Anatomy, Ch. 9 Muscle and Muscle Tissue
Anatomy, Ch. 9 Muscle and Muscle Tissue Biology 64
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This 13 page Bundle was uploaded by Lauren Zuniga on Saturday September 10, 2016. The Bundle belongs to Biology 64 at California State University Fresno taught by in Fall 2016. Since its upload, it has received 6 views. For similar materials see Anatomy in Biology at California State University Fresno.
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Date Created: 09/10/16
Muscles and Muscle Tissue – Part 1 Overview of Muscle Tissues • Types of Muscle Tissue o Muscle Fibers ! DEF: Describes the elongate skeletal and smooth muscle cells o Skeletal Muscle Tissue ! Skeletal ! Voluntary ! Striated o Cardiac Muscle Tissue ! Only in the heart ! Striated ! Involuntary o Smooth Muscle Tissue ! Visceral ! Nonstriated ! Involuntary • Special Characteristic of Muscle Tissue o 1. Excitablility ! DEF: The ability to receive and respond to a stimulus o 2. Contractility ! DEF: The ability to shorten forcibly when adequately stimulated o 3. Extensibility ! DEF: The ability to be stretched or extended o 4. Elasticity ! DEF: The ability of a muscle cell to recoil and resume its resting length after being stretched. • Muscle Functions o 1. Producing movement o 2. Maintaining posture and body position o 3. Stabilizing joints o 4. Generating heat Skeletal Muscle • Gross Anatomy of Skeletal Muscle o Nerve and Blood Supply ! In general: 1 muscle has 1 nerve, 1 artery, >1 veins ! Rich blood supply " Why: Skeletal muscle fibers require large amounts of oxygen and energy o Connective Tissue Sheaths ! 1. Epimysium " Outermost layer " Covers the entire muscle ! 2. Perimysium " Covers the fascicles • Fascicles o Bundles of muscle fibers ! 3. Endomysium " Covers each muscle fiber individually o Attachments ! Insertion " DEF: The point of attachment that is moved by the contraction • The moveable bone ! Origin " DEF: The point of attachment that is not moved by the contraction • The immovable bone ! Direct / Fleshy Attachments " DEF: The epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage ! Indirect Attachments " DEF: The muscle’s CT wrappings are extended beyond the muscle either as a tendon or aponeurosis • Tendon: Ropelike • Aponeurosis: Sheetlike o Microscopic Anatomy of A Skeletal Muscle Fiber ! Key Terms: " Sarcolemma • DEF: Muscle PM " Sarcoplasm • DEF: Muscle cytoplasm " Glycosomes • DEF: Granules of stored glycogen that provide glucose during periods of muscle cell activity " Myoglobin • DEF: A red pigment that stores oxygen in muscle cells " Sarcoplasmic Reticulum • DEF: Specialized ER " T-Tubules • DEF: Unique modifications of the sarcolemma ! Myofibrils " DEF: Rodlike contractile elements that run parallel to the muscle fiber’s length " Most of the cell’s volume " Striations, Sarcomeres, and Myofilaments • Striations o DEF: A repeating series fo dark and light bands o A band: ! Region where actin and myosin filaments overlap o I band: ! Only actin filaments o H zone: ! Only myosin filaments ! Disappears during contraction o M line: ! Proteins + thick filaments o Z disc: ! Boundary of the sarcomere ! Edge of I band • Sarcomere o DEF: Smallest contractile unit of a muscle fiber ! Region of the myofibril between 2 Z discs • Myofilaments o Myofilaments / Filaments ! DEF: Muscle equivalent of actin and myosin containing microfilaments in the cell ! Thick Filaments " Myosin " Extend the entire length of the A band ! Thin Filaments " Actin " Extend across the I band and part way in the A band " Ultrastructure and Molecular Composition of the Myofilaments • Myosin o 2 heads and a rod like tail ! Heads = the business end of the molecule ! Heads bear actin and ATP binding sites for cross bridge formation " Cross bridge: Actin and myosin link • Actin o Tropomyosin ! Block myosin binding sites on actin o Troponin ! Binds calcium ions • Elastic Filament o Composed of: ! Titin " Holds the thick filaments in place " Helps the muscle fiber recoil after being stretched " Helps resist excessive stretching ! Dystrophin " Links the thin filaments to integral proteins of the sarcoelmma ! Sarcoplasmic Reticulum & T-Tubules " Sarcoplasmic Reticulum (SR) • An elaborate SER • Surround each myofibril • Terminal cisternae o Run ! to length of myofibril • Role: o Regulate intracellular levels of ionic calcium " T-Tubules • DEF: Sarcolemma invaginations at each A band – I band junction • Increase surface area • Role: Conduct nerve impulses to the deepest regions of the muscle cell and to every sarcomere " Triads: • DEF: Successive groupings of three membranous structures (Terminal cisterna, t-tubule, terminal cisterna) • Triad Relationships o Integral proteins in these regions act as voltage centers ! Form voltage gated channels thru which calcium can be released from the SR cisternae o Sliding Filament Model of Contraction ! Contraction " DEF: The activation of myosin’s cross bridges ! Sliding filament model of contraction " DEF: During contraction the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree " Filaments are pulled toward the M line o Physiology of Skeletal Muscle Fibers ! Requirements for skeletal muscle fiber to contract " 1. Activation • Muscle fiber must be stimulated by a nerve ending • Membrane potential changes " 2. Must generate and action potential (AP) along the sarcolemma " 3. Rise in intracellular calcium levels ! The Nerve Stimulus and Events at the Neuromuscular Junction " Somatic motor neurons • DEF: Nerve cells that activate skeletal muscle fibers " Neuromuscular junction • DEF: Point where axons of a motor neuron form an elliptical junction with a single muscle fiber • One per muscle fiber " Synaptic cleft • DEF: Space separating the muscle fiber and axon terminal " Synaptic vesicles • DEF: Small membranous sacs containing the neurotransmitter acetylcholine " Acetylcholine (ACh) • DEF: Neurotransmitter for muscle cells " Junctional folds • DEF: Folds in the sarcolemma at the neuromuscular junction that increase the surface area for the ACh receptors located there " Acetylcholinesterase • DEF: Enzyme in the synaptic cleft that breaks down ACh preventing continued muscle fiber contraction " How a nerve stimulates skeletal muscle fibers • 1. AP arrives at axon terminal • 2. Voltage gated calcium channels open & calcium enters the axon terminal • 3. Calcium causes some synaptic vesicles to release ACh • 4. ACh diffuses accrose the synaptic cleft and binds to receptors on the sarcolemma • 5. Binding of ACh open ion channels allowing Na+ into and K+ out of the muscle fiber simultaneously o Membrane depolarization • 6. ACh brokendown by acetylcholinesterase in the synaptic cleft Muscles and Muscle Tissue – Part 2 • Generation of an AP Across the Sarcolemma o Sarcolemma = polarized o Steps: ! 1. Local depolarization and generation of an end plant potential " Binding of ACh opens calcium ion channels allowing Na+ and K+ to pass " Membrane depolarization • End Plate Potential o DEF: Local depolarization ! 2. Generation and propagation of the action potential " End plate potential spreads, opening voltage gated Na+ channels " Na+ enters cell and brings it to threshold • Threshold o DEF: The proper membrane voltage required to trigger an AP " AP propagated as the depolarization moves along and opens more Na+ gated channels ! 3. Repolarization " DEF: When the sarcolemma is restored to initial polarized state " Na+ channels close, K+ channels open o Refractory period ! DEF: The cell cannot be stimulated again until repolarization is complete • Excitation-Contraction Coupling o DEF: Sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments o Occurs during the latent period ! Latent period " DEF: The period between AP initiation and the beginning of contraction • Summary of Channels Needed to Initiate Contraction o 1. Calcium entry in axon terminal triggers release of ACh o 2. ACh binds to ACh receptors triggering the opening of chemically gated Na+ / K+ channels o 3. Local depolarization opens voltage gated Na+ channels in the neighboring sarcolemma. Futher depolarization opens more channels along the sarcolemma o 4. Transmission of AP along T-tubules leads to the release of calcium from the SR • Muscle Fiber Contraction: Cross Bridge Activity o Steps: ! 1. AP is propagated along the sarcolemma and down the t-tubules ! 