Muscle Contraction and Locomotion Quiz

PDF page 1296: Muscles move bones, and, in turn, muscle contraction is dependent upon input from the nervous systems. The activities at the neuromuscular junction are similar to the activities occurring at the synapses between neurons. There are approximately 650 skeletal muscles in the human body, each of which is composed of muscle fibers. (The body also contains specialized smooth and cardiac muscle tissue.) In addition to the collection of organelles typical of eukaryotic cells, each muscle fiber contains myofibrils, which, in turn, consist of arrangements of protein filaments called actin and myosin. In the sliding filament model of muscle contraction, the thicker myosin filaments have cross-bridges that attach and detach to thinner actin filaments. The binding of myosin to actin causes the actin filaments to slide, shortening the muscle fiber. ATP produced in cellular respiration provides the energy needed for contraction. However, contraction requires a signal from the nervous system (excitation-contraction coupling). Nerve impulses traveling down motor neurons cause the release of the acetylcholine from vesicles in the axon terminus into the synapse between the neuron and the muscle fiber. Acetylcholine binds to receptors on the plasma membrane (sarcolemma) of the muscle fiber, allowing an action potential to move to the endoplasmic reticulum where calcium ions

PDF page 1296: Muscles move bones, and, in turn, muscle contraction is dependent upon input from the nervous systems. The activities at the neuromuscular junction are similar to the activities occurring at the synapses between neurons. There are approximately 650 skeletal muscles in the human body, each of which is composed of muscle fibers. (The body also contains specialized smooth and cardiac muscle tissue.) In addition to the collection of organelles typical of eukaryotic cells, each muscle fiber contains myofibrils, which, in turn, consist of arrangements of protein filaments called actin and myosin. In the sliding filament model of muscle contraction, the thicker myosin filaments have cross-bridges that attach and detach to thinner actin filaments. The binding of myosin to actin causes the actin filaments to slide, shortening the muscle fiber. ATP produced in cellular respiration provides the energy needed for contraction. However, contraction requires a signal from the nervous system (excitation-contraction coupling). Nerve impulses traveling down motor neurons cause the release of the acetylcholine from vesicles in the axon terminus into the synapse between the neuron and the muscle fiber. Acetylcholine binds to receptors on the plasma membrane (sarcolemma) of the muscle fiber, allowing an action potential to move to the endoplasmic reticulum where calcium ions

PDF page 1296: Muscles move bones, and, in turn, muscle contraction is dependent upon input from the nervous systems. The activities at the neuromuscular junction are similar to the activities occurring at the synapses between neurons. There are approximately 650 skeletal muscles in the human body, each of which is composed of muscle fibers. (The body also contains specialized smooth and cardiac muscle tissue.) In addition to the collection of organelles typical of eukaryotic cells, each muscle fiber contains myofibrils, which, in turn, consist of arrangements of protein filaments called actin and myosin. In the sliding filament model of muscle contraction, the thicker myosin filaments have cross-bridges that attach and detach to thinner actin filaments. The binding of myosin to actin causes the actin filaments to slide, shortening the muscle fiber. ATP produced in cellular respiration provides the energy needed for contraction. However, contraction requires a signal from the nervous system (excitation-contraction coupling). Nerve impulses traveling down motor neurons cause the release of the acetylcholine from vesicles in the axon terminus into the synapse between the neuron and the muscle fiber. Acetylcholine binds to receptors on the plasma membrane (sarcolemma) of the muscle fiber, allowing an action potential to move to the endoplasmic reticulum where calcium ions

PDF page 1300: The motion of muscle shortening occurs as myosin heads bind to actin and pull the actin inwards. This action requires energy, which is provided by ATP. Myosin binds to actin at a binding site on the globular actin protein. Myosin has another binding site for ATP at which enzymatic activity hydrolyzes ATP to ADP, releasing an inorganic phosphate molecule and energy. ATP binding causes myosin to release actin, allowing actin and myosin to detach from each other. After this happens, the newly bound ATP is converted to ADP and inorganic phosphate, Pi. The enzyme at the binding site on myosin is called ATPase. The energy released during ATP hydrolysis changes the angle of the myosin head into a “cocked” position. The myosin head is then in a position for further movement, possessing potential energy, but ADP and Pi are still attached. If actin binding sites are covered and unavailable, the myosin will remain in the high energy configuration with ATP hydrolyzed, but still attached. If the actin binding sites are uncovered, a cross-bridge will form; that is, the myosin head spans the distance between the actin and myosin molecules. Pi is then released, allowing myosin to expend the stored energy as a conformational change. The myosin head moves toward the M line, pulling the actin along with it. As the actin is pulled, the filaments move approximately 10 nm toward the M line. This movement is called the power stroke, as it is the step at which force is

