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Flashcards in Musculoskeletal System Deck (85)
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What main functions are served by muscle?



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


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


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


What are the 3 major types of muscle?



What features characterize smooth muscle?

-mononucleated: single cell contains only one nucleus
-cells are rounded and irregular in appearance
-contain both actin and myosin but fibers are not well organized so no striation
-controlled by the autonomic NS (involuntary)
-can contract directly in response to stretch or other stimuli without NS input, known as myogenic activity


What features characterize skeletal muscle?

-multinucleated: single cell contains more than one nucleus
-innervated by somatic NS (voluntary control)
-actin and myosin arranged in repeating units called sarcomeres, which are striated in appearance
-contain both red fibers and white fibers



-oxygen carrier that uses iron in a heme group to bind oxygen
-red in color
-found in skeletal muscle
-picks up oxygen that hemoglobin releases in the tissues, meaning that is has a higher O2 affinity than hemoglobin
-only contains one monomer instead of 4 like Hb, meaning that is cannot undergo cooperative binding like Hb


Red Fibers

-known as slow-twitch fibers
-present in skeletal muscle
-have high myoglobin content
-primarily derive their energy aerobically
-contain many mitochondria to carry out oxidative phosphorylation
-found in muscles that contract slowly but can sustain activity
-during strenuous exercise they eventually switch to anaerobic metabolism and produce lactic acid


White Fibers

-known as fast-twitch fibers
-contain less myoglobin and therefore less iron so appear white in color
-found in muscles that contract rapidly but fatigue quickly
-have fewer mitochondria so must rely on glycolysis and fermentation to make ATP


What features characterize cardiac muscle?

-has characteristics of both smooth and skeletal muscle
-primarily uninucleated, but some cells may contain 2 nuclei
-innervated by autonomic NS (involuntary control)
-appears striated
-cells are connected by intercalated discs which contain many gap junctions (connections btw cytoplasm of adjacent cells, allowing for direct ion flow btw cells)
-can define and maintain their own rhythm through myogenic activity


What muscle types require Ca2+ for contraction?

all of them -- skeletal, smooth, and cardiac


What muscle types exhibit myogenic activity?

both smooth and cardiac muscle -- their cells respond to nervous input but do not require external signals to undergo contraction


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?

-The sample is probably skeletal muscle.

(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?

This information is 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


A biopsy is taken from the lining of an artery wall. Which type(s) of muscle might be found in this process?

-Smooth muscle would likely be found

(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?

-The sample would likely contain skeletal muscle.

(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?

muscle cells are likely to contain high numbers of 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)



-basic contractile unit of skeletal muscle
-made of thick and thin filaments
-each one is divided into different lines, zones and bands: Z-lines, M-line, I-band, H-zone, A-band


Thick Filaments

organized bundles of myosin


Thin Filaments

made of actin along with two other proteins: troponin and tropomyosin which help to regulate the interaction between the actin and myosin filaments



protein that acts a spring and anchors the actin and myosin filaments together, preventing excessive stretching of the muscle



*Z is at the end of the alphabet and the end of the sarcomere*
-define the boundaries of the sarcomere



*Middle of the Myosin filaments*
-runs down the center of the sarcomere through the middle of the myosin filaments



*I is a thin letter -- thin filaments only*
-the region containing exclusively thin filaments



*H is a thick letter -- thick filaments only*
-region containing exclusively thick filaments



*All of the thick filament, whether or not it is overlapping*
-contains thick filaments in their entirety, including any overlap with thin filaments


What happens to the zones/bands/lines during contraction?

-the H-zone, I-band, distance between Z-lines and distance between M-lines all become smaller
-size of A-band remains constant b/c it is the entire length of the myosin filament which does not change in length, it just slides



-sarcomeres that are attached end to end
-surrounded by a covering known as the sarcoplasmic reticulum (modified endoplasmic reticulum that contains a high concentration of Ca2+ ions)