Development of the Nervous and Musculoskeletal Systems for Limb Formation 2

Question 1

The sternum and appendicular skeleton, including the shoulder and pelvic girdles and limbs, arise from

Answer 1

Somatic mesoderm

Question 2

Projects from the anterolateral body wall and contains mesenchyme originating from somatic mesoderm and myoblasts originating from somitic

Answer 2

Limb bud

Question 3

The mesenchyme (somatic mesoderm) and myoblasts (somitic mesoderm) of the limb bud will differentiate to form

Answer 3

Connective tissues and skeletal muscles of limb respectively

Question 4

The chick embryo skull shows an unstained mesenchyme membrane that will soon undergo
intramembranous ossification to form

Answer 4

Flat bones of the skull

Question 5

Ossification continues after birth and ossification centers are completed at specific ages with varying rates between

Answer 5

Male and female

Question 6

Mesenchymal cells of the somitic dermatome and somatic mesoderm invade tissues deep to the surface ectoderm to form the

Answer 6

Dermis

Question 7

Forms the epidermis and epidermal derivatives like hair, nails, and sweat glands

Answer 7

Surface ectoderm

Question 8

Form the mesenchyme that differentiates into dermis connective tissue in the face and neck

Answer 8

Neural crest cells

Question 9

With the exception of some smooth muscle, skeletal, smooth, and cardiac muscle are all formed from the

Answer 9

Mesoderm

Question 10

In the MSK system, skeletal muscle is derived from

Answer 10

Paraxial mesoderm (which differentiates into somites and then myotomes)

Question 11

Myotomes contain cells that either remain in the somite region or migrate to the somatic mesoderm. These precursor muscle cells are called

Answer 11

Myoblasts

Question 12

Forms from the migration of somitic mesoderm cells into the somatic mesoderm

Answer 12

Skeletal muscle

Question 13

Myoblasts that do not migrate form the

Answer 13

Primaxial skeletal muscles of the back

Question 14

Include rhomboids, levator scapulae, latissimus dorsi, intercostals, and shoulder girdle muscles

Answer 14

Primaxial muscles

Question 15

Myoblasts that migrate to the somatic mesoderm form

Answer 15

Abaxial muscles of anterolateral body wall and limbs

Question 16

To form the large, cylindrical, multinucleate muscle fibers/cells seen in skeletal muscle, myoblasts fuse to form a

Answer 16

Syncytium

Question 17

Lie adjacent to skeletal muscle fibers and serve as stem cells to offer limited capacity for regeneration of damages skeletal muscle tissue

Answer 17

Satellite cells

Question 18

Nerves and muscle cells arise from the same level

adjacent to the

Answer 18

Neural tube

Question 19

A defect characterized by absence of the pectoralis muscles

Answer 19

Poland’s sequence

Question 20

Can present clinically with a flattened pectoral region, a missing anterior axillary fold, and a displaced nipple

Answer 20

Poland’s sequence

Question 21

Curves the embryo into a C-shape, with the embryo curving out towards the dorsal side

Answer 21

Cephalo/cranial-caudal folding of the embryo

Question 22

The process where the edges of the flat embryo bend and fuse ventrally in the midline to form a cylindrically shaped embryo

Answer 22

Lateral folding

Question 23

In lateral folding, the embryo is now a tube with two internal tubes, which are the

Answer 23

Gut tube and neural tube

Question 24

The epidermis and underlying tissues along

the anterior body wall are derived from the ventral folding and fusion of

Answer 24

Ectoderm and parietal mesoderm

Question 25

Also with folding of the lateral edges, the endoderm | fuses and creates the

Answer 25

Gut tube

Question 26

The gut tube is surrounded by the -lies between the lateral plate mesoderm layers with parietal and visceral mesoderm

Answer 26

Intraembryonic coelom (body cavity)

Question 27

Defects can arise when the ventral body wall of the thorax, abdomen, or pelvis fail to

Answer 27

Fuse

Question 28

Incomplete fusion in the thorax can lead to

Answer 28

Ectopia cordis (heart on the outside), gastroschisis (abdominal viscera on outside), and bladder extrophy (bladder on outside)

Question 29

Limb buds project from the anterolateral body wall by the end of

Answer 29

Week 4 of development

Question 30

Made up of a core of somatic mesoderm derived | mesenchyme covered by ectoderm

Answer 30

Limb buds

Question 31

The upper limb appears first, at day 24, followed by the hind limb at

Answer 31

Day 28

Question 32

Occurs between the fifth and eighth weeks and | involves growth, induction, apoptosis, and patterning, as described below

Answer 32

Differentiation of the limb buds

Question 33

Surface ectoderm cells overlying the distal border of | the limb thickens into an

Answer 33

Apical ectodermal ridge (AER)

Question 34

Acts as a signaling center that induces nearby mesenchyme (through FGF secretion) to proliferate rapidly without differentiating to maintain distal outgrowth of limb mesenchyme

Answer 34

The AER

Question 35

The area of mesenchyme proliferation and elongation is called the

Answer 35

Progress zone

Question 36

As the limb elongates, the AER moves distally. This distal movement allows the proximal portions of the limb to

Answer 36

Differentiate and develop into cartilage and bone

Question 37

As the limb grows, cells near the proximal end are exposed to retinoic acid that causes them to differentiate into

