Striated Muscle: Structure and Function

William J. Higgins

Introduction

You will investigatge 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.

Chapter 21 in your textbook, The World of the Cell, contains excellent coverage of this same material. Bring it to the laboratory and use it to supplement and complement the information presented in the CD program. Text figures 21.5 through 21.22 will be very helpful.

RUNNING THE PROGRAM

The Muscle Module CD will be installed in the computer and its icon will appear on the desk top.

DO NOT REMOVE THE CD FOR ANY REASON!!!

Your TA will tell you how to get the program started. You must wear the earphones to hear the accompanying sound effects and the narration (optional). When the opening screen appears, click once on the control panel box at the bottom left of the screen (it's the one with the little slide bars or levers on it).

Control Panel and Help Buttons

Turn off the virtual professor by clicking on that box. (Please note that all of the 'virtual buttons' in this module are turned on and off by clicking on them once, just like pushing a button.) You may elect to keep the narration on or turn it off. Notice that you may return to this panel at any time to adjust the volume and the speed of the animations.

The "?" button at the bottom left provides a series of instructive help screens. Use it when necessary.

Select the MUSCLE module from the menu at the right of the screen by clicking on it once. Now you are faced with a menu bar at the top left of the screen that includes a choice of TOPICS.

Æ

Upper Left Screen Menu Bar

Examine the options under this menu bar (place the pointer on the word TOPICS and hold down the mouse button) and select one (e.g., Anatomy Review: Skeletal Muscle Tissue) by dragging the mouse.

After making your choice, the introductory screen for that topic will appear along with some buttons at the bottom right:

Lower Right Screen Menu Bar

The forward and reverse arrow buttons advance you through the module one page at a time. The forward arrow will be highlighted to instruct you to turn the page, i.e., there are no more animations or text messages to observe on the page on the screen. The vertical, parallel double lines button is used to pause the action during the animations. Press it once, the action stops. Hit it again and the animation continues. (Remember: you can control the speed of the animations; see the Control Panel menu.) The return arrow at the far right returns you to the first, main menu.

By selecting the open book icon and holding down the mouse button, you will see an ordered list of pages and their contents in that section or chapter. By holding down the mouse button and dragging the mouse, position the pointer and highlight an item in this list. Release the mouse button and you are taken directly to that item or page in the chapter.

The other important choice from the upper menu bar is labeled "QUIZZES". You may use it to go directly to any quiz within the entire six chapter module.

Notice that many of the terms are highlighted in red. You may get a definition of these terms by placing the pointer on them and holding down the mouse button.

YOUR MISSION

Have some fun as you explore this module. Topic 4, Muscle Metabolism is not part of this assignment and should be viewed only if time permits! Of course, you will pay particular attention to the structure - function relationships, the functions and locations of the molecular components of muscle, and the point of each animated experiment. You should be able to complete the quizzes at the end of each topic section and answer the study questions on the following pages. Your TA will ask you to write and submit answers to some of these questions. Remember that Chapter 21 of your textbook will be helpful!

AN IMPORTANT NOTE:

ALL CDs MUST BE ACCOUNTED FOR

BEFORE ANYONE WILL BE PERMITTED

TO LEAVE THE LABORATORY!

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/describethe 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 Lo (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.