Lecture Notes

 Lab Manual Ch 16: Properties of Muscle Tissues: Skeletal, Cardiac and Smooth

 Exercise 16-1 - 16-3: Cardiac, Smooth and Skeletal Muscle Tissue

 Be able to distinguish the 3 types of muscle tissue on the basis of structure, function and location in the body (use Table 10.1 in text as a reference):

• Skeletal Muscle - striated, voluntary; cells are multinucleate and nuclei are at periphery of cells; cells are very uniform in shape; fiber shape is long and cylindrical; fibers are lined up parallel to each other, have definite striations (stripes); responsible for body movement; not capable of spontaneous contractions
• Cardiac Muscle - striated, involuntary; cells have one nucleus and nucleus is at center of cells; cells have a branched appearance, and are connected to each other with intercalated disks, forming a syncytium (action potentials flow from one cell to the next through the intercalated disks); cells are not lined up neatly as in skeletal muscle; capable of spontaneous contractions (autorhythmic); function is to pump blood throughout the body
• Smooth Muscle - non-striated, involuntary; cells have one nucleus that is centrally located in the cell; cells are spindle shaped; some types of smooth muscle are capable of spontaneous contraction; contraction of smooth muscle controls: movement of digestive tract, secretions from glands, change in pupil size, emptying of urinary bladder, diameter of blood vessels

Exercise 16-4: Skeletal Muscle Organ Structure

• Muscle fiber = one muscle cell or several
• Muscle fiber is surrounded by a membrane, the sarcolemma, and fine reticular fibers, the external lamina
• Each muscle fiber is also surrounded by a layer of loose connective tissue, the endomysium
• Muscle fibers are organized into bundles; each bundle is a fasciculus; the
• A muscle is made up of several fasciculi grouped together and surrounded by a layer of dense fibrous connective tissue, the epimysium or fascia. The epimysium is continuous with the perimysium and with tendons

 Exercise 16-5: The Mechanism of Muscle Contraction

• Be familiar with the structure and sequence of events at the neuromuscular junction - view the computer program "ADAM"
• Be familiar with the molecules involved in muscle contraction, and the events of excitation-contraction coupling and the sliding filament theory - view the computer program "ADAM"

Lab Manual Ch 17: Skeletal Muscle Contraction

 Lab Activity: Physiogrip by Intellitool

• The muscle twitch is a contraction of a muscle in response to a stimulus that produces an action potential at the level of the muscle cell membrane
• Know the events of the lag phase, contraction phase and relaxation phase. Why is there a lag phase associated with muscle contraction?
• Muscle contraction is governed by the all or none law - the contraction in a muscle fiber is initiated by an action potential; if the stimulus is not strong enough to generate an action potential in the muscle cell membrane, no contraction can occur
• Muscle contraction is also a graded response - as stimulus strength increases, more and more motor units are recruited (a motor unit consists of all the muscle fibers enervated by one neuron); this is called spatial summation - increasing the stimulus strength recruits more motor units, up to a point where the maximum number of motor units possible are contracting; at that point, increasing stimulus strength will not increase the force of the contraction any further
• An action potential can also restimulate a muscle fiber before it has had a chance to fully relax and cause it to contract again. As the time between action potential becomes shorter (temporal summation), there will eventually be no time for individual twitches to occur, and the twitches will fuse into one contraction, with no relaxation between twitches; this is called tetanus

Lab Activity: Isotonic vs Isometric Contractions (directions at the end of these lecture notes)

 Isometric - the length of the contracting muscle does not change, but tension develops in the muscle; eg., trying to lift a grand piano, or the contraction of postural muscles

 Isotonic - the length of the muscle changes during contraction, but tension remains constant; eg., lifting a book, flexion and extension

Exercise 17-2: Contraction of a Muscle Fiber

• Understand what molecules are required for muscle contraction and relaxation to occur
• Follow the directions in the experiment in exercise 17-2, except use 3 separate microscope slides, one for each muscle fiber; observe the size and shape of each muscle fiber, and the orientation of its striations, before and after you add the various ATP and salt solutions. Does the appearance of the fiber change when the chemicals are added? Does the length change?

Experiment 1
Have the subject rest his/her forearm on the table, palm up. Wrap a tape measure around the fullest part of your partner’s upper arm - the "belly" of the biceps brachii muscle. Measure the circumference of the biceps brachii muscle:

 Circumference
1.    at rest with forearm extended                       _________
2.    with the forearm flexed (no weight)              _________
3.    with the forearm flexed, holding a book       _________

Circumference
 
1.    at rest with forearm extended                       _________
2.    passive flexion (no weight)                           _________
3.    passive flexion with a weight                        _________

What type of contraction have you demonstrated? Explain.
 

Experiment 3
Have the subject stand and place the palm of his/her hand on the underside of the lab bench. Wrap a tape measure around the fullest part of the upper arm as before and measure the circumference of the biceps brachii muscle. Now, have the subject "pull up" on the table (with the entire arm, not just the forearm), while you again measure the biceps brachii muscle.
 

Circumference
1.    standing at rest with forearm extended        _________
2.    "pulling up" on table                                      _________

 
Which of these contractions would best promote joint stability? Which of these contractions would best promote muscle strength? Why? What was the purpose of exercise 2?