Embryology (Quiz 1/Test 1) Flashcards

1
Q

What develops first in the spinal column?

A

trilaminar disc

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2
Q

What does ectoderm develop into?

A

outer skin/skin of organism

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3
Q

What does mesoderm develop into?

A

“middle skin” organs, bones, muscle

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4
Q

What does endoderm develop into?

A

“inner skin” internal linings

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5
Q

Spinal column develops from 3 prior structures. What are they?

A

1) notochord
2) somites
3) sclerotomes

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6
Q

What is another name for the notochord?

A

chorda dorsalis

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7
Q

Where is the notochord derived from?

A

embryonic mesoderm which is a primitive support structure of the axial skeleton

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8
Q

The notochord extends from the _____________ to ___________

A

sphenoid (base of skull), coccyx

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9
Q

Is the notochord a temporary or permanent structure?

A

temporary structure (later will be obliterated by the vertebral bodies and part of it persists as nucleus pulposus and apical ligament)

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10
Q

When is the notochord first recognizable?

Think days

A

day 18

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11
Q

In what direction/axis does the notochord develop?

A

cranial to caudal axis

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12
Q

What is another name for somites?

A

mesodermal segments

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13
Q

What are somites?

A

coronally-paired mesodermal cell masses

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14
Q

When do somites first appear?

A

week 4 (day 21/22)

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15
Q

Where do somites develop?

A

on left and right sides of organism and follow the axial gradient

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16
Q

What forms in the first segmentation?

A

-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

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17
Q

____________________ 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

A

primary sclerotomes

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18
Q

The reunited cell masses form the secondary sclerotomes. The secondary sclerotomes proliferate rapidly in 3 directions. What are the 3 directions?

test q

A

1) medially
2) posteriorly
3) laterally

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19
Q

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?

A

-invades and obliterates the notochord
-the L/R secondary sclerotomes fuse to form centra (centrum) of the vertebral bodies obliterating the notochord

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20
Q

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?

A

-they surround the developing spinal cord
-they form pedicles, laminae, and spinous processes

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21
Q

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?

A

they project to form the lamina/pedicle junction

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22
Q

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….

A

nucleus pulposus

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23
Q

Where does chondrification/chondral/cartilaginous stage begin?

A

in distinct chondrification centers

24
Q

What happens in the ossification stage/endochondral ossification?

A

cartilaginous model becomes mineralized/calcified/ossified

25
Q

What are the 2 distinct types/stages of ossification?

test q

A

1) primary ossification (begins at birth and continuous through puberty)
2) secondary ossification (begins after birth and continues till 35-40 y/o)

26
Q

Does primary ossification follow the axial gradient?

A

NO

27
Q

Do all vertebrae have ossification centers?

A

YES

28
Q

If primary ossification doesn’t follow the axial gradient then how does it work?

A

-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

29
Q

Where are primary ossification centers found?

test q

A

C3-L5 has 3 primary centers
-1 in the center of the body
-1 in each lamina pedicle junction (LPJ, 2 total here)

30
Q

How many secondary ossification centers are there and where are they found?

test q

A

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

31
Q

What is the C7 anomaly?

A

C7 anterior transverse process may develop a primary ossification center and becomes a “cervical rib” on either or both sides

32
Q

How many ossification centers does the atlas have? Where are they?

A

3 ossification centers
-1 primary center in each lateral mass (2 total)
-1 secondary center in the anterior arch (active within 1st year)

33
Q

Is there a secondary center found in the posterior arch of the atlas?

A

NO will ossify back from the lateral masses

34
Q

How many ossification centers does the axis (C2) have? Where are they found?

A

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

35
Q

How many total ossification centers are there in the lumbar spine? Where are they?

A

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

36
Q

How many ossification centers are there in the sacrum?

A

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

37
Q

define hereditary

A

genetic code defects (at conception)

38
Q

define congenital

A

interference with fetal growth (external factors)

39
Q

define acquired

A

after birth

40
Q

What is congenital block vertebrae?

A

-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

41
Q

What is hemivertebra?

A

-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

42
Q

What is butterfly/cleft vertebrae?

A

-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

43
Q

What is true spina bifida/spina bifida vera?

A

-secondary sclerotomes fail to proliferate posteriorly to some extent
-may involve spinal cord malformation

44
Q

What is the mild form of true spina bifida/spina bifida vera?

A

-split spinous (L/R sides don’t fuse)
-clinically silent
-most common type
-common in L5-S1 and upper cervicals

45
Q

What is the most common type of true spina bifida/spina bifida vera?

A

mild true spina bifida/spina bifida vera

46
Q

What is the moderate form of true spina bifida/spina bifida vera?

A

-spinous completely fails to form (aka spinous aplasia)
-spinal cord is still protected
-less common than mild forms

47
Q

What is spinous aplasia?

A

spinous process completely fails to form (happens in moderate form of true spina bifida/spina bifida vera)

48
Q

What is moderately severe true spina bifida/spina bifida vera?

A

-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

49
Q

What is very severe true spina bifida/spina bifida vera?

A

-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)

50
Q

What is spina bifida occulta (hidden split spine)?

A

-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

51
Q

What is persistent epiphysis/apophysis?

A

-secondary ossification fails to fuse to primary ossification by maturity
-several manifestations depending on the site

52
Q

What is persistent spinous/transverse apophyses?

A

-secondary ossification tip never fuses with proximal primary ossification
-can occur throughout spine
-often mistaken for a fracture fragment
-clinically silent

53
Q

What is persistent vertebral body epiphysis (also called Scheuermann’s disease)?

A

-very destructive to spinal stability
-most common in the cervical spine

54
Q

What are the 2 types of odontoid anomalies?

A

os odontiodeum and os terminal

55
Q

What is os odontoideum?

A

base of dens fails to fuse with C2 body

56
Q

What is os terminal?

A

-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)