23 - Muscular System Devo Flashcards
What is muscle specialized for? What are the three types?
Tension.
Skeletal, cardiac (both striated), and smooth.
Why are named skeletal muscles considered organs?
because they contain multiple tissues- muscle, nerve, and CT.
What is skeletal muscle derived from?
Paraxial mesoderm.
Muscles of the body wall and limbs form from somites.
Skeletal muscle in the head region of the embyro and some in the neck originate from head mesoderm.
The smooth muscle of the constrictor and dilator papillae muscles as well as myoepithelial cells of hte mammary and sweat glands origintates from where?
Ectoderm.
What are characteristics of muscle precursor mesenchyme?
Muscle forming mesenchyme often migrates or is displaced from its site of origin.
Its development is mediated by specific transcription factors:
Myogenic regulatory factors: MyoD, Myf5, Myf4, myogenin, Mef2
Signaling molecules: FGF, Wnt, TgfB
Describe the formation of skeletal muscle precursors?
Tunk and limb sk. muscle derived from somites.
Somites are a transient structure in which precursor cells for sk. muscle, bone, cartilage, and CT can be grouped and redistributed to the appropriate areas.
What helps dorsal somites redistribute in the embryo?
Cells in the dorsolaeral or dorsal part of the somate are under the influence of Wnts originating from the neural tube and surface ectoderm.
These cells maintain their epithelial character and become dermamyotone (DM), a transient structure containing cells with multiple fates.
Some cells of the dermomyotome are exposed to a gradient of what? What other molecules are present? What is the result of these molecules being present?
Bmp4 originating from lateral mesoderm; gradient modulated acress the DM by noggin (a bmp inhibitor) originating from the neural tube.
Other DM cells are influenced by Wnt and Shh from the neural tube and notochord.
Cells in the dorolateral and dorsomedial edges of the DM undergo epithelium to mesenchyme transformation and relocate beneath the epithelial portion.
What happens after the epithelium to mesenchyme transformation (EMT)?
Cells become myogenic (muscle precursor) and form a layer called the myotome.
These are precursors for the skeletal muscle of the trunk and limbs.
Cells in the central portion of DM remain epithelium.
What happens to the two populations precursor cells: the ones that stay in the central portion of the DM and remain epithelium and the ones that have undergone EMT?
One population undergoes and EMT and migrate into the underlying myotome. Many of them form satelite cells.
Second population undergoes EMT andthese mesenchyme cells contibute to the formation of the dermis on the back and neck. This has been tradiaitonally called thedermatome.
The lateral somite frontier is the border between the lateral edge of the osmate and the medial edge of the lateral mesoderm, what is its significance?
It’s an interface of signaling molecules that defines two two environments within DM derived myogenic cells develop.
What happens to cells originating from the dorsomedial portion of the DM?
Remain by the neural tube and notochord where they are influenced by Wnt and Shh.
They express Myogenic Regulatory Factors Myf 5 and MyoD and form the intrinsic muscles of the back as well as the prevertebral and intercostal muscles.
All of these muscles become attached to bones derived from the scleratome cells of the somite. This domain is called the Primaxial Domain.
What happens to the myotome derived cells from the ventrolateral edge of the DM?
Migrate acress the LSF into somatic mesoderm where they recevie patterning signals.
Under influcence of Wnt and Bmp4, they express regulatory factor MyoD.
These will become muscle of the ab. wall and the limbs and the infrahyoid muscles. This is called the abaxial domain.
What are myogenic cells? What do these eventually become? What do they make?
Cells that have become part of the myotome portion of the DM and have had their developmental potency restricted to the skeletal muscle lineage.
These eventually become post-mitotic, commited myoblasts by upregulating factors that remove them from the cell cycle.
Myoblasts begin making actin and myosin.
Myoblasts secrete fibronectin, align into chain of myoblasts, and fuse to become what?
Multinucleated myotubes. This process requires M-cadherin.
In myotubes, troponin and topomyosin mediate myofiber and sarcomere formation resulting in a differentiated muscle cell/fiber.
What abnormalities are associated with Poland Sequence?
Absence of pec major and pec minor muscles, resulting in a nipple that’s displaced laterall or missing entirely.
- Associated breast tissue is hypoplastic of mission and there’s a deficiency in the subQ fat and axillary hair.
- Rib cage may also be hypoplastic
- Syndactyly and brachydactyly may occur
This condition is twice as common on the right side.
What is Prune Belly Syndrome? Who gets it?
Condition characterized by three defects:
- Absence of abd. muscles
- Undescended testicles
- Bladder and urinary tract anomalies
Prenatal accum of fluid in the lower abdomen due to anomalies may interfere with development. After birth this fluid os reduced, causing the skin over the area to be wrinkled.
Occurs exclusively in males (1 in 40,000)
What is {congenital} muscular torticollis?
Fixed rotation and tilting of the head to one side. More common in the right side, those affecterd have congenital hip dysplasia. May occur due to:
- Primary defect in the SCM or from insufficient space of the fetus in the uterus.
- Acquired plagiocephaly (symmetry distorted skull).
- In older kids, secondary to infections or SCM trauma
