Musculoskeletal Development 2: Muscle and innervation (S3)
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What induces spinal nerve growth from the neural tube?
Somite signals
What happens to the vertebra (sclerotome) as the nerve grows / how does the nerve get past it?
Horizontally splits it in half - cranial and caudal halves.
How do the nerves get to the myotomes and dermatomes?
As segmental innervation
What type of innervation are dermatomes for?
Sensory
What are the two parts of the myotome?
Epimere and hypomere
What group of nerves supply the epimere?
dorsal primary ramus
What group of nerves supply the hypomere?
ventral primary ramus
How is a neuromuscular junction developed?
• growth cone of axon approaches muscle fibre • growth cone forms contact with muscle fibre surface • terminal differentiates, basal lamina appears in cleft • other axons catch up as well • AChR laid down on muscle surface and one axon survives (competition) • axon develops myelin sheath (schwann cells) • increase in AChR density and elaboration of post-synaptic membrane
Where is the smaller dorsal portion, the epimere found?
Between transverse and spinous processes, forms epaxial compartment - extensor muscles of vertebral columb.
What do hypomeres give rise to?
Muscles of limbs and body wall
What lies in between dorsal and ventral muscle mass?
Precursor of bones and tendons (for endochondral ossification)
What forms the flexors of the spine?
Hypomere
What forms the expaxial extensor muscles of spine?
Epimere
What forms the layers of the thorax and abdomen?
Hypomere
What musculature does MYF5 form?
Epaxial
What musculature does MYO-D form?
Hypaxial
By which week/month do cross-striations of skeletal muscle appear, due to myoblasts fusing and forming long multinucleated fibres?
Week 12
What do transcription factors do? What do Myogenic factors do?
Transcription factors regulate other genes. Myogenic factors are an example, they drive skeletal muscle-specific cellular differentiation.
What are the stem cells involved in muscle fibre regeneration called?
Satellite cells
The development of a functional musculoskeletal system is dependent on mechanic regulation of what 4 things?
• Cartilage morphogenesis • Joint formation • Bone morphogenesis • Tendon homeostasis