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This 7 page Bundle was uploaded by kgrunwaldt on Monday January 25, 2016. The Bundle belongs to BIOL 214 at Truman State University taught by Dr. Guffey in Spring 2016. Since its upload, it has received 26 views. For similar materials see Anatomy and Physiology I in Science at Truman State University.
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Date Created: 01/25/16
Muscles TVDeS of Muscle Tissue Skeletal Muscle Tissue packaged into the skeletal muscles organs that attach to and cover the bony skeleton o Longest muscle cells and have obvious striations 0 Voluntary muscle Cardiac Muscle Tissue occurs only in the heart where it constitutes the bulk of the heart walls 0 Striated and branched o Involuntary muscle Smooth Muscle Tissue found in the walls of hollow visceral organs such as the stomach urinary bladder and respiratory passages 0 Long elongated fibers 0 No striations fusiform o Involuntary Special Characteristics of Muscle Tissue Excitability responsiveness the ability to receive and respond to a stimulus Contractility the ability to shorten forcibly when adequately stimulated Extensibility the ability to be stretched or extended Elasticity the ability of a muscle cell to recoil and resume its resting length after being stretched Muscle Functions Producing movement 0 Skeletal muscles are responsible for all locomotion and manipulation 0 Blood courses through the body with the help of cardiac muscle o Foodstuffs are squeezed through organs thanks to smooth muscle Maintaining posture and body position 0 Skeletal muscles help maintain posture against the force of gravity Stabilizing joints 0 Even as muscles pull on bones to cause movements they stabilize and strengthen the joints of the skeleton Generating heat 0 Muscles generate heat as they contract 0 Skeletal muscle accounts for 40 of the body s mass so it is the most responsible for generating heat Additional functions 0 Skeletal muscles protect the more fragile internal organs by enclosing them 0 Smooth muscle also forms valves that regulate the passage of substances through internal body openings dilates and constricts the pupils of your eyes and forms the arrector pilli muscles Gross Anatomv of Skeletal Muscle Nerve and Blood Supply 0 In general each muscle is served by one artery one nerve and one or more veins 0 Each skeletal muscle fiber is supplied with a nerve ending that controls its activity 0 Has a rich blood supply 0 Muscle cells also give off large amounts of metabolic wastes that must be removed through veins if contraction is to remain efficient Connective Tissue Sheaths o Epimysium overcoat of dense irregular connective tissue that surrounds the whole muscle I Sometimes blends with the deep fascia that lies between neighboring muscles or the superficial fascia deep to the skin 0 Perimysium and fascicles I Muscle fibers are grouped into fascicles I Surrounding each fascicle is a layer of fibrous connective tissue called perimysium o Endomysium a wispy sheath of connective tissue that surrounds each individual muscle fiber I Consists of fine areolar connective tissue Attachments 0 Insertion the movable bone 0 Origin the less movable bone I Typically lies proximal to the insertion o DirectFleshy Attachments epimysium of the muscle is fused to the periosteum of a bone or perichondrium of cartilage 0 Indirect Attachments the muscle s connective tissue wrappings extend beyond the muscle as either a ropelike tendon or a sheetlike aponeurosis Microscooic Anatomv of a Skeletal Muscle Fiber Myofilament extended macromolecular structure 0 Thick filaments contain bundled myosin and molecules 0 Thin filaments contain actin molecules plus other proteins 0 The sliding of thin filaments past the thick filaments produces muscle shortening 0 Elastic filaments maintain the organization of the A band and provide for elastic recoil when muscle contraction ends Sarcomere a segment of a myofibril o The contractile unit composed of myofilaments made up of contractile proteins Myofibril complex organelle composed of bundles of myofilaments o Rodlike contractile elements that occupy most of the muscle cell volume 0 Composed of sarcomeres arranged end to end 0 Appear banded Muscle fiber cell 0 Elongated multinucleate cell 0 Banded appearance 0 Surrounded by the endomysium Fascicle a portion of the muscle 0 Discrete bundle of muscle cells segregated from the rest of the muscle by a connective tissue sheath 0 Surrounded by the perimysium Muscle organ 0 Consists of hundreds to thousands of muscle cells 0 Contains connective tissue wrappings blood vessels and nerve fibers 0 Covered externally by the epimysium Slidinq Filament Model of Contraction Contraction the activation of myosin s cross bridges which are the force generating sites 0 Shortening occurs if and when the tension generated by the cross bridges on the thin filaments exceeds the forces opposing shortening and pulls the thin filaments toward the M line 0 Contraction ends when the cross bridges become inactive and the tension declines inducing relaxation of the muscle fiber Sliding Filament Model of Contraction during contraction the thin filaments slide past the thick filaments