Answer 37

Proximal bones

Question 38

Digits begin formation at the DISTAL end when apoptosis occurs in the

Answer 38

AER

Question 39

Final separation by apoptosis occurs between the webbing or rays in the interdigital spaces to form

Answer 39

Digits

Question 40

The fusion of two or more digits that may result from incomplete apoptosis between digits

Answer 40

Syndactyly

Question 41

Responsible for the differences in the structure of digits so that there is a “pinky side” and a “thumb side”

Answer 41

Zone of polarizing activity (ZPA)

Question 42

Communicates with the ZPA, which is a cluster of mesenchymal cells that secrete SHH to induce differentiation of anterior-posterior patterning of digits

Answer 42

The AER

Question 43

Dorsalizing factors that interact with ventralizing factors (such as engrailed-1) to establish the dorso-ventral axis of the limb

Answer 43

WNT7 and LMX1

Question 44

WNT7 and LMX1 lead to a limb with an

Answer 44

Extensor muscle side and a flexor muscle side

Question 45

Disruption of the proximal-distal development of the limbs results from loss of

Answer 45

FGF signaling

Question 46

Disruption of the proximal-distal development of the limbs can result in

Answer 46

Amelia (lack of limb), Meromelia (partial lack of limb), and adactylyl (absense of digits)

Question 47

Polydactyly (extra digits) and syndactylyl (fusion of digits) may be the result of

Answer 47

BMP or SHH disregulation or disruption

Question 48

At 7 weeks, what happens to the limbs?

Answer 48

They rotate

Question 49

Most cartilage templates of limb bones form between

Answer 49

5 and 12 weeks

Question 50

Ossification of proximal bones in the upper limb begins in the

Answer 50

7th week

Question 51

Ossification of proximal bones in the lower limb begins in the

Answer 51

8th week

Question 52

Most bones show ossification by the 12th week, although ischium and pubis not until the

Answer 52

15th and 20th weeks

Question 53

Smaller tarsal and carpal bones are not ossified until

Answer 53

Childhood

Question 54

As the AER advances distally with mesenchymal cell proliferation, proximal mesenchymal cells differentiate into

Answer 54

Chondroblasts (during week 6)

Question 55

Bone is vascular and replaces the avascular cartilage, which has a size limit due to reliance on

Answer 55

Diffusion through matrix for nutrients/waste exchange

Question 56

Cartilage calcification in the diaphysis (shaft) of long bones results in poor oxygen diffusion through the

Answer 56

Avascular cartilage

Question 57

As a result, the cartilaghe breaks down and is removed by

Answer 57

Osteoclasts

Question 58

Blood vessels invade the diaphysis and are accompanied by

Answer 58

Osteoblasts

Question 59

As cartilage is removed by osteoclasts, osteoblasts secrete bone matrix to form the -occurs during prenatal development

Answer 59

Primary ossification center

Question 60

Primary ossification centers are formed during prenatal development and are present in all long bones of limbs by the

Answer 60

12th week of development

Question 61

At birth, diaphyses of bones are completely ossified, but the ends, the epiphyses, are still

Answer 61

Hyaline cartilage

Question 62

Primary and secondary ossification centers form on either side of a cartilaginous

Answer 62

Epiphyseal growth plate

Question 63

The growth plate is made of hyaline cartilage that has chondrocytes that can proliferate in response to

Answer 63

Growth hormone from adenohypohpysis

Question 64

Located at the growth plate retain the ability to divide when stimulated by growth factors in order to increase length of long bones

Answer 64

Chondrocytes

Question 65

Once growth is completed into adulthood (20-25 years of age), the original primary and secondary ossification centers will meet as bone fills in the growth plates to form the

Answer 65

Epiphyseal line (and bone lengthening stops)

Question 66

The most common form of skeletal dysplasia (1/20,000 live births) and primarily affects long bones

Answer 66

Achondroplasia

Question 67

A gene associated with achondroplasia is

Answer 67

FGFR3

Question 68

One of the results of achondroplasia is shortened extremities due to reduced chondrocyte proliferation at

Answer 68

Growth plates

Question 69

Occurs while connective tissues are developing in somatic mesoderm

Answer 69

Muscle formation

Question 70

Somitic mesoderm invades somatic mesoderm during

Answer 70

Week 5

Question 71

Develops from ventral and dorsal condensations of somitic mesenchyme

Answer 71

Limb musculature

Question 72

The dorsal mass forms

Answer 72

Extensors and supinators of upper limb and Extensors and abductors of lower limb

Question 73

The ventral mass forms

Answer 73

Flexors and pronators of upper limb and Flexors and adductors of lower limb

Question 74

Based on induction of neuroepithelium to form neurons and neuroglia of the CNS and of neural crest to form neurons and neuroglia of the PNS

Answer 74

Nervous System Formation

Question 75

Based on origins from somites and somatic mesoderm

Answer 75

MSK formation

Question 76

Transforms the flat trilaminar disc into a cylindrical, C-shaped embryo whose limb buds project from the anterolateral wall

Answer 76

Body folding

Question 77

Involves orchestration of somatic mesoderm differentiation and migration of myotome myoblast cells with their innervation

Answer 77

Limb formation