29-*CHAPTER 29 Support, Protection, and MovementPowerpoints revised by Franklyn Tan TeCopyright McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

29-*An ant carries with ease a flower petal that is heavier than the ants body weight.

Grasshoppers and SupermanGrasshoppers can jump to a height of 50 times the length of their bodyBut their muscles are no more powerful than human musclesMuscles of small and large animals exert the same force per cross-sectional areaGrasshoppers leap high in proportion to their size because they are small and not because they have extraordinary muscles29-*

29-*IntegumentIntegument is a protective outer covering that includes skin, hair, setae, scales, feathers, and hornsTough and pliable to provide mechanical protection against abrasion and punctureProvide moisture proofing against water loss or gainEffective barrier against bacterial invasionProtect underlying layers from the damaging effects of ultraviolet lightHave other important regulatory functions

29-*The integument of endothermic animalsContributes to temperature regulationContains sensory receptors to provide essential information about the environmentHas excretory and respiratory functionsAssists in camouflage and signaling or display (pigmentation)Secretes molecules that may play role in mate attraction, predator repulsion, and detection of pheromonal cues that influence behavioral interactions between animals

Integument

29-*Invertebrate Integument Unicellular eukaryotes have either delicate plasma membranes or a protective pellicleMost invertebrates have complex tissue coverings and some secrete a noncellular cuticle over epidermisParasitic platyhelminths have syncytial tegument that is resistant to immune response of host and to digestive enzymesMolluscs have soft epidermis, which contains mucous glands that secrete calcium carbonate shell

Integument

29-*Cephalopods have more a complex integument made of cuticle; simple epidermis, connective tissue, and reflective cells called iridocytesArthropods have the most complex invertebrate integuments that provide protection and skeletal supportDeveloped a firm exoskeleton and jointed appendages that allow for muscle attachmentLed to the extraordinary diversification of this phylum to become the largest and most varied of all animal groupsIntegument

IntegumentArthropods have single-layered epidermis called hypodermis that secretes a complex cuticle in two zones on the bodyThicker, inner zone called procuticle made of protein and chitin that is deposited in layers called lamellaeThinner, outer zone called epicuticle is nonchitinous, made of proteins and lipids, and provides moisture-proofing barrierArthropod cuticle is one of the toughest animal materials that is resistant to pressure, boiling, and tearing but is very light and pliable

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29-*Cuticle may remain soft and flexible, like in many small crustaceans and insect larvae, but can also be found hardened in two general waysDecapod cuticle is hardened by deposition of calcium carbonate in the outer layer of the procuticle called calcificationInsect cuticle hardens by sclerotization, which is the formation of stabilizing cross-linkages between the protein molecules of the procuticle lamellaeThis results in sclerotin, which is very resistant to damage and insoluble in water

Integument

29-*Figure 29.1 Integumentary systems of animals, showingthe major layers.A, Arthropod body wall B, Amphibian integument. C, Human integument.

29-*Since arthropod cuticle is so tough, molting must occur to allow for growthMolting starts with epidermal cells dividing by mitosisEnzymes secreted by epidermis digest most of the procuticleDigested materials are absorbed and reusedSpace beneath the old cuticle grows new epicuticle and procuticle are formedAfter old cuticle is shed, new cuticle is thickened and calcified or sclerotizedIntegument

29-*Basic vertebrate integument and its derivatives are best exemplified by frog and human skin Thin, outer stratified epithelial layer called epidermis is derived from ectodermGives rise to hair, feathers, claws, and hoovesInner, thicker layer called dermis is derived from mesoderm Composed of dense connective tissue that contains blood vessels, collagenous fibers, nerves, pigment cells, fat cells, and unique connective tissue cells called fibroblasts

Integument

29-*Epidermis is made of several layers of stratified squamous epitheliumBasal layer of cells undergo frequent mitosis to renew cell layers lying above so new cells are made and old cells are displaced upwardExceedingly tough fibrous protein called keratin accumulates in the interior of cells in the process called keratinizationAs old cells die, keratin accumulates in all the cytoplasm of the cells and become cornifiedStratum corneum is formed when highly cornified cells become thick and highly resistant to abrasion and water diffusion that eventually forms calluses and footpads of mammalsIntegument

29-*Figure 29.2 Integument of bony fishes and lizards.

