Embryology (Quiz 1/Test 1) Flashcards
What develops first in the spinal column?
trilaminar disc
What does ectoderm develop into?
outer skin/skin of organism
What does mesoderm develop into?
“middle skin” organs, bones, muscle
What does endoderm develop into?
“inner skin” internal linings
Spinal column develops from 3 prior structures. What are they?
1) notochord
2) somites
3) sclerotomes
What is another name for the notochord?
chorda dorsalis
Where is the notochord derived from?
embryonic mesoderm which is a primitive support structure of the axial skeleton
The notochord extends from the _____________ to ___________
sphenoid (base of skull), coccyx
Is the notochord a temporary or permanent structure?
temporary structure (later will be obliterated by the vertebral bodies and part of it persists as nucleus pulposus and apical ligament)
When is the notochord first recognizable?
Think days
day 18
In what direction/axis does the notochord develop?
cranial to caudal axis
What is another name for somites?
mesodermal segments
What are somites?
coronally-paired mesodermal cell masses
When do somites first appear?
week 4 (day 21/22)
Where do somites develop?
on left and right sides of organism and follow the axial gradient
What forms in the first segmentation?
-usually 38-39 pairs form:
>1 occipital pair
>7 cervical pairs
>12 thoracic pairs
>5 lumbar pairs
>5 sacral pairs
>8-9 coccygeal pairs
>3-5 form the coccyx
excess caudal pairs usually get reabsorbed by the embryo
____________________ produce the spinal column. They begin to divide transversely. The lower 1/2 fuses with the top 1/2 of the primary sclerotome below to form the secondary sclerotome. The IVD begins to form between them
primary sclerotomes
The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions. What are the 3 directions?
test q
1) medially
2) posteriorly
3) laterally
The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions. One of the directions is medially. What does this do and what does it form?
-invades and obliterates the notochord
-the L/R secondary sclerotomes fuse to form centra (centrum) of the vertebral bodies obliterating the notochord
The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions. One of the directions is posteriorly. What does this do and what does it form?
-they surround the developing spinal cord
-they form pedicles, laminae, and spinous processes
The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions. One of the directions is laterally. What does this do and what does it form?
they project to form the lamina/pedicle junction
The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions: medially, posteriorly, laterally. Invading mesenchyme cells forms the annulus fibrosus of IVDs. Encapsulated notochord becomes the….
nucleus pulposus
Where does chondrification/chondral/cartilaginous stage begin?
in distinct chondrification centers
What happens in the ossification stage/endochondral ossification?
cartilaginous model becomes mineralized/calcified/ossified
What are the 2 distinct types/stages of ossification?
test q
1) primary ossification (begins at birth and continuous through puberty)
2) secondary ossification (begins after birth and continues till 35-40 y/o)
Does primary ossification follow the axial gradient?
NO
Do all vertebrae have ossification centers?
YES
If primary ossification doesn’t follow the axial gradient then how does it work?
-primary ossification first appears in C1 by week 7
-2nd in the sacrum by week 10 (chondrification just completed)
-3rd in mid-thoracics by week 12, and then starts to go up/down
-C2 and L5 are the last to ossify
Where are primary ossification centers found?
test q
C3-L5 has 3 primary centers
-1 in the center of the body
-1 in each lamina pedicle junction (LPJ, 2 total here)
How many secondary ossification centers are there and where are they found?
test q
C3-L5 has 5 secondary centers
-1 in each superior/inferior epiphysis (2 total)
-1 in each transverse apophysis (2 total)
-1 in spinous process apophysis
What is the C7 anomaly?
C7 anterior transverse process may develop a primary ossification center and becomes a “cervical rib” on either or both sides
How many ossification centers does the atlas have? Where are they?
3 ossification centers
-1 primary center in each lateral mass (2 total)
-1 secondary center in the anterior arch (active within 1st year)
Is there a secondary center found in the posterior arch of the atlas?
NO will ossify back from the lateral masses
How many ossification centers does the axis (C2) have? Where are they found?
7 ossification centers:
5 primary centers
-1 in the middle of the body
-1 in each lamina pedicle junction (2 total)
-2 side by side in the base of the dens
2 secondary centers
-1 in the apex of the odontoid process
-1 in the inferior epiphysis of the body
How many total ossification centers are there in the lumbar spine? Where are they?
