Embryological Development of the Spine Flashcards

1
Q

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

A

Notochord
Somites
Sclerotomes

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2
Q

What is the purpose of the notochord?

A

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

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3
Q

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

A

Nucleus pulposus of the intervertebral discs

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4
Q

On what day does the notochord appear?

A

18th day of development

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5
Q

From what is the notochord derived?

A

The mesoderm

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6
Q

Describe the position of the notochord within the embryo

A

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

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7
Q

What are the three basic embryonic tissues?

A

Ectoderm
Mesoderm
Endoderm

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8
Q

What does the ectoderm become?

A

Skin

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9
Q

What does the endoderm become?

A

Gastrointestinal tract

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10
Q

What are somites made of?

A

Mesoderm

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11
Q

Where are the somites during development?

A

Paired on either side of the neural tube

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12
Q

Generally how many pairs of somites are there?

A

42-44

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13
Q

How many somite pairs for occiput?

A

4

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14
Q

How many somite pairs for cervical?

A

8

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15
Q

How many somite pairs for coccyx?

A

8-10

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16
Q

What is special about the somites for the coccyx?

A

Most fail to develop - leaving 3-5 segments

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17
Q

Into what three parts do somites differentiate?

A

Sclerotomes
Myotomes
Dermatomes

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18
Q

Define dermatomes

A

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

19
Q

What do sclerotomes become?

A

Vertebrae and ribs

20
Q

True or false: sclerotomes are made from mesenchymal tissue

A

True

21
Q

Describe the transition from segmental vertebra to intersegmental vertebra.

A

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.

22
Q

What is the importance of intersegmental vertebra?

A

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

23
Q

Describe the three directions of intersegmental sclerotome growth

A

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)

24
Q

What is anulus fibrosis?

A

The result of growth of mesenchyme - outer disc fibers

25
Q

In what week do the chondrificiation centers appear?

A

Week 7

26
Q

How many chondrification centers appear and in what week?

A

4 chondrification centers appear in week 7

27
Q

What is synchondrosis?

A

The unfused joint between VB and posterior arch before ossification occurs

28
Q

What are the first chondrification centers to form?

A

2 for the vertebral body and 2 for the posterior arch

29
Q

What is ossification of cartilaginous vertebrae?

A

Replacement of cartilage with bone

30
Q

What is another term for ossification?

A

Mineralization

31
Q

At what week does ossification begin?

A

Week 9

32
Q

How many primary ossification centers are there? Name them

A

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

33
Q

In what region of the spine does ossification begin?

A

Thoracolumbar region and spreads

34
Q

Primary ossification for cervical spine is at what year?

A

3 years

35
Q

Primary ossification for lumbar spine is at what year?

A

6 years

36
Q

How many secondary ossification centers are there?

A

9 secondary ossification centers

37
Q

What are the secondary ossification centers?

A

(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

38
Q

Which ossification centers appear last and when?

A

Superior and Inferior endplates - 17 years

39
Q

By what age do all centers fuse?

A

25 years

40
Q

List 4 congenital anomolies of vertebra

A

Hemivertebra
Block vertebra
Spina bifida occulta
Butterfly Vertebra

41
Q

Describe block vertebrae

A

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

42
Q

Describe spina bifida occulta

A

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

43
Q

Describe butterfly vertebrae

A

Cleft left in the vertebra by a notochord not fully receding

44
Q

Describe hemivertebrae

A

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