AXIAL SKELETON

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AXIAL SKELETON AXIAL SKELETON By: Dr. Mujahid Khan By: Dr. Mujahid Khan

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AXIAL SKELETON. By: Dr. Mujahid Khan. Skeletal System. It develops from mesodermal and neural crest cells As the notochord and neural tube forms Embryonic mesoderm on each side of them proliferates Form a thick longitudinal columns of paraxial mesoderm - PowerPoint PPT Presentation

Transcript of AXIAL SKELETON

AXIAL SKELETONAXIAL SKELETON

By: Dr. Mujahid KhanBy: Dr. Mujahid Khan

Skeletal SystemSkeletal System It develops from mesodermal and neural crest It develops from mesodermal and neural crest

cellscells As the notochord and neural tube formsAs the notochord and neural tube forms

Embryonic mesoderm on each side of them Embryonic mesoderm on each side of them proliferatesproliferates

Form a thick longitudinal columns of paraxial Form a thick longitudinal columns of paraxial mesodermmesoderm

Each column is continuous with intermediate Each column is continuous with intermediate mesodermmesoderm

SomitesSomites

Paraxial mesoderm differentiates and Paraxial mesoderm differentiates and begins to divide into cuboidal bodies called begins to divide into cuboidal bodies called somites by the end of 3somites by the end of 3rdrd week week

These blocks of mesoderm are located on These blocks of mesoderm are located on each side of developing neural tubeeach side of developing neural tube

About 38 pairs of somites form during the About 38 pairs of somites form during the somite period of human development (20-somite period of human development (20-30 days)30 days)

SomitesSomites

Each somite differentiates into two parts:Each somite differentiates into two parts:

The ventromedial part is sclerotomeThe ventromedial part is sclerotome

Its cells form the vertebrae and ribsIts cells form the vertebrae and ribs

The dorsolateral part is the dermomyotomeThe dorsolateral part is the dermomyotome

Cells from myotome form myoblastsCells from myotome form myoblasts

Cells from dermatome form the dermisCells from dermatome form the dermis

Axial SkeletonAxial Skeleton

The axial skeleton is composed of:The axial skeleton is composed of:

Cranium (skull)Cranium (skull) Vertebral columnVertebral column RibsRibs SternumSternum

FormationFormation

During formation of this part of the During formation of this part of the skeleton, the cells in the sclerotomes of skeleton, the cells in the sclerotomes of the somites change their positionthe somites change their position

During the fourth week they surround the During the fourth week they surround the neural tube and the notochordneural tube and the notochord

Vertebral ColumnVertebral Column

During the precartilaginous or During the precartilaginous or mesenchymal stage, mesenchymal cells mesenchymal stage, mesenchymal cells are found in three main areas:are found in three main areas:

Around the notochordAround the notochord Surrounding the neural tubeSurrounding the neural tube In the body wallIn the body wall

Vertebral ColumnVertebral Column

In a frontal section of a 4 week embryo, In a frontal section of a 4 week embryo, the sclerotomes appear as paired the sclerotomes appear as paired condensations of mesenchymal cells condensations of mesenchymal cells around the notochordaround the notochord

Each sclerotome consists of loosely Each sclerotome consists of loosely arranged cells cranially and densely arranged cells cranially and densely packed cells caudallypacked cells caudally

Intervertebral DiscIntervertebral Disc

Some densely packed cells move cranially, Some densely packed cells move cranially, opposite the centre of the myotome, where they opposite the centre of the myotome, where they form the intervertebral discform the intervertebral disc

The remaining densely packed cells fuse with The remaining densely packed cells fuse with the loosely arranged cells of the immediately the loosely arranged cells of the immediately caudal sclerotome to form the mesenchymal caudal sclerotome to form the mesenchymal centrumcentrum

This is primordium of the body of a vertebraThis is primordium of the body of a vertebra

Intervertebral DiscIntervertebral Disc

Thus each centrum develops from two adjacent Thus each centrum develops from two adjacent sclerotomes and becomes an intersegmental sclerotomes and becomes an intersegmental structurestructure

The nerves lie in close relationship to the IV The nerves lie in close relationship to the IV discsdiscs

The intersegmental arteries lie on each side of The intersegmental arteries lie on each side of the vertebral bodiesthe vertebral bodies

In the thorax the dorsal intersegmental arteries In the thorax the dorsal intersegmental arteries become the intercostal arteriesbecome the intercostal arteries

Nucleus PulposusNucleus Pulposus

The notochord degenerates and disappears The notochord degenerates and disappears where it is surrounded by the developing where it is surrounded by the developing vertebral bodiesvertebral bodies

