Embryology of the Spine (Quiz 1)

Question 1

What are the 7 major stages of development?

Answer 1

1) fertilization (DNA of sperm unites with DNA of ovum)
2) Bilaminar disc (epiblast and hypoblast)
3) Gastrulation (formation of 3 germ layers)
4) Notochord (primordial axial support)
5) Neurulation (formation of brain and spinal cord)
6) Development of vertebrae (sclerotome)
7) Development of Matter (neuroblast to neurons)

Question 2

What week of development does gastrulation occur?

Answer 2

3rd week

Question 3

What happens during gastrulation?

Answer 3

-transforms a bilaminar disc into a trilaminar disc
-establishes the 3 primary germ layers
-begins with the formation of the primitive streak

Question 4

At the beginning of the 3rd week of development, the primitive streak appears as a localized thickening on the dorsal surface of the epiblast layer of the bilaminar disc at the caudal end. What does the primitive streak do?

Answer 4

-establishes the major body axis of the embryo (cranial end from caudal end and L/R sides)
-elongates towards the cephalic/cranial end
-forms circular depression at the cephalic end called the primitive node

Question 5

What happens during the invagination stage of development?

Answer 5

-migration of detached epiblast cells through the primitive streak into the median plane initiating the formation of the 3 primary germ layers
-once invaginated, some of the epiblast cells displaces the hypoblast layer to form the endoderm layer and some form a new layer between the epiblast and newly formed endoderm called the mesoderm layer and once the endoderm and mesoderm layers are formed, the remaining epiblast layer becomes the ectoderm layer
-epiblasts give rise to all 3 germ layers of the embryo

Question 6

What gives rise to all 3 germ layers of the embryo?

Answer 6

epiblast

Question 7

The ectoderm gives rise to what?

Answer 7

-epidermis of the skin, hair, and nails
-brain and spinal cord (neuroepithelium)
-neural crest cells (neuroectoderm)

Question 8

What does the endoderm give rise to?

Answer 8

epithelial lining of
-digestive
-respiratory
-vascular
-urogenital system and associated glands

Question 9

What does the mesoderm give rise to?

Answer 9

all other structures not formed by the ectoderm and endoderm, but mainly the notochord and somites

Question 10

How does the notochord form?

Answer 10

-mesodermal cells aggregate beneath primitive streak forming the notochord
-the notochord is the first primordial axial support of the embryo around which the vertebral bodies form
-the notochord becomes the nucleus pulposus of the IVD

Question 11

What week does neurulation begin?

Answer 11

week 3 (same as gastrulation)

Question 12

What happens during neurulation?

Answer 12

-differentiation of ectoderm into neuroectoderm then the neural tube
-forms brain and spinal cord
-initiated by chemical signals from the notochord
-ectoderm cells immediately above the notochord thicken forming the neural plate (which gives rise to the brain and spinal cord)

Question 13

Neural plate cells differentiates into the…

Answer 13

neuroectoderm

Question 14

Cells at the lateral margins of the neural plate become….

Answer 14

neural crest cells

Question 15

A neural groove forms along the length of the neural plate with folds on each side. The groove deepens and the folds close over it forming the….

Answer 15

neural tube (the primordium of the brain and spinal cord)

Question 16

As the neural folds close, neural crest cells detach between the surface ectoderm and developing neural tube. What does this give rise to?

Answer 16

PNS, specifically the DRG and the sympathetic ganglion chain

Question 17

How does the neural tube form?

Answer 17

-fusion of neural tubes begins in the cervical region and proceeds cranially and caudally
-cranial/rostral neuropore closes around day 25
-posterior/caudate neuropore closes around day 28
-neurlation is complete when the caudate neuropore closes

Question 18

The cranial/rostral end of the neural tube becomes the _______ and the remainder of the neural tube forms the ____________

Answer 18

brain, spinal cord

Question 19

At the end of neurulation, the cephalic/rostral end of the neural tube will have 3 dilations known as the primary brain vesicles. What are these 3 vesicles?

Answer 19

1) proencephalon (forebrain)
2) mesencephalon (midbrain)
3) rhombencephalon (hindbrain)

Question 20

During the 3rd week of development, mesoderm lateral to the notochord is paraxial mesoderm, which begins to organize into blocks of cells called….

Answer 20

somites

Question 21

Once somites are established along the length of the neural tube, they differentiate into 3 main components. What are they?

Answer 21

1) sclerotome
2) myotome
3) dermatome

Question 22

What does sclerotome differentiate into?

Answer 22

vertebrae and ribs

Question 23

What does myotome differentiate into?

Answer 23

mostly skeletal muscle (some head and neck muscles are derived from the pharyngeal arch)

Question 24

What does dermatome differentiate into?

Answer 24

dermis of the skin

Question 25

Sclerotome cells surrounding the notochord form the vertebral bodies called ___________ in the embryo

Answer 25

centrum

note: around the same time the sclerotome are forming primordial vertebrae, spinal nerves are emerging from the neural tube

Question 26

Sclerotome cells surrounding the neural tube form the vertebral arches called __________ arch in the embryo

Answer 26

neural

Question 27

After the neural tube closes, neuroectoderm differentiates into….

Answer 27

neuroepithelial tissue layer

Question 28

Neuroepithelial cells/tissue gives rise to….

Answer 28

neuroblast cells

Question 29

Neuroblast cells become…

Answer 29

neurons (cell bodies)

Question 30

Clusters of neuroblast cells form….

Answer 30

gray matter

Question 31

Cytoplasmic processes emerging from neuroblast become axons and dendrites. The axon cytoplasmic processes are covered with __________ to form _______ matter of spinal cord

Answer 31

myelin, white

Question 32

By the 6th week of development, the spinal cord has 2 clusters of gray matter formed by _________ cells

Answer 32

neuroblast

Question 33

Alar plate cell bodies become what neurons?

Answer 33

interneurons

Question 34

basal plate cell bodies become what neurons?

Answer 34

motor neurons

Question 35

Bundles of ________ neuron cell bodies in the basal plate give rise to axons. _________ axons exit the basal plate and spinal cord and form the ventral root of a spinal nerve

Answer 35

motor, Motor

Question 36

Bundles of ___________ neuron cell bodies in the dorsal root ganglia give rise to axons. _________ axons merge into the spinal cord to connect with interneuron cell bodies in the alar plate and form the dorsal nerve root of a spinal nerve.

Answer 36

sensory, Sensory

Question 37

Primordial motor and sensory axons form primordial ventral and dorsal nerve roots respectively that join proximal to the ______ to form a primordial spinal nerve

Answer 37

IVF

Question 38

Newly formed spinal nerves migrate out from the neural tube. Their goal is to connect with…..

Answer 38

paraxial myotomes and dermatomes

Question 39

Newly formed spinal nerves migrate out from the neural tube. Their goal is to connect with paraxial myotomes and dermatomes. This migration cuts through the sclerotomes, segmenting the sclerotome into a rostral portion and a caudal portion, initiating a process called…

Answer 39

resegmentation

Question 40

Resegmentation occurs when the caudal half of a sclerotome fuses with the cephalic/rostral half of the adjacent sclerotome. Once the 2 sclerotome halves fuse together, they form a…..

Answer 40

precartilaginous vertebrae

Question 41

How are IVDs formed?

Answer 41

-mesenchymal cells begin to condense around the notochord
-space created by segementation and then resegmentation becomes the IVD