29-*Dermis supports, cushions, and nourishes the epidermis May contain true bony structure of dermal origin much like scales of modern fishes, which evolved from bony armor of early fishesMost amphibians lack dermal bones in their skin but have vestiges of dermal scalesIn reptiles, dermal bones form the armor of crocodilians, the beaded skin of lizards, and the shell of turtlesFor some mammals, dermal bone gives rise to antlers and the bony cores of hornsIntegument

IntegumentClaws, beaks, nails, and horns are made up of combinations of epidermal and dermal componentsMost mammalian horns, nails, and claws have a bony core covered by vascularized nutritive layer of dermisThe outer epithelia layer has germinative role for continued growth and keratinizationOvergrowth is prevented by constant use that leads to wear and abrasion

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29-*Figure 29.3 Similarity of structure of integumentary derivatives. Claws, beaks, and horns are all built of similar combinations of epidermal (keratinized) and dermal components.

29-*Animal coloration tends to be vivid and dramatic when used for warning coloration or as recognition markersSome colors are subdued or cryptic for camouflage and disguiseIntegumentary colors can be from pigments or from surface structuresStructural colors are reflected by surface tissues that make bright iridescences and metallic hues as seen in insects and fishIn birds, small air-filled spaces or pores in feathers can reflect a portion of color spectrum while other animals use thin films to angle light

Integument

IntegumentPigments (biochromes) are molecules that reflect specific light rays and are more commonly used in the animal kingdomCrustaceans and ectothermic vertebrates have pigments that are in large cells with branching processes called chromatophores Pigments may concentrate in center of cell or be dispersed throughout cell Cephalopod chromatophores are very different in that small sac-like cells with pigment granules are surrounded by muscle cells that can stretch the cell into a pigmented sheetWhen muscles relax, the elastic cell shrinks quickly and allow rapid color changes

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29-*Figure 29.4 Chromatophores. A, The crustacean chromatophoredispersed ( left ) and concentrated ( right ). B, The cephalopod chromatophore muscles contracted ( left ) to expose the pigment

29-*Melanin pigments are the most widespread and are usually black or brown polymers responsible for earth-colored shades found in melanocytes or melanophoresCarotenoid pigments impart yellow and red colors contained inside xanthophoresOmmochromes and pteridines are for yellow pigments in molluscs and arthropods, while green coloration is produced by yellow pigment overlying blue structural colorIridophores contain crystals of guanine or other purines, not pigments, that produce silvery or metallic colors when these reflect light

Integument

29-*Mammals are relatively somber-colored (uncolorful) and most species are colorblindHowever, some primate species of baboons and mandrills have brightly colored skin patches since these have color-visionDermal melanophores deposit melanin in growing hair of mammals and give the general dull colors of most mammalian speciesIntegument

29-*Injurious effects of sunlight like human sunburn demonstrates the damaging effect of ultraviolet radiation on cellsFlatworms exposed to sun in shallow water are damaged or killedArthropod cuticle, scales of reptiles, feathers of birds, and fur of mammals provide screening action against the sunHumans are naked apes and lack furry protectionDepend on thickening of the stratum corneum and epidermal pigmentation

Integument

IntegumentThe epidermis absorbs most of the ultraviolet radiation but about 10% penetrate the dermisSunburn is from blood-vessel enlargement due to release of histamine and other vasodilator substancesA sun tan results from increased melanin secretion in the dermis and from pigment darkening in the epidermis Ultraviolet radiation causes about one million new cases of skin cancer annually in the U.S.High doses of ultraviolet radiation in childhood may result in genetic mutations that cause skin cancer later in life

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29-*Skeletal SystemsSkeletons provide support, rigidity, surface for muscle attachment, and protection of delicate body organsHydrostatic skeletons of invertebrates are not rigid and use their body fluidsMuscles in the body wall of earthworms contract against the incompressible coelomic fluids enclosed in a limited spaceAlternative contraction of muscles enable worm to be thin or thick and produce backward-moving waves of motion to propel the animal forward using tiny bristles (setae) as anchors

29-*Figure 29.5 Earthworm movement.

