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Muscular development


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Primary type of muscle precursor:
3 types of muscle precursor origin:
-Paraxial mesoderm
-Splanchnic mesoderm
-Neural crest ectomesenchyme
What will splanchnic mesoderm form?
Cardiac and smooth muscle (except goosebumps)
What will paraxial mesoderm become?
Skeletal muscle
Where will muscle derived from Neural Crest ectomesenchyme form?
In certain areas of the head, neck and upper thorax.
Specific marker of cells destined to become muscle:
MyoD gene
Paraxial mesoderm
What is the main difference between Premyogenic mesoderm and Myoblasts?
Premyogenic = mitotic

Myoblasts = postmitotic; can migrate
What are satellite cells?
Mitotic cells that stay with muscle fibers so that in case of injury they become postmitotic and help repair.
What are the 4 steps of muscle formation?
1. Mitotic cells turn on MyoD
2. Post-mitotic myoblasts migrate & become muscle spcfc.
3. Myoblasts fuse -> Myotubes
4. Myotubes -> skeletal muscle
What are muscles in Head/Neck derived from?
Innervated by?
Somitomeres & Occipital myotomes
-Cranial nerves
What are muscles in Trunk/Limbs derived from?
Innervated by?
Paraxial mesoderm
-Spinal nerves
What is smooth muscle derived from?
Splanchnic mesoderm
What is unique about smooth muscle cells?
Retain ability to divide
What germ layers contain vscular smooth muscle precursors?
How does cardiac muscle differ from smooth?
Immature cardiac myoblasts can divide while beating & maturing, but mature myocytes are postmitotic.
What is the most common muscle to be absent due to malformation of muscular system?
Sternocostal head of Pectoralis Major
What is the syndrome where abdominal muscles are absent?
Prune belly syndrome
What is the disease in which there is fixed rotation and tilting of the head?
Congenital Torticollis
Family of genetic diseases w/ progressive deterioration of skeletal muscle:
(what is NOT in the pathology?)
Muscular dystrophy - does not have nervous system pathology.
Most common type of muscular dystrophy:
Duchenne type
Inheritance pattern of duchenne type MD
X-linked recessive - in boys
What is the problem in Duchenne type MD?
Lack of Dystrophin in myocytes - myocytes susceptible to damage when physically stressed.
How does Connective Tissue change as it matures?
Embryonic CT: HI CELL:ecm ratio

Mature CT: High ECM:cell ratio
What is the only muscle to form from Ectoderm/Neural crest?
Iris muscles
What does lateral plate mesoderm associate with to form
-Skeletal components?
-Splanchnic mesoderm/Muscle?
Skeleton = w/ Ectoderm

Muscle = w/ Endoderm
What muscle forms from lateral plate splanchnic mesoderm?
-Cardiac muscle
-Smooth muscle
What can vascular smooth muscle have as its precursors?
Mesoderm OR neural crest

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