muscle organ development

Definition

Target type: biologicalprocess

The process whose specific outcome is the progression of the muscle over time, from its formation to the mature structure. The muscle is an organ consisting of a tissue made up of various elongated cells that are specialized to contract and thus to produce movement and mechanical work. [GOC:jid, ISBN:0198506732]

Muscle organ development is a complex and tightly regulated process that involves the coordinated action of multiple cell types and signaling pathways. It begins with the specification of muscle progenitor cells, known as myoblasts, from the mesoderm, the middle layer of the developing embryo. Myoblasts undergo a series of proliferative and differentiation steps to form mature muscle fibers, the basic functional units of muscle tissue.

**1. Muscle Progenitor Specification:**
* During early embryonic development, the mesoderm, a germ layer that gives rise to various tissues, is patterned into distinct domains.
* Signals from neighboring tissues, such as the notochord and the neural tube, induce the formation of somites, segmented blocks of mesoderm that will give rise to skeletal muscle, vertebrae, and dermis.
* Within the somite, a specific region called the dermomyotome gives rise to myoblasts.
* Transcription factors, such as Myf5 and MyoD, play crucial roles in specifying myoblasts and committing them to the muscle lineage.

**2. Myoblast Proliferation and Differentiation:**
* Once specified, myoblasts proliferate rapidly to increase their numbers.
* They express specific cell surface markers, such as Pax7, and exhibit a high level of cell division.
* When the appropriate signals are received, myoblasts exit the cell cycle and initiate the differentiation process.
* This involves the activation of genes encoding muscle-specific proteins, such as myosin, actin, and troponin.
* Myoblasts align themselves in parallel, fusing together to form multinucleated myotubes.

**3. Myotube Maturation and Fiber Formation:**
* Myotubes undergo further maturation, acquiring a characteristic elongated shape and developing a complex internal organization.
* The cytoplasm of myotubes is filled with myofibrils, the contractile units of muscle fibers.
* Myofibrils are composed of highly organized arrays of actin and myosin filaments, which interact to generate muscle contraction.
* Myotubes also form specialized junctions, such as neuromuscular junctions, where they receive signals from motor neurons.
* As myotubes mature, they differentiate into distinct muscle fiber types, such as slow-twitch fibers for endurance and fast-twitch fibers for strength and speed.

**4. Muscle Growth and Remodeling:**
* After birth, muscle growth continues through a process called hypertrophy, involving the increase in size and number of muscle fibers.
* Satellite cells, quiescent stem cells located within the muscle fiber membrane, contribute to muscle growth and repair.
* During muscle injury or exercise, satellite cells are activated and differentiate into myoblasts, which fuse with existing muscle fibers or form new fibers.
* Muscle tissue is constantly remodeled throughout life, responding to factors such as exercise, aging, and disease.

**5. Muscle Organogenesis:**
* Muscle development is not limited to the formation of individual muscle fibers.
* Different muscle fibers group together to form muscle fascicles, which are further organized into muscle bundles.
* Muscle bundles are surrounded by connective tissue sheaths, which provide structural support and allow for efficient transmission of force.
* Muscle organs, such as the biceps or triceps, are composed of multiple muscle bundles and their associated connective tissue, blood vessels, and nerves.'
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Proteins (10)

Compounds (184)