HSCI 206 Chapter 9 Lecture Notes Fall 2024 PDF

**HSCI 206** **Chapter 9 Lecture Notes** ***Characteristics of Skeletal Muscle Tissue*** 1. Excitability: ability of a muscle cell to generate an electrical signal in response to a stimulus 2. Contractility: occurs when skeletal muscle proteins within a cell slide past each other...

**HSCI 206** **Chapter 9 Lecture Notes** ***Characteristics of Skeletal Muscle Tissue*** 1. Excitability: ability of a muscle cell to generate an electrical signal in response to a stimulus 2. Contractility: occurs when skeletal muscle proteins within a cell slide past each other a. Shortening of a muscle cell 3. Extensibility: lengthening of a muscle cell when relaxed 4. Elasticity: ability of a muscle cell to return to its original length following shortening or lengthening ***Functions of Skeletal Muscle Tissue*** 1. Movement 2. Postural support 3. Joint stability 4. Heat production ***Skeletal Muscle Organization*** 1. Organs a. Each individual skeletal muscle is an organ. i. Examples 1. Biceps brachii 2. Rectus abdominis 3. Latissimus dorsi b. Each organ has skeletal muscle tissue, nervous tissue, epithelial tissue, and connective tissue (lots of types) working together to perform the functions listed above. 2. Skeletal muscles are bundles of bundles of bundles. c. *Complete the organizational chart with each missing level of bundling.*  3. Connective tissue does the bundling d. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_: dense regular connective tissue that bundles fascicles into muscles e. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_: dense regular connective tissue that bundles fibers into fascicles. ii. Contains blood vessels and neurons f. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_: areolar connective tissue that surrounds fibers and helps them connect to other fibers. g. Perimysium and epimysium come together at end of muscle to form a tendon that binds muscle to its attaching structure (usually bone). 4. Muscle Fibers/Cells h. Contain specific functional parts that are critical for muscle function. iii. Sarcolemma 4. Skeletal muscle plasma membrane iv. Sarcoplasm 5. Skeletal muscle cytoplasm v. Sarcoplasmic reticulum 6. Extensive series of membrane-bound tubes 7. Endoplasmic reticulum of skeletal muscle cells a. Store and release calcium vi. T-tubules 8. Transverse tubules 9. Inward extensions of sarcolemma that cut horizontally through fiber and wrap around myofibrils vii. Terminal cisternae 10. Enlarged section of sarcoplasmic reticulum 11. Flank each T-tubule viii. Triad 12. 2 cisternae with a t-tubule in the middle (like an oreo). 5. Myofibrils i. Composed of hundreds to thousands of myofilaments ix. Consist of proteins (myofilaments) 13. Thick filaments b. Myosin i. Contractile protein ii. Head binds to actin active site 14. Thin filaments c. Actin iii. Contractile protein iv. Actin active site receives myosin head d. Tropomyosin v. Regulatory protein vi. Covers actin active site, preventing myosin from binding e. Troponin vii. Regulatory protein viii. Locks tropomyosin in place 6. Sarcomere j. Smallest, repeating functional/contractile unit in skeletal muscle k. Line up along myofibril x. From one Z disc to another Z disc l. Consist of bundled and overlapping myofilaments. xi. Gives the appearance of striations xii. The interaction of the myofilaments (thick with thin) allows muscle fibers to generate force and cause movement. m. Parts xiii. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 15. Appear light. 16. Areas of thin filament only. 17. Disappears during contraction xiv. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 18. Area of only thick filament. 19. Located in center 20. Disappears during contraction xv. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 21. Midline of sarcomere. 22. Thick filament attaches here xvi. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 23. Appear dark 24. Areas of thick filament and overlap with thin 25. Does not change size during contraction xvii. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 26. 2 per sarcomere 27. End lines and where thin filaments attach n. Label the diagram and micrograph (picture) below with the parts of a sarcomere, and thin and thick filaments.  o. Sliding filament theory of contraction xviii. Write what happens to the parts of the sarcomere when contraction occurs (i.e. shorten, lengthen, stay the same): 28. A band: 29. I band: 30. H zone: 31. Z discs: 32. M line: ***Neural Control of a Muscle Fiber*** 1. Neuromuscular Junction (NMJ) a. Site of communication between a neuron and a muscle fiber. b. It works almost exactly like a synapse (review Chapter 11 notes). c. Components i. Axon terminal 1. Tips of telondendria 2. Synaptic vesicles only contain acetylcholine (ACh) ii. Synaptic cleft 3. Space between axon terminal and muscle fiber membrane 4. Ach diffuses from axon terminal across synaptic cleft to bind to chemically-gated Na^+^ channels on the motor end plate iii. Motor end plate 5. Specialized region of sarcolemma 6. Contain only chemically-gated Na^+^ channels a. Always excitatory i. They cause \_\_\_\_\_\_\_\_\_\_ potentials