BIO 163 Ch. 8 Learning Outline - Muscle Structure and Function

**BIO 163 Ch. 8 Learning Outline** You can also use this outline to take notes in class. You can refer to your textbook for more detailed information on these topics. **[Structure of Muscles and Muscle cells]** 1. Define the terms: a. **Tendon:** Cordlike or bandlike mass of dense connective t...

**BIO 163 Ch. 8 Learning Outline** You can also use this outline to take notes in class. You can refer to your textbook for more detailed information on these topics. **[Structure of Muscles and Muscle cells]** 1. Define the terms: a. **Tendon:** Cordlike or bandlike mass of dense connective tissue that connects a muscle to a bone b. Aponeurosis and name the two aponeuroses discussed in lecture Sheets of connective tissue that attaches muscles to bone, skin, or to the covering of adjacent muscles anterior abdominal aponeurosis and the posterior lumbar aponeurosis 2. Describe the connective tissues associated with muscles: a. **Fascia:** Layers of dense connective tissue, surround and separate each muscle b. **Epimysium:** Sheath of connective tissue, deep to the fascia, surrounding a skeletal muscle. c. **Perimysium:** Sheath of connective tissue that encloses a bundle of skeletal muscle fibers (encloses a fascicle). d. **Endomysium:** Sheath of connective tissue surrounding each skeletal muscle fiber. 3. **Explain what a fascicle is.** Small bundle of skeletal muscle fibers; also called a fasciculus 4. **Describe the structure and function of each part of a skeletal muscle cell:** a. **Sarcolemma:** Cell membrane of a muscle fiber, Maintaining Structural Integrity b. **Sarcoplasm:** Cytoplasm of a muscle cell, it contains many mitochondria and nuclei, contains parallel **myofibrils**, which are active in muscle contraction c. **Sarcoplasmic reticulum:** Membranous network of channels and tubules within a muscle fiber, corresponding to the endoplasmic reticulum of other cells. **Cisternae:** Enlarged portion of the sarcoplasmic reticulum near the actin and myosin filaments of a striated muscle fiber. d. **Transverse tubules:** Any of several membranous channels that extend deep into the cell from a muscle fiber membrane. e. **Myofibrils:** Contractile fiber in striated muscle cells. f. **Sarcomere:** Structural unit of a myofibril and the functional unit of muscle contraction 5. **Name and describe the two myofilaments found in the myofibrils.** **Thick filaments:** in myofibrils consist of the protein myosin **Thin filaments:** in myofibrils are mainly composed of the protein actin, but also contain troponin and tropomyosin **[Neuromuscular Junction (NMJ)]** 1. Explain the structure and function of each part of the neuromuscular junction: a. **Motor neuron:** Neuron that conducts impulses from the central nervous system to an effector b. **Axon:** a nerve fiber that transmits electrical impulses from a neuron to a muscle cell. Axons are long, thin projections that extend from the cell body of a neuron c. **Synaptic knob:** Tiny enlargement at the end of an axon that secretes a neurotransmitter. d. **Synaptic vesicles:** Membranous sac of the synaptic knob e. **Synaptic cleft:** Narrow extracellular space between two cells at a synapse, separates the membrane of the neuron and the membrane of the muscle fiber f. **Motor end plate:** Specialized portion of a skeletal muscle fiber that binds to the neurotransmitters released by the motor neuron in a neuromuscular junction. 2. **What neurotransmitter is released and the NMJ and what is its function?** Acetylcholine (ACh), and its function is to trigger muscle contraction by binding to receptors on the muscle fiber, initiating an electrical signal that leads to muscle fiber depolarization and subsequent contraction. **[Muscle Contraction and Relaxation]** 1. Explain the sliding filament model and explain what happens to actin and myosin The sliding filament theory is the explanation for how muscles contract to produce force.\ \ The actin and myosin filaments within the sarcomeres of muscle fibers bind to create cross-bridges and slide past one another, creating a contraction.\ \ The sliding filament theory explains how these cross-bridges are formed and the subsequent contraction of muscle. 2. **[Explain the function and each of the following proteins:]** a. **Myosin:** Protein in a muscle fiber that forms the thick filaments that pull on the thin filaments of the protein actin, contracting muscle fibers. molecules consist of two twisted strands, with globular heads projected outward along the strands b. **Actin:** Protein in a muscle fiber that forms the thin filaments that slide between thick filaments of the protein myosin, contracting muscle fibers. molecules consist of globular proteins arranged in twisted filaments (a double helix), containing myosin binding sites c. **Troponin:** Regulatory protein associated with the sarcomere that binds to calcium to initiate muscle contraction. proteins associated with the surface of the actin molecules(form thin filaments) d. **Tropomyosin:** Regulatory protein associated with the sarcomere that blocks the myosin binding site until contraction is initiated. proteins associated with the surface of the actin molecules (form thin filaments) 3. **Explain the events of the cross bridge cycle.