This presentation takes a breath look at the development pattern of the muscular system with specific reference to Human. It's Human Embryology.

1. Human Embryology (Zoo 404)
Development of The Muscular System
Presented by:
Benetta N. Kekulah
Rita V. B. Arkoi April 17, 2019

2. Presentation Outline
• Muscular system development
overview
• Striated skeletal musculature
• Sclerotome, dermatome, two
muscle-forming regions
• Development of somites
• Patterning of muscles
• Derivatives of precursor muscle
cells
• Head musculature
• Limb musculature
• Cardiac muscle
• Smooth muscle
• Conclusion

3. Muscular System Development Overview
• The formation of the muscular system begins about 4Th week of
embryonic development.
• The beginning cells are called Myoblasts
• Most of the muscular system develops from the mesodermal germ
layer
• Except some smooth muscle tissues (pupil, sweat glands and
mammary gland differentiate from ectoderm)

4. Overview Cont’d…
• The muscular system consist of;
• Skeletal musculature
• Cardiac musculature
• Smooth musculature
• Skeletal muscles are derived from paraxial mesoderm
• This forms;
• Somites from the occipital to the sacral regions
• Somitomeres in the head

5. Overview Cont’d…
• Smooth muscles differentiate from splanchnic mesoderm surrounding
the gut and its derivatives.
• Cardiac muscles are derived from splanchnic mesoderm surrounding
the heart tube

6. Striated Skeletal Musculature
• Musculature of the head, axial skeleton and body wall are formed by
Somites and somitomeres
• From the occipital region caudally, somites form and differentiate into;
• Sclerotome
• Dermatome
• Two muscle-forming regions
• One in the dorsolateral region of the somite provides progenitor cells for
limb and body wall musculature (hypomeric)
• The other in the dorsalmedial region forms the myotome (epimeric
musculature)

7. Development of Somites
Figure 1.1 Stages in the development of a somite.

8. Development of Somites

9. • Precursor cells, the myoblasts, fuse and form long, multinucleated
muscle fibers
• Myofibrils soon appear in the cytoplasm, and by the end of the third
month, cross-striations appear in skeletal muscle
• A similar process occurs in the seven somitomeres in the head region
rostral to the occipital somites
Development of Somites Cont’d…

10. Patterning of Muscles
• Patterns of muscle formation are controlled by connective tissue into
which myoblasts migrate
• In the head region these connective tissues are derived from neural
crest cells;
• in cervical and occipital regions they differentiate from somitic
mesoderm; and
• In the body wall and limbs they originate from somatic mesoderm

11. Derivatives of Precursor Muscle Cells
• By the end of the 5th week prospective muscle cells are collected
into two parts:
• Epimere (small dorsal portion) – innervated by the dorsal primary ramus
• Hypomere (larger ventral part) – innervated by the ventral primary ramus
• Myoblasts of the epimeres form the extensor muscles of the vertebral
column, and those of the hypomeres give rise to muscles of the limbs
and body wall

12. Derivatives of Precursor Muscle Cells
Figure 1.2 A. Transverse section through the thoracic region of a 5-week embryo. The dorsal portion of the body wall
musculature (epimere) and the ventral portion (hypomere) are innervated by a dorsal primary ramus and a ventral primary
ramus, respectively. B. Similar to A later in development. The hypomere has formed three muscle layers and a ventral
longitudinal muscle column.

13. Derivatives of Precursor Muscle Cells Cont’d…
• Myoblasts from cervical hypomeres form the scalene, geniohyoid, and
prevertebral muscles
• Those from thoracic segments split into three layers, which in the thorax
are represented by;
• External Intercostal
• Internal Intercostal
• Innermost Intercostal
• In the abdominal wall these three muscle layers consist of the external
oblique, the internal oblique, and the transversus abdominis muscles.