in the motor end plate. ***Skeletal Muscle Fibers at Rest*** 1. Resting membrane potential a. -90 mV b. Voltage-gated channels are closed 2. Thin and thick filaments are not interacting c. Troponin lock tropomyosin in place ***Physiology of Skeletal Muscle Contraction and Relaxation*** 1. Contraction Steps a. *Events at the neuromusclular junction* i. Action potential arrives at \_\_\_\_\_\_\_\_\_\_ of neuron. ii. Voltage-gated Ca^2+^ channels open and Ca^+^ \_\_\_\_\_\_\_\_\_\_. iii. Exocytosis of ACh from synaptic vesicles. iv. ACh diffuses across synaptic cleft to bind to chemically-gated Na^+^ receptors on motor end plate and opens chemically-gated Na^+^ channels. v. Na+ diffuses into the muscle fiber resulting in an end plate potential (EPP) 1. An EPP is the muscle fiber version of an excitatory post synaptic potential, a graded potential. b. *Excitation Phase* vi. End plate potential is a local depolarization that spreads to the adjacent sarcolemma c. *Excitation-Contraction Coupling Phase* vii. If EPP reaches threshold (and generates an AP), voltage-gated channels on the sarcolemma opens. 2. A muscle fiber has a resting membrane potential of \_\_\_\_\_\_\_ and a threshold potential of \_\_\_\_\_\_\_. viii. Voltage-gated \_\_\_\_\_\_\_ channels open first 3. They are faster 4. Cause depolarization ix. Then voltage-gated \_\_\_\_\_\_\_ channels open 5. Cause repolarization a. Just like in a neuron with slightly different timing x. AP spreads across the sarcolemma and through the T-tubules. 6. As the T-tubules are depolarized and reach threshold, voltage-gated Ca^2+^ channels in the \_\_\_\_\_\_\_\_\_\_ open and Ca^2+^ diffuses into the sarcoplasm (skeletal muscle fiber version of cytoplasm). d. Crossbridge Cycling Phase xi. Ca^2+^ reaches myofilaments 7. Ca^2+^ binds to troponin b. Troponin shifts, pulling tropomyosin with it. i. This exposes active sites on actin. xii. Myosin heads bind to exposed active sites on actin 8. Crossbridge xiii. The head of myosin pivots and "flexes" or "power strokes" to pull the thin filament toward the M line of the sarcomere. 9. Result of the release of ADP + P xiv. ATP binds to myosin head and breaks crossbridge. 10. Myosin detaches from actin xv. ATP is hydrolyzed into ADP + P 11. The energy from ATP "resets" or "cocks" the myosin head. c. This allows myosin to rebind to actin and complete another power stroke. xvi. The combination of millions of power strokes at the same time produces force capable of producing movement. xvii. Crossbridges continue to cycle (breaking and reforming) as long as both \_\_\_\_\_\_\_\_\_\_ (to break crossbridge and reset myosin) and \_\_\_\_\_\_\_\_\_\_ (to keep actin active sites exposed) are present. 2. Relaxation Steps e. Reverse process of contraction f. AP has to end xviii. No more signal/no more release of ACh g. ACh gets removed from receptors on motor end plate xix. Acetylcholinesterase (an enzyme) degrades ACh. h. Resting membrane potential is restored by the opening of voltage-gated K^+^ channels xx. Na+/K+ pumps and leaky channels maintain RMP once reestablished. i. Ca^2+^ removed from sarcoplasm and returned to cisternae via Ca^2+^ pumps j. Troponin changes back and tropomyosin re-covers active sites on actin  3. Practice k. Fill in the table to describe the state, or location of ACh, calcium, ATP, troponin, tropomyosin and myosin when the muscle is contracting or relaxed. ***Contracting*** ***Relaxed*** ----------------- ------------------- --------------- **ACh** **Ca^2+^** **Troponin** **Tropomyosin** **Myosin** **ATP** ***Skeletal Muscle Metabolism*** 1. Metabolism = ATP generation 2. 3 sources a. Creatine Phosphate i. Speed: very fast ii. The phosphate from creatine phosphate gets moved to ADP ATP. 1. Occurs in the cytosol iii. Capacity: low 2. Does not produce a lot of energy at once because it is limited by how much creatine phosphate is around. 3. Since it is fast, it will produce a high rate of supplying ATP for about 5-10 seconds. b. Glycolysis iv. Speed: Slower than creatine phosphate, but still pretty fast. v. It has around 10 steps (that you do not need to know) that makes ATP from glucose. 4. Occurs in the cytosol vi. Capacity: medium 5. Produces more energy total than creatine phosphate, but is limited by glucose/glycogen and the speed of some of the enzymes. 6. Maximally it can last around 1-2 minutes. c. Aerobic Cellular Respiration/Oxidative Catabolism vii. Speed: Slow viii. It has many, many steps and involves moving electrons around to make ATP. 7. Uses oxygen 8. Occurs in the mitochondria. 9. Proteins, lipids, and carbohydrates can be used to make ATP with this system. ix. Capacity: super high; inexhaustible. 10. Never runs out of energy unless you run out of lipids, proteins and carbs (which won't happen while you need ATP). 3. Skeletal muscle has metabolic flexibility and can make ATP in these three different ways depending on supply and demand. All three systems are always contributing, but depending on what you're doing you rely more or less on specific systems. 