Embryology Spine Flashcards
What are the derivates of the proatlas ?
- Caudal part of basiocciput and basion (clivus)
- Clival tubercle
- Apical dens
- Exocciput (occipital condyles and opisthion)
Which structure attaches at the clival tubercle?
Fibrous pharyngeal raphe
What is the condylus tertius?
Third condyle , rare anatomic variant. Small seperate ossicle formed by failure of the embryonic proatlas to unite with the condyle proper
what is the severance line?
Junction between the head and spine which follows and intersomitic, not an interscerotomic boundary
What are the derivatives of C1 sclerotome?
1.Anterior arch of atlas
2. Basal dens
3. lateral masses and posterior arch of atlas
The whole atlantal ring derives from C1 sclerotome
What are the derivatives of C2 sclerotome?
- Body of axis
2. Lateral and posterior elements of C2
Names of synchondrosis in the axis (C2)
How many vertebral bodies in Axis?
Apicodental synchondrosis
Subdental synchondrosis
2.5 vertebral bodies
What is gastrulation and which week?
Conversion of the bilaminar disk to a trilaminar arrangement and establishment of the notochord
Weeks 2bilaminar - 3 laminar
Structures of the bilaminar disk?
Epiblast (faces amniotic sac)
Hypoblast (primitive endoderm) faces yolk sac
What is the thickening in the middle of the epiblast called on day 16?
Primitive streak (Blastopore)
What structure is on the rostrar part of the primitive streak?
The primitive pit (Hensen’s node) the organizer
Describe gastrulation
Epiblastic cells migrate through the primitive streak to the epi-endoblast interface to form mesodermal and endodermal progenitors
How is notochord made?
Epiblastic cells that migrate through Hensen’s node produce the notochord
What is the main purpose of the notochord ?
Development of the neuroectoderm (neural plate)
What is debated in humans?
The existence of a neurenteric canal in the formation of notochord. Disputed in humans
What is the most common tumour in embryo?
Sarco-coccygeal teratoma due to persistence of cells in the primitive streak which moves caudally in the embryo
Most rostral point of the neural tube?
The lamina terminalis
When does the anterior neuropore closes?
30 days
When is the end of the primary neurulation?
The closure of the posterior neuropore at 31 days
Products of the secondary neurulation?
Terminal ventricle, Tip of conus medullaris and filum terminale
Describe secondary neurulation and weeks
Caudal cell mass that canalises and connects to the primary neural tube
4-6 weeks
What is the border of the secondary neural tube?
approx 32 somite
Where does junctional neurulation happen and what is the ‘danger’?
It happens in the posterior neuropore.
Αντί το neural plate να κάνει το neural tube, εκεί έρχονται κι αλλα κυτταρα γίνονται layers φτιάχνουν τον σωλήνα οπότε high incidence of spinal dysraphisms
what does the hypochordal bow of the pro-atlas form?
The clival tubercle
What does the hypochordal bow of the C1 sclerotome form?
The anterior arch of C1
What happens in the primary neurulation?
Neural plate cells proliferate, invaginate and pinch off the surface ectoderm to form the neural tube
Origin of somites and divisions?
Paraxial Mesoderm
4 Occipital 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 3-6 Coccygeal
Resegmented sclerotome description
Upper Ad + Lower Al = Vertebral body (from two somites!)
Upper Ld = neural arch and pedicle
Lower Lloose= nerve roots
what does the intervertebral boundary zone do?
Makes Intervertebral disc.
Annulus + Notochord = nucleus palposus
What is weird about the CCJ?
4 occipital somites
and first 3 cervical somites
No intersomitic boundary zone
No segmentation of the first 3 occipital axial sclerotomes