14. Derivatives of Precursor Muscle Cells Cont’d…
• Myoblasts from the hypoblast of lumbar segments form the quadrates
lumborum muscle
• Those from sacral and coccygeal regions form the pelvic diaphragm and
striated muscles of the anus.
• A ventral longitudinal column arises at the ventral tip of the hypomeres.
• This column is represented by the rectus abdominis muscle and the
infrahyoid musculature

15. Head Musculature
• All voluntary muscles of the head region are derived from paraxial
mesoderm (somitomeres and somites);
• Including muscle of the tongue, eye (except that of the iris, which is
derived from optic cup ectoderm), and that associated with the pharyngeal
(visceral) arches.
• Patterns of muscle formation in the head are directed by connective tissue
elements (Neural crest cells)

16. Limb Musculature
• Connective tissue dictates the pattern of muscle formation in the
limb
• Derived from the somatic mesoderm
• The mesenchyme is derived from dorsolateral cells of the somites
that migrate into the limb bud to form the muscles
• With elongation of the limb buds, the muscle tissue splits into flexor
and extensor components

17. Limb Musculature
Figure 1.3 Limb buds with their segments of origin indicated. With further development the
segmental pattern disappears; however, an orderly sequence in the dermatome pattern can still be
recognized in the adult. A. Upper limb bud at 5 weeks. B. Upper limb bud at 6 weeks. C. Limb buds
at 7 weeks

18. Limb Musculature
• The upper limb buds lie opposite the
lower five cervical and upper two
thoracic segments, and
• the lower limb buds lie opposite the
lower four lumbar and upper two
sacral segments

19. Limb Musculature Cont’d…
• As soon as the buds form, ventral primary rami penetrate into the mesenchyme.
• At first each ventral ramus enters with isolated dorsal and ventral branches, but
soon these branches unite to form large dorsal and ventral nerves
• The radial nerve is formed by a combination of the dorsal segmental branches
• The ulnar and median nerves are formed by a combination of the ventral
branches.
• Spinal nerves not only play an important role in differentiation and motor
innervation of the limb musculature, but also provide sensory innervations for
the dermatomes.

20. Cardiac Muscle
• Develops from splanchnic mesoderm surrounding the endothelia heart tube
• Myoblasts adhere to one another by special attachments that later develop
into intercalated discs.
• Myofibrils develop as in skeletal muscle, but myoblasts do not fuse
• During later development, a few special bundles of muscle cells with
irregularly distributed myofibrils become visible
• These bundles, the Purkinje fibers, form the conducting system of the heart.

21. Smooth Muscle
• Derived from splanchnic mesoderm surrounding the endoderm of the
gut and its derivatives
• ciliary muscle and sphincter papillae muscles of the eye are derived
from neural crest ectoderm
• Vascular smooth muscle differentiates from local mesoderm adjacent
to vascular endothelium

22. In Conclusion:
• Most muscles arise from the mesoderm in the 3rd week of embryonic development
• Skeletal muscles are derived from paraxial mesoderm, including somites, which give rise to
muscles of the axial skeleton, body wall, and limbs, and somitomeres, which give rise to muscles
of the head.
• Progenitor cells for muscle tissues are derived from the dorsolateral and dorsomedial portions of
the somites.
• Cells in the dorsolateral portion migrate to form hypomeric muscle; cells in the dorsomedial
portion migrate ventral to the dermatome to form the myotome, and ultimately form epimeric
musculature.
• By the 5th week muscle precursor cells are divided into a small dorsal portion, the epimere,
innervated by a dorsal primary ramus, and a larger ventral portion, the hypomere, innervated by a
ventral primary ramus

23. Reference
• Primary Reference : T.W. Sadler – Langman’s Medical Embryology -
9th And 12th Edi.
• Human Embryology and Developmental Biology – 4th Ed
Bruce M. Carlson, MD, PhD
Copyright © 2009, 2004, 1999, 1994

24. Thanks for your attention

25. → Nelson Mandela
“ Education is the great engine of personal development. It is through
education that the daughter of a peasant can become a doctor, that the
son of a mineworker can become the head of the mine, that a child of
farm workers can become the president of a great nation. It is what we
make out of what we have, not what we are given, that separates one
person from another.”