Skeletal System

Front 1

Paraxial Mesoderm

Back 1

-Forms a segmented series of tissue blocks on each side of the neural tube

-forms axial skeleton

Front 2

Somitomeres

Back 2

- Begins the segmented series of tissue blocks on each side of the neural tube in the Head region cranial vault)

Front 3

Somites

Back 3

-Begins the segmented series of tissue blocks on each side of the neural tube from the OCCIPITAL HEAD REGION CAUDALLY(BASE OF THE SKULL)

Front 4

Sclerotome(medial)

Back 4

-forms most of the axial skeleton (vertebrae, ribs, and base of the skull).

-ventromedial part

Front 5

Dermomyotome

Back 5

-dorsolateral part

-dermatome +myotome

Front 6

Dermatome(lateral)

Back 6

-migrates to form eye dermis of the skin

-dorsal epithelium

Front 7

Myotome(middle)

Back 7

-migrates to form skeletal head muscles

-Individual adult muscles are produced by merger of adjacent myotomes.

Front 8

Mesenchyme

Back 8

-polymorphous and form loosely organized tissue

-differentiates into

*fibroblast

*chondroblast

*osteoblast (bone forming cells)

Front 9

Embryogenesis of skeletal system

Back 9

Note that during the third week of embryogenesis, the paraxial mesoderm segments into somites along the neural tube.

-The somites differentiate into the sclerotome (ventromedially) and the dermomyotome (dorsolaterally).

-The dermomyotome includes the dermatome and myotome as shown in this figure.

Front 10

Fibroblast

Back 10

form much of "connections" of connective tissues in the form of capsules, sheaths, fascial planes, tendons, and ligaments.

Front 11

Chondroblast

Back 11

form cartilage

Front 12

Osteoblast

Back 12

Form bones

Front 13

Lateral Plate (parietal layer) mesoderm

Back 13

- mesoderm cells for the formation if

*pelvic girdle

*shoulder girdle

*long bone of limbs

Front 14

Neural crest

Back 14

-in the head region

- differentiate into mesenchyme

-it forms

*bone of face and skull

Front 15

Lateral Plate (parietal layer) mesoderm

Back 15

- mesoderm cells for the formation if

*pelvic girdle

*shoulder girdle

*long bone of limbs

Front 16

Neural crest

Back 16

-in the head region

- differentiate into mesenchyme

-it forms

*bone of face and skull

Front 17

Skeletal structure of skull

Back 17

Back (Definition)

Front 18

Ossification

Back 18

the gradual transition from a fibrous or cartilaginous template to bone.

Front 19

Intramembranous ossification

Back 19

-flat bones of the skull and mandible

-mesenchyme in the dermis differentiates directly into bone

Front 20

Endochondrial ossification

Back 20

-mesenchymal cells first givE rise to hyaline cartilage models , which in turn becomes ossified

Front 21

Intramembranous Ossification

Back 21

Intramembranous ossification follows four steps. (a) Mesenchymal cells group into clusters, differentiate into osteoblasts, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form. (d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red bone marrow.

Front 22

Endochondral ossification

Back 22

Endochondral ossification follows five steps. (a) Mesenchymal cells differentiate into chondrocytes that produce a cartilage model of the future bony skeleton. (b) Blood vessels on the edge of the cartilage model bring osteoblasts that deposit a bony collar. (c) Capillaries penetrate cartilage and deposit bone inside cartilage model, forming primary ossification center. (d) Cartilage and chondrocytes continue to grow at ends of the bone while medullary cavity expands and remodels. (e) Secondary ossification centers develop after birth. (f) Hyaline cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.

Front 23

Neurocranium

Back 23

Forms a protective case around the brain

Front 24

Viscerocranium

Back 24

-forms the skeleton of the face

Front 25

Membranous neurocranium

Back 25

- derived from neural crest and paraxial mesoderm

-flat bones which surround the brain as vault

-The neural crest cells create *adult frontal bone

*squamous portion of the temporal bone

The paraxial mesoderm produces

*intraparietal portion of the occipital bone

*the parietal bone itself.

Front 26

Newborn skull

Back 26

-at birth flat bones of the skull are separated by sutures and fontanelles

Front 27

Suture

Back 27

A fairly rigid joint between bones of the neurocranium

-narrow seams of connective tissue

Derived from:

1. Neural crest cells(sagittal suture)

2. Paraxial mesoderm (coronal suture)

Front 28

Fontanelles

Back 28

-at points where more than two bones meet

-sutures are wide

-growth areas of the skull that are present since before birth up until certain ages in young children

*anterior fontanelle

*posterior fontanelle

Front 29

Fontanelles

Back 29

-at points where more than two bones meet

-sutures are wide

-growth areas of the skull that are present since before birth up until certain ages in young children

*anterior fontanelle

*posterior fontanelle

Front 30

Anterior fontanelles

Back 30

Junction between two parietal and two frontal bones

-closes by 18 months of age

Front 31

Posterior fontanelle

Back 31

Junction of two parietal bones and two occipital bones

-close 1-2 months of age

Front 32

sphenoidal fontanelle (also known as the anterolateral fontanelle)

Back 32

-closes two and three months -called pterion

-It is located at the junction of the sphenoid, parietal, temporal, and frontal bones.

Front 33

mastoid fontanelle/ asterion fontane

Back 33

located at the junciton of the temporal, occipital, and parietal bones.

Front 34

Facts

Back 34

*bones of the vault continues to grow after birth because the brain grows

*some sutures remain open until adulthood

Front 35

sphenoidal fontanelle (also known as the anterolateral fontanelle)

Back 35

-closes two and three months -called pterion

-It is located at the junction of the sphenoid, parietal, temporal, and frontal bones.

Front 36

mastoid fontanelle/ asterion fontane

Back 36

located at the junciton of the temporal, occipital, and parietal bones.

Front 37

Facts

Back 37

*bones of the vault continues to grow after birth because the brain grows

*some sutures remain open until adulthood

Front 38

Cartilaginous Neurocranium (Chondocranium)

Back 38

-made up of paraxial mesoderm and the cells of the neural crest

-Forms bone on the base of the skull

-initially consists if separate cartilages

-neural crest maintains the development of the prechordal neurocranium anterior to the sella turcica.

- paraxial mesoderm is responsible for the growth of the chordal neurocranium, behind the sella turcica.

The prechordal and chordal neurocranium

-mature into the ethmoid and sphenoid bones as well as the petrous and mastoid portion of the temporal bone and the occipital bone respectively.

- all ossify via endochondral means.

Front 39

Rostral to Sella turcica

Back 39

-lie in-front of rostral limit of the notochord which ends at the level if the pituitary gland in the center of sella turnica

- derived from neural crest

-form prechordal chondrocranium

Front 40

Posterior to Sella turcica

Back 40

-arise from occipital sclerotomes

- formed by paraxial mesoderm

- form the chordal chondrocranium

Front 41

Sella turcica

Back 41

-landmark between prechordal and chordal chondrocranium

-depression in the sphenoid bone containing the pituitary gland

-the base of the skull is formed when cartilages fuse and ossify by endochondral ossification