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SIUE Skeletal Muscle
| Question | Answer |
|---|---|
| Building Blocks of Muscles | Myofilament -> Myofibril -> Muscle Fiber |
| What is the Sarcolema | The muscle cell membrane; The endings flatten out to tendons; Each muscle fiber is innervated by its own single nerve ending |
| Motor end plate | The nerve ending that secretes ACh in skeletal muscles. Sits 20-30nm fron cell. Axon terminates in the synaptic trough; Subneural clefts are present below the trough to increase the surface area for ACh binding |
| What are Myofibrils? | Subcomponent of muscle fibers; made up of myofilaments |
| What is Actin? | The thin filament made up of a double stranded protein molecule that attaches to the z-disks there are 3000 per myofibril |
| What is Myosin? | Thick fliament that has protruding crossbridges. It interacts with actin to cause muscle contraction. There are 1500 per myofibril |
| What is a Sarcomere? | The distance between the 2 z-disks on the myofibril They also connect muscles |
| What is sarcoplasm and what does it contain? | Cytoplasm of the skeletal muscle cells It has high concentration of K+, Mg+, PO4 and protein enzymes Contains many mitochondria for ATP production around myofibrils |
| Describe the SR | CA++ containing organelle of muscle cells; Most of the CA++ is located in the terminal cisternae; Releases Ca++ upon depolarization Contains Ca++ pumps that use ATP to resequester Ca++; If Ca++ is in the myofibrils the muscle remains contracted |
| Skeletal Muscle Myosin to Actin Ratio | 1:2 |
| Describe Tropomyosin | A protein that wraps around the actin; it blocks the active sites withn the muscle is relaxed; keeps the myosin from binding with the actin when the muscle is relaxed |
| Describe Troponin | It binds the tropomyosin to the actin; Exists in 3 forms (trop-i, trop-t, trop-c) |
| Troponin-i | has a high affinity for actin |
| Troponin-t | has a high affinity for tropomyosin |
| Troponin-c | has a high affinity for calcium |
| What is calcium's effect on the troponin-tropomyosin complex? | Ca++ blocks the inhibitory effects of the T-TM complex allowing myosin to bind to actin so that muscle contraction can occur |
| Describe the transverse Tubule | It's an extension of the sarcolema that extends transversly across the myofibril that increases the surface area of the sarcolema; Carries the AP to the middle of the muscle fiber so that the entire cell can depolarize |
| Power Stroke of Skeletal Muscles | Myosin heads bind to actin and pulls inward Cleavage of ATP to ADP on myosin head provides energy; New ATP allows release of myosin form actin; Binding and release occur independently form one another; (more effecient); Shortening of actin is faster |
| What is the point of greatest sarcomere tension? | When the myosin and actin are maximally overlapped tension decreases, though, when z-disks run into the myosin band |
| When is there no tension in the sarcomenre | When the myosin and actin are far apart |
| What is the relationship of velocity of muscle contraction and load | Increased load = decreased velocity Increased velocity = decreased load |
| How does the AP of Skeletal muscle compare to the AP of nerves? | Skel muscle AP is much slower, but has a longer duration (If they were the same the muscles would contract extremely fast possibly leading to damage. |
| What happens when the SR is depolarized? | It releases Ca++ ions into the muscle cell The Ca++ ions allow for contraction to occur |
| Describe Junctional Fatigue | When muscle contraction occurs at high frequencies (>100Hz) for several minutes the ACh vessicles become depleted and less is released with each stimulation |
| Describe Isometric Contraction | Muscle is continuously contracting without a change in its lenght |
| Describe Isotonic Contraction | The muscle contracts without a change in tension due to a fixed load |
| Describe Metabolic Fatigue | Muscle glycogen and phosphocreatine is depleted There is an interuption of blood flow leading to decreased oxygenation |
| Describe Skeletal Muscle Fiber Hypertropy | Muscle fibers increase in size and slightly in number as a result of maximal force exertion |
| Describe Disuse Atrophy | Muscle Fibers decrease in size because the rate of decay of contractile proteins excedes the rate of replacement |
| Describe skeletal muscle denervation atrophy | This atrophy occurs immediately following denervation Fibrous tissues replace the muscle tissue leading to contracture (a permanent shortening of the fibrous tissue over time) |
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SRNA84
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