intramembranous bonesMaxillary prominence of first pharyngeal arch

Squamous temporal bones, maxillary bone, and zygomatic bones

Mandibular prominence of first pharyngeal archMost of the mandible


80

Pharyngeal or Branchial ArchesComparative aspects of vertebrate heads

Pharyngeal arch designCraniocaudal patterning

Emergence of the phryngeal archesNeural crest tissue

Bone and connective tissue

Paraxial mesoderm (somitomeres)Skeletal muscles

Anatomy of the pharyngeal archesPharyngeal arch

Pharyngeal cleft

Pharyngeal pouch

Components of the archSkeletal elements

Muscle

Blood vessels

Cranial nerve

81


Arch Development – Details of Skeletal ElementsFirst pharyngeal archIncus

Malleus

Anterior ligament of the malleus

Sphenomandibular ligament

Meckel’s cartilage

Second pharyngeal archStapes

Styloid process

Stylohyoid ligament

Lesser cornu and cranial part of the hyoid bone

Third pharyngeal archGreater cornu and inferior part of the hyoid bone

Fourth and sixth pharyngeal archesThyroid cartilage

Cricoid cartilage

Arytenoid cartilages


82

Arch Development – Facial AnatomyEmergence of three key embryonic structures

Frontonasal prominenceNasal placodes

Lateral nasal process

Medial nasal process

Nasal pits

Intermaxillary process

First pharyngeal archMaxillary swelling or prominence

Nasolacrimal groove

Mandibular swelling or prominence

Second pharyngeal archCervical sinus

83



84

Arch Development – Nasal and Oral CavitiesNasal RegionNasal placode

Nasal pit

Nasal sac

Nasal finOronasal membrane

Primitive choanae

Nasal septumCartilaginous and boney nasal septum

Nasal passagesConchae

Osseous sinuses

Definitive choanae

Stomodeum

85


Palate and oral regionPrimary palate

Median palatine process

Secondary palateLateral palatine processes or palatal shelves

Nasal septum

Median palatine process

Hard palateNasopalatne canal – Incisive fossa

Soft palateUvula


86

Arch Development – External EarAuricle formationAuricular hillocks

Three from first archHillock 1

Hillock 2

Hillock 3

Three from second archHillock 4

Hillock 5

Hillock 6

Contributions to postnatal auricleTragus

Hillock 1

Helix and cymba conchaHillocks 2 and 3

Antihelix and conchaHillocks 4 and 5

AntitragusHillock 6

External acoustic meatusFirst pharyngeal cleft

Meatal plug

87


Arch Development – Middle EarFirst pharyngeal pouchTubotympanic recess

Distal expansion = tympanic cavity

Proximal part = pharyngotympanic tube

Tympanic membraneFirst pharyngeal membrane

Ectoderm

Endoderm

Mesodern

Middle ear ossiclesMalleus

Incus

Stapes

Middle ear musclesTensor tympani

Stapedius


88

Arch Development – Tongue AnatomyFloor of first archMedian tongue bud or tuberculum impar

Distal tongue buds or lateral lingual swellings

Median sulcus

Floor of second archForamen cecum

Copula

Floor of third and fourth archesHypopharyngeal eminence

Laryngotracheal groove

Rima glottidis

Terminal sulcus

Occipital somites

89


Arch Development – Skeletal Muscle AnatomyBasic arch design

Spread of the second archCervical sinus


90

Four Planes of Arch Muscle MigrationSecond arch muscles

First arch and lateral mesoderm muscles

Occipital somites 2 to 4 and cervical somite muscles

Third and fourth arch and occipital somite 1 muscles

Resulting anatomy

Pharyngeal arch 1

Pharyngeal arch 2

Pharyngeal arch 3

Pharyngeal arch 4

91


Summary of Head MusclesArch 1 Arch 2 Arch 3 Arch 4

Arch 1 Arch 2 Arch 3 Arch 4

Neural tube, notochord, prechoral mesoderm

Neural crest

Premuscular mesoderm

Muscle migration and development

Motor neuron development

Peripheral ganglia development


92

musculoskeletal development · 63 musculoskeletal development in this chapter you will begin to...

Documents