Unformatted text preview: Lecture 17 SmartSite: Lecture 17 Notes Review Skeletal muscle Announcements: Midterm 1: 30 MC ques:ons Covers lectures through Tuesday (Star:ng Wednesday, lectures on Midterm 2) Requires students to bring and use SCANTRON 2000 (blue) Muscle Smooth muscle Cardiac muscle Reading (Recommended): Relevant por:ons Chapter 8 1 REV: Muscle Power stroke & cross bridge cycle Excita:on-contrac:on coupling Force-Velocity curve Length-Tension rela:onship NMJ, T-Tubule, SR, Ca2+, Relaxa:on Mechanics of contrac:on (number of cross bridges) Regula:on of contrac:on force Types of skeletal muscle fibers Fast vs. Slow Summa:on Motor unit size & number of motor units 2 Excita:on- Contrac:on Coupling AP from motorneuron Ach! End Plate Poten:al (EPSP) " AP on muscle fiber cell membrane (sarcolema) " AP conducted over sarcolema/T-tubule " Excita:on of Sarcoplasmic Re:culum (SR) (increase PCa)! Diffusion of Ca2+ out of SR and into myofibril " Ca2+ binds with Troponin and shi]s Tropomysin " Ac:n ac:vated " Ac:n-Myosin cross bridge " Myosin power stroke " FORCE"
3 Deac:vate Ach " RELAXATION" Diffusion of Ca2+ into Myofibril " Ac:vates Ca2+ SR reuptake pump " Pump Ca2+ back into SR " Decrease Ca2+ and deac:vate Ac:n" Smooth Muscle 4 Smooth Muscle Found in walls of hollow organs and tubes No stria:ons Filaments do not form myofibrils Not arranged in sarcomere pa_ern found in skeletal muscle Spindle-shaped cells with single nucleus Cells usually arranged in sheets within muscle Have dense bodies containing same protein found in Z lines 5 Smooth Muscle Cell has three types of filaments Thick myosin filaments Longer than those in skeletal muscle Thin ac:n filaments Contain tropomyosin but lack troponin Filaments of intermediate size Do not directly par:cipate in contrac:on Form part of cytoskeletal framework that supports cell shape 6 Smooth Muscle Myosin & Ac:n Schema:c Representa:on of the arrangement of Thick and Thin Filaments in a Smooth Muscle Cell In Relaxed State Fig. 8-28, pg. 293 7 Smooth Muscle Myosin & Ac:n Schema:c Representa:on of the arrangement of Thick and Thin Filaments in a Smooth Muscle Cell In Contracted State Fig. 8-28, pg. 293 8 Ca2+ Ac:va:on of Myosin Cross Bridge Fig. 8-29, pg. 293 Note: No Troponin 9 Smooth muscle contrac:on Twitch is slower Cross bridges slower Ca2+ removal slower Fig. 8-27, pg. 292 10 Skeletal vs. Smooth Comparison of Role of Calcium In Bringing About Contrac:on in Smooth Muscle and Skeletal Muscle Fig. 8-30, pg. 294 11 Smooth Muscle Two major types Mul:unit smooth muscle Single-unit smooth muscle 12 Mul:unit Smooth Muscle Each cell receives input Very few gap junc:ons between cells Each cell may contract independently of its neighbor 13 Mul:unit Smooth Muscle Neurogenic (ANS) Consists of discrete units that func:on independently of one another Units must be separately s:mulated by nerves to contract Found In walls of large blood vessels In small airways to lungs In muscle of eye that adjusts lens for near or far vision In iris of eye At base of hair follicles 14 Single-Unit Smooth Muscle Motor neuronal input to a few cells Many gap junc:ons allow communica:on The cells contract as a group Func:onal syncy:um 15 Single-unit Smooth Muscle Self-excitable does not require nervous s:mula:on for contrac:on Also called visceral smooth muscle Fibers become excited and contract as single unit Cells electrically linked by gap junc:ons Can also be described as a func:onal syncy:um Contrac:on is slow and energy-efficient Well suited for forming walls of distensible, hollow organs (diges:ve, reproduc:ve and urinary tracts) 16 Pacemaker Poten:al Fig. 8-31a, pg. 295 17 Slow Wave Poten:al Fig. 8-31b, pg. 295 18 ANS Postganglionic Innerva:on Fig. 8-32, pg. 297 Synapse "en passant" 19 Cardiac Muscle Found only in walls of the heart Striated Cells are connected by gap junc:ons Intercalated disks Innervated by ANS Involuntary 20 ...
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- Spring '08