Lec 2 (12) - MCB 136 Professor Terry Machen 2/26/09 Lecture...

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MCB 136 Professor Terry Machen 2/26/09 Lecture 12 ASUC Lecture Notes Online is the only authorized note-taking service at UC Berkeley. Do not share, copy or illegally distribute (electronically or otherwise) these notes. Our student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. LECTURE Let’s start by talking about cardiac muscle. Cardiac muscle cells, also called cardiocytes or cardiac myocytes , are relatively small. A typical cardiac muscle cell has a single and a centrally placed nucleus. A few may have two or more. Cardiac muscle tissue is found only in the heart. Cardiac muscle shares similarities with skeletal muscle. It has a striated appearance and similar contraction. Cardiac muscle is mononucleated and branched. The t-tubules in a cardiac muscle are short and broad. There are no triads. The t-tubules encircle the sarcomeres at the z-lines . The primary structural proteins of cardiac muscle are actin and myosin . As in skeletal muscle, action potentials trigger calcium release from the sarcoplasmic reticulum (SR) and the contraction of sarcomeres; it also increases the permeability of the sarcolemma to extracellular calcium ions. Cardiac muscle cells are almost totally dependent on aerobic metabolism to obtain energy. The sarcoplasm of a cardiac muscle cell contains large numbers of mitochondria and myoglobin. Myoglobin stores energy. At an intercalated disc , the cell membranes of two adjacent cardiac muscle cells are bound together by gap junctions and desmosomes . These connections help stabilize the cells and maintain the three-dimensional structure of the tissue. The gap junctions allow ions and small molecules to move from one cell to another. This arrangement creates a direct electrical connection between the two muscle cells. An action potential can travel across an
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Lec 2 (12) - MCB 136 Professor Terry Machen 2/26/09 Lecture...

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