Between the vertebrae, the notochord expands Between the vertebrae, the notochord expands to form the gelatinous center of the intervertebral to form the gelatinous center of the intervertebral disc called nucleus pulposusdisc called nucleus pulposus

The nucleus later surrounded by circularly The nucleus later surrounded by circularly arranged fibers that form the anulus fibrosusarranged fibers that form the anulus fibrosus

Vertebral ColumnVertebral Column

The nucleus pulposus and anulus fibrosus The nucleus pulposus and anulus fibrosus together constitute the IV disctogether constitute the IV disc

The mesenchymal cells, surrounding the The mesenchymal cells, surrounding the neural tube, form the vertebral archneural tube, form the vertebral arch

The mesenchymal cells in the body wall The mesenchymal cells in the body wall form the costal processes that form ribs in form the costal processes that form ribs in the thoracic regionthe thoracic region

Cartilaginous StageCartilaginous Stage

During the sixth week chondrification During the sixth week chondrification centers appear in each mesenchymal centers appear in each mesenchymal vertebravertebra

The two centers in each centrum fuse at The two centers in each centrum fuse at the end of the embryonic period to form a the end of the embryonic period to form a cartilaginous centrumcartilaginous centrum

The centers in the vertebral arches fuse The centers in the vertebral arches fuse with each other and the centrumwith each other and the centrum

Cartilaginous StageCartilaginous Stage

The spinous and transverse processes The spinous and transverse processes develop from extensions of chondrification develop from extensions of chondrification centers in the vertebral archcenters in the vertebral arch

Chondrification spreads until a Chondrification spreads until a cartilaginous vertebral column is formedcartilaginous vertebral column is formed

Bony StageBony Stage

Ossification of typical vertebrae begins Ossification of typical vertebrae begins during the embryonic periodduring the embryonic period

It usually ends by the twenty-fifth yearIt usually ends by the twenty-fifth year

There are two primary ossification centers, There are two primary ossification centers, ventral and dorsal for the centrumventral and dorsal for the centrum

These primary ossification centers soon These primary ossification centers soon fuse to form one centerfuse to form one center

Bony StageBony Stage

Three primary centers are present by the Three primary centers are present by the end of the embryonic period:end of the embryonic period:

One in the centrumOne in the centrum One in each half of the vertebral archOne in each half of the vertebral arch

Ossification becomes evident in the Ossification becomes evident in the vertebral arches during the eighth weekvertebral arches during the eighth week

Bony StageBony Stage

At birth each vertebra consists of three bony At birth each vertebra consists of three bony parts connected by cartilageparts connected by cartilage

The bony halves of the vertebral arch usually The bony halves of the vertebral arch usually fuse during the first 3 to 5 yearsfuse during the first 3 to 5 years

The arches first unite in the lumber regionThe arches first unite in the lumber region

This union progresses craniallyThis union progresses cranially

The vertebral arch articulates with the centrum The vertebral arch articulates with the centrum at cartilaginous neurocentral jointsat cartilaginous neurocentral joints

Bony StageBony Stage

These articulations permit the vertebral These articulations permit the vertebral arches to grow as the spinal cord enlargesarches to grow as the spinal cord enlarges

These joints disappear when the vertebral These joints disappear when the vertebral arch fuses with the centrum during the arch fuses with the centrum during the third to sixth yearsthird to sixth years

The vertebral body is a composite of the The vertebral body is a composite of the anular epiphyses and the mass of bone anular epiphyses and the mass of bone between thembetween them

Bony StageBony Stage

Five secondary ossification centers appear in the Five secondary ossification centers appear in the vertebrae after puberty:vertebrae after puberty:

One for the tip of the spinous processOne for the tip of the spinous process

One for the tip of each transverse processOne for the tip of each transverse process

Two anular epiphysis, one on the superior and Two anular epiphysis, one on the superior and one on the inferior rim of the vertebral bodyone on the inferior rim of the vertebral body

Bony StageBony Stage

The vertebral body includes the centrum, The vertebral body includes the centrum, parts of the vertebral arch, and the facets parts of the vertebral arch, and the facets for the heads of the ribsfor the heads of the ribs

All secondary centers unite with the rest of All secondary centers unite with the rest of the vertebra around 25 years of agethe vertebra around 25 years of age

Exceptions to the typical ossification of Exceptions to the typical ossification of vertebrae occur in the atlas, axis, C7, vertebrae occur in the atlas, axis, C7, lumbar vertebrae, sacrum and coccyxlumbar vertebrae, sacrum and coccyx

