Skeletal Muscle

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Skeletal Muscle
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Bursa(e)

• Represent a device for freedom of motion between
  connective tissue surfaces.
• Found where a tendon glides over the periosteum
  of a bone.

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• Bursae are closed sacs resembling structually a
  joint capsule.
• Bursae are of two types
• 1. congenital-develop before birth and are
  constantly present at the same site of body.
• 2. aquired bursae-devlop after birth and
  generally develop subcutaneously over bony
  enlargements

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• Can also be submuscular, subfascial,
  subtendinous, and subligamentous.
• Bursae are frequently the site of pain, and once
  diagnosed, it is important to find the bursae and
  directly reach it.
• Two subcutaneous bursae are of special
  importance
• Olecranon bursae-elbow
• Calcaneal bursa-hock

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Tendons

• Composed of dense , white , fibrous, connective
  tissue.
• Can be seperated into peritendon-surrounds the
  bundles
• mesotendon-provides blood supply to the tendon

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• paratendon-surrounding nonsheathed
  tendons-furnishes blood supply and aids the
  tendon to glide.
• Tendon sheaths, thoracic limb
• 1. flexor carpi radiallis tndon sheath-begins
  above knee to almost insertion
• 2. carpal synovial sheath-begins 3or 4" proximal
  to carpus to middle of metacarpus
• 3. Digital synovial sheath-2or 3" proximal to
  fetlock to middle of PII.
• 4. Extensor carpi radialis -begins 3to 4"
  proximal to carpus to middle of carpus

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• 5. Common digital extensor- 3 or 4" proximal to
  carpus to proximal end metacarpus
• 6. lateral digital extensor tendon-3 to 4"
  proximal to carpus to end metacarpus
• 7. Ulnaris lateralis- begins 3 to 4" proximal to
  carpus to almost insertion.
• Pelvic limb
• 1. Fibularis peroneus-present at hock

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• 2. Long digital flexor- distal fourth of tibia to
  proximal third of metatarsus
• 3. Tarsal sheath-- two to 3 inches of lateral
  malleolus to prosimal quarter of
  metatarusus-covers deep digital flexor tendon.
• 4. Long digital extensor- proximal to lateral
  malleolus to level where it hoins lateral digital
  extensor tendon.
• 5. Lateral digital extensor- inch proximal to
  lateral mealeolus ends 1.5" proximal to union
  with extensor tendon.
• 6. Digital synovial sheath- same as thoracic

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Components and Function

• In the human there are over 400 voluntary
  skeletal muscles, comprising 40-50 of the body
  weight.
• Muscles that decrese joint angle are called
  flexors.

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• Muscles that increase joint angle are called
  extensors.
• Composed of several kinds of tissue muscle,
  glood, nerves and connective tissue.
• Muscles seperated by fascia. Connective tissue
  that surrounds each muscle is epimysium.
• Perimysium surrounds individual bundles of muscle
  fibers. Individual compartments are called
  fasiculi.
• Each muscle fiber within the fasciculus is
  surrounded by connective tissue called
  endomysium.

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• Muscle cells are multinucleated. Appear striated
  or striped under the microscope.
• Muscle cells have cell membranes which are called
  sarcolemma. The muscle cytoplasm is called the
  sarcoplasm. Contained in the sarcolemma are the
  myofibrils.
• Myofibrils contain two principal types of protein
  filaments thick (myosin) and thin (actin).
• Two additional molecules located on the actin
  molecule are troponin and tropomyosin.
• Myofibrils can be divided, based on the
  appearance of the above fibers and where they
  attach, into sarcomeres. These again are divided
  by connective tissue- called a Z line.

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• Myosin is primarily in the dark "A" band, where
  actin is primarily in the light "I" band. "H"
  zone is a region where no myosin overlaps actin.
• Within each muscle are channels called
  sarcoplasmic reticulum-store Ca. Transverse
  tubules run from each of the sarcoplamic tublules
  and pass through muscle fiber.
• Each muscle fiber is innervated by the nervous
  system motor neurons which run from spinal cord.
  A motor unit exists where motor neuron and muscle
  fiber meets. The site where the motor meuron and
  muscle cell meet is the neuromuscular junction.
• AcH (Acetycholine) is released from nerve ending
  and travels to muscle sarcolemma-excitation of
  muscle cell membrane results.

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Muscle contraction

• Sliding filament hypothesis
• Shortening of myofibrils, which results in a
  reduction of distance from Z line to Z line.
• Cross bridges extend out from myosin and attach
  on to myosin.

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• Energy comes from enzyme ATP ase.
• Regulation is from troponin and tropomyosin.
• These molecules prevent binding in relaxed state.
• Trigger for contraction lies in release of stored
  Ca.