Embryology 5 - Development of Bone and Muscle

Question 1

What does the mesoderm give rise to?

Answer 1

Most of bones and muscles

Question 2

Where does the mesoderm emerge from?

Answer 2

Primitive streak

Question 3

What four things does the mesoderm further divide into?

Answer 3

1. Notochord
2. Somite (paraxial mesoderm)
3. intermediate mesoderm (IM)
4. lateral plate mesoderm (LPM)

Question 4

____ form segmented blocks next to the neural tube.

Answer 4

Somites

Question 5

What are the three layers of somite?

Answer 5

Dermatome

Myotome

Sclerotome

Question 6

What structure does the dermatome form?

Answer 6

Dermis of skin

Question 7

What structure(s) do the myotome form?

Answer 7

Skeletal muscles

Question 8

What structure(s) do the sclerotome form?

Answer 8

Vertebrae, ribs

Question 9

Where does the sclerotome develop and what does it eventually form?

Answer 9

Surrounds neural tube and forms vertebra

Question 10

Where is the sternum derived from?

Answer 10

Lateral plate mesoderm

Question 11

How many somite pairs have formed at day 20 of development?

Answer 11

1 (at occipital level)

Question 12

How many somite pairs have formed at day 22 of development?

Answer 12

7-10 pairs

Question 13

How many somite pairs have formed at day 24 of development?

Answer 13

13-17

Question 14

How many somite pairs have formed during the 5th week of development?

Answer 14

42-44 (some occipital and coccygeal somite pairs later disappear)

Question 15

What controls somite segmentation?

Answer 15

cyclic NOTCH signaling

Question 16

A new somite pair appears every __ hours.

Answer 16

8

Question 17

What is DELTA protein?

Answer 17

Surface protein on the signal-sending cell that binds to NOTCH protein on neighboring cell to activate NOTCH signaling

Question 18

What is Lunatic Fringe?

Answer 18

A protein in the signal-receiving cell that mediates whether NOTCH mRNA is translated to NOTCH protein and whether the protein is expressed on the cell surface

Question 19

What does the NOTCH Protein do?

Answer 19

When bound to delta protein, activates MESP2 gene transcription in signal-receiving cell

Question 20

What is Spondylocostal dysostosis?

Answer 20

Vertebral defects (scoliosis, hemivertebra, rib fusion) caused by mutations in NOTCH signaling components

Question 21

The identity of each vertebrae is determined by ____ gene code.

Answer 21

HOX

Question 22

Loss of HOX10 gene results in ___.

Answer 22

Extension of thoracic-appearing vertebrae into lumbar and sacral regions

Question 23

Expanded HOX10 expression results in ____.

Answer 23

Extension of lumbar-appearing vertebrae into thoracic region of spine

Question 24

What are Cervical ribs?

Answer 24

Abnormal Extra rib formation from C7 vertebra

Question 25

Lateral plate mesoderm gives rise to which bones?

Answer 25

Bones in arms, legs, shoulders, pelvis, and chest

Question 26

Neural crest (ectoderm) gives rise to which bones?

Answer 26

Bones in the face and jaws

Question 27

What are the Two Types of Ossification Processes?

Answer 27

1. Intramembranous ossification 2. Endochondral ossification

Question 28

What is Intramembranous Ossification?

Answer 28

Osteoblasts deposit mineralized matrix → bone

Question 29

What is Endochondral Ossification?

Answer 29

1. Mesoderm cells come together to form mesenchyme that differentiates to chondrocytes 2. Chondrocytes deposit matrix → formation of cartilage as template for future bone 3. Osteoblasts invade cartilage via blood vessels at the primary ossification center and replace cartilage with mineralized matrix → bone

Question 30

What bones do endochondral ossification occur in?

Answer 30

* Vertebrae * Ribs * Pelvis * Limb bones * skull base

Question 31

What causes Achondroplasia?

Answer 31

Caused by precocious endochondreal ossification Caused by mutations in fibroblast growth factor receptor 3 (FGFR3) gene

Question 32

What bones do intramembranous ossification occur in?

Answer 32

Flat skull bones (frontal, parietal, occipital), clavicle

Question 33

What Ossification process is involved in healing of bone fractures?

Answer 33

Intramembranous ossification

Question 34

What gene is essential for ossification?

Answer 34

RUNX2 gene (CBFA1)

Question 35

What does Cleidocranial dysplasia (CCD) affect?

Answer 35

RUNX2 heterozygous mutation → Intramembranous ossification is impaired

Question 36

What causes Craniosynostosis?

Answer 36

Caused by premature ossification of skull bones

Question 37

Skeletal muscle is derived from:

Answer 37

Somite (myotome)

Question 38

Cardiac muscle is derived from:

Answer 38

Lateral plate mesoderm (cranial region)

Question 39

Smooth muscle is derived from:

Answer 39

Lateral plate mesoderm

Question 40

How does skeletal muscle differentiate?

Answer 40

Myogenic progenitor cells → Differentiate into myoblasts → Myoblasts line up to form myotube → Fuse to form muscle fiber (multi-nucleated cell)

Question 41

What are Myosatellite Cells?

Answer 41

Myoblast-like stem cells that persist throughout life and proliferate and differentiate upon injury to regenerate skeletal muscle

Question 42

What brings the cardiogenic mesoderm to the thorax?

Answer 42

Cephalic and lateral folding

Question 43

What is Prune Belly Syndrome?

Answer 43

Defects in urinary system (bladder, urethra) → Degeneration of abdominal muscles

Question 44

What is Poland Syndrome?

Answer 44

Underdevelopment of unilateral chest wall muscle Often accompanied by finger defects on the same side May be caused by an interruption of subclavian arteries during embryo development