PDF page 1296: Muscles move bones, and, in turn, muscle contraction is dependent upon input from the nervous systems. The activities at the neuromuscular junction are similar to the activities occurring at the synapses between neurons. There are approximately 650 skeletal muscles in the human body, each of which is composed of muscle fibers. (The body also contains specialized smooth and cardiac muscle tissue.) In addition to the collection of organelles typical of eukaryotic cells, each muscle fiber contains myofibrils, which, in turn, consist of arrangements of protein filaments called actin and myosin. In the sliding filament model of muscle contraction, the thicker myosin filaments have cross-bridges that attach and detach to thinner actin filaments. The binding of myosin to actin causes the actin filaments to slide, shortening the muscle fiber. ATP produced in cellular respiration provides the energy needed for contraction. However, contraction requires a signal from the nervous system (excitation-contraction coupling). Nerve impulses traveling down motor neurons cause the release of the acetylcholine from vesicles in the axon terminus into the synapse between the neuron and the muscle fiber. Acetylcholine binds to receptors on the plasma membrane (sarcolemma) of the muscle fiber, allowing an action potential to move to the endoplasmic reticulum where calcium ions

PDF page 1304: Na into the cell when they receive neurotransmitter signal. Acetylcholine (ACh) is a neurotransmitter released by motor neurons that binds to receptors in the motor end plate. Neurotransmitter release occurs when an action potential travels down the motor neuron’s axon, resulting in altered

PDF page 1297: Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell. Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle. Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.

PDF page 1297: Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell. Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle. Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.

PDF page 1297: Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell. Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle. Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.

PDF page 1297: Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell. Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle. Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.

PDF page 1297: Each skeletal muscle fiber is a skeletal muscle cell. These cells are incredibly large, with diameters of up to 100 μm and lengths of up to 30 cm. The plasma membrane of a skeletal muscle fiber is called the sarcolemma. The sarcolemma is the site of action potential conduction, which triggers muscle contraction. Within each muscle fiber are myofibrils—long cylindrical structures that lie parallel to the muscle fiber. Myofibrils run the entire length of the muscle fiber, and because they are only approximately 1.2 μm in diameter, hundreds to thousands can be found inside one muscle fiber. They attach to the sarcolemma at their ends, so that as myofibrils shorten, the entire muscle cell contracts (Figure 29.34).

PDF page 1310: sarcolemma plasma membrane of a skeletal muscle fiber sarcomere functional unit of skeletal muscle scapula flat, triangular bone located at the posterior pectoral girdle sesamoid bone small, flat bone shaped like a sesame seed; develops inside tendons short bone bone that has the same width and length, giving it a cube-like shape skeletal muscle tissue forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled skull bone that supports the structures of the face and protects the brain smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels spongy bone tissue forms the inner layer of all bones sternum (also, breastbone) long, flat bone located at the front of the chest supination movement of the radius and ulna bones of the forearm so that the palm faces forward suture short fiber of connective tissue that holds the skull bones tightly in place; found only in the skull suture bone small, flat, irregularly shaped bone that forms between the flat bones of the cranium symphysis hyaline cartilage covers the end of the bone, but the connection between bones occurs through fibrocartilage; symphyses are found at the joints between vertebrae synarthrosis joint that is immovable synchondrosis bones joined by hyaline cartilage; synchondroses are found in the epiphyseal plates of growing bones in children syndesmosis joint in which the bones are connected by a band of connective tissue, allowing for more movement than in a suture synovial joint only joint that has a space between the adjoining bones tarsal one of the seven bones of the ankle thick filament a group of myosin molecules thin filament two polymers of actin wound together along with tropomyosin and troponin thoracic cage (also, ribcage) skeleton of the chest, which consists of the ribs, thoracic vertebrae, sternum, and costal cartilages

PDF page 1298: The striated appearance of skeletal muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded. Each I band has a dense line running vertically through the middle called a Z disc or Z line. The Z discs mark the border of units called sarcomeres, which are the functional units of skeletal muscle. One sarcomere is the space between two consecutive Z discs and contains one entire A band and two halves of an I band, one on either side of the A band. A myofibril is composed of many sarcomeres running along its length, and as the sarcomeres individually contract, the myofibrils and muscle cells shorten (Figure 29.35).