Skeletal SystemsSepta separate the worm body into compartments that allow each part to develop pressure even when other compartments are punctured or cut into piecesThe elephant trunk, tongues of mammals and reptiles, and tentacles of cephalopods are examples of structures that lack any obvious skeletal support but is capable of bending, twisting, and lifting heavy objectsThese structure are called muscular hydrostats because of incompressible tissues that remain at constant volume and arranged in complex patterns29-*

29-*Figure 29.6 Muscular trunkof an elephant, an example of amuscular hydrostat.

29-*Rigid skeletons provide firm elements to which muscles can attach and serve as anchor points for the extension and flexion of muscle movementTwo types of rigid skeletons are the outer exoskeleton and inner endoskeleton Exoskeleton is typical of mollusks, arthropods, and other invertebrates that will have shells, spicules, and calcareous, proteinaceous or chitinous platesCan be for protection and locomotion but has to be periodically molted since it does not grow with the animal in many casesSkeletal Systems

Skeletal SystemsEndoskeleton is found in echinoderms, some cnidarians and vertebratesVertebrate endoskeleton is formed inside the body and composed of specialized connective tissue like bone and cartilageFunctions as protection and support but also as reservoir for calcium and phosphorusIn amniotic vertebrates, the bone marrow makes red blood cells, white blood cells, and platelets

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29-*Notochord is a semi-rigid supportive axial rod of protochordates and all vertebrate larvaeMade of large vacuolated cells surrounded by layers of elastic fibrous collagen sheathsAct as stiffening structure to maintain body shape during locomotionNotochord surrounded or replaced by vertebrae during development except in jawless vertebrates like lampreys and hagfishesCartilage is a major skeletal element of jawless fishes and elasmobranchs Skeletal Systems

Skeletal SystemsMost vertebrates have bony skeletons with some interspersed cartilageCartilage is soft, pliable tissue that resists compression with a basic form called hyaline cartilage that is clear and glassy in formThis type of cartilage is made of cartilage cells called chondrocytes that are surrounded by a firm complex protein-carbohydrate gel interlaced with a meshwork of collagen fibersForms most of the cartilaginous skeletons of vertebrate embryos, the articulating surfaces of joints and the supportive structures for tracheal, laryngeal and bronchial rings; most have no blood vessels so heal slowly29-*

29-*Other types of cartilage include elastic and fibrous tissues that form bundles and are arranged in herringbone designCartilage structure similar to hyaline cartilage are found in the radula of gastropods and lophophore feeding structures of brachiopodsCephalopods have specialized cartilage with long, branching processes that resemble cells of vertebrate boneSkeletal Systems

29-*Bone is living tissue with significant deposits of inorganic calcium salts in an extracellular matrix of collagen fibers in protein-carbohydrate gelHighly vascular and capable of rapid healing, unlike cartilage Nearly as strong as cast iron, yet only one-third as heavy due to its structural organizationBone never forms in vacant space but is laid down by the replacement of connective tissueSkeletal Systems

Skeletal SystemsMost bone develops by replacing hyaline cartilage called endochondral bone replacement (within cartilage)Embryonic cartilage is eroded and becomes honeycombed; it is then filled with bone-forming cellsExtracellular bone matrix gets deposited and later calcified around strand-like remnants of the cartilageIntramembranous bone comes directly from sheets of embryonic cells Forms face, cranium, and clavicle while the rest of the skeleton is endochondral bone

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Skeletal SystemsFully formed bone varies in density and comes in two types- spongy (cancellous) and compact (lamellar) bonesSpongy bone usually has open interlacing framework of bony tissue that is oriented to give maximum strength under normal stress and strainsCompact bones are denser bones formed from spongy bones through further deposition of bone matrix arranged in concentric ringsBoth spongy and compact bones form the long bones of tetrapods

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29-*Figure 29.7 Structure of compact bone. A, Adult long bone with a cut into the medullary cavity. B, Enlarged section showing osteons C, Enlarged view of an osteon D, An osteocyte within a lacuna.

