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Muscle Function.

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Presentation on theme: "Muscle Function."— Presentation transcript:

1 Muscle Function

2 Functional Anatomy of skeletal muscle
3 layers of connective tissue Epimysium – surrounds entire muscle Perimysium – divide muscle into compartments Endomysium – surrounds individual muscle cells Blood vessels and nerves Skeletal muscle fibers

3 Skeletal Muscle Fibers
Multinucleate – Each contains hundreds of nuclei just internal to membrane Large Sarcolemma – Cell membrane Sarcoplasm - cytoplasm

4 During Contraction The whole fiber must contract simultaneously
Signal to contract must distribute quickly via Transverse Tubules Transverse Tubules (T Tubules) – narrow tubes that are continuous with the sarcolemma and extend into the sarcoplasm at right angles to the cell surface Like a belt

5 During Contraction Myofibril – Cylindrical structures. Each muscle fiber contains hundreds to thousands of myofibrils Contain a thick and thin filament Thin Filament – Actin Thick Filament – Myosin

6 During Contraction Sliding Filament Theory – Thick and thin filaments slide across each other therefore shortening and causing a contraction.

7 Important structures Neuromuscular Junction Sarcoplasmic Reticulum
Ca (Calcium Ions) Sarcomere (~10,000/myofibril) Actin Myosin Acetylcholine (ACh) Troponin Tropomyosin 2+ Rope around Actin

8 Steps of Contraction ACh is released at Neuromuscular junction
Production of action potential along surface of muscle fiber/T tubules Sarcoplasmic reticulum (SR) releases calcium ions that were stored into sarcoplasm Calcium bind to troponin changing oritentaion and exposing active sites of actin. Cross-bridges form when myosin head binds to active site

9 Steps of contraction Bind, pivot, detach via hydrolysis of ATP (therefore filament sliding and fiber shortens) Action potential ends with ACh break down SR resorbs calcium Active sites recover to prevent cross-bridge Muscle relaxation occurs

10 Figure 10-10 The Exposure of Active Sites
SARCOPLASMIC RETICULUM Calcium channels open Myosin tail (thick filament) Tropomyosin strand Troponin G-actin (thin filament) Active site Nebulin In a resting sarcomere, the tropomyosin strands cover the active sites on the thin filaments, preventing cross-bridge formation. When calcium ions enter the sarcomere, they bind to troponin, which rotates and swings the tropomyosin away from the active sites. Cross-bridge formation then occurs, and the contraction cycle begins. 10

11 Figure 10-12 The Contraction Cycle
Contraction Cycle Begins The contraction cycle, which involves a series of interrelated steps, begins with the arrival of calcium ions within the zone of overlap. Myosin head Troponin Tropomyosin Actin 11

12 Figure 10-12 The Contraction Cycle
Active-Site Exposure Calcium ions bind to troponin, weakening the bond between actin and the troponin– tropomyosin complex. The troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energized myosin heads. Sarcoplasm Active site 12

13 Figure 10-12 The Contraction Cycle
Cross-Bridge Formation Once the active sites are exposed, the energized myosin heads bind to them, forming cross-bridges. 13

14 Figure 10-12 The Contraction Cycle
Myosin Head Pivoting After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke; when it occurs, the bound ADP and phosphate group are released. 14

15 Figure 10-12 The Contraction Cycle
Cross-Bridge Detachment When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge. 15

16 Figure 10-12 The Contraction Cycle
Myosin Reactivation Myosin reactivation occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head. 16

17 Table 10-1 Steps Involved in Skeletal Muscle Contraction and Relaxation
Steps in Initiating Muscle Contraction Steps in Muscle Relaxation Synaptic terminal Motor end plate T tubule Sarcolemma Action potential reaches T tubule ACh released, binding to receptors ACh broken down by AChE Sarcoplasmic reticulum releases Ca2 Sarcoplasmic reticulum recaptures Ca2 Ca2 Active site exposure, cross-bridge formation Actin Active sites covered, no cross-bridge interaction Myosin Contraction ends Contraction begins Relaxation occurs, passive return to resting length 17

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