PDF page 1310: sarcolemma plasma membrane of a skeletal muscle fiber sarcomere functional unit of skeletal muscle scapula flat, triangular bone located at the posterior pectoral girdle sesamoid bone small, flat bone shaped like a sesame seed; develops inside tendons short bone bone that has the same width and length, giving it a cube-like shape skeletal muscle tissue forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled skull bone that supports the structures of the face and protects the brain smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels spongy bone tissue forms the inner layer of all bones sternum (also, breastbone) long, flat bone located at the front of the chest supination movement of the radius and ulna bones of the forearm so that the palm faces forward suture short fiber of connective tissue that holds the skull bones tightly in place; found only in the skull suture bone small, flat, irregularly shaped bone that forms between the flat bones of the cranium symphysis hyaline cartilage covers the end of the bone, but the connection between bones occurs through fibrocartilage; symphyses are found at the joints between vertebrae synarthrosis joint that is immovable synchondrosis bones joined by hyaline cartilage; synchondroses are found in the epiphyseal plates of growing bones in children syndesmosis joint in which the bones are connected by a band of connective tissue, allowing for more movement than in a suture synovial joint only joint that has a space between the adjoining bones tarsal one of the seven bones of the ankle thick filament a group of myosin molecules thin filament two polymers of actin wound together along with tropomyosin and troponin thoracic cage (also, ribcage) skeleton of the chest, which consists of the ribs, thoracic vertebrae, sternum, and costal cartilages

PDF page 1298: The striated appearance of skeletal muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded. Each I band has a dense line running vertically through the middle called a Z disc or Z line. The Z discs mark the border of units called sarcomeres, which are the functional units of skeletal muscle. One sarcomere is the space between two consecutive Z discs and contains one entire A band and two halves of an I band, one on either side of the A band. A myofibril is composed of many sarcomeres running along its length, and as the sarcomeres individually contract, the myofibrils and muscle cells shorten (Figure 29.35).

PDF page 1298: Myofibrils are composed of smaller structures called myofilaments. There are two main types of filaments: thick filaments and thin filaments; each has different compositions and locations. Thick filaments occur only in the A band of a myofibril. Thin filaments attach to a protein in the Z disc called alpha-actinin and occur across the entire length of the I band and partway into the A band. The region at which thick and thin filaments overlap has a dense appearance, as there is little space between the filaments. Thin filaments do not extend all the way into the A bands, leaving a central region of the A band that only contains thick filaments. This central region of the A band looks slightly lighter than the rest of the A band and is called the H zone. The middle of the H zone has a vertical line called the M line, at which accessory proteins hold together thick filaments. Both the Z disc and the M line hold myofilaments in place to maintain the structural arrangement and layering of the myofibril. Myofibrils are connected to each other by intermediate, or desmin, filaments that attach to the Z disc. Thick and thin filaments are themselves composed of proteins. Thick filaments are composed of the protein myosin. The tail of a myosin molecule connects with other myosin molecules to form the central region of a thick filament near the M line, whereas the heads align on either side of the thick filament where the thin filaments overlap. The primary component of thin filaments is the actin protein. Two other components of the thin filament are tropomyosin and troponin. Actin has binding sites for myosin attachment. Strands of tropomyosin block the binding sites and prevent actin–myosin interactions when the muscles are at rest. Troponin consists of three globular subunits. One subunit binds to tropomyosin, one subunit

PDF page 1310: tibia (also, shinbone) large bone of the leg that is located directly below the knee trabeculae lamellae that are arranged as rods or plates tropomyosin acts to block myosin binding sites on actin molecules, preventing cross-bridge formation and preventing contraction until a muscle receives a neuron signal