29-*Microscopic structure of bone consists of bundles of osteons cemented together with interconnected blood vessels and nervesOsteons (Haversian system) are elongated cylindrical ring structures containing organized lacunae and canaliculiLacunae are cavities between the rings that contain bone cells called osteocytes, which are connected by minute passages called canaliculi that allow nutrients and growth factors to be distributed throughout the boneSkeletal Systems

29-*Blood vessels and nerves interconnect within the bones and allow rapid healingBone is a dynamic tissue such that bone growth and remodeling are complex restructuring processesOsteoclasts slowly resorb bone (cell destruction) while osteoblasts deposit new additional bone (cell building)These simultaneous processes allow growth of the bone without any weakeningBone marrow cavity grows larger by bone resorption of the inner surfaces of surrounding bone with new bone being laid down on the outer surface by bone deposition

Skeletal Systems

29-*Bone growth responds to several hormones Parathyroid hormone stimulates bone resorptionCalcitonin is a hormone from thyroid gland that inhibits bone resorptionBoth hormones and vitamin D3 (1,25-dihydroxyvitamin D3), maintain constant blood calcium levelsBone growth responds to usage much like muscles When astronauts have been living without gravity for some time, they can suffer bone loss and weakness

Skeletal Systems

29-*Plan of the vertebrate skeleton has both the axial and appendicular skeletal divisionsAxial skeleton includes the skull, vertebral column, sternum, and ribsAppendicular skeleton are bones of limbs along with pectoral and pelvic girdlesMovement from water to land forced dramatic changes in body formIncreased cephalization made the skull the most intricate part of the skeleton

Skeletal Systems

29-*Figure 29.8 Skeleton of a perch.

29-*Vertebrate skulls have increased concentration of brain, sense organs, and food gathering apparatusSome early fishes had 180 skull bones but over time, many skull bones were lost or fusedand now are greatly reducedAmphibians have from 50 to 95, mammals have 35 or fewer while humans have 29Vertebral column is the main stiffening axis and serves as points for muscle attachment while preserving body shapeMovement from water to land implies that body is no longer supported by water

Skeletal Systems

29-*Vertebral column became structurally adapted to withstand new regional stresses given by the two pairs of limb appendagesAmniotic tetrapod vertebrae are separated into cervical (neck), thoracic (chest), lumbar (back), sacral (pelvic), and caudal (tail) vertebraeIn frogs, birds, and humans, the caudal vertebrae reduced in size and number while the sacral vertebrae are fusedThe python has over 400 vertebrae while the human child has 33 vertebrae and the adult has 5 fused to form the sacrum and 4 form the coccyx or tail bone

Skeletal Systems

29-*Figure 29.9 Human skeleton. A, Ventral view. B, Dorsal view.

29-*Humans also have 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebraeNearly all mammals have 7 cervical vertebraefrom the short necks of dolphins to the long necks of giraffesThe first two cervical vertebrae are present in all vertebratesAtlas is the 1st cervical vertebra and supports the skull while allowing it to pivotAxis is the 2nd cervical vertebra and allows the head to turn side-to-side

Skeletal Systems

29-*Ribs are either long or short skeletal structures that articulate medially with the vertebrae and extend into the body wallFishes have single or paired of ribs for every vertebra that serve as stiffening rods for improved effectiveness of muscle contractionsMany fishes have both dorsal and ventral ribs, some with numerous rib-like intermuscular bonesSome vertebrates have reduced ribs The Leopard frog that has no ribs at allMammalian ribs form a thoracic basket to prorect the heart, lungs, and other soft body partsSkeletal Systems

Skeletal SystemsSloths have 24 pairs of ribs, while horses have 18 pairsPrimates other than humans have 13 pairs of ribsHumans generally have 12 pairs; some have a rare 13th pairMost vertebrates and fishes have paired appendagesMost fishes, except agnathans, have pectoral and pelvic girdles supporting thin pectoral and pelvic finsSome eels lack pectoral or pelvic fins while the Moray eels are lacking in both

