V.C - A - Development (1) - Curvatures/Pathology, - Primary Ossification Centra/Neural Arches/Neural Arch&Central Fusion Flashcards
The adult vertebrae consists of 33 vertebrae 24 of these vertebrae are presacral and known as true 9 are sacral/coccygeal and are known as false What does it mean by having true and false vertebra?
24 presacral vertebrae * 7 cervical * 12 thoracic * 5 lumbar
- These are true vertebrae as they are single entities and not fused
9 sacral/coccygeal vertebrae * 5 sacral * 4 coccygeal
- These are false vertebra as they have fused together

In the early embryo, what is the primary curvature of the spine described as?
The primary curvature of the back is described as being a concave curvature of the spine

The curved segments of the spine act like independent strings conferring flexibility and and resilience to the structure as a whole What are the primary and secondary curves of the adult spine?
Remember the primary curvature of the early embryo is a concave curve anterioly Primary curvature - concave anteriorly * Thoracic and sacral/coccygeal curvature Secondary curvature - convex anteriorly * Cervical & lumbar curvature

In the fetus, the vertebral column is āCā shaped - a single primary curvature The thoracic and the sacrococcygeal primary curvatures are established in fetal development When do the cervical and lumbar secondary curvatures develop?

The cervical and lumbar secondary curvatures develop after childbirth during infancy with the cervical being the first of the two to develop
At what ages do the cervical and lumbar secondary curvatures develop and what milestone is reached by the child?
At 2-3 months when a child can independently hold head up a compensatory secondary curvature develops in cervical region At 6-8 months when a child sits unaided a further compensatory secondary curvature develops in the lumbar region
Primary curvatures are maintained through the shape of the vertebrae Why do secondary curvatures of the spine arise? What happens to the spinal curvature in the elderly?
Secondary curvatures arise due to modification in shape of the intervertebral discs - there is a difference in thickness of anterior and posterior parts of the disc
In the elderly, the degeneration of the discs begins to occur resulting in a return to a more pronounced primary curvature

Lordosis in the human spine makes it easier for humans to bring the bulk of their mass over the pelvis. This allows for a much more efficient walking gait than that of other primates, whose inflexible spines cause them to resort to an inefficient forward leaning ābent-knee, bent-waistā gait. Describe each of the three pathological vertebral curvatures? * Kyphosis * Lordosis * Scoloisos
Kyphosis - this is an exaggeration of the primary curvature (thoracic or sacral/coccygeal) - known as a hunchback deformity Lordosis - exaggeration of the secondary curvature (cervical or lumbar) - known as a swayback deformity Scoliosis - this is where there is a lateral deviation of the spine greater than 10 degrees from the midline
What is a lordosis (swayback deformity) of the spine often associated with? What is scoliosis of the spine often accompanied by? It can be congenital, idiopathic or secondary to a primary condition eg?
Lordosis is often associated with pregnancy and a forward pelvic tilit Scoliosis is often accompanied by rotational defect Can often be secondary to a primary neuromuscular condition

The terminology used for the juvenile vertebrae is slightly different (perhaps slightly more confusing) than terminology used for the adult vertebrae What is the adult vertebral body derived from? (pic on left shows the adult vertebral body is more than just the big block)

The adult vertebral body is derived from the juvenile centrum PLUS a small portion of the neural arches - specifically the anterior parts of the neural arches known as boutons
In developmental terms it is incorrect to use the term āvertebral bodyā as the term ācentrumā is more appropriate

The juvenile vertebrae is formed form three different parts which form independent ossification centres What are these three parts known as?
The left half or the neural arch The right half of the neural arch The juvenile centrum
As said, the three parts of the juvenile vertebrae are the left and right half of the neural arch and the centrum and these form independent ossification centres One in each part LETS TALK ABOUT THE OSSIFICATION CENTRES REGARDING THE CENTRA FOR THE NEXT FEW FLASHCARDS Where is ossification of the centra initiated?
The ossification of the vertebrae is initiated just dorsal to the notochord
Notochord is the small white circle in the centra
The three black areas are the sights of ossification - remember it is the black circle next to the notochord which is the initial sight

