Animal Muscles

at rest tropomyosin blocks the binding sites on

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Unformatted text preview: pomyosin blocks the binding sites on actin. ! The Release of Ca2+ from the Sarcoplasmic Reticulum Triggers Muscle Contraction 47.1 How Do Muscles Contract? When Ca2+ is released, it binds to troponin, which changes conformation. If Ca2+ remains ATP hydrolysis: available, the myosin head cycle repeats! returns to extended Actin filament! conformation! Tropomyosin! ! myosin-movie.mov ! Troponin! Myosin binding site! Ca2+! Myosin filament! Troponin is bound to tropomyosin—twisting of tropomyosin exposes binding sites on actin. When Ca2+ pumps remove Ca2+ from sarcoplasm, contraction stops. Ca2+ binds troponin Ca2+ is released from and exposes SR! myosin-binding sites on actin! Power stroke: myosin head changes conformation! ADP released; ATP binds causing dissociation from actin! Myosin heads bind actin; release of Pi initiates power stroke! sliding-actin.mov ! Heart muscle cell ! Heart muscle cell: mitochondria ! Heart muscle cell: M-band Heart muscle cell: thin filaments (actin) ! ! Heart muscle cell: ribosomes ! Junction between two muscle cells ! Junction between two muscle cells: plasma membranes Junction between two muscle cells: desmosomes Junction between two muscle cells: Z-lines Junction between two muscle cells: T-tubules and SR ! ! ! ! Figure 47.7 There are Three Kinds of Muscle! Cardiac muscle Cardiac muscle •  Is also striated. •  Cells are smaller than skeletal muscle cells. •  Cells have one nucleus. •  Cardiac muscle cells also branch and interdigitate: can withstand high pressures. ! Cardiac Muscle Pacemaker and conducting cells initiate and coordinate heart contractions. The heartbeat is myogenic—generated by the heart muscle itself. The autonomic nervous system modifies the rate of pacemaker cells, but is not necessary for their function. ! this makes heart transpla...
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This note was uploaded on 02/13/2014 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.

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