Development of Muscular System Flashcards
What is skeletal muscle derived from?
Paraxial mesoderm
What is cardiac and visceral smooth muscle derived from?
Splanchnic Mesoderm
What is vascular smooth muscle derived from?
Local Mesenchyme
What developmental anatomy do the skeletal muscles of truck and limbs originate from?
Somites
What part of the somite does the dermomyotome derive from?
The dorsolateral or dorsal part of the somite under the influence of Wnts
What part of the dermatomyotome undergoes an epithelial to mesechymal transformation? And what happens when this occurs?
The dorsomedial and dorsolateral edges
They become myogenic – called Myotome
What is the myotome a precursor for?
For skeletal muscle of the trunk and limbs
What regulatory factors form the intrinsic muscles of the back? What domain is this?
Myf5 and MyoD
Primaxial domain
What myogenic regulatory factor induces the muscles of the abdominal walla nd the limbs of the infrahyoid muscles? What domain is this?
MyoD
Abaxial domain
What happens after myogenic cells become comitted byoblasts?
They being to synthesize actin and myosin
They reach their definitive location in the embroy and secrete adhesive glycoprotein, fibronectin.
They align in chains of myoblasts – which fuse to become multinucleated myotubes (requires M-cadherin)
What mediates myofiber and sarcomere formation?
Troponin and tropomyosin
Create a differentiated muscle cell/muscle fiber
When is skeletal muscle fiber formatino completed?
At birth!
What accomplishes myogenic postnatal growth of skeletal muscle? What mediates their expression?
Myogenic stem cells – satellite cells
Pax 3 and Pax 7
What are some proposed strategies for the formatin of individual skeletal muscles?
- Change in fiber direction
- Fusion of adjacent myotomes
- Longitudinal splitting
- Tangential splitting into layers
- Atrophy of a part
- Migration
How do skeletal muscles become innervated?
Myotome is divided into Epaxial (dorsal) and Hypaxial (ventral) portions
Epaxial portion of myotome (intrinsic muscles of back) receives motor innervation from dorsal primary rami.
Hypaxial portion of dermatome (ventrolateral body wall and limb muscles) receives motor innervation from ventral primary rami.
What are the master regulators of smooth muscle gene expression?
Serum Response Factor (SRF)
Myocardin
What does smooth muscle orignate from?
Splanchnic mesoderm
What are smooth muscles able to do postnatally?
Divide in response to extracellular signals
What is cardiac muscle derived from?
Splanchnic mesoderm of the primary and secondary heart fields
What transcription factors regulat cardiac myocyte formation?
GATA 4 & 6, Foxp1, Nkx2.5 and twist
Also BMP and FGF
What is muscular dystrophy?
Family of genetic diseases exhibiting progressive weakness and deterioration of skeletal muscle cells without CNS or peripheral nervous pathology
Duchenne Type: most common, x-linked recessive, affects boys in early childhood, myocytes lack dystrophin
Becker’s Type: later onset and milder condition
What is congenital torticollis?
Fixed rotation and tilting of the head to one side
More common on rights side
May have congential hip dysplasia too
What is Prune Belly Syndrome?
Three defects:
1) absence of abdominal muscles
2) undescended testicles
3) bladder and urinary tract abnormalities
Prenatal accumulation of fluid in the lower abdomen due to urinary system snomalies may interfere with devo or cause degen of ab muscles
What is Poland Sequence?
Characterized by absence of pectoralis major and the pectoralis minor muscles
Nipple on that side is displaced laterally or missing
Rib cage hypoplastic, Upper limb anomalies – shortened limb segments and hand defects (syndactyly and brachydactyly)
Twice as common on right side, and more prevalent in males