Development of RibsDevelopment of Ribs

The ribs develop from the mesenchymal costal The ribs develop from the mesenchymal costal processes of the thoracic vertebraeprocesses of the thoracic vertebrae

They become cartilaginous during the embryonic They become cartilaginous during the embryonic period period

They ossify during the fetal periodThey ossify during the fetal period

The original site of union of the costal processes The original site of union of the costal processes with the vertebra is replaced by costovertebral with the vertebra is replaced by costovertebral jointsjoints

Development of RibsDevelopment of Ribs

These are the plane type of synovial jointThese are the plane type of synovial joint

Seven pairs of ribs (1 to 7) are true ribs Seven pairs of ribs (1 to 7) are true ribs

They attach through their own cartilages to the sternumThey attach through their own cartilages to the sternum

Five pairs of ribs (8 to 12) are false ribsFive pairs of ribs (8 to 12) are false ribs

They attach to the sternum through the cartilage of They attach to the sternum through the cartilage of another rib or ribsanother rib or ribs

The last two pairs (11 - 12) are floating ribsThe last two pairs (11 - 12) are floating ribs

Development of SternumDevelopment of Sternum

A pair of vertical mesenchymal bands, A pair of vertical mesenchymal bands, sternal bars develop ventrolaterally in the sternal bars develop ventrolaterally in the body wallbody wall

Chondrification occurs in these bars as Chondrification occurs in these bars as they move mediallythey move medially

They fuse craniocaudally in the median They fuse craniocaudally in the median plane to form the cartilaginous models of plane to form the cartilaginous models of the manubrium, sternebrae and xiphoid the manubrium, sternebrae and xiphoid processprocess

Development of SternumDevelopment of Sternum

Fusion at the inferior end of the sternum is Fusion at the inferior end of the sternum is sometimes incompletesometimes incomplete

As a result the xiphoid process in these infants As a result the xiphoid process in these infants is bifid or perforatedis bifid or perforated

Centers of ossification appear craniocaudally in Centers of ossification appear craniocaudally in the sternum before birththe sternum before birth

But xiphoid process appears during childhoodBut xiphoid process appears during childhood

Development of CraniumDevelopment of Cranium

The cranium develops from mesenchyme The cranium develops from mesenchyme around the developing brainaround the developing brain

The cranium consists of:The cranium consists of:

The neurocranium, a protective case for The neurocranium, a protective case for the brainthe brain

The viscerocranium, the skeleton of the The viscerocranium, the skeleton of the faceface

Cartilaginous NeurocraniumCartilaginous Neurocranium

Initially the cartilaginous neurocranium or Initially the cartilaginous neurocranium or chondrocranium consists of the chondrocranium consists of the cartilaginous base of the developing cartilaginous base of the developing craniumcranium

It forms by the fusion of several cartilagesIt forms by the fusion of several cartilages

Later, endochondral ossification of the Later, endochondral ossification of the chondrocranium forms the bones in the chondrocranium forms the bones in the base of the craniumbase of the cranium

Cartilaginous NeurocraniumCartilaginous Neurocranium

The ossification pattern of these bones The ossification pattern of these bones beginning with occipital bone, body of sphenoid, beginning with occipital bone, body of sphenoid, and ethmoid boneand ethmoid bone

The parachordal cartilage or basal plate forms The parachordal cartilage or basal plate forms around the cranial end of the notochordaround the cranial end of the notochord

It fuses with the cartilages derived from the It fuses with the cartilages derived from the sclerotome regions of the occipital somitessclerotome regions of the occipital somites

Cartilaginous NeurocraniumCartilaginous Neurocranium

This cartilaginous mass contributes to the This cartilaginous mass contributes to the base of the occipital bonebase of the occipital bone

Later extensions grow around the cranial Later extensions grow around the cranial end of the spinal cordend of the spinal cord

These extensions form the boundaries of These extensions form the boundaries of the foramen magnumthe foramen magnum

Cartilaginous NeurocraniumCartilaginous Neurocranium

Hypophysial cartilage forms around the Hypophysial cartilage forms around the developing pituitary glanddeveloping pituitary gland

It fused to form the body of the sphenoid boneIt fused to form the body of the sphenoid bone

The trabeculae cranii fuse to form the body of The trabeculae cranii fuse to form the body of the ethmoid bonethe ethmoid bone

The ala orbitalis forms the lesser wing of the The ala orbitalis forms the lesser wing of the sphenoid bonesphenoid bone

Cartilaginous NeurocraniumCartilaginous Neurocranium

Otic capsules develop around the otic vesicles, Otic capsules develop around the otic vesicles, the primordia of the internal earsthe primordia of the internal ears

