Muscles Development: Mesoderm Derivatives

Muscles in Different Life Stages

• Muscles and their annexes derive from the mesoderm.
• The mesoderm includes the paraxial mesoderm (1), intermediate mesoderm (2), and lateral mesoderm (3), which includes somatic (4) and splanchnic (5) components.
• Paraxial mesoderm develops into somites, then into dermatome, miotome, and sclerotome.
• Precordal myotomes form the ocular musculature.
• Paracordal myotomes form tongue muscles, specifically from occipital somites.
• Spinal myotomes form the muscles of the spine; epiaxial portions create the muscles of the rachis, while hypoaxial portions form the flexors of the rachis on the anterior of the neck, torso, abdomen and diaphragm.
• The dermatome forms the cutaneous muscles and dermis.
• Intermediate mesoderm forms the smooth musculature of the urogenital ducts.
• Lateral mesoderm forms the branchial, somatic, and splanchnic mesoderm.

Mesoderm Derivatives

• Branchial mesoderm creates masticatory muscles, facial muscles, palatal muscles, pharynx and larynx muscles, sternocleidomastoid, and trapezius.
• Somatic or parietal mesoderm forms the muscles of extremities (ventral-flexor, dorsal-extensor)
• It also forms the thoracic diaphragm, anal sphincters, and urogenital sphincters.
• Splanchnic or visceral mesoderm gives rise to the digestive system, respiratory system, heart, blood vessels, bladder and urethra.

Muscle System Development

• Muscle system development involves:
  • Preotic myotomes
  • Branchial mesoderm
  • Occipital myotomes
  • Cervical myotomes
  • Thoracic myotomes
  • Lumbar myotomes
  • Sacrococcygeal myotomes

Myogenesis

• Myogenesis is the process of determination and formation of muscular tissue.
• In the embryo, there are mesodermal progenitor cells, which differentiate into myoblasts.
• Early myotubes form, maturing into mature myotubes.
• The process is influenced by growth factors, myogenin (MEF2), MRF4, and MLP.
• Myogenesis involves determination, differentiation, and maturation.

Myogenesis Cellular Process

• Mesodermal precursor cells become embryonic myoblasts.
• Then those become primary myotubes and secondary myotubes.
• Then those become mature myotubes that specialize metabolically to become contractible muscle fibers forming the motrices.
• Satellite cells contribute to plasticity.

Myogenesis Signals

• Signals involved in myogenesis include BMP4, Noggin, Wnts, Myf5, Pax3, MyoD, and Wnt7a.
• Pax3 influences somitic and endothelial cells.
• MyoD/Myf5 create myoblasts.
• Myogenin/MRF4 create myocytes.
• Pax7 influences satellite cells.
• The stages of myogenesis are induction, proliferation, and aggregation.
• Induction involves cells of the dermatome and somite.
• Myoblasts differentiate into epaxial and hipoaxial structures due to varying signals.
  • Epaxial structures are Wnt1 related and connected with the Myf5 gene due to Pax 3.
  • Hypoaxial structures are Wnt7a, BMP4, and Noggin related, connecting with MyoD via Pax 3.
• Proliferation and Migration: Myoblastes are subject to migration.
• Aggregation occurs when myoblastes differentiate to miochits which leads to: changes of proteic expression, activation of the miogenic cycle, and MAPK p38 process
• Determination of specific myochit type that leads to maturation.

Muscle Fiber Specification and Time

• Somitic dermomyotome differentiates into myotomal cells.
• Stem progenitor cells (Pax3 and Pax7) becomes embryonic myoblasts becomes If fibers.
• Stem progenitor cells (Pax3 and Pax7) becomes fetal myoblasts becomes If fibers.
• The myotomal cells form myocytes (myotome) and one fiberes.
• Satellite cells go through regeneration.
• There is a non-somitic progenitor developmental pathway timeline for mouse muscle.

Brown vs White Adipose Tissue

• Paraxial mesoderm creates Myf5-positive cells which differentiate into brown adipose tissue.
• Lateral mesoderm creates Myf5-negative cells which differentiate into white adipose tissue.

Satellite Cells and Differentiation

• Satellite cells are activated through MyoD/Myog, leading to proliferation and differentiation.
• Process leads to fusion to mature myotubes which leads to myofibers.
• Adipocytes form from pre-adipocytes.

Myogenesis Key Points

• Somites migrate, proliferate, and differentiate into myoblasts.
• Myoblasts undergo fusion, forming myotubes.
• Myogenesis involves the formation of islets of cells that then fuse into myoblasts, which becomes a myotub.
• Fusion occurs through interdigitations and pores

Myogenesis and Myofibrillogenesis

• Myogenesis leads to a myotube where myofibrillogenesis begins
• Myofibrillogenesis steps:
  • Synthesis
  • Aggregation
  • Assembly

Muscle Annexes

• Muscle annexes include fasciae, sheaths, and synovial bursae.
• Vessels include arteries, veins, and capillaries (2000 cap/mm²).

