ZOO428 - Exam II Index Cards

ZOO428 - Exam II Index Cards - Three muscle types are...

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Three muscle types are found: ( i ) skeletal muscle, ( ii ) cardiac muscle, and ( iii ) smooth muscle. The muscles in the body have two important functions: ( i ) to generate force; and ( ii ) to generate motion. A third function of muscle cells (particularly skeletal muscle) is to generate heat through multiple contractions (referred to as shivering thermogenesis ). Cellular Organelle or Ultrastructure Muscle Equivalent Plasma membrane Sarcolemma, myolemma Cytoplasm Sarcoplasm, myoplasm Endoplasmic reticulum Sarcoplasmic reticulum Gross anatomical muscle Fascicles Myofibers = muscle fibers = muscle cells Myofibrils Myofilaments (myosin and actin)
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Z disks. Two adjacent Z disks along the myofibril mark the boundaries of a single sarcomere. The Z disks are the attachment sites for the thin filaments. Therefore, from each Z disk, thin filaments extend to two neighboring sarcomeres. When a muscle fiber contracts, the Z disks of a sarcomere move closer together (see Sliding Filament Model of Contraction below). Thus, the sarcomere shortens as the muscle contracts. A band. The A band is the entire length of the thick filament. At the outer edges of the A band, the thick and the thin filaments overlap and, therefore, this region is the darkest region of the sarcomere. The center of the A band is composed only of the thick filament (see H zone below). The length of the A band does not change as the muscle contracts. H zone. The H zone refers to the center of the A band where there is no overlap between the thick and the thin filaments. Therefore, in the H zone, the filaments consist only of the thick filament. The H zone becomes smaller as the muscle contracts because the overlap between the thick and the thin filaments increases (i.e., region of naked or non-overlap of the thick filament decreases). I band. This region is closest to the Z disk, and is the lightest region of the sarcomere. The I band is occupied by the thin filaments only. Each Z disk runs through the middle of the I band. Therefore, half of each I band belongs to one sarcomere, and the other half belongs to the neighboring sarcomere. The I band also shortens as the muscle contracts.
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M line. The M line is the attachment site for the thick filaments. The M line is in the middle of the A band and, thus, it is in the middle of the sarcomere. every thin filament is surrounded by three thick filaments, and every thick filament is surrounded by six thin filaments. Structural proteins The structural integrity of the sarcomere is ensured by the presence of accessory structural proteins titin and nebulin . Titin is a very large elastic protein that stretches from one Z disk to the M line. Its function is to bring the stretched muscle to its resting length. Nebulin is positioned alongside the thin filaments and
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ZOO428 - Exam II Index Cards - Three muscle types are...

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