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NPB 101 - CARDIAC MUSCLE CHEAT SHEET
Intro
Cardiac Muscle |
found only in the heart and shares characteristics of both skeletal and smooth muscles |
Basic Vocabulary
Sarcoplasmic Reticulum |
modified endoplasmic reticulum composed of a fine network of interconnected tubules into which Ca++ is actively transported and stored |
T-Tubules |
invagination of the plasma membrane at each sarcomere |
Foot Proteins |
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 |
Lateral Sacs |
enlared regions of the sarcoplasmic reticulum that come into close contact with the transverse tubules |
Dihydropyridine Receptors |
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++ |
Thin Filament
Actin |
globular cytoskelatal protein linked to form two long chains arranged in a double helical strands |
Tropomyosin |
pairs of threadlike filamentous proteins that lie alongside the grooves formed by the actin helix |
Troponin |
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 and Unstriated Muscles
Striated Muscles |
Skeletal and Cardiac Muscles |
Visually has striped lines across the muscle |
Unstriated Muscles |
Smooth Muscles |
Has no striped lines |
Excitation-Contraction Coupling
1. ACh released by axon of motor neurons binds to receptors on the motor end plate |
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 |
3. Action potential triggers Ca++ release from the sarcoplasmic reticulum |
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 |
5. Myosin cross bridges attach to actin and bend, pulling actin filaments towards the center of the sarcomere; powered by energy provided by ATP |
6. Ca++ actively taken up by sarcoplasmic reticulum when there is no longer local action potentials |
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 |
Thick Filament
Myosin |
cytoskeletal protein composed of two interwoven subunits, eqch with a long tail and a globular head region |
Actin Binding Site |
specialized region of the myosin head capable of binding to actin |
Myosin ATPase |
specialized region of the myosin head capable of ATP hydrolysis |
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Voluntary and Involuntary Muscles
Voluntary Muscles |
Skeletal Muscles |
Involuntary Muscles |
Cardiac and Smooth Muscles |
Sarcomere Vocabulary
Sarcomere |
functional unit of a muscle |
Z-Line |
defines boundary of sarcomere; site where thin filaments attach |
A-Band |
made up of thick filaments along with portions of thin filaments that overlap |
H-Zone |
lighter area within middle of A-band where thin filaments do not reach |
M-Line |
extends vertically down middle of A-band within center of H-zone |
I-Band |
consists of remaining portion of thin filaments that do not project into A-band |
Excitation-Contraction Coupling
Intercalated Discs
specialized cell-to-cell junctions found in cardiac muscle tissue |
contains desmosomes (maintaining the structural integrity and mechanical stability of the heart) |
also contains gap junctions (allows electrical signals (action potentials) to pass directly between cells) |
located at the ends of the cardiac muscle cells which form a zigzag connection between them |
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