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BPIII
Week 1
| Question | Answer |
|---|---|
| "sacro" and "myo" | indicate muscle |
| Globular actin (G-actin) | are the monomers that polymerize to form F-actin chain |
| Filamentous actin (F-actin) | Is a polymeric chain of Globular Action (G-actin) monomors. Each thin filament contains two F-actin chains wound in a double helix. |
| myofilaments | in skeletal muscle fibers they consist of two types: Thick (Myosin) Filament and Thin (actin) filaments. |
| Describe the structure of the thin fillaments in muscle fiber | Actin filaments consist of two linear F-actin chains wound in a double helix that have a tropomyosin polypeptide wound around it, and three troponin proteins (TnT, TnI, & TnC) connected to the tropomyosin. |
| Sacromere | many exist within myofibrils and are basic contractile unit of a muscle's cross-striated myofibril. It is delineated by the Z disks at each end. Each sacromere contains one full A band in center and one-half of two I bands on either side of the A band. I |
| Myofibril (sarcostyles) | Cylindrical organelles that are found within muscle cells. Are bundles of actomyosin (actin & mysoin) thick and thin filaments that make up the Sacromere contractile units. |
| What is a Muscle Fiber? - What is present in sarcoplasm? | Muscle fiber is a muscle cell. They are cylindrical long cells that have flattened and long nuclei on the periphery of numerous bundles of myofibrils. The cell/fiber is surrounded by Endomysium. Sarcoplasm contains many mitochondria, myoglobin, glycogen |
| Describe the structure of the thick fillaments in muscle fiber | Looks like a golf club with the heads of the clubs pointing towards the Z-disks, this is the portion that connects to and walks along actin filament. Consist of a 6 polypeptide chains. 2 Heavy chains in a linear alpha-helix and 4 Light chains divided bet |
| Tropomyosin | is a long thin bouble helix polypeptide that raps around Thin (actin) filaments and blocks the binding site for myosin (thick) fillaments |
| Troponin (TnT,TnI, TnC) | Three separate proteins that form a complex connected to tropomyosin. TnT binds to tropomyosin, TnI inhibits interaction between tick and thin filaments by covering myosin binding site. TnC binds 4 calcium ions cooperatively; this causes a conformation c |
| Sliding filament mechanism - describe it | Atp disconnects myosin from actin. Myosin hydolyzes ATP to ADP producing energy for conformational change that walks myosin towards the positive end of actin (this in essence pulls the actin in towards the M line decreasing/contracting the Sacromemer). |
| Bands | A band - contains mostly Thick filament but there is some overlap of Thin - its center contains H zone with only thick fillaments present and at the very center is the M line; I band contains only thin filamant and its center lyes at Z disk/line., |
| During a contraction does a sacromere shorten? | Yes, the Z-disks that deliniate the ends of the sacromere can clealry be seen to move closer together. |
| During a muscle contraction does the thick & thin fillament, A-band, I-band, and H (Bar) zone shorten? | A-band and the thick and thin filaments remain constant. The I-band and H-zone shorten. |
| What proteins interact with the thin (actin) filament in sacromeres - function of each? | Nebulin (extends entire thin filament - setting its length), alpha-actinin and CapZ (beta-actinin) (both anchor thin filaments to Z disk and maintin spatial distribution), and Tropomodulin (caps the thin fillament - maintining and stabalizing its length) |
| What protein interacts with the thick (myosin) filament in sacromeres - function? | Titin; it stabalizes thick fillament position in the center of the sacromere b/c titin has an elastic portion that is anchored to Z-disk and it then extends through thick filament all the way to the M line. As the lenth of the sacromere changes so does t |
| Titin | Cytoskeleton protien present ins acromeres that stabalizes thick fillament position in the center of the sacromere b/c titin has an elastic portion that is anchored to Z-disk and it then extends through thick filament all the way to the M line. As the le |
| alpha-Actinin | major Z disc protein, anchors one end of the thin fillaments and helps mainatin spatial distribution |
| What is a cross bridge formation and where in the sacromere does it occur? | The overlapping of think and thin filaments and it can occur in the A-band. |
| T (Transverse) tubules | Are the invaginations of the sarcolemma (plasma membrane) that allows for the quick movement of charge from the post synaptic fibir down into the sarcoplasmic reticulum. T tubules penetrate the muscle fiber and overlies the surface of myofibrils, connect |
| Triads - what is its significance in muscle contraction? | Located at A-Iband junctions and is where you find two terminal cisternae and an inervating T-tubule. Are important in intiating muscle contraction b/c they receive the depolarizing stimulus from T-tubule that initiates the depolarizing of the sarcoplasm |