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29-*Tetrapods, unless they are limbless, have two pairs of pentadactyl limbs (five-toed) that are supported by respective girdlesThe pentadactyl limb is similar in all tetrapods , alive or extinct, even when these are highly modified for various modes of lifeModifications due to different living environments often involve bone loss or fusion rather than addition of new bonesThe ends of the appendages like fingers and toes are more likely to change

Skeletal Systems

29-*Horses and their relatives have gained speed by elongation of a longer third toe with the horse standing on its third finger nail (hoof)Bird embryos demonstrate distal modification where 13 distinct wrist and hand bones (carpals and metacarpals) and finger bones (phalanges) are reduced to only 4 bones in 3 digits as found in the adultsIn tetrapods, the pelvic girdle is firmly attached to the axial skeleton and absorb the greatest locomotory force transmitted by hind limbsThe pectoral girdle is more loosely attached to provide forelimbs with greater freedom for manipulationSkeletal Systems

29-*Effect of body size on bone stress follows what Galileo realized in 1638:The ability of limbs to support a load decreases as the animals increase sizeConsider one animal twice as long, wide, and tall as a second animal:The larger animal has eight times the volume and eight times the weightThe strength of the legs, however, is based on the cross-sectional area of bones, tendons and muscles, which is only four times greaterTherefore, eight times the weight is to be carried by four times the strengthSkeletal Systems

29-*Mammalian bone is uniform per cross-sectional area, which places an upper limit on overall sizeBone shape in different sized animals does not change much, so many mammals adapted by shifting limb posture to align with body axisBones and muscles are capable of carrying more weight when aligned closely with the ground reaction force, as in the horses legPeak bone stresses during strenuous activity is no greater for a galloping horse than for a running chipmunkElephants and large dinosaurs had thick and robust bones but this decreases running speedSkeletal Systems

29-*Figure 29.10 Comparison of postures in small and large mammals, showing the effect of scale.

29-*Animal MovementMovement is an important characteristic of animals and includes streaming of cytoplasm and massive muscular movementsAnimal movement relies on a fundamental mechanism called contractile proteins that facilitate relaxation and contractionContractile machinery is composed of ultrafine fibrils that are arranged to relax or contract when powered by ATPThe most important protein contractile system is composed of actin and myosin

29-*The actomyosin system is almost a universal biomechanical systemFound from protozoa to vertebrates with a diverse set of functional rolesHowever, cilia and flagella are composed of proteins other than actin and myosinThe three principal types of animal movement areAmeboidCiliary and flagellarMuscular

Animal Movement

29-*Ameboid movement:Occurs in wandering cells of metazoansIs characteristic of amebas and other unicellular formsAlso occurs in macrophages, white blood cells, embryonic mesenchyme, and other mobile cells that move in tissue spacesAmeboid cells change shape by extending and withdrawing pseudopodia (false feet) Non-granular gel-like ectoplasm that encloses a more liquid endoplasmAnimal Movement

Animal MovementMovement depends on actin, actin-binding proteins, and other regulatory proteinsUnder one model, as the pseudopod extends, hydrostatic pressure forces actin subunits into the pseudopod, the subunits dissociate from actin-binding proteins and reassemble into a network to form a gel-like ectoplasmAt trailing edge of the gel, the network disassembles; actin filaments interact with myosin to create a contractile force that pulls the cell along behind the extending pseudopodLocomotion is assisted by membrane-adhesion proteins that attach temporarily to substrate, providing traction that enables the cell to crawl

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29-*Ciliary and flagellar movement Are particularly distinctive for ciliated unicellular eukaryotesOccur in all animal groups except nematodes and arthropodsCilia are minute, hairlike, motile processes that extend from surfaces of many animal cells Function to move whole unicellular organisms and ctenophores in their aquatic environmentsAlso used to propel fluids and materials across epithelial surfaces in larger animalsAnimal Movement

