Understanding Skeletal Muscle Contraction and Movement in Complex Organisms, Slides of Biology

Download Understanding Skeletal Muscle Contraction and Movement in Complex Organisms and more Slides Biology in PDF only on Docsity! Chapter 40 Protection, Support, and Movement docsity.com Movement  Movement in complex organisms includes beating of the heart, contraction of the digestive organs, etc. Locomotion is the movement of the entire body.  Locomotion occurs because of the coordinated activities of the skeletal, muscular, nervous, circulatory and etc. systems. docsity.com Muscles Move Bones at Joints  3 types of joints Sutures = immovable joints, ex. Skull Cartilagenous = slightly movable joints, bones are bridged by cartilage, ex. vertebral discs, pubic symphysis. Synovial joints = freely movable , bones are separated by a fluid filled capsule, ligaments hold bones in place. Ex. knees, elbows, shoulders, and hips. docsity.com Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fibrous connective tissue Bone Immovable joint Suture Slightly movable joints Body of vertebra Articular cartilage Intervertebral disk docsity.com ° fi BP rvivancsareue joints swivel Hinge joints hinge it Alright A Fi Copyright © 2008 Pearson Benjamin Cummings. All rights reserve docsity .com Figure 46-18 Endoskeleton Flexor (hamstring) contracts Exoskeleton Extensor muscle contracts Hydrostatic skeleton Extensor (quadriceps) contracts Flexor muscle contracts Longitudinal muscles contract Circumferential muscles relax Longitudinal muscles relax Circumferential muscles contract docsity.com Skeletal Muscles  Types of contractions  Isotonic (same tension) – the force produced by muscle shortening moves a load.  Ex., flexing bicep muscle  Isometric (same length)– the force produced by muscle does not move the load.  Ex., holding a weight at arm's length docsity.com Skeletal Muscles  Anatomy of a muscle Muscles are composed of bundles of muscle cells (= muscle fibers) Muscle fibers are composed of many myofibrils. Myofibrils are composed of many myofilaments – actin (thin) and myosin (thick) docsity.com Skeletal Muscle Contraction  Sliding Filament Theory Theory explaining how the sarcomere shortens. Actin filaments slide past the myosin filaments toward the middle of the sarcomere. docsity.com Skeletal Muscles  Mechanism: Myosin has globular heads that attach to actin filaments at special (active) sites. Once attached, myosin pulls the actin filaments toward the center of the sarcomere. The attachment between the myosin head and the actin is called a cross-bridge docsity.com Figure 46-20 Myofibril Relaxed Contracted Thin filament (actin) Thick filament (myosin) Z disk A A C C D D B B docsity.com Skeletal Muscle Contraction  Mechanism cont’d Activation of actin – role of Ca++  Myosin binding sites (active sites) on actin are covered by a protein, tropomyosin, held in place by another protein, troponin.  Increased Ca++ in the sarcoplasm binds to troponin and moves it and tropomyosin away from the active site allowing myosin heads to bind. docsity.com Figure 46-23 Tropomyosin and troponin work together to block the myosin binding sites on actin. Myosin head Troponin Tropomyosin Actin Myosin binding sites blocked Calcium ions Myosin binding sites When a calcium ion binds to troponin, the troponin- tropomyosin complex moves, exposing myosin binding sites. Myosin binding site exposed to myosin head Calcium ion Troponin-tropomyosin complex, moved docsity.com Skeletal Muscle Contraction  Mechanism Activation of actin – where does Ca++ come from?  In skeletal muscle, Ca++ is stored in the sarcoplasmic reticulum (SR). The SR is continuous with T-tubules (invaginations of the plasma membrane).  Release of Ca++ from the SR is controlled by nerve impulses. After a contraction Ca++ is “pumped” back into the SR.  **Requires energy from ATP docsity.com SSS HOW DO ACTION POTENTIALS TRIGGER MUSCLE CONTRACTION? 1. Action potential arrives, and ACh is released. ns ad as 2. Acetylcholine binds to ACh a ae , : receptors on the muscle cell, Muscle cell . ( as triggering depolarization that leads to action potential. 3. Action potentials propagate across muscle cell's plasma membrane and into interior of cell via T tubules. 4. Proteins in T tubules open Ca2+ channels in sarcoplasmic reticulum. 5. Ca2+ is released from sarcoplasmic reticulum. Sarcomeres contract when troponin and tropomyosin move in response to Ca2+ and expose actin binding sites in the thin filaments. T tubule Motor neuron Figure 46-24 Biological Science, 2/e © 2005 Pearson Prentice Hall, Inc. (® docsity.com Figure 46-24a HOW DO ACTION POTENTIALS TRIGGER MUSCLE CONTRACTION? Motor neuron Muscle cell Motor neuron Action potential ACh ACh receptor Action potentials 1. Action potential arrives; acetylcholine (ACh) is released. 2. ACh binds to ACh receptors on the muscle cell, triggering depolari- zation that leads to action potential. docsity.com Figure 46-24b HOW DO ACTION POTENTIALS TRIGGER MUSCLE CONTRACTION? Motor neuron Muscle cell Thick filaments (myosin) Thin filaments (actin) Ca2+ ions 3. Action potentials propagate across muscle cell’s plasma membrane and into interior of cell via T tubules. 4. Proteins in T tubules open Ca2+ channels in sarcoplasmic reticulum. 5. Ca2+ is released from sarcoplasmic reticulum. Sarcomeres contract when troponin and tropomyosin move in response to Ca2+ and expose actin binding sites in the thin filaments (see Figure 46.23). docsity.com