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outline 11
Comparative Physiology- Renner Lecture 11
| Question | Answer |
|---|---|
| another name for skeletal muscle fibers | myofibrils |
| plasma membrane of skeletal muscles is called the _______________, the cytoplasm is the ____________________ and the endoplasmic reticulum is the ___________________ | sarcolemma, sarcoplasm, sarcoplasmic reticulum |
| T/F most muscle fibers are the same length | FALSE. muscle fibers vary in length |
| what is the usual diameter range for muscle fibers? | few microns to 100 microns |
| shortest and longest muscle fiber examples | shortest: insect flight wing, longest: giraffee |
| what has to happen to a muscle in order for it to function? what induces a fiber to function | muscle fibers function by shortening to create tension in response to a stimulation from a motor neuron |
| what are muscles usually connected to? why? any exclusions? | usually attached to one or more joints through cartelagenous structures called tendons, or aponeurosis which is just a sheet of connective tissue. Some exceptions to that are eye muscles, orifices (sphinctors), and upper esophagus |
| the repeated contractile units that form a myofibril are called __________________ | sarcomeres |
| myofibrils are arranged in a __________________ and in a single myofibril the sarcomeres are arranged in a __________________ | parallel, series |
| what separates sarcomeres from each other? | z line forms the boundary of sarcomeres |
| given the structure of a sarcomere, what unit form the boundary, contains alpha actinin and contains the transverse tubule | Z-line |
| given the structure of a sarcomere, what structure forms a gap between end of actin filaments? | H zone |
| given the structure of a sarcomere, in what region does myosin not have a globular head? | Pseudo H-zone, it is also the center of the H zone |
| given the structure of a sarcomere, what region has myosin heads in a parallel? | A band |
| what does the A in A band stand for? what does that indicate? | Means Anisotrophic, meaning it polarizes light-dark in color |
| what does alpha actinin do? | anchors actin to the z line |
| given the structure of a sarcomere, what region contains actin filaments and shorten during contractions ? | I band |
| what does the I in I band stand for? what does it mean? | Isotrophic: does not polarize light. appears lighter in electron micrograph |
| given the structure of a sarcomere, what region contains enzymes? | M line |
| what enzymes are found in the M line of a sarcomere? | creatine, phosphatase, and myokinase |
| what is the role of enzymes in a sarcomere? | produce energy when ATP is depleted during anaerobic conditions |
| each myosin is surrounded by ______________ actin filaments that are shared with surrounding myosins. so that each actin surrounds ____________ myosin filaments | six, three |
| what forms cross bridges? | projections that arise at regular intervals from myosin |
| what is the myosin filament composed of? | two heavy chains that wind around each other at the end. an unwound portion that forms globular head associated with it are 2 lighter protein chains that have ATPase activity, actin binding site and flexible portion aka neck |
| the thick filament has approx ____________ myosin molecules | 400 |
| where are globular heads positioned in the thick filament of myosin? | globular head protrude from the thick filament |
| functions of proteins associated with thick filament of myosin? | 1. C protein- keeps thick myofilaments together 2. proteins at the M line- contain enzymes for energy, is binding point between myosin molecules |
| functions of proteins associated with thin filaments of myosin? | 1. G and F actin- G: binding site for globular head, forms F actin (2 chain helix 2. tropomyosin- in groove of F actin, makes contact with 1 strand. 3. troponin- C site-Ca2+ binding site, I-inhibit head from binding actin, T- bind tropomyosin->troponin |
| tropomyosin is made up of __________polypeptide chains and troponin is made up of _______________ | two, three |
| length of each strand of tropomyosin is enough to cover ___________ g actin subunits | seven |
| C site on troponin can bind up to how many Ca2+ ions? | four |
| function of troponin I? | inhibits globular head from binding actin |
| function of troponin T? | binds tropomyosin to troponin |
| what are the condition in a skeletal muscle fiber at rest? | 1. Ca2+ concentrations are low 2. ATP concentrations are high 3. globular myosin head is oriented close to the filament |
| what happens following a stimulation of a motor neuron AP in skeletal muscle fiber? | 1. Ach releases into synapse 2. Ach binds to nicotinic receptors stimulating end plate potential-local potential analogous to EPSP 3. if signal is sufficient to depolarize membrane of muscle to threshold, then muscle AP results |
| What happens in neuromuscular junctions to result in motor neuron AP? | 1. open VgCa2+ channel in presynaptic terminal 2. Ca2+ influx stimulates vesicular docking & exocytosis 3. Ach releases into synapse 4. Ach binds to nicotinic receptors-> Increase Na+/K+ perm.->depolarize 5. endplate-> sum to threshold-->AP results |
| where does most docked Acetylcholine go? | most is catabolized by Acetylcholinestrase, ~10% bind to nicotinic receptors |
| what happens as a result of muscle AP? | 1.increase Ca sarcoplasm 2.Ca binds to C site troponin-conformational change->move tropomyosin 3.tropomyosin moves inward between F actins->F myosin binding site exposed 4.ATP on Myosin binds it to actin perpend 5. power stroke 6.ATP releases myosin head |
| what causes myosin head to bind to actin? | ATP on myosin head is hydrolyzed, with presence of ATPase, that charges the myosin head allowing myosin to bind to actin-myosin binding site perpendicularly |
| What is the power stroke? | movement of thin actin filament after being attached to myosin head. Myosin head tilts at approximately 45 degrees. The release of ADP and Pi from hydrolyzing ATP causes it. |
| how is actin released from myosin head? what happens if that doesn't happen? | new ATP binds to myosin head causing it to detach from actin. If it doesn't happen, body goes stiff-> rigor mortis bc there is no ATP |
| the cycle of muscle contraction happens _______________ times per min. Each cycle is _____________msec with _____________nm of movement | 50-100, 10, 10 |
| rigor mortis is followed by ________________ | putrefaction |
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