What main functions are served by muscle?
Key Terms
What features characterize smooth muscle?
mononucleated, meaning that a single cell contains only one nucleus, rounded and irregular in appearance and not striated, generally controlled inv...
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| Term | Definition |
|---|---|
What main functions are served by muscle? | movement, support, thermoregulation, circulation |
Briefly explain the role of the muscular system in thermoregulation. | In cold conditions, skeletal muscles are involved in shivering, in which they contract and convert energy to heat. Smooth muscle also facilitates vasoconstriction and piloerection (goosebumps), both of which reduce heat loss. In warm conditions, smooth muscle facilitates vasodilation, which promotes the dissipation of body heat to the external environment. |
Briefly explain the role of skeletal muscle in circulation. | Skeletal muscles in the legs contract to compress nearby veins, assisting venous blood as it returns to the heart. Specifically, blood returning from the lower regions of the body must counteract gravity. Since venous pressure is relatively low, the function of skeletal muscle is vital. |
Briefly explain the role of smooth muscle in circulation. | Smooth muscle lines arteries, arterioles, and veins. In response to a variety of factors, this muscle can contract (promoting vasoconstriction) or relax (promoting vasodilation). Nervous system signaling and temperature changes, among other factors, are involved in promoting these responses. |
Name the three major types of muscle. | cardiac, skeletal, smooth |
What features characterize smooth muscle? | mononucleated, meaning that a single cell contains only one nucleus, rounded and irregular in appearance and not striated, generally controlled involuntarily |
What features characterize skeletal muscle? | multinucleated, meaning that a single cell contains more than one nucleus, striated, or striped in appearance, generally controlled voluntarily |
In what way(s) does cardiac muscle resemble smooth muscle? | It is controlled involuntarily. In general, its cells are also mononucleated. (However, a small proportion of cardiac muscle cells do contain two nuclei.) |
In what way(s) does cardiac muscle resemble skeletal muscle? | Like skeletal muscle, cardiac muscle appears striated due to the presence of sarcomeres. However, the two muscle types differ in the shapes of their cells. Striated muscle contains orderly, cylindrical cells, while cardiac muscle cells are more branched and irregular. |
Which muscle types require calcium for proper contraction? | All three muscle types—skeletal, cardiac, and smooth—require calcium ions to contract. Note that these types use different mechanisms of contraction. In short, skeletal and cardiac muscle require calcium to bind to troponin, while smooth muscle needs the ion to trigger a signaling cascade. |
How does the role of calcium in skeletal and cardiac muscle contraction differ from its function in smooth muscle? | Skeletal and cardiac muscle require calcium to bind to troponin, exposing the myosin binding site. Smooth muscle contains no troponin, but still relies on calcium for a signaling cascade that promotes contraction. |
A certain tissue sample displays three nuclei in a single cell. This sample is likely which type of muscle? | skeletal muscle. In humans, skeletal muscle is the only one of the three types that is generally multinucleated. |
A certain tissue sample displays numerous mitochondria and large amounts of microfilament-based structures. This sample is likely which type of muscle? | inconclusive. All three muscle types contain mitochondria and substantial amounts of actin, a motor protein composed of microfilaments. While skeletal muscle does tend to possess more mitochondria than the other types, we do not know enough to answer this question. |
Which division of the nervous system is involved in the control of involuntary muscles? | The autonomic nervous system controls muscles that are not under voluntary influence. These include both smooth and cardiac muscle. The autonomic nervous system is a division of the peripheral nervous system, or PNS. |
Which division of the nervous system is involved in the control of voluntary muscles? | The somatic nervous system controls muscles that are influenced consciously, or voluntarily. This category includes skeletal muscles. The somatic nervous system is a division of the peripheral nervous system, or PNS. |
A biopsy is taken from the lining of an artery wall. Which type(s) of muscle might be found in this process? | smooth muscle. Arteries, veins, arterioles, and larger venules contain smooth muscle in addition to endothelium and connective tissue. Note that capillary walls contain only a single layer of endothelial cells. |
A tissue sample is taken from the diaphragm. Which type(s) of muscle could this sample contain? | skeletal muscle. The diaphragm is the main muscle involved in respiration. It is composed of skeletal muscle, but can be controlled either voluntarily or involuntarily. |
Muscle cells are likely to have large amounts of which eukaryotic organelle? | mitochondria. These organelles provide the ATP needed for contraction. Some types of muscle fiber, generally those specialized for aerobic respiration, are higher in mitochondria than others. For example, slow-twitch or red muscle fibers contain extremely high numbers of the structures. |
Define: sarcomere | A highly organized unit within striated muscle. These are composed of alternating thick filaments (myosin) and thin filaments (actin). Together, many sarcomeres make up a myofibril, and many myofibrils form a muscle cell. |
Label the following parts of a sarcomere on the diagram below: M line, Z line, H zone, I band, and A band. |