development of the Back

skull

axial

scapula

appendicular

arm bones

appendicular

ribs

axial

coccyx

axial

pelvic girdle

appendicular

os coxae

appendicular (hips)

sternum

axial

verterbral column

axial

clavicle

appendicular

pectoral girdle

appendicular

Intervertebral disc is made of what

cartilage

msucles aroudn the verterbral column are called

Epaxial

muscles associated with the body wall

Hypaxial

are limb muscles hypxaial or epaxial?

hypxaial

the paraxial mesoderm gives rise to what 3 things?

dermatomes give rise to

dermis of skin

when do somites start forming?

end of third week

part of the notochord persists to form a part of the intervertebral disc called the —

nucleus pulposus

a specialized region of mesoderm that marks the cranial end of the embryonic axis.

the prechordal plate

The prechordal plate acts as an—

anterior signalling centre

The prechordal plate helps pattern the — and —

developing forebrain

and overlying neural plate.

the notochord acts as a Signalling centre – it releases morphogens (e.g., —

Sonic hedgehog

what does Sonic hedgehog help do?

pattern surrounding tissues, including the neural plate and the paraxial mesoderm, helping establish somite formation

As development proceeds, the primitive streak regresses in what direction?

caudally

The primitive streak also functions as a signaling center, secreting — and —

FGFs and Wnt proteins.

what activates the segmentation clock?

When the streak has regressed sufficiently, cranial mesoderm cells encounter a sufficiently low concentration of “caudal morphogens”(??)

The first — pairs of somitomeres do not go on to form somites

seven

The first seven pairs instead contribute to the development of —

skeletal muscle of the head instead of the trunk

somitomeres have what kind of cells?

compact mesenechymal cells

what happens to the cells in the somitomeres?

undergo a mesenchymal-to epithelial transition

once they have undergone the MET, what happens now?

the epithelial-like cells organize around a central cavity called the somitocoele

First pair of somites appears ~embryonic day 20 in the—region.

occipital

Somite pairs appear sequentially at a rate of —

~3 pairs per day.

A total of ~ — somite pairs form in humans

~42-45

The final number is reduced to ~—somite pairs, with the last few pairs disappearing to correspond to the segmentation of the adult vertebral column

38

Somite period ends ~ day X

30

how many occipital somites?

5

how many cervical somites?

7

how many thoracic somites?

12

how many lumbar somites?

5

how many sacral somites?

5

how many coccygeal somites?

4

Somites are most prominent during week - and -

4 and 5.

what carnegie stage do we stop using somites?

14 (13 is the last one to include it)

Wave 1 (early): Somite differentiation makes 2 fates

Wave 2 (late)

which part of the somite becomes sclerotome?

ventral part

which part of the somite becomes dermamyotome?

dorsal

process of Differentiation of Somites begins when?

in week 4

what kind of signals specify the dermomyotome fate

Wnt

where do these wnt signals come from?

dorsal neural tube and ectoderm

what signal helps maintain the dermomyotome fate and inhibit premature differentiation

BMP signlas

where are those BMp signals coming from?

the lateral plate mesoderm

what signal makes sclerotome?

sonic hedgehog

where does teh SHH come from?

from the notochord and the floor plate of the neural tube

how is the “dorsal fate” of the sclerotome inhibited?

Noggin from the notochord and floor plate inhibits BMP signalling

what weird thing do scleorotome cells do?

undergo an epithelial-to mesenchymal transition, and migrate medially

sclerotome cells express sclerotome-specific markers: called — and —

Pax 1 and Pax9.

when is the somatocoele lost?

when they do the EMT

As the sclerotome cells move medially, they form what shape around the notochord and neural tube?

triangular mass

Dorsal Sclerotome will form the

neural arch of the vertebrae and spinal meninges

which scleorotome surrounds the notochord?

ventral and central???

forms the vertebral bodies of the vertebrae

Ventral and Central Sclerotome

Lateral Sclerotome forms what 3 things

• costal processes

• transverse process

• ribs

Vertebral Body derived from

ventral sclerotome

whats the blue thing called?

vertebral foramen

whats the green thing called?

Vertebral or Neural Arch

Vertebral or Neural Arch derived from what?

dorsal sclerotome

Anulus Fibrosis derived from

ventral sclerotome

Each sclerotome segregates into cranial and caudal halves, in a process referred to as—

resegmentation.

Cranial segment = — packed cells

loosely

Caudal segment = — packed cells

densely

The caudal half of one sclerotome fuses with the cranial half of the adjacent sclerotome to form a —

vertebra

The caudal half of one sclerotome fuses with the cranial half of the adjacent sclerotome to form a vertebra during the — week.

5th (they are still mesenchymal at this time)

Chondrification centres form during the —week

6th

how many chondrification centres form within the centrum?

2

Ossification centres start to form during the— week.

7th

Ossification begins in the —

centrum.

Ossification of the neural arches begins in the—week

8th

Ossification is complete by ~—years of age

25

A failure of one of the chondrification centers to form in the centrum

Hemivertebra (scoliosis!!!) leads to a curve in the spine

The dermomyotome gets subdivided into 3:

which sections migrate and form the myotome?

dorsal medial lip (DML) and ventral lateral lip (VLL)

what forms the dermatome?

central dermatome (cDM)

The dorsal neural tube secretes -

neurotrophin 3 (NT-3

NT3 induces the expression of — in the central dermatome (cDM) specifying the dermatome fate

Pax 3

The dermatome cells undergo an —transition and spread beneath the ectoderm to form the — of the back .

epithelial-to - mesenchymal

dermis

Prior to formation of the myotome, around how many cells migrate to the limb bud?

30-100

which cells migrate to the limb bud?

the ones in the ventral lateral lip (most laterla ones, it makes sense)

ventral lateral lip (VLL) migrate to the limb bud where they will contribute to — of the limb

skeletal muscles

Dorsal medial lip make what?

epaxial msucles of the back cayuse they are closest to the vertebra so it makes sense

the dorsal medial lip expresses an epaxial specific muscle marker called-

MYF5

what induces the cells to express MYF5?

SHH (notochord and floor plate) and WNTs (dorsal neural tube and overlying ectoderm)

VLL expresses a hypaxial specific muscle marker, called —

MYO-D

what causes them to express MYO-D?

WNTs (dorsal neural tube and overlying ectoderm) and BMPs (lateral plate mesoderm),

Ventral lateral Lip will make

hypaxial msucles of the trunk