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• Rigor Mortis

  • Upon death, muscle cells are unable to prevent calcium entry.
  • This allows myosin to bind to actin.
  • Since there is no ATP made postmortem, the myosin cannot unbind and the body remains in a state of muscular rigidity for almost the next couple days.
• Myasthenia Gravis

  • My-muscle, asthen=weakness, gravi=heavy
  • Autoimmune disease where antibodies attack the ACh receptors on neuromuscular junctions.
  • Results in progressive weakening of the skeletal muscles. Why?
  • Treated w/ anticholinesterases such as nestigmine or physostigmine. These decrease the activity of acteylcholinesterase.
  • Why would this help someone with myasthenia gravis?
• Muscular Dystrophy

  • Group of inherited muscle-destroying diseases that generally appear during childhood.
  • Dys-faulty; Troph=growth
  • Most common is Duchenne muscular dystrophy

  1. DMD is caused by an abnormal X-linked recessive gene
  2. Diseased muscle fibers lack the protein dystrophin which normally links the cytoskeleton to the ECM and stabilizes the sarcolemma
  3. Age of onset is btwn 2 and 10. Muscle weakness progresses. Afflicted individuals usually die of respiratory failure, usually by age 25.
• Flaccid paralysis

  • Weakness or loss of muscle tone typically due to injury or disease of motor neurons

  Spastic paralysis

  • Sustained involuntary contraction of muscle(s) with associated loss of function

  Spasm

  • A sudden, involuntary smooth or skeletal muscle twitch. Can be painful. Often caused by chemical imbalances.
• • Cramp
  • A prolonged spasm that causes the muscle to become taut and painful.

  Hypertrophy

  • Increase in size of a cell, tissue or an organ.
  • In muscles, hypertrophy of the organ is always due to cellular hypertrophy (increase in cell size) rather than cellular hyperplasia (increase in cell number)
  • Muscle hypertrophy occurs due to the synthesis of more myofibrils and synthesis of larger myofibrils.
• Atrophy

  • Reduction in size of a cell, tissue, or organ
  • In muscles, its often caused by disuse. Could a nerve injury result in disuse? Why might astronauts suffer muscle atrophy?

  Fibrosis

  • Replacement of normal tissue with heavy fibrous connective tissue (scar tissue). How would fibrosis of skeletal muscles affect muscular strength? How would it affect muscle flexibility?
• Single Unit Smooth Muscle

  • More common
  • Cells contract as a unit because they are all connected by gap junctions - protein complexes that span the PM's of 2 cells allowing the passage of ions between them, 1.e., allowing the depolarization of one to cause thedepolarization of another.
  • Some will contract rhythmically due topacemaker cells that have a spontaneous rate of depolarization.
• Multi-Unit Smooth Muscle

  • Innervated in motor units comparable to those of skeletal muscles
  • No gap junctions. Each fiber is independent of all the others.
  • Why is good to have the digestive smooth muscle single unit and the internal eye muscles multi-unit?
  • Found in large airways to the lungs, large arteries, arrector pili, internal eye muscles (e.g., the muscles that cause dilation of the pupil)
  • Less common
  • No pacemaker cells
  • Responsible to neural & hormonal controls
• Categories of skeletal muscle actions

  • Categories

  Actions

  • Extensor - Increases the angle at a joint
  • Flexor - Decreases the angle at a joint
  • Abductor - Moves limb away from midline of body
  • Adductor - Moves limb toward midline of body
  • Levator - Moves insertion upward
  • Depressor - Moves insertion downward
  • Rotator - Rotates a bone along its axis
  • Sphincter - Constricts an opening