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Questions and Answers
What type of muscle is formed from splanchnic mesoderm surrounding the endothelial heart tube?
What type of muscle is formed from splanchnic mesoderm surrounding the endothelial heart tube?
Which nerves supply the flexor musculature?
Which nerves supply the flexor musculature?
Where do Purkinje fibers originate in the cardiac muscle system?
Where do Purkinje fibers originate in the cardiac muscle system?
What type of mesoderm contributes to the formation of smooth muscle in the gut?
What type of mesoderm contributes to the formation of smooth muscle in the gut?
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Which of the following structures is derived from ectoderm?
Which of the following structures is derived from ectoderm?
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Which cells give rise to the dorsal primary rami that innervate the epaxial muscles?
Which cells give rise to the dorsal primary rami that innervate the epaxial muscles?
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What type of connective tissue directs muscle formation in the head region?
What type of connective tissue directs muscle formation in the head region?
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At what point in development is the first indication of limb musculature observed?
At what point in development is the first indication of limb musculature observed?
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Which structure does mesenchyme derived from dorsolateral cells of the somites contribute to?
Which structure does mesenchyme derived from dorsolateral cells of the somites contribute to?
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Which muscles are associated with the visceral arches and derived from paraxial mesoderm?
Which muscles are associated with the visceral arches and derived from paraxial mesoderm?
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Which type of mesodermal layer originates the connective tissue that dictates muscle formation in the limbs?
Which type of mesodermal layer originates the connective tissue that dictates muscle formation in the limbs?
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As limb musculature develops, how does the tissue composition change over time?
As limb musculature develops, how does the tissue composition change over time?
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The innervation of hypaxial muscles comes from which type of rami?
The innervation of hypaxial muscles comes from which type of rami?
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From which germ layer does the muscular system primarily develop?
From which germ layer does the muscular system primarily develop?
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Which type of muscle is derived from splanchnic mesoderm?
Which type of muscle is derived from splanchnic mesoderm?
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What is the primary source of skeletal muscle in the human body?
What is the primary source of skeletal muscle in the human body?
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What do the ventrolateral and dorsomedial lips of the somite form?
What do the ventrolateral and dorsomedial lips of the somite form?
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What is the significance of the lateral somitic frontier in muscle development?
What is the significance of the lateral somitic frontier in muscle development?
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How do muscle cells that cross the lateral somitic frontier differ from those that do not?
How do muscle cells that cross the lateral somitic frontier differ from those that do not?
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What is a primary function of the neural tube in muscle development?
What is a primary function of the neural tube in muscle development?
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Which pair of terms is incorrectly matched according to the modern description of muscle development?
Which pair of terms is incorrectly matched according to the modern description of muscle development?
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Study Notes
Musculature Development
- The muscular system, with the exception of some smooth muscle, develops from the mesodermal germ layer.
- Skeletal muscle originates from paraxial mesoderm.
- Smooth muscle differentiates from splanchnic mesoderm.
- Cardiac muscle also originates from splanchnic mesoderm.
Striated Skeletal Musculature
- Head musculature is derived from seven somitomeres, which are paraxial mesoderm-derived.
- Axial skeleton, body wall, and limb musculature develop from somites, with the ventral region forming the sclerotome (vertebrae and ribs).
- The ventrolateral and dorsomedial lips of the somite form progenitor muscle cells that develop into dermomyotomes.
- Some cells from the ventrolateral region migrate to lateral plate mesoderm, contributing to infrahyoid, abdominal wall, and limb muscles.
- The remaining cells in the myotome develop into back, shoulder, and intercostal muscles.
Striated Skeletal Musculature (Continued)
- A border, the lateral somitic frontier, separates primaxial and abaxial mesodermal domains within the embryo.
- Muscle cells that cross the frontier into lateral plate mesoderm develop into abaxial muscle cells, receiving signals for differentiation from lateral plate mesoderm.
- Muscle cells remaining in the paraxial mesoderm (primaxial) receive developmental signals from the neural tube and notochord.
- Each myotome receives innervation from spinal nerves within the same segment.
Innervation of Axial Skeletal Muscles
- The new description of muscle development (primaxial and abaxial domains) replaces the older concept of epimeres and hypomeres (based on function).
- The new description is based on embryological origin rather than innervation.
- Epaxial muscles (e.g., back) receive innervation from dorsal primary rami.
- Hypaxial muscles (e.g., body wall, limbs) are innervated by ventral primary rami.
Patterning of Muscles
- Connective tissue guides muscle formation and myoblast migration.
- Neural crest cells contribute to head region connective tissue.
- Somatic mesoderm forms connective tissue in cervical and occipital regions.
- Parietal layer of lateral plate mesoderm contributes to connective tissue of body wall and limbs.
Head Musculature
- All voluntary head muscles and associated musculature of the tongue, eyes, and pharynx are derived from paraxial mesoderm (somitomeres and somites).
- Head muscle patterning is controlled by neural crest cells.
Limb Musculature
- Limb musculature develops in the seventh week as mesenchyme condensation near limb buds from dorsolateral somite cells.
- Connective tissue (from parietal layer of lateral plate mesoderm) guides formation and is essential for limb skeletal development.
- Limb muscles initially have segmental organization (flexors/extensors).
- Ultimately, limb muscles fuse and consist of tissue from multiple segments.
Limb Musculature (Continued)
- Ventral primary rami from the appropriate spinal nerves penetrate limb bud mesenchyme, with initial separate dorsal and ventral branches.
- These unify to form larger dorsal and ventral nerves, ultimately contributing to nerves like the radial (extensor musculature) and ulnar/median (flexor musculature).
- Spinal nerves also innervate limb musculature and supply sensory input to dermatomes.
Cardiac Muscle
- Cardiac muscle develops from splanchnic mesoderm adjacent to the heart tube.
- Myoblasts connect via intercalated discs, resembling skeletal muscle myofibrils.
- Specialized bundles (Purkinje fibers) emerge for conducting the heart's electrical system.
Smooth Muscle
- Smooth muscle for the dorsal aorta and large arteries originates from lateral plate mesoderm and neural crest cells.
- Coronary arteries derive smooth muscle from proepicardial cells (proximal segments).
- Smooth muscle within the digestive system arises from the splanchnic layer of lateral plate mesoderm.
- Muscles of the pupil and mammary/sweat glands develop from ectoderm.
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Description
Explore the intricate processes involved in the development of the muscular system, including skeletal, smooth, and cardiac muscles. Learn how each muscle type originates from different mesodermal layers and the significance of somitomeres and somites in muscle formation.
