MSK Embryology

Question 1

nucleus pulposus of IV discs derived from

Answer 1

notochord

Question 2

vertebrae, ribs, muscles of limbs and trunk, skin derived from

Answer 2

paraxial mesoderm, somites

Question 3

limb skeleton derived from

Answer 3

lateral plate mesoderm

Question 4

paraxial mesoderm forms ____ which then give rise to ____

Answer 4

somites; segments

Question 5

each body “segment” contains what

Answer 5

skin or dermatome, underlying muscle, skeleton, blood vessels

Question 6

somites divide into 3 divisions…

Answer 6

dermatome- dermis

myotome- skeletal muscle

sclerotome- cartilage and bone

Question 7

two types of mesoderm divided by coelom

Answer 7

two parts of lateral plate mesoderm

inner splanchnic layer forms GI wall

outer somatic layer forms limb skeleton and anterolateral body wall

Question 8

two ways mesoderm forms bone

Answer 8

intramembranous ossification- flat bones of skull

endochondral ossification- rest of bones

Question 9

osteoblasts derive from

Answer 9

mesenchymal cells

Question 10

osteoblasts fn

Answer 10

make bone matrix or osteoid, creates flat bones of skull directly w/o cartilage matrix

Question 11

outline 4 steps of endochondral ossification

Answer 11

1. embryonic hyaline cartilage model develops
2. bone collar forms around cartilage diaphysis, chondrocytes w/i die
3. vessels, osteoblasts, and osteoclasts invade from periosteum and form primary ossification center, begin bone formation
4. secondary ossification centers form in epiphyses, mostly after birth

Question 12

exceptions for bone replacement of hyaline cartilage

Answer 12

articular hyaline cartilage- remain for life for joint movement

epiphyseal plates- aka growth plates, needed for bone growth but are replace w/ bone at adulthood

Question 13

all 4 limb buds have begun to form by…

Answer 13

week 4

Question 14

upper and lower limb buds arise as..

Answer 14

lateral extensions of trunk somites- upper from somites C5-T1

lower limb from L2-S2

Question 15

molecules initiating mesoderm mitosis and limb bud outgrowth

Answer 15

Fibroblast Growth Factors- produced by apical ectodermal ridge cells at the distal end of the limb bud

Question 16

how are hyaline cartilage models made for limb

Answer 16

proximal cells differentiate into chondroblasts, progresssively add distal elements progressively

all models formed by week 8

Question 17

development of digits

Answer 17

distal end of limb forms wide paddle, forms digital rays

apoptosis separates the digits

Question 18

polydactyly vs syndactyly

Answer 18

poly- extra digits

syn- fused digits

Question 19

achondroplasia pathogenesis

Answer 19

less endochondral ossification in limb bones cause short limbs

no effect on membranous ossification, large head relative to limbs

Question 20

achondroplasia epi and etiology

Answer 20

epi- common type of dwarfism

etiology- AD, most are spontaneous paternal mutations of FGFR 3 genes (for FGF receptor)

Question 21

most common muscles of upper limb affected by agenesis and partial development

Answer 21

palmaris longus
part of pectoralis major
serratus anterior

Question 22

describe migration of sclerotome cells for axial development

Answer 22

toward midline notochord (becomes nucleus pulposis) and neural tube- vertebral

laterally- ribs

Question 23

vertebral cartilage model formed by..

Answer 23

sclerotome cells, later followed by ossification centers (cont til adulthoods)

Question 24

how do sclerotomes allow spinal nerves to exit vertebral column?

Answer 24

sclerotomes divide into cranial and caudal parts, provide space for spinal nerves along intersegmental boundary

initially the neural tube and vertebral column develop in parallel w/o nerves passing thru laterally

Question 25

final vertebra are formed from __ and ___ sclerotomes

Answer 25

cranial; caudal

half of adjacent sclerotomes form vertebrae

Question 26

hemivertebra

Answer 26

lack of formation of part of vertebra

from either ossification center failure or improper subdivision of sclerotomes

cause of scoliosis

Question 27

neural tube defects

Answer 27

aka spina bifida

lack of development of dorsal vertebral arch from sclerotome, spinal chord elements protrude out of vertebral column

Question 28

supernumary/ accessory ribs

Answer 28

small rudimentary rib in addition to nl 12

Question 29

typical location/sx of supernumary ribs

Answer 29

lumbar- extra from area of L1 vertebra, asx (more common)

cervical- area of C7, can compress brachial plexus and sometimes subclavian

Question 30

dorsal vs ventral migration of myotomes

Answer 30

dorsally- intrinsic back muscles innervated by dorsal rami

ventrally- anterolateral body wall and limbs, innervated by ventral rami