2. Calcium ions released from SR ! 3. Calcium binds to troponin and removes the blocking action of tropomyosin ! 4. Contraction begins " Cross bridge formation process: • 1. Cross bridge formation o Energized myosin head binds actin • 2. Power stroke o ADP Pi released changing myosin head shape o Pulls actin toward M line • 3. Cross bridge detachment o ATP binds myosin head o Myosin detaches from actin • 4. Cocking of myosin head o ATP hydrolyzed o Myosin prepped for cross bridge formation • Contraction of A Skeletal Muscle o Muscle tension ! DEF: Force exerted by a contraction muscle on an object o Load ! DEF: The opposing force exerted on the muscle by the weight of the object to be moved o The Motor Unit ! DEF: Consists of a motor neuron and all the muscle fibers it innervates ! Number of muscle fibers innervated can vary ! Stimulation of one motor unit results in contraction of the entire muscle o The Muscle Twitch ! Myogram " DEF: A graphic recording of contractile activity ! Muscle twitch " DEF: The response of a motor unit to a single AP of its motor unit ! Phases: " 1. Latent period • First few milliseconds following EC coupling • Muscle tension begins to increase, no response on myogram " 2. Period of contraction • When cross bridges form • Myogram peaks " 3. Period of relaxation • Initiated by reentry of Ca into SR • Myogram declines o Graded Muscle Responses ! DEF: Variations in strength of muscle contractions ! Way they are graded: " 1. Changing the frequency of stimulation " 2. Changing the strength of stimulation ! Muscle Response to Changes in Stimulus Frequency " Wave Summation • DEF: The second twitch appears to ride on the shoulders on the first wave • Cause: o The second contraction occurs before the muscle has completely relaxed " Incomplete Tetanus • DEF: A sustained but quivering contraction • Cause: o The stimulus is held constant and the muscle is stimulated at an increasingly faster rate with relaxation time decreasing more and more " Complete Tetanus • DEF: All evidence of relaxation disappears and the contractions fuse into a smooth, sustained contraction plateau • Cause: o Stimulation frequency increases until maximum muscle tension is reached ! Muscle Response to Changes in Stimulus Strength " Recruitment • DEF: Controls the force of contraction by calling upon more or less muscle fibers " Subthreshold stimuli • DEF: Stimuli that produce no observable contractions " Threshold stimulus • DEF: The stimulus at which the first observable contraction occurs " Maximal stimulus • DEF: The strongest stimulus that produces increased contractile force o Muscle Tone ! DEF: Relaxed muscles are almost always slightly contracted ! Keeps the muscle healthy and ready for contraction o Isotonic and Isometric Contractions ! Isotonic contractions " DEF: Muscle length changes and moves the load • Load < Force of contraction " Types: • 1. Concentric contractions o Muscle shortend and does work • 2. Eccentric contractions o The muscle generates force and lengthens ! Isometric contractions " DEF: Muscle length does not change, load is not moved • Load > Force of contraction • Muscle Metabolism o Providing Energy for Contraction ! Regeneration of ATP " 1. Direct phosphorylation of ADP by creatine phosphate (CP) • CP + ADP ! Creatine + ATP • EZ: Creatine kinase • Lasts 14-16 secs " 2. Glycolysis • Glucose ! 2 ATP + Lactic acid • Lasts 60 secs " 3. Aerobic respiration • Glucose ! 32 ATP + CO2 + O2 • Lasts Hours ! Energy Systems Used During Sports Activities " Aerobic Endurance • DEF: The length of time a muscle can continue to contract using aerobic pathways " Anaerobic Threshold • DEF: The point at which muscle metabolism converts to anaerobic glycolysis Smooth Muscle • Microscopic Structure of Smooth Muscle Fibers o Spindle shaped cells o Arranged in sheets ! Longitudinal layer " Muscle fibers run parallel to the long axis of the organ ! Circular layer " Muscle fibers run around the circumference of the organ o Peristalsis ! DEF: Alternating of contraction relaxation resulting in propulsive movement o Varicosities ! DEF: Bulbous swellings that release neurotransmitters o Diffuse junctions
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