Embryology

Question 1

What layer is the musculoskeletal system derived from?

Answer 1

mesoderm

Question 2

What are the 4 parts of the mesoderm?

Answer 2

notochord
paraxial
intermediate
lateral plate

Question 3

What does the notochord give rise to?

Answer 3

nucleus pulposus (IV discs)

Question 4

What does the paraxial mesoderm give rise to?

Answer 4

forms somites
vertebrae/ribs
muscles
skin

Question 5

What three parts do somites divide into?

Answer 5

dermatomes
myotomes
sclerotome (skeletal)

Question 6

What two sections is the lateral plate divided into?

Answer 6

splanchnic layer

somatic layer

Question 7

What does the somatic layer of lateral plate form?

Answer 7

anterolateral body wall

limb skeleton

Question 8

What are the two ways bones form?

Answer 8

intramembranous (flat skull bones)

endochondral

Question 9

How does intramembranous ossification work?

Answer 9

mesenchymal cells diff into osteoblasts which make bone matrix within collagen fiber

Question 10

What are the 4 steps of endochondral ossification?

Answer 10

1. hyaline cartilage model develops
2. bone collar forms around diaphesis and kill cartilage
3. bone cells enter from the periosteum and make matrix (primary ossificatoin center)
4. same thing starts in epiphyses

Question 11

What cartilage survives endochondral ossification?

Answer 11

articular cartilages

epiphysial plates

Question 12

All 4 limbs have started forming by what week?

Answer 12

week 4

Question 13

Limb buds form as extensions of what?

Answer 13

somites

Question 14

Which somites form the upper limb?

Answer 14

C5-T1 (brachial plexus)

Question 15

What makes the limb buds grow?

Answer 15

mesodermal cells due to Fibroblast Growth Factors (made by apical ectodermal ridge)

Question 16

How does the hyaline cartilage model form?

Answer 16

proximal cells diff into chondroblasts and form cartilage from proximal to distal

Question 17

When is the cartilage model finished forming?

Answer 17

week 8

Question 18

What separates the digits after cartilage is formed?

Answer 18

apoptosis

Question 19

What is polydactyly?

Answer 19

too many digits

Question 20

What is syndactyly?

Answer 20

digits that are fused together

Question 21

What causes achondroplasia?

Answer 21

decreased endochondral ossification leading to shorter bones

due to FGF-receptor mutation

Question 22

How does muscle form in the limbs?

Answer 22

myotomal myoblasts migrate to limb bud and divide into extensor and flexor masses (forms after bone)

Question 23

What are the three most common muscles for agenesis and partial development?

Answer 23

palmaris longus
pec major
serratus anterior

Question 24

The sclerotome is divided into three sections that migrate where?

Answer 24

notochord (nucleus pulposis)
neural tube (vertebrae)
laterally (ribs)

Question 25

Where are the vertebral ossification centers?

Answer 25

around notochord

pedicles

Question 26

How do spinal nerves develop?

Answer 26

spinal nerves cut through vertebrae to stay in its somite, so vertebrae split in half and two adjacent bones join between nerves

Question 27

What is hemivertebra?

Answer 27

malformation of part of a vertebra

due to failure of ossification or improper subdivision of sclerotomes

Question 28

What is supernumerary rib?

Answer 28

extra rib, either at the top or bottom

Question 29

What is a complication of a cervical rib?

Answer 29

compression of brachial plexus or subclavian artery

Question 30

How do the trunk muscles develop?

Answer 30

myotome cells split and migrate dorsally (intrinsic back) and ventrally (all others)