What is the notochord? What does it arise from and what is it the precursor to?
The notochord is a flexible cartilaginous rod that supports the body by running vertically in the centrum It arises from mesoderm and is the precursor to the nucleus pulposus of the IV discs

As stated, ossification of the vertebral column is initiated posterior to the notochord (found in the juvenile centrum) What are the two types of ossification and which type occurs in the juvenile centrum?
Two types of ossificaiton
Intramembranous ossification - where ossification occurs from a mesenchymal membrane
Endochondral ossification - OCCURS IN CENTRA - distinguished from intramembranous due to the fact that cartilage is present during -
Flat bones eg skull & facial

Endochondral ossification- Mesochyme goes to cartilage, then the cartilage becomes ossifiied which then becomes bone. Cartilage is avascular- only survives by allowing diffusion of nutrients into its core. Bone requires blood vessels. When cartilage turns to bone- the cartilage blob gets bigger and bigger meaning the core of the cartilage Is further away from the nutrients that diffuse into it, therefore it starts to die How does the cartilage promote blood vessels attraction?
As the cartilage is avascular, it sends out angiogenic signals which attract the growth of blood vessels to keep the cartilage/bone alive -
Where does the endochondral ossification first appear in the vertebrae? Ie which vertebral levels and when does endochondral ossification first appear?
It first appears in the lower thoracic and upper lumbar vertebrae (T10-L1) between 9-10 foetal weeks
The initial endochondral ossification begins dorsal to the notochord in the lower thoracic and upper lumbar vertebrae. What direction does the ossificaiton then go onto continue?
The endochondral ossification has a bidrectional progession - ie it extends both cranially and caudally
Where does ossification reach cranially by the 4th month and caudally by the 3rd month?
Ossification reaches the C2 vertebral level cranially by the 4th month and reaches the L5 vertebral level caudally by the 3rd month
Endochondral ossification * Begins in T10-L1 vertebra * Reaches C2 vertebra by month 4 * Reaches L5 vertebra by month 3 What prevents the attraction of blood vessels to the notochord?
The notochord contains angiogenic inhibiting cells and hence prevents the attraction of blood vessels here but the rest of the vertebral centra is highly vascularised
Notochord cells contain angiogenic inhibiting factor which delays vascular penetration into this region Vertebral centra from first trimester display an axial avascular area around the notochord region What shape of ossification does this central avascular area result in?
This results in a ringed shaped area of ossification in the centra
The morphology and development of the juvenile centrum is heavily influenced by a profuse vascular supply What are the vessels supplying each of the three ossification centres?
Each of the ossification centres is supplied by paired nutrient arteries and an accompanying venous network

As said, the three parts of the juvenile vertebrae are the left and right half of the neural arch and the centrum and these form independent ossification centres One in each part WE HAVE TALKED ABOUT THE OSSIFICATION CENTRES REGARDING THE CENTRA, NOW LETS TALK ABOUT THE NEURAL ARCHES Where does ossification of the neural arches begin?
Ossification of each of the neural arches begins on the inner surface of each of the hemi-arches

Where is ossification initiated in the centra and the neural arches? It was stated that ossification of the centra is endochondral ossification What type of ossification takes place in the neural arches?
Ossification initiated: * Centra - dorsal to the notochord * Neural arches - on the inner surface of each hemi arch In the neural arches, intramembranous ossification takes place followed by endochondral ossification
In the centra, ossification first appears in the lower thoracic and upper lumbar regions (T10-L1) between 9-10 foetal weeks Where does ossification first appear for the neural arches and at what age of foetal development?
Neural arch ossification first appears in the lower cervical and upper thoracic regions in the 2nd foetal month and then subsequently spreads in upwards and downwards directions
WHat is the spread of ossification in the upwards and downwards direction for both ossification of the centra and neural arches known as?
This is known as bidrectional progression of ossification





