Development Of Musculoskeletal System

Question 1

Trilaminar disc mesoderm:
1. Paraxial mesoderm produces?

2. Lateral plate mesoderm produces?

Answer 1

1. Striated muscle cells and paraxial bone and connective tissue
2. Abaxial (away from axis) bone and connective tissue

Question 2

What does lateral plate mesoderm form? (The outer, somatic layer of it)

Answer 2

Connective tissue framework for abdominal body wall muscles, pelvic diaphragm, limb muscles and infrahyoid

Question 3

What is mesenchyme?

Answer 3

The sclerotome (future bone) that eventually forms the bony components of the trunk

Question 4

Somite formation week 4: sclerotome forms?

Dermomyotome forms?

Answer 4

Axial skeletal tissues (vertebrae and ribs) — becomes mesenchymal and travels around notochord and neural tube

Dermis and muscle tissues — elongates

Question 5

Function of SHH and noggin

Where are they secreted from?

Answer 5

Initiates transition from epithelium to mesenchyme

Ventral neural tube and notochord

Question 6

Function of PAX1

Answer 6

Initiates chondrogenesis and the formation of vertebrae

Question 7

Each somite corresponds to what?

How do the nerves and muscle blocks cross the bone?

Answer 7

A block of bone (sclerotome), a block of muscle (myotome) and spinal nerve

Bony elements resegment (each vertebra consists of cranial and caudal halves of two sclerotomes- why we have 8 cervical spinal nerves)

Question 8

How many days until the limb bud develops?

When do digits form?

What develops first: arms or legs?

Answer 8

24

Day 37

Arms

Question 9

What keeps the limbs growing

What ensures that the limbs are fully developed?

Answer 9

FGFs

Length of exposure to signaling molecules emitted by the apical ectodermal ridge (AER)

Question 10

Anterior posterior axis is also called?

What is located in this axis

What specifically is dependent on the specification of this axis?

Answer 10

Cranial (anterior) - caudal (posterior)

The limbs

Digit identity

Question 11

A-P axis is defined by?

Significance?

What does it produce?

Answer 11

ZPA (zone of polarizing activity)

Helps maintain AER and vice versa

Produces SHH

Question 12

Endochondral ossification forms bone. What two factors are necessary to initiate the proliferation of chondrocytes in this process?

Answer 12

BNP and FGF

Question 13

Where do joints form?

Answer 13

In interzones - between the cartilage precursors of bone

Question 14

What in the interzone eventually forms the synovial lining of joint?

What forms to become the synovial cavity?

Answer 14

DCT

Vacuoles

Question 15

Dorsal muscles vs ventral

Answer 15

Dorsal- elevators (extend and abduct limb)

Ventral- depressors (flex and adduct limb)

Question 16

Are quads ventral or dorsal?

Answer 16

Quads are ventral but developmentally dorsal (rotated- aligns limb parasagittally)

Question 17

Paraxial mesoderm will form

Answer 17

Sclerotome (future bone) and dermamyotome (dermis and muscle tissue)

Question 18

Function of Shh and noggin

Answer 18

Secreted from ventral neural tube and notochord to transition epithelium to mesenchyme

Question 19

What does PAX1 do

Answer 19

Initiates chondrogenesis and formation of vertebrae

Question 20

Function of FGF (and retinoic acid/WNTs)

Why is FGF8 significant

Answer 20

Create pattern of limb regionalization

If something happened to the AER, FGF8 is powerful enough to continue limb growth and development

Question 21

What will happen if you have something wrong at the AER

Answer 21

Limb will not fully develop

Question 22

Overactive ZPA will cause

Answer 22

Mirror image limb duplication (ZPA produces Shh)

Question 23

Direction of development caused by the following:

1. Retinoic acid
2. FGF8
3. Shh
4. WNT
5. BMP

Answer 23

1. Proximal
2. Distal
3. Anterior/posterior
4. Dorsal
5. Ventral

Question 24

Function of BMP

Answer 24

Stops limb bud outgrowth (when finished)

Question 25

Concentration of what needs to be low in order for somites to form? What is anatagonistic to this

Answer 25

FGF needs to be low Retinoic acid

Question 26

AER produces which type of elongation?

Answer 26

Proximal to distal (longitudinal limb growth)

Question 27

What is the progress zone

Answer 27

Mesodermal cells underlying the AER that make the limb elongate (controls dorsal ventral axis growth) (controlled by Wnt genes - expressed in dorsal part of progress zone)

Question 28

Where is ZPA located What is it important for

Answer 28

Below AER along proximal posterior limb bud Anterior/posterior patterning (radius ulna limb growth)

Question 29

Loss of ZPA ? Upregulation of ZPA ?

Answer 29

Loss of ulnar digits Additional posterior elements; concentration of Shh will be high (extra fingers)

Question 30

Where in the ZPA is Shh highest

Answer 30

Posterior side