Answers, BIO 2310, Muscle Tissue


1. Capable of contraction and relaxation. It functions to produce movement, maintain posture, support, guard exits/entrances (e.g. sphincter), and maintain body temperature.

2. Skeletal muscle is attached to skeleton, is striated, voluntary and causes body movement. Cardiac muscle is heart muscle, is striated with intercalated discs, is involuntary and causes heart pumping. Smooth muscle is found in the wall of tubular viscera and is not striated, is involuntary and causes mixing & movement called peristalsis.

3. Connective tissue around groups of muscles or filling spaces if fascia. Epimysium is connective tissue around a single muscle, perimysium is connective tissue around fascicles, fascicles are bundles of muscle cells, a tendon is connective tissue cord attaching muscle to (periosteum of) bone, aponeurosis is a broad sheet-like tendon.

4. Skeletal muscle must have nerve supply to function and has an excellent blood supply.

5. Sarcolemma is muscle cell membrane, myofiber is muscle cell, myofibril is the striated cylinders in the muscle cell, myofilaments are the contractile proteins. A band is the dark colored region, I band is light. Z lines separate the myofibril into sarcomeres which are comprised of thin myofilaments attached to the Z lines called actin and the thick myosin myofilaments. The sarcomere is the functional unit of muscle contraction because it squeezes together during contraction from the myosin pulling on the actin. The sarcoplasmic reticulum with its expanded regions called terminal cisternae are the muscle cell’s version of an endoplasmic reticulum. It functions to store calcium ions. Tropomyosin is a thin ribbon-like protein that wraps around actin and blocks myosin from attaching its head to the actin. It prevents contraction. Troponin is a small protein that acts like the glue holding the tropomyosin in place. Troponin has a binding site for calcium. Transverse tubules are inward extensions of the sarcolemma into the interior of the cell.

6. Stimulation of the muscle cell’s sarcolemma travels into the cell through the T-tubules causing calcium release from the sarcoplasmic reticulum. The calcium binds to troponin causing it to release the tropomyosin which can then move out of the way. Now, the myosin head can form a cross bridge binding to actin. The myosin head is energized with the binding of ATP and swivels toward the center of the sarcomere causing the power stroke. This causes the sarcomere to squeeze together. ATP is also needed for the actin & myosin to release from each other so that relaxation can occur. ATP is also needed for putting the calcium back into the sarcoplasmic reticulum because it is active transport.

7. All skeletal muscle cells need a motor neuron (movement nerve cell) to provide stimulation for contraction. There is a gap between the distal end of the neuron and the muscle cell and this is the neuromuscular junction. A chemical called acetylcholine is released from the neuron to bridge the gap and take the stimulation to the muscle cell. The motor neuron plus how ever many muscle cells it supplies is the motor unit. It may be one neuron and one muscle cells for the motor unit in areas where your movement is precise (e.g. eye movement) or one neuron for 500 muscle cells where your movement is not precise (e.g. lower back muscles).

8. It is really the ‘on-off’ switch. It binds troponin causing the physical blocker, the tropomyosin, to move out of the way.

9. A little bit of ATP is present in this state in the muscle cell. More can be quickly manufactured by converting creatine phosphate to ATP. Rapidly, but inefficiently, you can make ATP from anaerobic metabolism. As long as oxygen supply is sufficient, you can very efficiently make a lot of ATP from aerobic metabolism, a slow process.

10. Oxygen debt is to restore the ATP aerobically and to remove lactic acid (end-product from anaerobic metabolism) from muscle cells. Glycogen debt is to restore glucose stores and the best way to restore these is to eat carbohydrates.

11. Lack of ATP. Lactic acid also contributes to the soreness of these muscles.

12. Latent period, Contraction period, Relaxation period

13. All stimuli strong enough to cause a muscle twitch will cause identical muscle twitches. However, the all-or-none principle applies to the muscle CELL only, not the entire muscle.

14. For a small contraction of your biceps muscle, some (say 10%) of the muscle cells will do their “all.” For a bigger contraction of your biceps muscle (say 60%) more muscle cells contract maximally. For a maximal contraction of the whole biceps muscle, all of the muscle cells will be contracting maximally.

15. Multiple motor unit summation = spatial summation and occurs when many muscle cells or motor units contract at the same time making a bigger whole muscle contraction (as is described for number 14). Temporal summation = wave summation and is when muscle cells contract repeatedly and rapidly, so that the next contraction is occurring before the previous one has totally relaxed. Examples of temporal summation include incomplete tetanus (repeated contraction due to repeated stimuli with a little bit of contraction between each stimulus) and complete tetanus (sustained contraction with no relaxation). Treppe is the bigger muscle twitch that is achieved upon warming up for exercise. Asynchronous motor unit summation is when not all muscle cells are working at the same time so that some can rest while others are contracting. This allows posture muscles to be contracted all day without tiring, because the motor units take turns. Muscle tone is when some of the motor units are contracting making the muscle firm, but not enough are contracting to result in movement.

16. Isometric contractions occur when you pick up something that is too heavy. While your muscle is working and creating tension, it is not shortening. Isotonic contractions result in shortening, as in bending your elbow.

17. Slow fibers are fatigue resistant and are red. They have excellent blood supply and myoglobin for oxygen storage (think of dark meat of chicken). Therefore they are geared toward aerobic metabolism and while this is not fast these fibers do not run out of ATP and do not fatigue (think of the chicken walking around all day long). Fast fibers are fatiguable and are white. They do not have great blood supply and do not have myoglobin. They are geared toward anaerobic metabolism. They can make the ATP very quickly (think of the breast meat of chicken and the chicken flying quickly to a tree when being chased) but will run out of it soon and cannot endure (the chicken cannot fly long distances, but the goose has dark meat for the breast, why?). Intermediate are more fatigue-resistant fast fibers. You can get these through endurance training, but the fast and slow fibers are genetically determined.