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Cardiac Muscle
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found only in the heart and shares characteristics of both skeletal and smooth muscles
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Sarcoplasmic Reticulum
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modified endoplasmic reticulum composed of a fine network of interconnected tubules into which Ca++ is actively transported and stored
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T-Tubules
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invagination of the plasma membrane at each sarcomere
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Foot Proteins
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proteins that span the gap between the lateral sacs and the transverse tubules and mediate a change in permeability to Ca++ by the lateral sacs; also known as ryanodine receptors because they are locked open by the plant chemical ryanodin
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Lateral Sacs
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enlared regions of the sarcoplasmic reticulum that come into close contact with the transverse tubules
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Dihydropyridine Receptors
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receptor proteins in the transverse tubule membrane that come into contact with the foot proteins; voltage dependent and gate the change in permeability of the foot proteins to Ca++
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Actin
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globular cytoskelatal protein linked to form two long chains arranged in a double helical strands
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Tropomyosin
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pairs of threadlike filamentous proteins that lie alongside the grooves formed by the actin helix
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Troponin
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protein complex composed of three subunits, one that binds to actin, one that binds to tropomyosin, and one that binds to Ca++; multiple copies of this complex are bound to the strands of actin and tropomyosin
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Striated Muscles
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Skeletal and Cardiac Muscles
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Visually has striped lines across the muscle
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Unstriated Muscles
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Smooth Muscles
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Has no striped lines
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1. ACh released by axon of motor neurons binds to receptors on the motor end plate
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2. Action potential generated in response to binding of ACh and subsequent end plate potential is propagated across surface of membrane and down T-Tubule of muscle cell
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3. Action potential triggers Ca++ release from the sarcoplasmic reticulum
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4. Ca++ ions released from lateral sacs bind to troponin on actin filaments; tropomyosin physically moved aside to uncover cross-bridge binding sites on actin
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5. Myosin cross bridges attach to actin and bend, pulling actin filaments towards the center of the sarcomere; powered by energy provided by ATP
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6. Ca++ actively taken up by sarcoplasmic reticulum when there is no longer local action potentials
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7. With Ca++ no longer bound to troponin, tropomyosin slips back to its blocking position over the binding sites on actin; contraction ends; actin slides back to original resting position
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Myosin
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cytoskeletal protein composed of two interwoven subunits, eqch with a long tail and a globular head region
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Actin Binding Site
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specialized region of the myosin head capable of binding to actin
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Myosin ATPase
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specialized region of the myosin head capable of ATP hydrolysis
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Voluntary Muscles
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Skeletal Muscles
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Involuntary Muscles
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Cardiac and Smooth Muscles
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Sarcomere
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functional unit of a muscle
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Z-Line
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defines boundary of sarcomere; site where thin filaments attach
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A-Band
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made up of thick filaments along with portions of thin filaments that overlap
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H-Zone
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lighter area within middle of A-band where thin filaments do not reach
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M-Line
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extends vertically down middle of A-band within center of H-zone
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I-Band
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consists of remaining portion of thin filaments that do not project into A-band
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specialized cell-to-cell junctions found in cardiac muscle tissue
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contains desmosomes (maintaining the structural integrity and mechanical stability of the heart)
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also contains gap junctions (allows electrical signals (action potentials) to pass directly between cells)
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located at the ends of the cardiac muscle cells which form a zigzag connection between them
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