The Musculoskeletal System Chapter 47

2 Types of Skeletal Systems Changes in movement occur because muscles pull against a support structure, called the skeletal system -Zoologists recognize three types: -Hydrostatic skeletons -Exoskeletons -Endoskeletons

3 Chitinous outer covering Exoskeleton Sagittal section Vertebral column Pelvis Femur Tibia Fibula Ulna Radius Humerus Skull Scapula Ribs Exoskeleton Endoskeleton a. b. axial skeleton appendicular skeleton 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 Hydrostatic skeletons Found primarily in soft-bodied invertebrates

4 Hydrostatic Skeletons Chaetae get lifted in regions of circular muscle contraction. During longitudinal muscles contraction, chaetae anchor into the ground

5 Hydrostatic Skeletons Locomotion in aquatic invertebrates occurs by fluid ejections or jetting -Jellyfish produce regular pulsations in bell -Squeezing some of water contained beneath it -Squids fill mantle cavity with sea water -Muscular contractions expel water forcefully through the siphon, and the animal shoots backward

6 -Unlike chitin, bone and cartilage are living tissues...they change and remodel in response to injury or physical stress -Echinoderms have calcite skeletons, that have calcium carbonate -Bone, on the other hand, has calcium phosphate. Vertebrate endoskeletons have bone and/or cartilage Endoskeletons Endoskeletons vs. Exoskeletons

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Undifferentiated Mesenchymal Cells ChondroblastFibroblastOsteoblasts Chondrocyte Collagen (fibrous tissue) Osteocyte Osteoclast Secrete Alkaline phosphatase causes Calcium Phosphate to form Hydroxyapatite In the EXTRACELLULAR MATRIX Cells in Bone Tissue Make cartilage = Chondroitin and collagen

8 Endoskeleton Bone 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

9 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.

10 *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 Endochondrial Bone Development

11 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

12 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 fish and birds

13 Bone Structure Based on density and structure, bone falls into three categories -Compact bone = Outer dense layer -Medullary bone = Lines the internal cavity...contains bone marrow in some species (site of red blood cell production) -Spongy bone = Honeycomb structure forms the epiphyses inside a thick shell of compact bone

14 Joints are the locations where one bone meets another 3 general kinds

15 Skeletal Muscle Structure 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 Bone periosteum & skeletal Muscle Are united by a tendon

16 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

17 Sarcomere H band A band I band a. b. Z line Thin filaments (actin)Thick filament (myosin)Cross-bridges Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Why do Myofibrils contract and shorten??? Because thick and thin filaments slide over each other Sarcomere = distance between 2 Zlines... Smallest subunit of muscle contraction

18 Cross-bridge cycle

19 Relaxed Versus Contracted Muscle Troponin + Tropomyosin = NO Muscle Contraction Because Tropomyosin binds to Actin Ca 2+ + Troponin + Tropomyosin = Muscle Contraction Because Ca 2+ + Troponin displace Tropomyosin... Actin-myosin cross-bridges form

20 Myofibril Na + Sarcolemma Neuromuscular junction Motor neuron Nerve impulse Neurotransmitter Sarcoplasmic reticulum Transverse tubule (T tubule) Release of Ca 2+ Ca 2+ Muscle depolarization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal Muscle Contraction acetylcholine -The membrane becomes depolarized -Depolarization is conducted down the transverse tubules (T tubules)

21 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

22 Types of Muscle Fibers A muscle stimulated with a single electric shock quickly contracts and relaxes in a response called a twitch Summation is a cumulative response when a second twitch “piggy-backs” on the first Tetanus occurs when there is no relaxation between twitches -A sustained contraction is produced

23 Amplitude of Muscle Contractions Complete tetanus Twitches Incomplete tetanus Time Summation Stimuli ' ' ' Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24 Types of Muscle Fibers Skeletal muscle fibers can be divided based on their contraction speed -Slow-twitch, or Type I, fibers -Rich in capillaries, mitochondria and myoglobin pigment (red fibers) -Sustain action for long periods of time -Fast-twitch, or Type II, fibers -Poor in capillaries, mitochondria and myoglobin (white fibers) -Adapted for rapid power generation

25 Contraction Strength Time (msec) eye muscle (lateral rectus) calf muscle (gastrocnemius) deep muscle of leg (soleus) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Muscle Fibers Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers

26 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!!!