Muscular muscles

• Actin


  Protein that is pulled by myosin to initiate muscle contraction
• Myosin


  Protein that pulls actin to initiate muscle contraction
• Muscle contraction


  Pulling together of actin and myosin
• Components of vertebrate muscular system

  • Atrial
  • Appendicular
  • Branchiomeric
  • Hypobranchial
• Hypobranchial muscles are included in the branchiomeric muscles
• Axial muscles


  Muscles that run along the axial region of the body
• Appendicular muscles


  Muscles that are inserted to the appendages and function to move the appendages
• Branchiomeric muscles


  Muscles in the pharyngeal visceral region
• Integumentary muscles


  Muscles that function for the skin, either for protection or for thermoregulation
• Types of muscle tissue

  • Skeletal
  • Cardiac
  • Smooth
• Microscopic organization of contractile proteins

  • Actin and myosin are arranged very regularly in the cytoplasm of individual muscle cells (muscle fibers) in skeletal and cardiac muscles
  • Actin and myosin are not arranged in such intimate regular fashion in smooth muscle, resulting in a uniform, non-striated appearance
• Smooth muscle lines the visceral organs
• Individual muscle cells are referred to as fiber or muscle fiber
• Epimysium


  Dense connective tissue that covers skeletal muscles
• Tendon


  Connects skeletal muscles to bones
• Fascia


  Connective tissue outside the epimysium that surrounds and separates the muscles
• Fascicle


  Bundle of muscle fibers within a muscle
• Perimysium


  Connective tissue layer that surrounds each fascicle
• Endomysium


  Connective tissue layer that surrounds each individual muscle fiber
• Myofibrils


  Contractile units within each muscle fiber
• Muscle contraction


  Nerve impulses cause the actin and myosin filaments to slide over each other, resulting in muscle contraction
• Skeletal muscles arise from embryonic mesoderm
• Somites


  Blocks of cells that form from the parietal mesoderm adjacent to the neural tube
• Skeletal muscles, excluding those of the head and limbs, develop from the myotome of the mesodermal somites
• Skeletal muscles in the head and limbs develop from the general mesoderm
• Myoblasts


  Muscle-forming stem cells that migrate to different regions and fuse to form myotubes
• Myotube


  Structure formed by the fusion of multiple myoblasts, containing many nuclei but a continuous cytoplasm
• Skeletal muscle cells are multinucleated due to the intact nuclei from the contributing myoblasts
• Cardiac and smooth muscle cells do not fuse during development, hence they are not multinucleated
• Satellite cells


  Stem cells that incorporate into muscle cells and facilitate protein synthesis for growth and repair
• Sarcolemma


  Membrane that covers each muscle fiber, containing myofibrils and mitochondria
• Pericytes


  Stem cells found in small blood vessels that allow smooth muscles to regenerate and repair more readily compared to skeletal and cardiac muscles
• Development of Skeletal Muscles

  • Skeletal muscles in the head and limbs develop from the general mesoderm
  • Myoblasts, originating from somites, form myotubes by fusing together
  • Myotubes have multiple nuclei but continuous cytoplasm
  • Skeletal muscle cells are multinucleated due to intact nuclei from contributing myoblasts
  • Cardiac and smooth muscle cells do not fuse during development, hence they are not multinucleated
  • Satellite cells incorporate into muscle cells, facilitating protein synthesis for growth and repair
  • Satellite cells can regenerate muscle fibers to a limited extent
• Types of Skeletal Muscle Fibers

  • Slow twitch muscle fibers (Type 1) use oxygen for extended contraction, providing endurance
  • Slow twitch fibers have numerous blood vessels, mitochondria, and myoglobin
  • Fast twitch muscle fibers (Type 2A and 2B) utilize anaerobic metabolism
  • Fast twitch fibers have fewer blood vessels, mitochondria, and myoglobin
  • Different muscles contain varying combinations of slow and fast twitch fibers
• Categories of Muscles

  • Somatic or skeletal muscles arise from the epimere or parietal mesoderm, attached to axial and appendicular skeleton
  • Visceral muscles arise from splanchnic mesoderm, operate involuntary movements in internal organs
  • Brachymeric somatic muscles operate movement of pharyngeal arches, innervated by cranial nerves
• Muscle Anatomy and Function

  • Muscles have origins, insertions, and bellies
  • Tendons connect muscles to bones; aponeurosis acts as insertion sites and absorbs energy
  • Skeletal muscle actions depend on origin, insertion, and shape, regulated by the cerebellum
  • Muscles classified by actions such as extensors, flexors, adductors, abductors, pronators, supinators
• Axial and Appendicular Muscles

  • Axial muscles extend from base of skull to tails, categorized into apexials, longissimus, spinalis, and iliocostalis
  • Hypaxial muscles categorized into subvertebralis, oblique sheaths, transverse sheaths, and rectus abdominis
  • Diaphragm, a major muscle for respiration, is an example of a hypaxial muscle
  • Appendicular muscles categorized as intrinsic and extrinsic, with intrinsic muscles lying deep and extrinsic superficially
• Branchiomeric and Integumentary Muscles


  • Branchiomeric muscles operate jaws and gill arches in fishes, and support vocal cords and tongue muscles in tetrapods
  • Hypobranchial muscles innervated by cervical spinal nerves
  • Integumentary muscles categorized as intrinsic and extrinsic, with intrinsic muscles lying within the dermis
• Specialized Muscles

  • Paniculous carnosus in mammals provides skin twitching and contraction functions
  • Platysma and facial muscles derived from hyoid arch muscles, innervated by cranial nerves
  • Electric organs in eels serve as specialized muscles for generating electric discharges
• Muscles are categorized into

  • Somatic or skeletal muscles
  • Visceral muscles
  • Brachymeric somatic muscles