10 total- 5 primary and 5 secondary
primary:
-1 in body
-1 in each LPJ (2)
-1 in each MP (2)
secondary:
-1 in inferior/superior epiphysis (2)
-1 in each transverse apophysis (2)
-1 in SP apophysis
How many ossification centers are there in the sacrum?
49 ossification centers!!!!!
Its like 5 lumbar segments (10 centers each) BUT there is no room at the sacral hiatus to have one, so its 49
define hereditary
genetic code defects (at conception)
define congenital
interference with fetal growth (external factors)
define acquired
after birth
What is congenital block vertebrae?
-primary sclerotomes on 1-2 levels fail to split
-L/R sides are symmetrical (both fail to split)
-no intervertebral fissure or IVD
-results in 2+ vertebrae fused together
-usually clinically silent
-reduced local mobility
-most common in mid/lower cervicals and can occur in any region
What is hemivertebra?
-primary sclerotome on one side only fails to split
-opposite secondary sclerotome splits normally
-centrum forms asymmetrically (shorter on one side)
-arch formation is variable
-produced a half vertebra
-asymmetrical supporting structure embedded in the spine
-spine is unbalanced from there up
-body recurves spine upright to a severe congenital scoliosis
-may involve other spinal deformations
-can occur anywhere but is most common in thoracics or lumbars
What is butterfly/cleft vertebrae?
-secondary sclerotomes fail to proliferate medially
-dont obliterate notochord
-vertebral body consists of 2 masses joined by fibrous tissue
-secondary sclerotomes form a normal arch
-named for AP x-ray appearance (butterfly)
-often clinically silent
-weak link within spinal structure (may fail in trauma such as a car accident)
-IVD structure is variable
What is true spina bifida/spina bifida vera?
-secondary sclerotomes fail to proliferate posteriorly to some extent
-may involve spinal cord malformation
What is the mild form of true spina bifida/spina bifida vera?
-split spinous (L/R sides don’t fuse)
-clinically silent
-most common type
-common in L5-S1 and upper cervicals
What is the most common type of true spina bifida/spina bifida vera?
mild true spina bifida/spina bifida vera
What is the moderate form of true spina bifida/spina bifida vera?
-spinous completely fails to form (aka spinous aplasia)
-spinal cord is still protected
-less common than mild forms
What is spinous aplasia?
spinous process completely fails to form (happens in moderate form of true spina bifida/spina bifida vera)
What is moderately severe true spina bifida/spina bifida vera?
-spinous and laminae aplasia (spinous and lamniae never form)
-may be external signs like faun’s beard (hair growth on back where vertebra is malformed without sp and laminae)
-spinal cord is not well protected but otherwise well-formed
What is very severe true spina bifida/spina bifida vera?
-complete arch aplasia (never formed)
-spinal cord formation is disturbed
-ectodermal anomaly associated with mesodermal anomaly
-poorly developed tissue may be exposed on surface
-motor/sensory dysfunctions
-clinically evident at birth
-multi-level forms
-may extend several levels (rachischisis)
-may involve entire spine and neural tube (anencephaly)
-crippling (rachioschisis) or fatal shortly after birth (anencephaly)
What is spina bifida occulta (hidden split spine)?
-incomplete ossification of posterior structures (spinous/laminae)
-vertebral structure completely formed/chondrified
-cartilaginous arch protects cord
-only final ossification is disturbed
-clinically silent
-usually detected on routine x-ray
-x-ray mimics true spina bifida
-differentiated from true spina bifida by palpation
-may occur anywhere throughout spine
-most common site is C1 posterior arch with no secondary ossification center
What is persistent epiphysis/apophysis?
-secondary ossification fails to fuse to primary ossification by maturity
-several manifestations depending on the site
What is persistent spinous/transverse apophyses?
-secondary ossification tip never fuses with proximal primary ossification
-can occur throughout spine
-often mistaken for a fracture fragment
-clinically silent
What is persistent vertebral body epiphysis (also called Scheuermann’s disease)?
-very destructive to spinal stability
-most common in the cervical spine
What are the 2 types of odontoid anomalies?
os odontiodeum and os terminal
What is os odontoideum?
base of dens fails to fuse with C2 body
What is os terminal?
-apex of dens fails to fuse with base of dens
-only evident after maturity
-very dangerous anomaly
-usually clincally silent
-may go undetected unless pt receives routine x-ray
-may be fatal in trauma cases (guillotine injury to the cord)
