Striated Muscle:  Structure and Function

Introduction

 You will investigate the structure - function relationships in striated muscle using the Skeletal Muscle Interactive Physiology Module  co-produced by Benjamin/Cummings Publishing Co. and A.D.A.M. Software.  You will utilize this program to gain an understanding of the:
 

                                    • cellular and subcellular structure of striated muscle;
                                    • molecular components of this tissue;
                                    • mechanism and regulation of contraction;
                                    • control of tension developed by a muscle cell and by a
                                       collection of cells, i.e., a whole muscle.

STUDY QUESTIONS

  TOPIC 1.  ANATOMY REVIEW: SKELETAL MUSCLE TISSUE:

• List the components of:

                 - thick filaments:

                                        _________________________________
                 - thin filaments:

                                        _________________________________
                 - sarcomere:

                                        _________________________________
                 - A band:

                                        _________________________________
                 - I band:

                                        _________________________________
                 - H zone:

                                        _________________________________
                 - M line:

                                        _________________________________

• Define and list the functions of:

                 - sarcoplasmic reticulum:

                                        _________________________________

                                        _________________________________
                 - transverse or t tubule:

                                        _________________________________

                                        _________________________________
                 - muscle fiber:

                                        _________________________________
 
 

TOPIC 2.  THE NEUROMUSCULAR JUNCTION

• Based on previous lectures,
             - Describe the basis for the resting membrane potential (Vm):
 
 
 
 
 

             - Draw an action potential as it would appear in an intracellular
               recording made from a striated muscle cell.  Describe the ionic
               events responsible for the epsp and the rising and falling phases
               of the AP:
 
 

                - What is the role of the voltage-gated calcium channels located
                   in the plasma membrane of the presynaptic terminal?
 

                - Describe the relationships among the frequency of motor neuron
                  action potentials, the amount of ACh released, and the strength of
                  the resulting muscle cell contraction.
 

                 - What happens to an individual poisoned by an anti-cholinesterase?
                   by a nicotinic antagonist?  by a nicotinic agonist?
 
 

TOPIC 3.  THE SLIDING FILAMENT THEORY

• Describe the proteins that comprise the thin and thick filaments.  Include the
  prominent structural features (e.g., important 2o, 3o, and 4o structures, molecular
  shape, binding sites, etc.) and functional properties.
 
 

• What is a cross bridge?  What determines how many of them are formed in a
  muscle cell?  What is the relationship between the number of cross bridges formed
  and the amount of tension developed?
 

• Characterize/describe the calcium 'pumps' contained in the SR.
 

• How does myosin actually use the energy contained in the terminal phosphate
  bond of ATP?

• Explain the relationship between cytosolic calcium concentration and muscle tension.
  What determines the cytosolic calcium concentration?
 
 

TOPIC 4.  MUSCLE METABOLISM

• This section is not required.  Look at it only if you have time and you wish to review
   this topic.
 
 

TOPIC 5.  CONTRACTION OF MOTOR UNITS

• Define:
                 - Motor unit:

                                     ______________________________
                 - Muscle tone:

                                     ______________________________
                 - Recruitment:

                                     ______________________________

• Describe the size of the motor unit (i.e., the relative number of muscle cells
   innervated by a motor nerve) in your index finger and in the postural muscles
   of your back.  Explain your reasoning.
 
 

TOPIC 6.  CONTRACTION OF WHOLE MUSCLE

• Define isotonic and isometric contractions:

• What are the three factors that determine the tension developed by a whole muscle?

1.

2.

3.
 

• What is the molecular basis for the latent period.  If the muscle is required to lift
  successively heavier weights, will the latent period increase or decrease in duration?
  Why?
 

• Explain temporal summation.  Why is the second twitch stronger than the first?
 

• Draw a typical length - tension curve for a striated muscle.  Explain the active,
  passive, and total tensions at muscle lengths less than, equal to, and greater
  than L_o (resting length).

• Consider the length - tension curves for a smooth (non-striated) muscle.  Draw
  and label it on the axes on the previous page and explain the differences from
  those obtained with striated muscles:
 
 
 

• FINAL QUESTION #1:  Lift a pen from the top of your desk.  Now lift the desk.  Describe processes that regulated the tension and permitted you to perform both of those tasks.
 
 
 

• FINAL QUESTION #2:

Smooth muscle is constructed to perform certain tasks.  This means it has certain functional characteristics.  Striated muscle has different structural features and different characteristics that make it suited for fulfilling its functional role.  Consider the structure - function relationships of both striated and smooth muscles.  You should be able to compare/contrast the latent periods, the velocity of muscle isotonic contraction, maximum active tensions developed, and range of effective muscle cell lengths and explain the physical/molecular  structural bases for these differences.