MUSCULAR

• Endomysium


  Connective tissue covering each muscle fiber
• Fasciculi


  A group of muscle fibers
• Perimysium


  Connective tissue (rich in elastin) covering each fasciculi
• Epimysium


  Dense connective tissue covering the entire muscle
• Skeletal muscles are attached to the skeleton "bones" by tendons
• Sarcomere


  Structural unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band
• Sarcomere


  • Main functional/contractile unit of the muscle
  • Consists of two types of protein filaments: Actin (thin) and Myosin (thick)
• A band


  Dark-colored area consisting of myosin
• I band


  Lighter-colored area consisting of actin
• Z line


  Dark central line formed from actin and myosin overlapping, giving the muscle its striated appearance
• H zone


  Lighter in color and located at the center of the sarcomere
• Classification of muscles according to shape

  • Longitudinal/Parallel
  • Pennate
  • Convergent
  • Circular
• Longitudinal/Parallel muscles


  Muscle fibers are attached in a parallel manner
• Pennate muscles


  Muscle fibers are attached in an oblique manner to the tendon
• Convergent muscles


  Muscle fibers have a widespread expansion over a sizeable area, but then the fascicles come to a single, common attachment
• Circular muscles


  Muscle layer encircling an orifice or constricts a passage
• Muscle naming conventions


  • Location
  • Shape
  • Direction of muscle fibers
  • Size
  • Position
  • Number of origins
  • Action
• Insertion


  Where the movable end of the muscle is connected
• Origin


  Immovable end of the muscle connected to the fixed bone
• Muscle actions


  • Prime mover or agonist
  • Synergist
  • Antagonist
• Physiology of muscles


  • Body's Movement
  • Maintenance of the posture and structure
  • Respiration
  • Generation of heat
  • Blood flow
  • Facial expressions and gesticulation
  • Levers
• First class lever


  Effort is applied at one end of the lever, load is at the other, fulcrum is somewhere in between
• Second class lever


  Effort is at one end of the lever and fulcrum is located at the other, with the load between them
• Third class lever


  Effort is applied between the load and the fulcrum
• Motor unit


  The branch of a neuron targeting a specific group of muscle fibers
• Muscle contraction cycle


  1. Neuron signals (nerve impulses) are released from the spinal cord

  2. Acetylcholine attaches to acetylcholine receptors in muscle fibers

  3. Cross-bridge cycle through the connection between the head of myosin filaments and actin filaments causes action

  4. ATP hydrolyses to ADP and phosphate

  5. Calcium attaches to troponins, exposing the site of attachment in actin filaments

  6. ATP plays an important role in the separation of the myosin and actin
• Types of muscle contractions

  • Isotonic (Concentric, Eccentric)
  • Isometric
  • Yielding
  • Overcoming
• Isotonic contraction


  Muscle length changes
• Concentric contraction


  Muscle gets shorter during contraction
• Eccentric contraction


  Muscle gets longer by generating force
• Isometric contraction


  Muscle length is not affected, but contraction generates force
• Yielding contraction


  Force is opposed by resistance
• Overcoming contraction


  Force is opposed by immovable force
• Glycogen → Glucose → (aerobic) ATP and CO2
• Glycogen → Glucose → (anaerobic) Lactic acid → muscle cramps
• Clinical conditions related to muscles

  • Muscular dystrophy
  • Cerebral palsy
  • Dermatomyositis
  • Myasthenia gravis
  • Rhabdomyolysis