4. Review Question d. A sprinter would rely on what type of ATP generation compared to a marathon runner? ***Muscle Mechanics*** 1. Contraction of a single muscle fiber and of a skeletal muscle are the same. 2. Muscle tension is the force exerted by a contracting muscle on an object. 3. Load is the weight of the object to be moved by a contracting muscle. a. Opposing force to muscle tension 4. Skeletal muscle contraction varies in terms of force and length of contraction ***Motor Unit*** 1. A single \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ and all of the muscle fiber it innervates. 2. Recall that axons branch and can have many synaptic terminals, each of which releases neurotransmitter as the termination of an action potential. 3. A single neuron can control many or a few muscle fibers. 4. Small motor units a. Can be as small as 3 fibers b. Used for fine motor control. i. Moving your hands or the muscle moving your eye. ii. You need small, fine, controlled movements and not large force. 5. Large motor units c. Can be as big as 1000 fibers d. Used for big movements and high force production. e. Not good for fine motor control, which is why we don't write with our legs. f. Muscles that move your hips have large motor units, for example. ***Twitch Contraction*** 1. Muscle twitch is the simplest contraction a. Muscle fiber's response to a single action potential from motor neuron. b. Muscle fiber contracts quickly, then relaxes. 2. Twitch only occurs in a laboratory but allows us to study contractions. 3. Three phases of muscle twitch c. Latent period i. Events of excitation-contraction coupling ii. Action potential propagates across sarcolemma iii. No muscle tension seen because there is no contraction! d. Contraction period iv. Cross bridge formation v. Tension increases e. Relaxation period vi. Ca^2+^ reentry into SR vii. Tension decreases ***Tension Produced by a Muscle Fiber*** 1. Force generated by a contracting muscle fiber/muscle cell 2. Factors influencing muscle tension b. Frequency of stimulation c. Muscle fiber size d. Motor units recruited e. Degree of muscle stretch ***Frequency of Stimulation*** 1. The muscle tension produced with each contraction is the same as long as the muscle completely relaxes before the next stimulus. 2. Wave summation a. Partial relaxation between stimuli b. Contraction waves are added together ---\> increased tension 3. Unfixed tetanus c. Partial relaxation between stimuli d. How does this differ from wave summation? i. The retaliation period is shorter ii. The stimuli are occurring more frequently iii. It is occurring after the maximum tension has been reached 4. Fused tetanus e. No relaxation between stimuli due to further frequency increase in stimulation f. Contractions waves fuse together forming a continuous contraction g. Can lead to muscle fatigue ***Motor Unit Recruitment*** 1. If greater force is needed, more motor units are activated. 2. Motor units that contain the smallest muscle fibers are recruited first. ***Skeletal Muscle Fiber Types*** 1. Not all skeletal muscle fibers are equal. 2. 3 general types a. Most of our muscle fibers are some hybrid of types. b. They are categorized based on metabolism (how they make their ATP), their speed, and their force production). x. A given motor unit will be all one the same type of fiber. c. *Slow Oxidative* i. Slow twitch fibers 11. Slow contraction ii. Small diameter 1. Low force iii. Fatigue resistant iv. Reliant on oxidative catabolism 2. Many mitochondria 3. Large blood supply 4. Low levels of glycogen d. *Fast Oxidative* v. Fast twitch 5. Fast contraction xi. Large diameter 12. High force xii. Intermediate fatiguability xiii. Utilizes oxidative catabolism (primarily) and glycolysis 13. Moderate mitochondria 14. Moderate blood supply 6. Moderate levels of glycogen e. *Fast glycolytic fibers* vi. Fast twitch 7. Fast contractions (faster than fast oxidative) vii. High force production (big fibers) viii. Highly fatigable ix. Utilizes primarily glycolysis 8. Few mitochondria 9. Low blood supply 10. High levels of glycogen 3. We have mixed fiber types in every muscle. a. Some muscles like the ones that move the eyes are mostly Type II and others like the soleus is mostly Type I. b. But every other muscle is some combination that is largely genetically determined. 4. Challenge f. What type of muscle do we find in turkey wings vs duck wings? How is it related to their wing functions? ***Length-Tension Relationship*** 1. Degree of muscle strength c. How much overlap is there between thick and thin filaments? 2. Relationship of sarcomere length and force produced by contraction 3. There is an optimal length for sarcomeres to produce the most force. d. It's a middle length where there is ideal overlap between the thin and thick filaments. ***Types of Contraction*** 1. Isometric a. Iso = same ; Metric = length i. Muscle length stays the same with changing tension b. Muscles do not move ii. Force is being produced though 2. Isotonic c. Iso = same ; Tonic = tension iii. Same tension as muscle length changes d. Concentric contraction iv. Muscle shortens v. Generates enough force to move an object e. Eccentric contraction vi. Muscle lengthens despite trying to pull vii. Used to slow down movements (deceleration) 1. Protective