Muscle Metabolism and Repair

• ATP production involves phosphocreatine, glycolysis, and aerobic metabolism.
• Muscles metabolize glucose, lipids, and proteins during exercise.
• Nutritional intake of aliments favors the reparation and regeneration which leads to HC like proteins.
• Hormonal system consists of adrenaline, and testosterone and IGF-1 hormones increase synthesis that produces muscle mass.
• Activation occurs through muscle workout, hormones, creixement and forca.
• Muscle injury causes sarcomere and membrane breakage, leading to inflammation and myalgia.
• Breakage stimulates muscle growth.
• The response to muscular injury is an immune response, shown through increasing blood flow and tumefaction leading to oxygen, nutrients and the eliminating of material.
• Stimulated myonuclei synthesize protein which leads to muscle size and muscle capacity.
• Exercise facilitates synthesis through available amino acids, hormonal regulation, mechanic stress, and proper hydration.
• Adequate intake is achieved through proteins and carbohydrate dieting.

Muscle Growth

• Muscle growth requires stimulation and sufficient energy intake (diet).

Increasing Fiber Size

• Fiber size increases through the hormonal and immune system and support of satellite cells.

Skeletal Muscle Regeneration

• Resting myofibers, activated from HGF go through self-renewal and then they become differentiated.
• Regenerating muscle is through the differentiation and fusion to damaged myofibers.
• Activated, proliferating, and quiescent cells undergo regeneration through the caveolin 1 protein.

Lesion Results

• Muscle lesions result in degeneration, which then branches through a line to regeneration and there is a branch to reparation.

Muscle Degeneration

• Muscle degeneration is initiated by a lesion.
• Sarco tubule leads to H2O entrance into the degeneration area.
• There is an output of the citoplasmic contengut which causes an inflamatory reaction which leads to: Hidratacio Sarco Plasam and that leads to: balonitzacio Sarco tubular and mitochondria.
• Ruptura causes the sarcotubiccular and mitochondria to move out.
• Ca2+ starts to move into the muscle lesion.
• CANP then goes into the muscles which aids the digestió of ap contràctil which causes an entrance of c. inflamatories.

Muscle Cleanup

• A cleanup process through the removal of protein rests
• Inflammatory cells are then released.
• There is a muscle satellite cell activation.
• The satellite cell transforms to mioblasts which creates proliferació of muscle.

Myoblast Fusion and Repair

• Miblast merges with rest of muscles.
• Miofibrilogènesi causes a release reaction to create new myofibres.
• Assemblage happens to form miofibres.

Regenerated muscle

• Regenerated myofibers are interconnected by existing fibres.
• Ensamblatge causes muscle fibres to connect

Muscle Repair without regeneration

• The fibroblaste starts to operate to repair the lesioned fibers which leads to H20 entrance.
• This then leads to infammatory cells.
• Formation of miofibres starts to grow, but the ensamblatge causes a muscle with scaring.

Muscle Healing Timetable - 24-48 hrs

• High score on inflamatòria of +++.
• There is a high Balonitzacio between the Mitocondries and Sistema sarcotubular.
• The cell satèl·lit gets activated and has a large spread of mioblasts.
• Moderate activity of fibroblastes (Colli II)
• Inflammatory score is ++
• Mitoblasts +++
• Mitotubs +
• there is a high level of Activitat in fibroblastes (Colli II): +++

Muscle Healing Timetable - 4-10 Days

• Day 4, + inflamatories, ++ mioblasts and +++ in miofilaments in collagen.111
• Day 5, +++ in sarcomers and Col. lagen +++
• Day 6, ensamblatge level starts to get more stable and the Col lagen amount is moderate ++
• Day 10, muscles get super mature and the collagen levels are on +

Muscle Healing Considerations

• 24-28 hour, Retracció(lesió propera) and Cons de creixement (sprouts) occur
• Possible Combinations during Muscle Healing: -normal + retracció with sprouts+ retractio and sprouts.
• Day 3, The majority of muscle fibers which 80% have injury will have sinapsis.
• Day 5, if something bad happens to the l’area where synaptic activities take place that means that a “sinaptogènesi” occurred in the muscles.

Muscle Healing Factors

• Preservation in a good muscle healing environment is: The laminin, irrigation, architecture which determines what good muscle regenerations looks like.
• In terms of areas of the lesioned injury, having small area lesions will cause less chance of injuries to other tissue in that areas.
• The types of lesion helps determine the right type of regeneration.

Muscle Injury Considerations

• Factors for a good muscle regeneration depends upon type.
  • Area of injury.
  • Irrigation level.
  • The laminin integrity -The architecture.
• Different types of Talls Fractura Matxacat, Congrelacio cremada and exercicis and anestesics are factors that affect the muscle.