Dr. Sama ul Haque
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Understand the development of muscles
(skeletal, cardiac and smooth).
Explain somite formation.
Describe the development of limb musculature.
Enlist the derivatives of Primaxial & Abaxial
domains.
Define the relation of muscle with its nerve
supply.
Formation of Bilaminar Germ Disc
Primary Germ Layers (Gastrulation)
 Endoderm forms epithelial lining of GIT & respiratory
Systems.
 Mesoderm forms muscle, bone & other connective tissues.
 Ectoderm develops into epidermis of skin & nervous
System.
Primary Germ Layers (Gastrulation)
Development of the Notochordal Process
About 18 days of development the intraembryonic
mesoderm divides into three parts:
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Paraxial mesoderm
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Intermediate mesoderm
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Lateral mesoderm
The muscular system develops from Mesoderm
EXCEPT
Iris which develop from ectoderm
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Skeletal muscle is derived from paraxial
mesoderm
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Smooth muscle differentiates from
splanchnic mesoderm surrounding the gut
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Cardiac muscle is derived from splanchnic
mesoderm surrounding the heart tube
Myoblasts: Embryonic muscle cells
(Derived from mesenchyme)
Mesenchyme: Embryonic connective tissue
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Somite - At the end of the third week, the paraxial
mesoderm forms a segmented series of tissue blocks
on each side of neural tube, known as Somitomeres
in the head region and somites from the occipital to
the sacral region
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Myotome - A muscle or group of muscles derived
from one somite and innervated by a single segment
of a spinal nerve
At the end of the fifth week, muscle cells are
collected into two parts:
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Primaxial domain (Epimere) – Portion of the
somite (Paraxial mesoderm) around neural tube
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Abaxial domain (Hypomere) – Somites having
cells along with lateral plate mesoderm
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Dorsal primary ramus innervating segmental muscles
for the epimere and a ventral primary ramus for the
hypomere
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Myoblast:
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Fused and form long, multinucleated muscle
fibers.
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Myofibrils appear in the cytoplasm during or
after fusion of the myoblast.
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By the end of the third month cross-striations
appear.
From Primaxial:
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Scalenes
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Prevertebral
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Geniohyoid
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Intercostals
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Rhomboids
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Levator scapulae
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Latissimus dorsi
From Abaxial:
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Infrahyoid
Pectoralis major and minor
External and Internal Oblique
Tranversus Abdominus
Sternalis
Rectus Abdominus
Pelvic Diaphragm
Distal limb muscles
All lower limb muscles
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All voluntary muscles of the head, eye,
tongue and pharyngeal arches derived from
Somitomeres (Paraxial Mesoderm).
Except Iris which develop from ectoderm
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In the 7th week of development limb musculature is
developed from mesenchyme near the base of the limb bud
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The mesenchyme is derived from Dorsolateral cells of the
Somites.
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With elongation of the limb buds, the muscle tissue splits
into flexor and extensor components
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The upper limb buds lie opposite the lower five cervical
and upper two thoracic segments
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The lower limb buds lie opposite the lower four lumbar
and upper two sacral segments
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Develops from splanchnic mesoderm surrounding
the heart tube
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Myoblast adhere to one another by special
attachments that develop into intercalated discs
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Myofibrils develop in the cytoplasm
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A few special bundles of muscle cells with
irregularly distributed myofibrils, called Purkinje
fibers - form the conducting system of the heart
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Smooth muscle in the wall of the gut and gut
derivatives is derived from splanchnic
mesoderm surrounding the gut tube
Vascular smooth muscle differentiates from
splanchnic mesoderm adjacent to vascular
endothelium