B6A13MusculoskeletalS11 - Musculoskeletal systems Animas:...

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Unformatted text preview: Musculoskeletal systems Animas: Locomotion Organismal motility: • Cellular motility - flatworms & larval annelids Muscles! Requires coordination of longitudinal + circular muscles - annelids cilia amoeboid flagellum Muscles & Skeletons • For much more power & versatility of movements: • muscles attach to skeleton across hinge or joint Only longitudinal muscles - roundworms & large flatworms MUSCLES • Muscle Function • Muscle Structure & Action • Muscle Types Muscle Functions • Body movement – Locomotion & other behaviors • Stabilizing body form and position • Pumping & controlling areas of fluids – Within: blood, lymph, air, food – Without: secretion/excretion of exocrine products & wastes • Generate heat Heyer Got Mesoderm? • Diploblastic organisms lack true muscle • Other contractile tissues: – Sponges — myocytes • Close pores – Cnidaria — myoepithelia • Also found in epithelial exocrine glands of other taxa (including us!) 1 Musculoskeletal systems Myoepithelia (Epitheliomuscular cells) Characteristics of muscle • Cnidarian body wall • • • • Muscle terms an external force Mus-, mys- = “mouse” mus cle, myo fiber Biceps contracts, elbow bends Vertebrate Skeletal Muscle Structure Triceps exerts force to lengthen biceps, straighten arm insertion origin Contraction: shorten via internal force Extension: muscle can be lengthened only by Contractility: shorten actively Extensibility: stretch passively Elasticity: recoil to resting length Excitability: respond to stimulation Sarco- = “meat”; “flesh” Especially with respect to modified cell components of the mulinuclear myofiber: • cytoplasm · sarco plasm • plasmalemma (cell membrane) · sarco lemma • [smooth] endoplasmic reticulum · sarco plasmic reticulum Muscle fiber organization • Muscle fascicle (bundle) • Muscle fiber (1-cell) • Myofibril Heyer 2 Musculoskeletal systems Myofibrils Have Myofilaments: Actin & Myosin Sarcomere: contractile unit of a myofibril (Z-line to Z-line) I-band Myofilaments — protein engines within the myofibril Two types: thin filaments and thick filaments Actual muscle (TEM) A-band I-band Sliding Filament model of muscle contraction •  Thin filaments are pulled over the thick filaments. •  Filaments do not change length — but increase degree of overlapping. •  A-band does not change size; but Z-lines get closer together (sarcomeres get shorter). •  Tiny changes in length of each of the thousands of sarcomeres add to a big change in length for the myofibril/myofiber/muscle. Skeletal muscles are “voluntary” Nerve impulses must say “Contract!” Heyer 3 Musculoskeletal systems Conveying Contraction Signal •  Nerve impulses to neuromuscular junction opens Na+ channels. •  Depolarization travels across membrane and conducted through the fiber by T-tubules. •  Voltage-gated Ca++ channels . on sarcoplasmic reticulum . open. •  Ca++ enters cytoplasm and starts contraction. Sliding Filaments •  Ca++ opens binding sites for myosin heads. •  Myosin heads swivel as they bind to actin. •  This requires ATP. . . . . Sliding Filament Model •  Myosin-actin interactions underlying muscle fiber contraction Thick filament Thin filaments 1 5 Binding of a new molecule of ATP releases the myosin head from actin, and a new cycle begins. Starting here, the myosin head is bound to ATP and is in its low-energy confinguration. Thin filament Myosin head (lowenergy configuration) ATP ATP 2 The Thick filament Thin filament moves toward center of sarcomere. myosin head hydrolyzes ATP to ADP and is in its highenergy configuration. Actin ADP Myosin head (lowenergy configuration) Pi Myosin head (highenergy configuration) Cross-bridge binding site ADP 4 Initiation of contraction by Ca++ + Pi ADP Pi Releasing ADP and (Pi), myosin relaxes to its low-energy configuration, sliding the thin filament. Cross-bridge 13 The myosin head binds to actin, forming a cross-bridge. Review of contraction in a skeletal muscle fiber •  Myosin-Actin cross-bridges •  Thin filament constructed of double chain of actin wrapped in fibers of troponin/tropomyosin •  Tropomyosin strand blocks myosin-binding sites of actin •  Ca++ binds to troponin → tropomyosin moves aside → binding sites exposed → sliding filament cycle starts http://www.sci.sdsu.edu/movies/actin_myosin_gif.html Heyer 4 Musculoskeletal systems Review of contraction in a skeletal muscle fiber 1 Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. Synaptic cleft 2 ACh Twitch Summation one motor neuron signal one twitch PLASMA MEMBRANE T TUBULE Tetanus Action potential is propagated along plasma membrane and down T tubules. SR 3 Action potential triggers Ca2+ release from sarcoplasmic reticulum (SR). Ca2+ 7 Tropomyosin blockage of myosinbinding sites is restored; contraction ends, and muscle fiber relaxes. 4 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. Ca2+ Tension Synaptic terminal of motor neuron Summation of two twitches Single twitch CYTOSOL ADP P2 6 Cytosolic Ca2+ is removed by active transport into SR after action potential ends. Action potential 5 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. “Twitch”: All seven steps in <0.1 second! Spinal cord Motor unit 1 •  Motor unit: A single neuron and all the muscle fibers it controls –  Divergence •  When motor neuron produces action potential all the muscle fibers in its motor unit contract as a group. Motor unit 2 Synaptic terminals Nerve Time Pair of action potentials Series of action potentials at high frequency Optimizing filament overlap •  Muscle force depend on the degree of overlap between thin & thick filaments –  Too little: not many cross-bridges –  Too much: no room to shorten sarcomere Motor neuron cell body Motor neuron axon Muscle Muscle fibers Tendon Long sarcomere vs. short sarcomere Skeletal Muscle •  Multi-nucleated / striated / “voluntary” •  White: short-term & mitochondria-poor –  high power / fast twitch / low endurance •  Red: long-term & mitochondria-rich –  high myoglobin content [red] for enhanced O2 –  slow twitch (except in birds) / high endurance •  swim muscles of oceanic fish •  extra myoglobin in marine mammals Heyer 5 Musculoskeletal systems Types of skeletal muscle fibers •  Any muscle may have more than one type •  But only one muscle fiber type per motor unit (the motor neuron determines the muscle fiber type) Three types of vertebrate muscle tissue •  Skeletal muscle –  Attached to bone (usually) –  Striated: contractile proteins stacked in visible columns; contraction is linear –  Voluntary: contract only in response to somatic motorneuron stimulation •  Cardiac muscle –  Found only in heart –  Striated –  Involuntary: contract in response to intrinsic pacemaker; modifiable by autonomic motorneurons •  Smooth muscle –  Found in lining of visceral organs, blood vessels, skin, etc. –  Unstriated: contractile proteins aligned in 3-dimensional arrays; contraction may be multi-dimensional –  Involuntary: contract either in response to intrinsic reflexes, or from extrinsic autonomic motorneuron stimulation Skeletal muscle Cardiac Muscle •  Striated: Contain actin and myosin arranged in sarcomeres. •  Contract via slidingfilament mechanism. •  Branched, mononuclear cells. •  Adjacent myocardial cells joined by gap junctions. • Skeletal muscle cells are long, multi-nuclear fibers. • Most of the cell’s volume is taken up by stacks of protein filaments. • Nuclei and mitochondria are displaced to the periphery. Smooth Muscle •  Filaments not arranged into sarcomeres. •  Contains > content of actin than myosin (ratio of 16:1). •  Myosin filaments attached at ends of the cell to dense bodies. •  Long, slow contractions –  APs spread through cardiac muscle through gap junctions. –  All cells contribute to contraction. –  Single-unit muscle: entire muscle contracts as a single unit Arthropod Skeletal Muscle Fiber Types http://entomology.unl.edu/ent801/muscles.html Striated & aerobic •  Tubular: fibrils are arranged radially about a central column –  Dragonfly flight muscles & legs of most insect species. •  Microfibrillar (close-packed): 1.5 to 2.0 µm diameter fibrils –  Lepidoptera and Orthoptera flight muscles •  Fibrillar: large, 3–5 µm fibrils –  Hymenoptera, Diptera, Coleoptera and Hemiptera flight muscles –  Resonating: contract 20-30 times/impulse; contract 1000 times/sec Heyer 6 Musculoskeletal systems Obliquely striated muscle • found only in some invertebrate groups – nematodes, annelids, and mollusks Skeletons Functions: • Support • Protection • Mineral storage • Movement – Structure for muscle to pull against – True skeleton vs. “shell”, “test”, or “cuticle” • Types – Hydrostatic skeletons – Exoskeletons – Endoskeletons Figure 3: The arrangement of the myofilaments in obliquely striated muscle. Hydrostatic Skeletons • Flexibility – – – – cnidarians annelids nematodes echinoderms • Peristalsis – longitudinal & circular muscles • Best developed in annelids. Muscle action with a hydrostatic skeleton Changes in body form in wormlike soft-bodied animals. A. The longitudinal muscle contracting. B. The circular muscle contracting. C. The longitudinal muscle above contracting while the circular muscles maintain a constant length, stretching the longitudinal muscles below. – septa let segments work independently Muscle action with a hydrostatic skeleton • Echinoderm tube feet Calcareous Shells Calcium carbonate (CaCO3) • Tubes – Cnidarians – Polychaetes foraminifera • Globe-shaped test – Echinoderm ossicles w/ sutures – Foraminiferans spiral • Mollusc Shells Figure 6: Tube foot of the sea urchin. Heyer – Spiral of snails – Bivalve shells 7 Musculoskeletal systems Ecdysozoans: Chitinous Cuticles Chitin & Cellulose: polymers similar in structure & function. Polymer of N-acetyl-glucosamine Arthropod Chitinous Exoskeleton • Terrestrial: waterproof waxy layer • Marine: calcified • Chitin fibers layered like plywood for strength • 30–50% of arthropod exoskeleton Polymer of glucose The two most abundant polysaccharides in nature. Arthropod Exoskeleton • Epidermis & basement membrane – Simple epithelia on a layer of collagen & polysaccharides • Procuticle – Layers of chitin fibers in a protein matrix – Proteins may may elastic — membranes & joints – Or, outer layers may cross-link (sclerotization) to form hardened plates (sclerites) • Epicuticle – Layers of lipoproteins & fatty acids covered by a layer of wax Sensory setae Growth, Molt, & Exoskeletons • Recycle materials • Vulnerable to predation during molt • Growth is step-like Epicuticle Procuticle Epidermis Basement membrane Exocrine gland Skeletal muscle John R. Meyer, North Carolina State Univ. http://www.cals.ncsu.edu/course/ent425/ Arthropod joints Parallel vs. pinnate muscle fibers • muscles attach to skeleton across hinge or joint • No room for bulging biceps within exoskeleton Human Grasshopper Extensor muscle relaxes Biceps contracts Triceps relaxes Tibia flexes Extensor muscle contracts Biceps relaxes Forearm extends Triceps contracts Heyer Flexor muscle contracts Forearm flexes Tibia extends Flexor muscle relaxes 8 Musculoskeletal systems Insect flight Insect flight muscles • • • Double-hinge attachment of wings to thoracic segment Dorsoventral muscles, running from the tergum to the bottom of the thorax, contract to raise the wings. Longitudinal muscles, running along the length of the thorax, contract to lower the wings. • Synchronous systems: tubular or microfibrillar muscles; neurogenic; slow beat frequency: 4–20/sec • Asynchronous systems: fibrillar muscles; myogenic; fast beat frequency:100–1000/sec – Butterflies & dragonflies Indirect flight musculature Indirect flight muscle action – Bees, flies, mosquitoes Endoskeletons • Minor endoskeletons – spicules of sponges • calcareous or siliceous • Vertebrates – cartilage & bone Basic motion of the insect wing in insect with an indirect flight mechanism Scheme of dorsoventral cut through a thorax segment with: –a: wings –b: joints –c: dorsoventral muscles –d: longitudinal muscles Not-so-Endo-skeletons • Imbedded armor — endodermal bone – Armored fish dermal bone – Turtle carapace – Vertebrate skull • Intramembranous ossification • Within dermal connective tissue Cartilage & Endoskeletons • Flexible endoskeletons – Agnathans & Chondrichthyes • Embryonic skeleton of all vertebrates – Cartilage later replaced by endochondral bone • Forms articulating surfaces of bones. • Supports trachea, nose, pinnae. – Sutures allow growth w/out shedding it. Heyer 9 Musculoskeletal systems Endochondral Bone Growth • Cartilagenous skeleton derived from embryo mesoderm. • Ossification centers form within cartilage fi grow/replace cartilage w/ bone Endochondral Bone Growth • Epiphyseal plate – Cartilage cells are produced by mitosis on the epiphyseal side of the plate. – Cartilage cells are destroyed and replaced by bone on the diaphyseal side of plate. • As reproductive maturation approaches, the epiphyseal plates close. – Cartilage cells in the plate stop dividing and bone replaces the cartilage. The human skeleton key Axial skeleton Appendicular skeleton Skull Examples of joints Bone Structure Head of humerus • Extracellular matrix of Scapula 1 Shoulder girdle Clavicle Scapula Sternum Rib Humerus 2 Vertebra 3 Radius Ulna Pelvic girdle 1 Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. Humerus Carpals Ulna Phalanges Metacarpals 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. Femur Patella Tibia Fibula Ulna Tarsals Metatarsals Phalanges Radius – collagen and other proteins – calcified : hydroxyapatite calcium phosphate (Ca 10[PO 4]6OH 2) • Spongy bone is at ends. • Dense bone in mid-region. – surrounds blood-forming marrow – nourished by osteonic canals w/ capillaries • Ligaments join bone to bone. • Tendons join bone to muscle. 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. Figure 49.26 Exercise and Bone Tissue • Mechanical Stress- the pull on bone by skeletal muscle and gravity. – Mechanical stress increases deposition of minerals (50% of bone) and the production of collagen (25% of bone). Levers & Fulcrums • FinLin = Fout Lout \ › Lin/Lout Æ ↑ Fout for a given Fin (more power) • But, Vin/Lin = V out /Lout • Lack of Mechanical Stress Results in Bone Loss. \ fl Lin/Lout Æ ↑ Vout for a given Vin (faster) Lin = length of bone from fulcrum (pivot point) to muscle attachment Lout = length of appendage from fulcrum to tip Heyer 10 Musculoskeletal systems Levers & Fulcrums Modes of Locomotion: ››› Lout Æ ››› V out • Each has its costs & benefits Comparing Costs of Locomotion Comparing Costs of Locomotion • The energy cost of locomotion – Depends on the mode of locomotion and the environment EXPERIMENT Physiologists typically determine an animal’s rate of energy use during locomotion by measuring its oxygen consumption or carbon dioxide production while it swims in a water flume, runs on a treadmill, or flies in a wind tunnel. For example, the trained parakeet shown below is wearing a plastic face mask connected to a tube that collects the air the bird exhales as it flies. ßbike Flying Energy cost (J/Kg/m) This graph compares the energy cost, in joules per kilogram of body mass per meter traveled, for animals specialized for running, flying, and swimming (1 J = 0.24 cal). Notice that both axes are plotted on logarithmic scales. Running 102 CONCLUSION 1. For animals of a given body mass, swimming is the most energy-efficient and running the least energy-efficient mode of locomotion. * * For energy per distance ! * Flying has highest cost per time ! 10 1 Swimming 10–1 10–3 103 1 106 Body mass(g) Comparing Costs of Locomotion human CONCLUSION RESULTS ßswim 2. In any mode, a small animal expends more energy per kilogram of body mass than a large animal. Comparing Costs of Locomotion • Bigger animals have lower transport costs – Another reason smaller animals have higher metabolic rates per body mass • Do they have enough energy stores to sustain locomotion? Heyer – E.g., moving uphill 7 6 5 mouse 4 O2 use/mass Long-range migrators • Small animals work much harder to move faster • But bigger animals have more cost for working against gravity 3 2 1 chimpanzee 0 1 2 3 4 5 6 Running velocity 7 ...
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