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
What is ossification of the neural arches in the lower cervical and upper thoracic regions initiated in response to?
The ossification of the lower cervical and upper thoracic neural arches begins in the 2nd foetal month and is initiated by the gasp reflex - it is the muscles that contract during the gasp reflex that initiate this ossification
By the 3rd fetal month, a second group of ossification centres appear where? What are these groups of ossification centres initiated in response?
By the 3rd foetal month a second group of ossification centres appears in the lower thoracic and upper lumbar regions Ossification in these regions is initiated due to muscle contraction bringing about lower limb movement
When does the neural arch fusion commence and where in the vertebra does it commence?
Neural arch fusion commences during the first year posteriorly at the spinous process
When does the neural arch fusion commence, where in the vertebra does it commence and where in the vertebral column does it begin?
Neural arch fusion commences during the first year of life posteriorly at the spinous processes It begins in the lower thoracic and upper lumbar regions in the latter part of the first year before progressing systematically in a cranial and caudal direction
When may cervical and lumbar arches not fuse by?
Cervical arches may not fuse until the beginning of the 2nd year Lowest Lumbar arches may not fuse until the end of the fifth year
Neural arch fusion - begins posteriorly at the spinous processes in the lower thoracic and upper lumbar regions in the first year * Cervical arches may not fuse until the beginning of the 2nd year * Lowest lumbar arches may not fuse until the end of the fifth year What can be expected with regards to neural arch fusion in individuals below 6 years old? What is the fusion of the neural arches posteriorly known as?
Therefore in any individual <6 years old, some degree of non-fusion of the arches can be expected Fusion of the neural arches posteriorly is known as a synchondrosis
We have talked about ossification of the centra and neural arches and talked about neural arch fusion LETS NOW TALK ABOUT NEUROCENTRAL FUSION Where does the fusion between the neural arches and the centra occur? and at what age?
Fusion of the neural arches and the centra occurs ventral to the pedicles at the neurocentral junction between 2 and 5 years
What is the adult vertebral body formed from? What components of the juvenile vertebrae does the head of the rib articulate with?
The adult vertebral body is formed from the centrum and the boutons of the pedicles The head of the rib only ever articulates with the boutons of the pedicles and never the centrum
Evidence of the neurocentral junction is maintained throughout life The neurocentral fusion in the spinal column doesnt occur systematically What order does neurocentral fusion occur in?
Neurocentral fusion occurs initially in the lumbar region and then the cervical region with the thoracic vertebrae being the last to fuse
OSSIFICATION OF CENTRA / NEURAL ARCHES AND NEURAL ARCH / NEUROCENTRAL FUSION SUMMARY * Where does ossification of the centrum begin and when? Where has it reached by 3 and 4 months? * Where does ossification of the neurala rches begin and when? Where is it by 3rd foetal month? * Where does neural arch fusion begin and when? * Where does neurocentral fusion occur and when?
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What is the difference between Bagnall vs Traditional theory for neural arch ossification?
Bagnall theory suggests neural arch ossification begins in the 2nd month of foetal life in the lower cervical and upper thoracic vertebrae in response to muscle contraction during the gasp reflex. Second primary ossification centres then appear by 3months in the lower thoracic and upper lumbar regions in response to muscle contraction bringing about lower limb movement.
Traditional theory suggest neural arch ossification begins in the lower cervical vertebrae in the 2nd month of foetal life then proceeds in bidirectional progression. There are no second primary ossification centres.
