Week 1 - MSK development Flashcards
What does the skull develop from?
- What are the two parts of this?
Mesenchyme (developed from neural crest cells) around the brain:
- Viscerocranium
- Neurocranium
What does each vertebra develop from?
From the sclerotome of 4 somites.
What are the two parts of an intervertebral disk?
- and what is their orientation relative to each other?
Nucleus Pulposus - inner center of disk
Annulus Fibrosis - outer ring of disk (fibrous part)
What forms the nucleus pulposus of the intervertebral disk?
The notochord
What does the annulus fibrosis develop from?
The mesoderm (connective tissue) between the vertebrae.
What are the two divisions of the of the myotome (within the thorax and abdominal regions)?
Epaxial division
Hypaxial division
What muscles are part of the epaxial division?
Back and neck muscles
What innervates the epaxial division?
dorsal rami
What muscles are part of the hypaxial division?
Trunk and limb muscles
What innervates the hypaxial division?
Ventral rami
When does muscle tissue begin to differentiate?
At week 4-5 in development
What muscle cell precursors for at 4-5 weeks of development?
Myoblasts
What is the embryonic origin of the skull (head mesenchyme)?
Neural crest cells
When do muscle cells begin to differentiate?
Week 5-6 in development
Describe the process of muscle development after the muscle cells have begun to differentiate.
- myoblasts fuse
- multinucleated myotubes
- more myoblasts added at the ends
- begin synthesizing actin & myosin
What is a myotube?
Multi-nucleated, undifferentiated contractile apparatus (sarcomere)
What is a myofibre?
Multinucleated differentiated sarcomere
What happens between week 9 and 5 months of muscle development?
Nuclei migrate to the outside of the myotube - actin & myosin organized to form contractile elements
What is the difference between primary and secondary myotubes?
Primary myotubes do not need nerve cell involvement.
Secondary myotubes need nerve cells present to form.
When does development of the limbs begin?
Week 4 of development.
What is the primary axial artery in the upper limb?
Brachial artery
What gene controls the anterior/posterior axis of limb?
Shh (Sonic Hedgehog gene)
What gene controls the dorsal/ventral axis of limb?
Wnt
What gene controls the outgrowth (proximal/distal axis) of limb?
Wnt & Shh
What is secreted by the mesenchyme in the centre of the deveolping limb?
BMP (Bone Morphogenic Protein)
What is the function of Bone Morphogenic Protein?
Necessary for the mesenchyme to develop into cartilage and then bone.
What is secreted by the regions where synovial joints will form?
Noggin
What does Noggin do on a molecular level?
Antagonizes BMP
How does the synovial joint form?
- ie. what happens between bones, on the surface of bones, and around the bones?
There is condensation of mesenchyme in Noggin-rich areas which leads to apoptosis and formation of a fluid filled space between two cartilage rods.
Articular cartilage forms on the ends of these rods where mesenchyme will condense to for m perichondrium which becomes periosteum.
Mesenchyme adjacent to the joint region will form synovium & ligaments of the joint capsule and tendons.
What is an Apical Ectodermal Ridge (AER)?
A thickened portion of epithelium at the tip of the limb buds.
What is the function of the Apical Ectodermal Ridge (AER)?
It secretes fibroblast growth factors and interacts with the mesenchyme of the limb to promote growth outwards.
What does Retinoic Acid do in limb development?
Acts on Zone of Polarizing Activity (ZPA) to induce Shh abd bone morphogenetic proteins.
–> Determines pattern of limb development and programmed cell death (ie. causes apoptosis in areas of tissue between fingers).
What is amelia?
Complete failure of limb development
What is the term for partial failure of limb development?
Meromelia
What is a cause of polydactyly or syndactyly?
Improper gradient of ZPA (zone of proliferating activity) and Shh.