** When myosin heads bind to actin they use chemical energy from the breakdown of ATP to generate a pulling force against actin filaments, then detach and prepare to bind again 4. **Explain the steps in muscle relaxation and explain why ATP is needed.** Nervous stimulation ceases. Acetylcholinesterase rapidly breaks down acetylcholine (ACh) within the neuromuscular junction so that ACh can no longer stimulate the muscle fiber. Calcium ions in the cytosol are then pumped back into the sarcoplasmic reticulum, using ATP in the process. Tropomyosin can then block the myosin binding sites on the actin. ATP is also used to break the cross-bridge linkages between the myosin and actin, allowing the muscle fiber to relax. **[Energy for Muscle Contraction]** 1. Explain the role of creatine phosphate in terms of an energy source for muscle contraction. - Creatine phosphate is present to initially regenerate ATP from ADP and phosphate, as it also contains high energy bonds - Whenever the supply of ATP is sufficient, the enzyme creatine phosphokinase promotes the synthesis of creatine phosphate - As ATP decomposes, the energy from creatine phosphate can be transferred to ADP molecules, converting them back to ATP - Creatine phosphate is rapidly used up too, and as its supply declines, the cell must rely on cellular respiration to generate ATP 2. **Explain how the oxygen debt develops.** Oxygen debt (also called excess post-exercise oxygen consumption, or EPOC) equals the amount of oxygen that liver cells require to convert the accumulated lactate into glucose, plus the amount muscle cells require to restore ATP and creatine phosphate to their original concentrations and to return blood and tissue oxygen levels to normal. The conversion of lactate back into glucose is slow. Repaying an oxygen debt following vigorous exercise may take several hours, 3. **Explain what hemoglobin and myoglobin are.** **Hemoglobin:** Oxygen-carrying protein in red blood cells **Myoglobin:** Oxygen-storing protein in muscle tissue **[Muscle responses]** 1. Define the following; a. **Threshold stimulus:** is the minimal stimulus required to elicit a muscular contraction b. **All or none response:** When a muscle fiber contracts, it contracts to its full extent, with each twitch generating the same force c. **Twitch:** is a single contraction reflecting stimulation of a muscle fiber d. **Summation:** A muscle fiber receiving a series of stimuli of increasing frequency reaches a point when it is unable to relax completely, and the force of individual twitches combine e. **Tetany:** When exposed to higher frequency of stimulation, relaxation time becomes very short f. **Motor unit:** A motor neuron and the muscle fibers that it controls g. **Recruitment:** An increase in the number of activated motor units within a muscle at higher intensities of stimulation, causes an increase in the strength of a contraction **[Muscle fibers]** 1. **Explain the differences between fast and slow twitch fibers.** fast twitch relies more on anaerobic glycolysis and slow twitch utilizes aerobic respiration 2. **Explain what happens in muscle hypertrophy and atrophy.** **Hypertrophy:** enlargement of a muscle due to repeated exercise **Atrophy:** decrease in muscle size and strength, due to disuse 3. **Describe the characteristics of smooth muscle** - Smooth muscle cells are elongated with tapered ends, lack striations (look "smooth"), and have a relatively undeveloped sarcoplasmic reticulum - Contain thick and thin filaments, but they are arranged more randomly 4. Explain the differences between multi-unit and visceral smooth muscle and give examples in the body. **multiunit smooth muscle:** such as in the blood vessels and iris of the eye, fibers occur separately rather than as sheets; stimulated by neurons and some hormones **Visceral smooth muscle:** occurs in sheets, and is found in the walls of hollow organs; these fibers can stimulate one another and display rhythmicity; these features accomplish peristalsis in tubular organs 5. **Describe the characteristics of cardiac muscle** Cardiac muscle consists of branching, striated cells that interconnect in three-dimensional networks **[Muscle Anatomy]** 1. Define: a. **Origin**: the less movable end of a skeletal muscle b. **Insertion:** The more movable end of a skeletal muscle c. **Agonists (prime mover):** The muscle that causes an action, and does the majority of the work d. **Synergists:** Muscles that assist the prime mover e. **Antagonists:** Muscles that oppose an action 2. For each muscle from the BIO 163 muscle list in Moodle be able to identify and give the action of the muscle.