| Sacroplasmic reticulum & relationship to T Tubules | Is the smooth ER of striated muscle cells (fibers) and specializes in sequestering Ca2+ that it releases when it receives a depolarizing stimulus from the T-Tubule. |
| Ryanodine receptor | Skeletal muscle Calcium release channels on the sarcoplasmic reticulum that releases Calcium into ICF and leads to calcium binding to Troponin and eventual muscle contraction. This channel is activated by the depolarization of the T tubules. |
| Ca2+ ATPase (SERCA) | pumps calcium from ICF of muscle fibirs into the sarcoplasmic reticulum interior. |
| Calsequestrin | A low affinity, high capacity Calcium binding protein present in the sarcoplasmic reticulum; maintains low concentration inside sarcoplasmic reticulum, thus maing Ca2+ ATPase pupms job easier. |
| What is meant by calcium induced calcium released? | process by which little calcium enters muscle cell due to a stimulus from depolarization at T-tubule and this then induces the release of calcium from the sarcoplasmic reticulum. |
| IP3-channels receptor | Smooth muscle Calcium release channels on the sarcoplasmic reticulum that releases Calcium into ICF and leads to calcium binding to Troponin and eventual muscle contraction. This channel is activated by the depolarization of the T tubules. |
| Dystrophin | Actin-binding protein that anchors the myofibrillar array to the cell membrane (cytoplasmic side). This protein is defective or absent in Muscular Dystrophy. |
| myofillaments | consist of two special contraction protein fillaments containing Actin and Myosin |
| Histogenesis of skeletal muscle? | arises from mesenchyme of mesodermal origin. Produce Myoblast - they fuse to form multinucleated Myotubues - elongate producing myofilaments in cytoplams that add up to produce myofibrils. |
| What are the main muscle tissue types? | Striated muscle (skeletal and cardiac) and Smooth Muscle |
| Striated Muscle | Is a type of muscle tissue that consists of skeletal (voluntary) and cardiac muscle (involuntray) |
| Smooth Muscle | Is a type of muscle tissue that occurs mainly in the walls of hollow organs (blood vessels and intestine) it actions are slow and involunatry] |
| Sacrolemma | plasma membrane of muscle fibir |
| Sacroplasm | Cytoplasm of muscle fibir |
| Can mature skeletal muscle fibirs divide/mitosis? | no |
| What are the skeletal muscle fiber types? - How do they differ? | Red (slow-myoglobin), White (fast), and intermediate fibers; they differ in the myoglobin content, number of mitochondria, glycogen, and speed of contraction |
| Red Fibers (Slow fibers) | Type I. Slow, Oxidative (myoglobin), Abundant Mitochondria, Slow to fatigue, found in postural muscle and great for endurance |
| White Fibers (Fast fibers) | Type II. Fast, Glycolytic, Abundant, Glycogen, Quickly fatigued, are in most limb muscles and great for burst activities like sprinting. Contain less myoglobin and fewer mitochondria than red fibers. |
| Primary synaptic cleft | presynaptic cleft |
| Secondary synaptic cleft | Post synaptic cleft |
| Epimysium | layer of dense connective tissue surrounding bundle of muscle fascicles |
| Perimysium | layer of dense connective tissue surrounding one fascicle ( bundle of muscle fibers) |
| Endomysium | Delicate connective tissue consisting of basal lamina and reticular fibers that surrounds the sarcolema of one muscle fiber that consists of a bundle of myofibrils |
| Fascicles | bundle of muscle fibers (each muscle fiber consists of a bundle of myofibrils) |
| Rigor Mortis | Most muscle stiffen 3-4 hours after death and peak rigidity occurs 12 hours due to: inability of dying cells to exclude calcium, Calcium in ICF promotes binding of myosin cross bridges, there is no ATP available for cross bridge detachment, myosin-actin |
| Satellite cells (skeletal muscle) - location and function? | Scattered in adult skeletal muscles within the basal lamina (endomysium) of mature fibers. Satellite cells can divide after muscle injury, differntiate into myoblast and fuse to form new skeletal muscle fibers. This is of re;lavence b/c mature muscle is |
| What produces muscle atrophy? | Degreadtion of myofibrils due to disusue of muscle fibers (cachexia neurogenic) |
| What is the greatest factor contributing to the strength of muscle contraction? | Diameter of muscle fiber. Strength of muscle contraction is directly proportional to fiber diameter. Larger fiber -more sacromeres - greater strength |
| When would one experience hypertrophy of muscle fiber? | During exercise; increases muscle fiber diamater and mass by inc number of actin and myosin fillaments; also may be possible to increase the length of the muscle (adding new sacromere at end of fiber). |
| What is muscle hyperplasia | Rare condition where there is an increase in the number of muscle fibers (cells) |