They form the petrous and mastoid parts of the They form the petrous and mastoid parts of the temporal bonetemporal bone

Nasal capsules develop around the nasal sacsNasal capsules develop around the nasal sacs

They contribute to the formation of the ethmoid They contribute to the formation of the ethmoid bonebone

Membranous NeurocraniumMembranous Neurocranium

Intramembranous ossification occurs in the Intramembranous ossification occurs in the mesenchyme at the sides and top of the brain mesenchyme at the sides and top of the brain forming calvaria (cranial vault)forming calvaria (cranial vault)

During fetal life the flat bones of the calvaria are During fetal life the flat bones of the calvaria are separated by dense connective tissue separated by dense connective tissue membranes, that form the suturesmembranes, that form the sutures

Six large fibrous areas fontanelles are present Six large fibrous areas fontanelles are present where several sutures meetwhere several sutures meet

Membranous NeurocraniumMembranous Neurocranium

The softness of bones and their loose connections at the The softness of bones and their loose connections at the sutures enable the calvaria to change shape during birthsutures enable the calvaria to change shape during birth

During molding of the fetal cranium, the frontal bones During molding of the fetal cranium, the frontal bones become flat become flat

The occipital bone is drawn outThe occipital bone is drawn out

Parietal bone overrides the other oneParietal bone overrides the other one

Shape of the calvaria returns to normal in few days after Shape of the calvaria returns to normal in few days after birthbirth

Cartilaginous ViscerocraniumCartilaginous Viscerocranium These parts of the fetal cranium are derived from These parts of the fetal cranium are derived from

the cartilaginous skeleton of the first two pairs of the cartilaginous skeleton of the first two pairs of pharyngeal archespharyngeal arches

11stst arch: malleus and incus arch: malleus and incus

22ndnd arch: stapes, styloid process, lesser cornu arch: stapes, styloid process, lesser cornu and body of hyoid boneand body of hyoid bone

33rdrd arch: greater horn and lower part of hyoid arch: greater horn and lower part of hyoid bonebone

44thth to 6 to 6thth arches: laryngeal cartilages arches: laryngeal cartilages

Membranous ViscerocraniumMembranous Viscerocranium

Intramembranous ossification occurs in the Intramembranous ossification occurs in the maxillary prominence of the first pharyngeal archmaxillary prominence of the first pharyngeal arch

Subsequently forms the squamous temporal, Subsequently forms the squamous temporal, maxillary, and zygomatic bonesmaxillary, and zygomatic bones

The squamous temporal bones become part of The squamous temporal bones become part of the neurocraniumthe neurocranium

Mandibular prominence undergoes Mandibular prominence undergoes intramembranous ossification to form mandibleintramembranous ossification to form mandible

Newborn CraniumNewborn Cranium

Newborn’s cranium is round and thinNewborn’s cranium is round and thin

It is large in proportion to the rest of the skeletonIt is large in proportion to the rest of the skeleton

Face is relatively small compared with the Face is relatively small compared with the calvariacalvaria

The small facial region of cranium results from:The small facial region of cranium results from:

Small size of the jawSmall size of the jaw Absence of paranasal air sinusesAbsence of paranasal air sinuses Underdeveloped facial bones at birthUnderdeveloped facial bones at birth

Postnatal Growth of CraniumPostnatal Growth of Cranium

The fibrous sutures of the newborn’s calvaria The fibrous sutures of the newborn’s calvaria permit the brain to enlarge during infancy and permit the brain to enlarge during infancy and childhoodchildhood

The increase in the size of the calvaria is The increase in the size of the calvaria is greatest during the first 2 yearsgreatest during the first 2 years

This is the period of rapid postnatal growth of This is the period of rapid postnatal growth of the brainthe brain

Calvaria normally increases in capacity until Calvaria normally increases in capacity until about 16 years of ageabout 16 years of age

Postnatal Growth of CraniumPostnatal Growth of Cranium

There is a rapid growth of the face and jaws coinciding There is a rapid growth of the face and jaws coinciding with eruption of teethwith eruption of teeth

These facial changes are more marked after the These facial changes are more marked after the secondary teeth eruptsecondary teeth erupt

Enlargement of frontal and facial regions also increase Enlargement of frontal and facial regions also increase with increase in size of paranasal sinuseswith increase in size of paranasal sinuses

Most paranasal sinuses are rudimentary or absent at Most paranasal sinuses are rudimentary or absent at birthbirth

Growth of these sinuses alter the shape of the face and Growth of these sinuses alter the shape of the face and adding resonance to the voiceadding resonance to the voice