HUMAN SYSTEMS QUESTION 1994:                    L. PETERSON/AP BIOLOGY

               Discuss how cellular structures, including the plasma membrane, specialized endoplasmic reticulum, cytoskeletal 
               elements, and mitochondria, function together in the contraction of skeletal muscle cells.
  

  
  To earn credit a student needed to demonstrate an understanding of basic cell anatomy and
  physiology as they relate specifically to the structure and function to muscle contraction.
  Standards were established to follow the cellular activities pertinent to muscle contraction from the
  neuromuscular junction, through contraction, and returning to the non-contractive state. Points
  were also awarded if the student included information from the neuromuscular junction,
  demonstrated an exceptional understanding of chronological information from the neuromuscular
  junction, demonstrated an exceptional understanding of chronological or spatial relationships, or
  included an elaboration of special features specific to the process of muscle contraction.
  
  (2 pts) Neuromuscular junction
          Action potential of neuron  > neurotransmitter
          Concept of neurotransmitter
  (1 pt)   Idea of a sarcomere as a functional unit
  (1 pt)   Actin and Myosin in a sarcomere   (well labeled diagram w/text)
  (2 pts) Plasma membrane / sarcolemma (no point for name alone)
          Receptor sites for neurotransmitters
          Change in permeability / Na+  K+
          Action potential distributed / depolarization
          T-tubules (continuous with specialized E.R.)
  (2 pts)  Specialized E.R.   Sarcoplasmic reticulum (no point for name alone)
          T-tubule (only if not given above)
          Ca++ release / Calcium is involved with muscle contraction
          Change in permeability   release of Ca++
           Ca++ recaptured into S.R.   contraction ends / active transport
  (5 pts)  Cytoskeletal Elements
          Actin and myosin (linked to muscle function) 
                microfilaments / myofibrils / myofibrils
          Actin   thin fiber (protein structure)
               Troponin (Ca++ interaction exposes active sites)
               Tropomyosin (is therefore unblocked)
          Myosin   thick fiber (protein structure)
          'clubs'   bridges   paddles for interaction with actin / ATP binding site
               ATPase site / hydrolysis of ATP
          Sliding Filament Concept
          Z line as a protein which separates sarcomeres (needs strong linkage)
          ATP functions to release mysoin heads from actin sites
  (2 pts)  Mitochondria
          ATP production   cellular respiration
          Number of mitochondria is higher in muscle cells due to...
          Proximity within muscle fiber
          Chemiosmosis   elegant elaboration of ATP production
  
  
  
  (2 pts) Other   Rarely Mentioned:
          Fast twitch / slow twitch (1 pt)
          Elaboration (1 pt)  
               (FT)   glycogen and anaerobic
               (ST)   oxidation of glycogen via TCA and thus aerobic
          All or nothing response
          Switches to anaerobic respiration after oxygen consumed / Myoglobin
          Muscles can only contract
          Rigor mortis 
            (showing that ATP functions in release rather than contractive phase)
          Muscle cell is a muscle fiber or muscle cell is multinucleate
          Glycogen storage (mitochondria functions)
          Creatine phosphate - PO4 replacement
  (1 pt)  Synoptic synchronization - exceptional chronology or spatial relationships