| What is the difference between hypertrophy and hyperplasia ? | Hypertrophy is the building of muscle fiber mass (common result from exercise) and hyperplasia is the inc in number of muscle fibers, ie cells (rare). |
| How is energy produced for muscle contraction | Metabolism of Phosphocreatine, Glycogen, Glucos, fatty acids, and amino acids |
| Tetanus | When a muscle fiber is stimulated so rapidly (constant Ca2+ released in cytosol) that it does not have an opportunity to relax at all between stimuli and reaches its maximal sustained contraction (not good). |
| In cross bridge cycling what end does myosin filament move towards on actin filament? | Cross bridge cycling is the mechanism by which myosin (thick) filament walks towards the positive end of actin (thin) filament |
| Motor Unit | 1 axon and all the muscle fibers it innervates |
| Which provides for fine control over skeletal muscles - large or small motor unit | Small motor unit that contains fewer muscle fibers per motor unit. |
| Why does Passive Tension occur? | Due to tension generated from the stretching of none muscular elements within the whole muscle, such as ligaments or tendons. |
| Why does Active Tension occur? | B/c tension is generated from the cross bridge cycling of contractile elements (muscle/myofibrils) and this tension can be transmitted to the load for movement to occur. |
| Name the two types of contraction | Isometric (trying to lift 500lbs - tension present but muscle length constant - no shortening of muscle), and Isotonic (tension constant - muscle shortens) |
| How are Isotonic and Isometric tensions associated? | Isometric must come first and then isotonic will follow leading to muscle shortening - contraction and moving of load. |
| Differentiate between twitch summation and tetanus | Twitch summation is when a muscle fiber is restimulated (action potential) before it is allowed to relax, this allows for the summation of contractile activity, tetanus is when there are non stop stimuli that lead to the muscles maxiumum contractile acti |
| What is the Stair Case affect? - another name for it? | Treppe, it is having gradual increase in stimuli and tension that is possible by increasing the availability of calcium and as muscle release heat the enzyme system becomes more efficient. |
| What relationship between Thick and Thin fillaments in skeletal and cardiac muscle will allow for Maximal Contraction to be achieved? | Optimal Overlap between thick and thin filaments while muscle fiber is at rest. |
| In skeletal muscle, when is passive tension at its highest? | While at "rest" - when muscle length is at its longest; the peak of Passive Tension also represents zero Active Tension. |
| In skeletal muscle, when is active tension at its highest? | When muscle length has been decreased and passive tension has reached zero; this is also the area of maximal tension in the muscle. |
| What happens to the velocity of contraction when the load is equal to the maximum force that muscle can exert | Velocity contraction is zero; there is no contraction and this would be an example of an Isometric contraction. |
| When would the contraction velocity be the fastest/shortest? | Fast - light loads, or no load; slow - heavy loads |
| What type of muscle fiber would predominate in a muscle fiber with a long duration of isometric contractions? - short isometric duration? | Long duration would occur in Type I - Slow/Red Muscle fibers. Short duration would occur in Fast/White Muscle fibers. |
| Muscle fibers according to Dr. Elmoselhi | Type IA is slow oxidative (Red); Type IIA is fast oxidative (Red); Type IIB is fast glycolytic (White). Need to be able to differentiate difference in ATP source, mitochondria, glycogen, myoglobin, fatigue resistance, contraction speed, fiber diameter, f |
| Which muscle fiber type has the smallest diameter? - largest? | Type IA - slow twitch (Red) has smallest muscle fiber diameter and Type IIB - fast twicth (White) has largest diameter. |
| In cardiac muscle can treppe and tetanus occur. | Treppe may be observed, howeevr tetanus is not possibel b/c of the long duration of action potentials, and thus the long duration of the refractory period of muscle fibers. |
| Myostatin | Protein that inhibits muscle differntiation and growth, produced primarily in skeletal muscle cells and circulates in blood to then act on muscle tissue. Creates MIGHT MOUSE. |
| Muscle Spindle | Is a sensroy receptor (Propriocepters) that monitors muscle tension or the strecth of a muscle and adjusts the contraction strength accordingly. They convey info to CNS through the afferent sensory axon, and respond in the reflex arc through the efferent |
| When would you find myoglobin in urine? | Muscle trauma or injury. Can be casued by CPT 2 and McArdle syndromes as well. The muscle has been broken down and released into urine. This can lead to acute kidney failure if myoglobin becomes trapped in kidney tubules/capallaries. |
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