Embryological Development of the Spine

Question 1

What are the three main structures of embryological development of the spine?

Answer 1

Notochord
Somites
Sclerotomes

Question 2

What is the purpose of the notochord?

Answer 2

Creates the axial support structure - first body framework to appear in human embryo

Question 3

What does the notochord transition into once it’s served its purpose?

Answer 3

Nucleus pulposus of the intervertebral discs

Question 4

On what day does the notochord appear?

Answer 4

18th day of development

Question 5

From what is the notochord derived?

Answer 5

The mesoderm

Question 6

Describe the position of the notochord within the embryo

Answer 6

Runs midline between the neural tube and the primitive gut, extending from the skull to the coccyx

Question 7

What are the three basic embryonic tissues?

Answer 7

Ectoderm
Mesoderm
Endoderm

Question 8

What does the ectoderm become?

Answer 8

Skin

Question 9

What does the endoderm become?

Answer 9

Gastrointestinal tract

Question 10

What are somites made of?

Answer 10

Mesoderm

Question 11

Where are the somites during development?

Answer 11

Paired on either side of the neural tube

Question 12

Generally how many pairs of somites are there?

Answer 12

42-44

Question 13

How many somite pairs for occiput?

Answer 13

4

Question 14

How many somite pairs for cervical?

Answer 14

8

Question 15

How many somite pairs for coccyx?

Answer 15

8-10

Question 16

What is special about the somites for the coccyx?

Answer 16

Most fail to develop - leaving 3-5 segments

Question 17

Into what three parts do somites differentiate?

Answer 17

Sclerotomes
Myotomes
Dermatomes

Question 18

Define dermatomes

Answer 18

A specific area of skin innervated by a single spinal nerve root

Question 19

What do sclerotomes become?

Answer 19

Vertebrae and ribs

Question 20

True or false: sclerotomes are made from mesenchymal tissue

Answer 20

True

Question 21

Describe the transition from segmental vertebra to intersegmental vertebra.

Answer 21

Sclerotomes proliferate from the right and left to surround the notochord.
They again proliferate on the caudal end of the segment.
Splitting into caudal and cephalad portions, the caudal segment drops to join the cephalad segment below.

Question 22

What is the importance of intersegmental vertebra?

Answer 22

Muscles attach to two spinal levels
Nerves exit between two segments
Intersegmental artery now at the level of vertebrae

Question 23

Describe the three directions of intersegmental sclerotome growth

Answer 23

Medial surrounds the notochord - forms the membranous VB
Dorsal - surrounds the neural tube - forms the posterior arch
Anterolateral - space btwn myotomes - forms costal processes (TPs and ribs)

Question 24

What is anulus fibrosis?

Answer 24

The result of growth of mesenchyme - outer disc fibers

Question 25

In what week do the chondrificiation centers appear?

Answer 25

Week 7

Question 26

How many chondrification centers appear and in what week?

Answer 26

4 chondrification centers appear in week 7

Question 27

What is synchondrosis?

Answer 27

The unfused joint between VB and posterior arch before ossification occurs

Question 28

What are the first chondrification centers to form?

Answer 28

2 for the vertebral body and 2 for the posterior arch

Question 29

What is ossification of cartilaginous vertebrae?

Answer 29

Replacement of cartilage with bone

Question 30

What is another term for ossification?

Answer 30

Mineralization

Question 31

At what week does ossification begin?

Answer 31

Week 9

Question 32

How many primary ossification centers are there? Name them

Answer 32

3 primary ossification centers Vertebral body Right and left portion of posterior arch

Question 33

In what region of the spine does ossification begin?

Answer 33

Thoracolumbar region and spreads

Question 34

Primary ossification for cervical spine is at what year?

Answer 34

3 years

Question 35

Primary ossification for lumbar spine is at what year?

Answer 35

6 years

Question 36

How many secondary ossification centers are there?

Answer 36

9 secondary ossification centers

Question 37

What are the secondary ossification centers?

Answer 37

(1) for epiphyseal plate on cranial surface of segment (1) for epiphyseal plate on caudal surface of segment (2) for superior articular processes (2) for inferior articular processes (2) for transverse processes (1) for spinous process

Question 38

Which ossification centers appear last and when?

Answer 38

Superior and Inferior endplates - 17 years

Question 39

By what age do all centers fuse?

Answer 39

25 years

Question 40

List 4 congenital anomolies of vertebra

Answer 40

Hemivertebra Block vertebra Spina bifida occulta Butterfly Vertebra

Question 41

Describe block vertebrae

Answer 41

The result of intersegmental vertebra not dividing properly (congenital nonsegmentation)

Question 42

Describe spina bifida occulta

Answer 42

Posterior arch does not unite (occulta is the congenital anomaly)

Question 43

Describe butterfly vertebrae

Answer 43

Cleft left in the vertebra by a notochord not fully receding

Question 44

Describe hemivertebrae

Answer 44

Lack of formation of one half of a vertebral body - results in one half less vert or one half more vert - forms wedge