Musculoskeletal Development

Question 1

Paraxial mesoderm gives rise to

Answer 1

Most of axial skeleton, most skeletal muscles, and dermis of the skin

Question 2

Lateral plate mesoderm gives ride to

Answer 2

Pectoral and pelvic girdle, sternum, and long bones of the limbs

Question 3

Somite formation process

Answer 3

Paraxial mesoderm proliferates and organizes into two columns on either side of notochord
Longitudinal columns differentiate into series of paired masses called somites

Question 4

Occipital somites form

Answer 4

Occipital bone

Question 5

Caudal occipital somites form

Answer 5

First cervical vertebra

Question 6

Sequence of somite formation

Answer 6

Rostral to caudal

Question 7

Somite regions

Answer 7

Sclerotome
Myotome
Dermatome

Question 8

Sclerotome is future

Answer 8

Axial skeleton

Question 9

Myotome is future

Answer 9

skeletal muscles

Question 10

Dermatome is future

Answer 10

Dermis of skin in axial regions

Question 11

Scelrotome migration

Answer 11

Cells on medial side begin to migrate toward notochord and neural tube

Question 12

What forms vertebral arch

Answer 12

Dorsally migrating sclerotomes that pass posterior to neural tube

Question 13

What forms vertbral body

Answer 13

Ventral migrating sclerotome cells that surround and incorporate the ventral side of the neural tube

Question 14

What happens to migrated slcerotome cells

Answer 14

Programmed cell death that shapes into primitive vertebral body and neural arch

Question 15

Somite resegmentation

Answer 15

Somites will split into a rostral and caudal part

Rostral migrates and fuses with migrating somite cells from the caudal part of the more rostral somite

Question 16

Purpose of somite resegmentation

Answer 16

Allows growing spinal nerve to pass between adjacent vertebrae

Question 17

CS1

Answer 17

Rostral half migrates to fuse with lower occipital somite to form occipital bone along with the rostral four occipital somites

Question 18

First cervical spine nerve located

Answer 18

Superior to the first cervical vertebrae

Question 19

Rib development

Answer 19

Develop from costal processes of developing thoracic vertebrae (somites)
Elongate in week 5 to form ribs

Question 20

Sternum development

Answer 20

Lateral plate somatic mesoderm differentiates into mesenchyme
Mesenchyme migrates anteriorly and condenses to form sternal bars
Sternal bars fuse at cranial ends first and then “zip”

Question 21

Dermatome migration

Answer 21

Migrates to lateral part of somite to form dermis of the skin
Everywhere but head

Question 22

Myotome migration

Answer 22

Most migrates ventrally, while some dorsal
Ventrally forms hypomere (muscles and limbs)
Dorsally forms epimere (true back muscles)

Question 23

Hypomere

Answer 23

Becomes body wall and limbs

Hypomere of thorax and abdomen forms three layers

Question 24

Muscles derived from hypomere innervated by

Answer 24

ventral primary rami of spinal nerves

Question 25

Epimere

Answer 25

Migrates minimally and stays on posterior side of vertebral column

Question 26

Epimere derivatives innervated by

Answer 26

dorsal primary rami of spinal nerves

Question 27

Limb development

Answer 27

At end of fourth week, limb buds begin forming upper limb and lower limb
Somatic mesoderm induces ectoderm to form AER
AER induces mesoderm to continue dividing which lengthens the limb

Question 28

Upper limb development spinal cord level

Answer 28

C4-T1

Question 29

Lower limb development spinal cord level

Answer 29

L1-S3/4

Question 30

Limb buds composed of

Answer 30

Composed of surface ectoderm and core of somatic mesoderm

Question 31

AER

Answer 31

Apical ectodermal ridge
Induced by ectoderm
Induces mesoderm to continue divding and legnthen limb

Question 32

Bones of limbs develop from

Answer 32

Mesenchyme from somatic lateral plate mesoderm that first forms cartilage

Question 33

Precursor to bone development

Answer 33

Cartilage

Question 34

Lateral plate mesoderm also contributes to cartilage of

Answer 34

Pectoral and pelvic girdles of each limb

Question 35

What happens as hypomere enters the limb?

Answer 35

Splits into a ventral muscle mass and odrosal muscle mass

Question 36

Ventral and dorsal muscle mass functions

Answer 36

Ventral - flexors, pronators, adductors

Dorsal - extensors, supinators, abductors

Question 37

Dorsal and ventral mass innervation

Answer 37

Respective primary rami

Question 38

Dorsal and ventral branches of the VENTRAL primary rami correlate with

Answer 38

posterior and anterior divisions of the brachial plexus

Question 39

Timeline of limb development

Answer 39

5 weeks from day 24(upper)/28(lower)

Question 40

Most sensitive period of limb formation

Answer 40

Weeks 4-5

Question 41

What sculpts inter-digit regions

Answer 41

AER is turned off so cells stop dividing

Question 42

Limb rotation

Answer 42

During development, upper limbs rotate laterally and lower limbs rotate medially

Question 43

Meromelia

Answer 43

Absence of part of a limb

Question 44

Polydactyly

Answer 44

Presence of extra digits

Question 45

Amelia

Answer 45

Absence of one or more limbs

Question 46

Syndactyly

Answer 46

Fusing of digits

Question 47

Simple syndactyly

Answer 47

Cutaneous syndactyly

Failure of mesenchyme between digital rays to break down

Question 48

Complex syndactyly

Answer 48

Digits joined by bone or cartilaginous union