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Understanding Muscle Function: Mechanisms of Contraction and Relaxation in Vertebrate Skeletal Muscle

This chapter explores the sensory and motor mechanisms involved in muscle function, focusing on vertebrate skeletal muscle. It highlights the structure of muscle fibers, myofibrils, and myofilaments, detailing the sliding-filament model of contraction. Key concepts include the roles of actin and myosin in muscle contraction, the formation of cross bridges, and the regulatory function of calcium ions and the sarcoplasmic reticulum. The chapter also explains the importance of antagonistic muscle pairs and the biochemical processes governing muscle contraction and relaxation.

raymond-dickson
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Understanding Muscle Function: Mechanisms of Contraction and Relaxation in Vertebrate Skeletal Muscle

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  1. Chapter 49 Sensory and Motor Mechanisms Muscle Function

  2. Vertebrate Skeletal Muscle • Contract/relax: antagonistic pairs w/skeleton • Muscles: bundle of…. • Muscle fibers: single cell w/ many nuclei consisting of…. • Myofibrils: longitudinal bundles composed of…. • Myofilaments: •Thin~ 2 strands of actin protein and a regulatory protein •Thick~ myosin protein • Sarcomere: repeating unit of muscle tissue, composed of…. • Z lines~sarcomere border • I band~only actin protein • A band~actin & myosin protein overlap • H zone~central sarcomere; only myosin

  3. Sliding-filament model • Theory of muscle contraction • Sarcomere length reduced • Z line length becomes shorter • Actin and myosin slide past each other (overlap increases)

  4. Actin-myosin interaction • 1- Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” • 2- Myosin head binds to actin; termed a “cross bridge” • 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration” • 4- Binding of new ATP releases myosin head • Creatine phosphate~ supplier of phosphate to ADP

  5. Muscle contraction regulation, I • Relaxation: tropomyosin blocks myosin binding sites on actin • Contraction: calcium binds to toponin complex; tropomyosin changes shape, exposing myosin binding sites

  6. Muscle contraction regulation, II • Calcium (Ca+)~ concentration regulated by the…. • Sarcoplasmic reticulum~ a specialized endoplasmic reticulum • Stimulated by action potential in a motor neuron • T (transverse) tubules~ travel channels in plasma membrane for action potential • Ca+ then binds to troponin

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