Unformatted text preview: Lecture 15 SmartSite: Lecture 15 Notes Exam covers lectures through Tuesday (Lecture 17) CAF Office Hrs (197 Briggs) KR Office Hrs (2041A SLB) M-W 5-6 Tuesday 9-10 Wednesday 3-4 Thursday 11:30-12:30 (normal) Canceling Thursday 3-4 Review Muscle Announcements: Motor Control Skeletal muscle Reading (Recommended): Extended Time Reply to my email Relevant porSons of Chapter 8 1 REV: Motor Control LocomoSon: Rhythmic contracSon of flexor-extensor muscle pairs produced at the level of the spinal cord NegaSve feedback regulaSon Cortex: Control of fine / voluntary movement Cerebellum: Planning, coordinaSon & posture Basal Ganglia: Posture & Planning of movement Thalamus: Sensory relay ganglia to the cortex Brain Stem: Control of posture and spinal cord Complex integraSon of afferent informaSon and CNS processing to accomplish voluntary movement Set Point (along with Cortex) Controller 2 descending upper motor neuron pathways 2 Muscle Physiology 3 Muscle Comprises largest group of Sssues in body Three types of muscle Produce force; different control mechanisms Similar contracSle mechanisms; different morphologies Skeletal muscle (40-50% of body mass) Smooth muscle (5-10% of body mass) Cardiac muscle Make up muscular system - voluntary Appears throughout the body systems as components of hollow organs and tubes involuntary; ANS control Found only in the heart Classified in two different ways Striated or unstriated Voluntary or involuntary 4 CategorizaSon of Muscle Fig. 8-1; pg. 258 5 Muscle Controlled muscle contracSon allows Purposeful movement of the whole body or parts of the body ManipulaSon of external objects Propulsion of contents through various hollow internal organs Emptying of contents of certain organs to external environment 6 Skeletal Muscle ContracSon Fig. 8-13; pg. 268 7 Structure of Skeletal Muscle Muscle consists a number of muscle fibers lying parallel to one another and held together by connecSve Sssue. Single skeletal muscle cell is known as a muscle fiber: MulSnucleated Large, elongated, and cylindrically shaped Fibers usually extend enSre length of muscle 8 Structure of Skeletal Muscle Myofibrils ContracSle elements of muscle fiber Regular arrangement of thick and thin filaments Thick filaments myosin (protein) Thin filaments acSn (protein) Sarcomere FuncSonal unit of skeletal muscle Found between two Z lines (connects thin filaments of two adjoining sarcomeres) 9 Structure of Skeletal Muscle Fig. 8-2ab; pg. 259 10 Structure of Skeletal Muscle 2 Kinds of Protein Contrac:le Regulatory Fig. 8-2cd; pg. 259 11 Myosin Component of thick filament Protein molecule consisSng of two idenScal subunits shaped somewhat like a golf club Tail ends are intertwined around each other Globular heads project out at one end Tails oriented toward center of filament and globular heads protrude outward at regular intervals Heads form cross bridges between thick and thin filaments Cross bridge has two important sites criScal to contracSle process An acSn-binding site A myosin ATPase (ATP-splihng) site 12 Structure and Arrangement of Myosin Molecules Within Thick Filament Fig. 8-4; pg. 260 13 AcSn Primary structural component of thin filaments Spherical in shape Thin filament also has two other proteins Tropomyosin and troponin Each acSn molecule has special binding site for aiachment with myosin cross bridge Binding results in contracSon of muscle fiber 14 AcSn & Myosin AcSn and myosin are ojen called contracSle proteins. Neither actually contracts. AcSn and myosin are not unique to muscle cells, but are more abundant and more highly organized in muscle cells. 15 Tropomyosin and Troponin Ojen called regulatory proteins Tropomyosin Thread-like molecules that lie end to end alongside groove of acSn spiral In this posiSon, covers acSn sites blocking interacSon that leads to muscle contracSon Made of three polypepSde units One binds to tropomyosin One binds to acSn One can bind with Ca2+ Troponin 16 ComposiSon of a Thin Filament Fig. 8-5; pg. 261 17 Tropomyosin and Troponin Troponin When not bound to Ca2+, troponin stabilizes tropomyosin in blocking posiSon over acSn's cross-bridge binding sites When Ca2+ binds to troponin, tropomyosin moves away from blocking posiSon With tropomyosin out of way, acSn and myosin bind, interact at cross-bridges Muscle contracSon results 18 Role of Calcium in Cross-Bridge FormaSon Fig. 8-6; pg. 262 19 Sliding Filament Mechanism Cross-bridge interacSon between acSn and myosin brings about muscle contracSon by means of the sliding filament mechanism. 20 Sliding Filament Mechanism Increase in Ca2+ starts filament sliding Decrease in Ca2+ turns off sliding process Thin filaments on each side of sarcomere slide inward over staSonary thick filaments toward center of A band during contracSon As thin filaments slide inward, they pull Z lines closer together Sarcomere shortens All sarcomeres throughout muscle fiber's length shorten simultaneously ContracSon is accomplished by thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments 21 Changes in Sarcomere During Shortening Fig. 8-8; pg. 263 22 ...
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- Spring '08