REVIEW SHEET FOR LECTURE EXAM 3 Muscular System 1. Define:Endomysium – covers each skeletal muscle fiber (muscle fibers are long multinucleate cells)perimysium – covers each fascicle Epimysium - covers perimysium creating a skeletal muscle Fascicles – consists of a group endomysium-covered muscle fibers wrapped in a coarse CT membrane called Permimysium Tendons – cord of dense fibrous tissue attaching muscle to bone. This is an indirect attachment of muscle to bonesarcolemma – plasma membrane of a muscle fibersarcoplasm – cytoplasm of muscle fibersarcoplasmic reticulum - stores/ releases calcium into the sacroplasm to cause skeletal muscle contraction necessary for muscle contractionmyoglobin – red pigment that binds and stores oxygensarcomere – distance between 2 successive Z lines. It is the structural unit of skeletal muscleM line – line that bisects and anchors the A bands Z line (z disc) – anchor the thin filaments H zone – middle region of the A band not overlapping with the thin Filaments (only thick filaments) A band – length of a thick filament (includes overlapping thin filaments) I band – regions of the thin filament not overlapping with the A band Triad – compose of a transverse tubule between 2 terminal cisterene and it releases calcium ions into the sacroplasm when the sarcolemma depolarizes Motor unit – a motor neuron and all the muscle fibers it innervates via its axon terminals.Motor units come in different sizes: small, medium and large. 2. Describe the neuromuscular junction. What is the motor end plate? - Neuromuscular junction is the junction between the axon terminal of a motor neuron and a skeletal muscle fiber separated by a small space call the neuromuscular cleft (synaptic cleft) and each muscle fiber only has one neuromuscular junction. - The motor end plate is the highly folded region of the sacrolemma of the muscle fiber at the neuromuscular junction. It expresses acetylcholine receptors on the surface. 3. Name the 3 proteins in a thin filament. What is the function of tropomyosin in a relaxed skeletal muscle?Actin – contains the binding sites for myosin headsTropomyosin – rod-shaped regulatory protein that spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscleTroponin – a three-polypeptide complex namely:TnC – binds calcium ionsTnT – binds tropomyosinTnI – inhibitory subunit that binds to actin4. How are the myosin heads activated?When the tropomyosin blockade ends. Myosin heads are activated when the myosin heads are attached by ADP + Pi. When ATPase splits into ATP and ADP and inorganic phosphate (Pi), the ADP and Pi are still attached to the myosin globular heads and cause the myosin globular head to be activated. 5. Describe skeletal muscle contraction - Motor neuron is activated- Axon of motor neuron generates and transmits action potential to the axon terminal- Results in the release of acetylcholine from the axon terminals into the neuromuscular cleft- Acetylcholine binds to acetylcholine receptors on the motor end plate to cause depolarization which leads to generation of action potential at the motor end plate- The action potential spreads across the entire sacrolemma and into the T-tubules of the triads- Results in the release of calcium ions from the terminal cisternae of the triads into the sacroplasm- Calcium ions bind to TnC which results in a conformational change and the removal of tropomyosin from blocking the myosin-binding sites on actin 6. Give the role of ATP in muscle contraction; Differentiate between muscle fatigue and rigor mortis - 3 ATPs are used in muscle contraction and relaxationo ATP is hydrolyzed by ATPase to produce ADP and Pi to activate the myosin headso ATP binds to the ATP site on the cross bridge (attached myosin head to its site onactin) to cause cross bridge detachment from the actin relaxing the muscle and stopping contractiono ATP is required for the sequestration of calcium ions back into the SR for storage (active transport)- Rigor Mortis occurs when an individual dies and ATP synthesis ceases – actin and myosin are irreversibly cross linked and skeletal muscles remain contracted- Muscle fatigue is a physiological inability if a stimulated skeletal muscle to contract due to ATP deficit, which is the rate of ATP production lags behind ATP demand7. Define the sliding filament mechanism - list structures that a) shorten b) remain the same when a skeletal muscle contracts. States that the sliding of the thin filaments past the A bands results in muscle contraction. According to this mechanism when a muscle contracts there is more overlap between the thin filaments and the A bands. Sacromere length shorten = skeletal muscle shortens(contracts)H zone and I band decreases or disappears Length of the A bands and the thin filaments remain the same8. Discuss the factors that affect the strength of skeletal contraction- Size of motor units activated – larger motor units generate more force than smaller motor units- Number of motor units activated – force increases as the number of motor units activated increases. Recruitment – smaller motor units are activated first followed by larger motor units- Frequency of skeletal muscle activation – force increases as the rate of stimulation by motor neurons increases- The length of the sacromeres prior to contraction – sacromeres at the optimum length generate the maximum force; sacromere length below the optimum length (shortened sacromeres) results in decreased force; sacromere length greater than the optimum length (stretched sacromeres) results in decreased force of contraction.9. Name and give the characteristics of the 3 types of skeletal muscle fibers: Which type is fatigable and why? Which type is also known as red fiber and why? - Slow Oxidative fibers – known as red fiber because it has a huge amount of myogoblin. Itis mainly used for endurance type activities since it slow oxidation- Fast Oxidative fibers - Fast Glycolytic fibers – low amount of myogoblin so is known as white fibers. It is mainly used in short intense activities.10. Define isotonic and isometric contractions. Isometric contraction – force generated by the muscle is increasing at a constant musclelength (“isometric” = same length); occurs when the weight exceeds the force generated by the muscleIsotonic contraction – muscle shortens at a relatively constant force (isotonic = same force);
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