I. Ch. 16: Properties of Muscle Tissues: Skeletal, Cardiac, Smooth.
    A.     Ex 16-1: Cardiac Muscle Tissue

• Found in the walls of the heart and vena cavae where they enter the heart
• Unique because it can contract rhythmically and continuously due to its own internal pacemaker.
• Striated
• darker staining band are intercalated disks which are where cardiac cells branch and join one another.
• Uninucleated
• Involuntary

• Found in the walls of blood vessels, walls of hollow organs, and the walls of the urinary bladder.
• nonstriated
• uninucleated
• long spindle-shaped fibers
• involuntary

• Fibers are long and cylindrical
• Striated - cross bands
• Multinucleated - nuclei on peripheray
• Voluntary
• muscles of pharynx are not voluntary
• reflexes using skeletal muscles are not voluntary

    D.    Ex 16-4: Skeletal Muscle Organ Structure

• muscle fiber - can be one cell or several
• sarcolemma - is the cell membrane of a muscle fiber
• endomysium - is a network of delicate connective tissue which surrounds muscle fibers.
• perimysium - surrounds a bundle of muscle fibers, is also made of connective tissue
• fasiculus - is the bundle of muscle fibers surrounded by the perimysium
• epimysium or fascia- is a dense fibrous connective tissue sheath that is continuous with the perimysium and also with tendons.
• For directing the contraction of muscles
• Keeps muscles separate, reduce chance of infection

• For this exercise be familiar with the structures involved and the sequence of events at the neuromuscular junction.
• View this on the program ADAM

• Be familiar with the molecules involved in muscle contraction, and the events of excitation-coupling and the sliding filament theory
• View this in the program ADAM

• The area where the nerve meets with the muscle.
• In the nerve there is a presynaptic cleft which contains the neurotransmitter ACH. The synaptic cleft separates the axon from the motor end plate of the muscle.
• At the terminal axon, Na+ flows into the neurolemma and K+ flows out creating an action potential. This ionic interchange allows Ca++ to flow into the neurolemma, which stimulates the secretory vesicles to release their ACH into the synaptic cleft.
• ACH can cause ligand gated NA+ channels to open an create a local potential on the muscle cell membrane(sarcolemma). If the local potential exceeds threshold, then an action potential is produced and contraction will follow.

• AP’s along the sarcolemma depolarize the T-tubules which brings the depolarization into the interior of the muscle fiber.
• The depolarization causes voltage gated CA²⁺ channels to open in the sarcoplasmic reticulum and CA²⁺ diffuse out and bind to the troponin molecules on the actin.
• The calcium binding causes the troponin-tropomyosin complex to move deeper into the grooves and expose G-actin sites for bonding
• ATP is required for Cross bridge cycling to occur

• Actin
• double helix strand of protein filaments
• G-actin, tropomyosin, and troponin molecules
• myosin can bind at the G-actin globular molecules.
• tropomyosin and troponin regulate interactions between g- actin and myosin

• composed of many myosin molecules which are shaped like golf clubs.
• Heads contain ATPase, which is the enzyme necessary for breaking down ATP for energy.

               3.    The heads move the actin in a ratchet-like motion using energy which was

    4.    After the first power stroke ATP again combines with the myosin head
            causing its release from the actin strand.

    5.    ATP-ase in the myosin head breaks down the ATP and provides energy for

           the recocking, reattachment and power stroke phase of another
           cross-bridge event.

• this is a contraction of a muscle in response to a stimulus that causes an action potential.
• Explain lag phase, contraction phase, relaxation phase.

• Muscle contraction is determined by AP’s and if the stimulus is not strong enough to generate and AP, then no contraction occurs.
• Muscle contraction is graded in its response. This is due to increasing numbers of motor units being recruited as the stimulus intensity increases.
• Spatial Summation - Increasing the strength of the stimuli will cause more fibers to respond up to the point at which the maximal number of motor fibers are stimulated. This increases the force generated by the muscle.

• An AP can restimulate a muscle before it has completely relaxed and cause it to contract again. As this happens again and again the individual twitches begin to add together and there is no relaxation between stimuli.
• Temporal Summation - As more AP’s show up in close temporal succession the muscle twitches begin to sum together until there is virtually no relaxation between twitches =TETANY

• isometric - length of muscle does not change but tension increases
              e.g. - trying to lift a grand piano, postural muscles

• isotonic - length of muscle changes and the tension remains constant.

    e.g. - lifting a guitar., flexion and extension
 

• Do the handout on muscle contraction and hand in next week.

(handout at end of lecture notes)

• Be able to distinguish between the 3 types of muscle tissue histologically.

• Be sure to look at the three tissue types under the microscope.
• Know where each type is found throughout the body and whether it is voluntary or involuntary.

• be able to distinguish between the different layers of muscle on the figures.
• know the function of the fascia and perimysium.

• Know the sequence of events that occur during synaptic transmission.
• Be sure to look at computer program for the functioning of the neuromuscular junction.
• Know the sequence of events that produce muscle contraction and relaxation.
• Look at the computer program for the Sliding Filament Theory.

• be able to tell the difference between spatial and temporal summation
• be able to differentiate between isometric and isotonic contraction.
• Do exercise on handout
• Hand in handout with next week's lab report.
• Look at ex 17-2 in order to do rabbit psoas muscle experiment.

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?