1. vertebral column - evolution and development Flashcards
chordates
have a notochrod at some stage
vertebrates
column develops in response to notochord signals
- notochrod exists before vertebral column
- most chordates dont have a vertebral column
neotony
evolutionary process where juvenile characteristics are retained in the adult and passed on
3 step process of vertebral development
- mesenchymatous
- cartilagenous
- osseus
mesenchymatous stage
undifferentiated mesoderm sclerotome cells of somites migrate to form: 1. perinotochordal sheath 2. neural arch 3. costal element
body wall vessels from the aorta form
between the somites
why do body wall vessels foorm between the somites
tissue is less dense there
when does mesenchymatous stage occur
4-6 weeks
vertebrae from in line with
the gap between 2 adjacent somites
perinotochordal cells near body wall vessels
have better nutrition
- grow larger and will become cartilage (vertebral bodies)
- vertebral bodies form in line with the gap between adjacent somites
- each vertebra is formed from part of 2 adjacent somites = intersegmental
1 invertebral muscle is from
1 somite
why are vetebral bodies called intersegmental
because they form inbetween somites
notochord once vertebral bodies are formed
squeezed into areas between vertebral bodies - intervertebral disks
when does cartilagenous stage occur
6-9 weeks
cartilagenous stage
centres of chrondrification
- centrum
- neural arches
- costal
annulus fibrosis
fibrocartilage that forms in circles arund the notochrodal remnant
notochordal remnant
nucleus pulposus
what happens when cartilage centres fail to form
doesnt stop the other sde from forming
causes vetebral asymmetry - hemivertebrae
can cause structural scoliosis
when does osseous stage occur
8-10 weeks
primary centres of ossification appear
centrum - unparied
neural arches
costal
primary ossification centre in the centrum is
unpaired
cartlage growth plates dont ossify until
6-8 years
costal centres either
fuse with the rest of the vertebra or become ribs and develop joints (thorax only)
what happens if there arent enough notochordal cells
block vertebra - too few notochrodal cells remaining, therefore there is not enough intervertebral disk
failure of segmentation
vertebra form together - may not happen simetrically, can cause formation of scoliosis
what happens when there is too many notochrodal cells
butterfly vertebra
too many notochordal cells remain
notochord seems to inhibit bone
failure of formation - middle of the vertebral body is much thinner
vertebral elements
- centrum element
- neural arch element
- costal element
centrum element
central portion of vertebral bodies
does not make the whole vertebral body
neural arch element
dorsal arch surrounds spinal cord
zygapophyseal joints, mammillary processes
contributes to lateral aspect of vertebral body
costal element
forms ribs of the thorax, but in different regions it forms different features of respective vertebra
not the gap between the costal and neural elements
hox genes control
body segment features
growth of the vertebral column by 6-8 years
the growth plates close, but the VB endplates and processes are still in cartilage ie. can still grow taller
endplate
where vertebral bodies meet intervertebral discs
growth of the vertebral column at puberty
secondary centres of ossification appear
- spinous process
- transverse process
- ring apophysis
processes continue to grow larger
VBodies can continue to grow taller due to the ring epiphysis
all epiphysis close at
adulthood
growht can only continue by surface remodelling (impacts surface area, not height)
3 steps of the vertebral development process
- mesenchymatous
- cartilagenous
- osseus
mesenchyme is
undifferentiated mesoderm
vertebral colum is developed from
sclerotome cells of somites
sclerotomal cells of ssomites migrate to form
perinotochordal sheath
neural arch
costal element
sclerotomal cells of somites migrate in which stage
mesenchymatous stage
which cells are nearest to body wall vessels from the aorta in mesenchymatous stage
perinotochordal cells
have better nutrition because of this
why are vertebral bodies called intersegmental
because they are formed from part of 2 adjacent somites
why are myotomes segmental
1 intervertebral muscle is from 1 somite
resegmentation
an entire somite splits
to explain how one vertebral body s formed by 2 somites
mesenchyme is gradually replaced by
hyaline cartilage
z-joints
zygapophyseal joints
connect neural arches to each other from one vertebra to the next
does the centrum element make the whole vertebral body
no-the lateral portion is made by the nueral arch element
mammillary process
tiny bump next to the z joint
mammillary processes are from
neural arch elements
in the thoracic, the transverse process is from
neural arch elements
in the cervical, sacral and lumbar the transverse process is from
costal elements
end plate is where
vertebral body meets the intervertebral disks
what allow us to grow in height
secondary ossification centres
- spinous process
- transverse process
- ring apophysis
