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Chapter 47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Changes in movement occur because muscles pull against a skeletal system... 3 types Exoskeleton Exoskeleton Chitinous outer covering Sagittal section a. Endoskeleton Skull Ribs Vertebral column axial skeleton appendicular skeleton Pelvis Scapula Humerus Radius Ulna Hydrostatic skeletons Found primarily in soft-bodied invertebrates b. Femur Tibia Fibula 2 Hydrostatic Skeletons Chaetae get lifted in regions of circular muscle contraction. During longitudinal muscles contraction, chaetae anchor into the ground 3 Exoskeletons •Exoskeletons consist of a rigid outer covering •Must be shed for the organism to grow. •Limits body size. •Made of Chitin 4 Endoskeletons vs. Exoskeletons Unlike chitin, bone and cartilage are living tissues...they change and remodel in response to injury or physical stress More rigid Echinoderms have skeletons, that have calcium carbonate Bone, on the other hand, has calcium phosphate. Vertebrate endoskeletons have bone and/or cartilage 5 Cells in Bone Tissue Secrete Alkaline phosphatase causes Calcium Phosphate to form Hydroxyapatite In the EXTRACELLULAR MATRIX 6 Endoskeletons Bone is unique to vertebrates Bones can be classified by the two fundamental modes of development Intramembranous development (simple) E.g.: External bones of skull Endochondral development (complex) E.g.: Bones that are deep in the body 7 Intramembranous Bone Development Osteoblasts from dermis in skin initiate bone development (onto collagen fiber scaffold). Some cells become trapped in the bone matrix that they have produced. change into osteocytes, which reside in tight spaces called lacunae The cells communicate through little canals termed canaliculi. Osteoclasts break down the bone matrix. 8 Endochondrial Bone Development *First there is cartilage in the general shape of the bone *A fibrous sheath with osteoblasts surrounds cartilage *Osteoblasts use cartilage to make Calcium Phosphate (Extracellular Matrix) *Blood vessels from fibrous sheath (now periosteum) go deeper into the original cartilage *Osteoblasts and Osteoclasts follow blood supply to further change cartilage into bone tissue 9 Endochondral Development Superficial cartilage that remains after the development of epiphyses serves as a pad between bone surfaces Osteoclasts create medullary cavity Growth plates made of cartilage grow towards distal ends until approaching bone coming from the shaft changes it all to bone 10 Vascular Bone Structure Most mammals retain internal blood vessels and are called vascular bones These typically have osteocytes and are also called cellular Bones & have a Haversian system Not seen in fish and birds 11 Types of Freely Movable Joints Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ball-and-Socket a. Gliding Joint Hinge Joint b. c. Combination Joint 12 Skeletal Muscle Movement Origin vs. Insertion Skeletal muscles occur in antagonistic pairs Agonist = Muscle group causing an action Antagonist = Muscle group that counters movement Isotonic contraction – The tension of contraction remains relatively constant as the muscle shorten in length Isometric contraction – The length of the muscle does not change as force is exerted 13 Skeletal Muscle Structure Bone periosteum & skeletal Muscle Are united by a tendon Each skeletal muscle contains numerous muscle fibers (CELLS) Each muscle fiber encloses a bundle of structures called myofibrils Each myofibril in turn is composed of thick and thin myofilaments 14 Thick filament is composed of myosin protein, two polypeptide chains w/ a globular head wrapped around each other Thin filament Is two chains of actin protein, twisted together in a helix 15 The Sliding Filament Mechanism Somatic motor neurons fire. Meet NMJ Release Ach Muscle Cell releases Na+ Depolarization throughout cell, the SR, and T-tube. T-tube releases Ca2+ Ca2+ binds to troponin Calcium bound troponin changes shape. 16 The Sliding Filament Mechanism Tropomyosin changes shape Exposes myosin binding sites on actin Cross bridge cycle begins Myosin hydrolize ATP to ADP and is ready to attach to actin. Myosin binds actin—power stroke. Myosin binds another ATP, releases and is ready to bind again. 17 Why do Myofibrils contract and shorten??? Because thick and thin filaments slide over each other Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sarcomere Z line A band H band Thin filaments (actin) Cross-bridges Sarcomere = distance between 2 Zlines... Smallest subunit of muscle contraction I band Thick filament (myosin) a. b. 18 Cross-bridge cycle 19 Relaxed Versus Contracted Muscle Troponin + Tropomyosin = NO Muscle Contraction Because Tropomyosin binds to Actin Ca2+ + Troponin + Tropomyosin = Muscle Contraction Because Ca2+ + Troponin displace Tropomyosin... Actin-myosin cross-bridges form 20 21 Skeletal Muscle Contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron Nerve impulse acetylcholine Neurotransmitter Neuromuscular junction Muscle depolarization Sarcolemma Na+ Sarcoplasmic reticulum Myofibril Transverse tubule (T tubule) Ca2+ Release of Ca2+ -The membrane becomes depolarized -Depolarization is conducted down the transverse tubules (T tubules) 22 23 24 A motor unit consists of a motor neuron and all of the muscle fibers it innervates Recruitment is the cumulative increase in motor unit number and size leading to a stronger contraction 25 Types of Muscle Fibers Skeletal muscles at rest get energy from aerobic respiration of fatty acids During muscle use, energy comes from glycogen and glucose Muscle fatigue is related with the production of lactic acid via anaerobic fermentation during glycolysis!!! 26