so that the actin and myosin filaments overlap to a greater degree o In a relaxed muscle fiber thick and thin filaments overlap only at the ends of the A band When muscle fibers are stimulated by the nervous system the myosin heads on the thick filaments latch onto myosinbinding sites on actin in the thin filaments and the sliding begins thsioloqv of Skeletal Muscle Fibers For a skeletal muscle fiber to contract o It must be activated by a nerve ending so that a change in membrane potential occurs 0 Next it must generate and propagate an electrical current called an action potential along its sarcolemma 0 Then a shortlived rise in intracellular calcium ion levels that is the final trigger for contraction must occur Nerve Stimulus and Events at the Neuromuscular Junction 0 Nerve cells that activate skeletal muscle fibers are called somatic motor neurons or motor neurons of the somatic voluntary nervous system I These motor neurons reside in the brain or spinal cord but their long threadlike extensions called axons travel bundled within nerves to the muscle cells they serve I Neuromuscular Junction where axons meet with a single muscle fiber I Each muscle fiber only has one neuromuscular junction located at approximately midway its length I Synaptic Cleft the separation between an axon terminal and the muscle fiber filled with a gellike extracellular substance that is rich in glycoproteins and collagen fibers I Synaptic Vesicles small membranous sacs containing the neurotransmitter acetylcholine that resides in the axon terminal I Junctional Folds provide a large surface area of the millions of ACh receptors I A motor neuron stimulates a skeletal muscle fiber when nerve impulses reaches the end of the axon and the axon terminal releases ACh into the synaptic cleft ACh diffuses across the cleft and attaches to ACh receptors on the sarcolemma of the muscle fiber which triggers electrical events that ultimately cause action potential generation I After ACh binds to ACh receptors its effects are quickly terminated by its enzymatic breakdown to its building blocks acetic acid and choline by acetylcholinerase an enzyme located in the synaptic cleft The removal of ACh prevents continued muscle fiber contraction in the absence of additional nervous system stimulation Events at the Neuromuscular Junction When a nerve impulse reaches a neuromuscular junction acetylcholine is released Upon binding to sarcolemma receptors ACh causes a change in sarcolemma permeability leading to a change in membrane potential Action potential arrives at axon terminal of motor neuron Voltagegated calcium ion channels open and the calcium ion enters the axon terminal Calcium ion entry causes some synaptic vesicles to release their contents acetylcholine by exocytosis Acetylcholine a neurotransmitter diffuses across the synaptic cleft and binds to receptors in the sarcolemma ACh binding opens ion channels that allow simultaneous passage of sodium ions into the muscle fiber and potassium ions out of the muscle fiber More sodium ions enter than potassium ions leave and this produces a local change in the membrane potential depolarization ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinerase Contraction of a Skeletal Muscle Principles of Muscle Mechanics o The principles governing contraction of a single muscle fiber of a skeletal muscle consisting of a large number of fibers are pretty much the same o The force exerted by a contracting muscle on an object is called muscle tension and the opposing force exerted on the muscle by the weight of the object to be moved is called the load 0 A contracting muscle does not always shorten and move the load If muscle tension develops but the load is not moved the contraction is called isometric If the muscle tension overcomes the load and muscle shortening occurs the contraction is isotonic o A skeletal muscle contracts with varying force and for different periods of time in response to stimuli of varying frequencies and intensities Motor Unit consists of a motor neuron and all the muscle fibers it supplies Muscle twitch o Myogram a graphic recording of contractile activity 0 Muscle Twitch the response of a motor unit to a single action potential of its motor neuron I Latent Period first few milliseconds following stimulation when excitationcontraction coupling is occurring During this period muscle tension is beginning to increase but no response is seen on the myogram I Period of Contraction when cross bridges are active from the onset to the peak of tension development and the myogram tracing rises to a peak This period lasts 10100 milliseconds If the tension becomes great enough to overcome the resistance of the load the muscle shortens I Period of Relaxation final phase lasting 10100 milliseconds initiated by the re entry of calcium ions into the SR Because contractile force is declining muscle tension decreases to zero and the tracing returns to the baseline lsotonic and Isometric Contractions o lsotonic muscle length changes and moves the load I Concentric muscle shortens to do work I Eccentric muscle elongates to do work 0 Isometric muscle neither shortens nor lengthens
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