Animal MovementAll cilia have a uniform diameter of 0.2 to 0.5 micrometers and a basal body (kinetosome) similar to centriolesBasal body gives rise to peripheral circle of 9+2 arrangement of microtubules, forming the structural support and machinery of ciliary movementMicrotubules are composed of a spiral array of tubulin protein subunits Microtubule doublets around the periphery are connected to each other and the central pair by microtubule-associated proteins (MAPs)Extending from each doublet is a pair of arms composed of the MAP called dynein29-*

Animal Movement Dynein arms act as cross bridges between doublets and produce a sliding force between microtubulesDuring ciliary movement, microtubules behave like sliding filaments that move past one another much like vertebrate muscular actionDuring ciliary flexion, dynein arms link to adjacent microtubules then swivel and release in repeated actions, causing the microtubules on one side to slide outwards past the microtubules on the other sideDuring the recovery stroke, the microtubules of the opposite side slide outward to bring the cilia back into its starting position

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29-*Figure 29.11 A, Longitudinal and cross section of a cilium showing the microtubules and microtubule-associated proteins (MAPs) B, Electron micrograph of section through several cilia. (x133,000)

29-*Flagella occur in flagellated protozoans, animal spermatozoa, and in spongesThe flagellum is whiplike, longer than a cilium, and occurs singularly or in small numbers at one end of the cellFlagella have the same basic internal structure as cilia although several exceptions to this 9+2 arrangement are in the sperm tails of flatworms (9+1) and mayflies (9+0)Cilia and flagella differ more in their beating patterns than in structureA flagellum beats symmetrically with snakelike undulations to propel water parallel to the long axis of the flagellum

Animal Movement

29-*Figure 29.12 A, Flagellum beats in wavelike undulations, propelling water parallel to its main axis B, Movement of cilia in comb plates of a ctenophore.

29-*A cilium beats asymmetrically with a fast power stroke in one direction followed by a slow recovery, wherein water is propelled parallel to the ciliated surface Muscular movement occurs via contractile tissue called muscle fibers and are the most highly developed form of muscle cellsMuscle fibers generally work only by contraction and cannot actively lengthenCan be arranged in a variety of ways to make every movement possible

Animal Movement

29-*The types of vertebrate muscles are characterized by appearance: skeletal, cardiac, and smooth muscles Skeletal (striated) muscles are transversely striped with alternating dark and light bands (striations) and are multinucleatedOrganized into sturdy, compact bundles that are mostly attached to skeletal elements that move the trunk, appendages, eyes, respiratory organs, mouthparts, and other body structuresMuscle fibers are long cylindrical cells that are packed together in bundles called fascicles and enclosed by tough connective tissue

Animal Movement

29-*Figure 29.13 Photomicrographs of types of vertebrate muscle. A, Skeletal muscle (human) showing several striated fibers B, Cardiac muscle(monkey) is striated, similar to skeletal muscle, C, Smooth muscle (human) showing absence of striations.

29-*Fascicles are grouped into a discrete muscle enclosed by another layer of thick connective tissue Some muscles taper at ends as they connect to bones via tendons, while others are flattened sheets as in abdominal musclesSkeletal muscles can contract powerfully and quickly, but fatigues more rapidly than smooth muscleGenerally called voluntary muscle as these are stimulated by motor fibers under conscious control

Animal Movement

29-*Figure 29.14 Organization of skeletal muscle from gross to molecular level.

29-*Cardiac muscle is the tireless muscle of the vertebrate heart; it shares some characteristics of skeletal muscleMade of closely opposed, separated uninucleated cells joined by junctional complexes within vertical bars called intercalated discsFast acting, striated, and with similar contraction mechanism as skeletal muscle but has involuntary autonomic and hormonal control like smooth muscleHeart beat originates within a specialized cardiac muscle and can continue to beat outside of the bodyAnimal Movement

29-*Smooth (visceral) muscle lacks striations and the cells are much smaller, tapering at both ends with a single, central nucleusCells interdigitate with each other such that the tapered ends of one cell is next to the central nuclear region of the next cellSmooth muscle cells form sheets of muscle circling the walls of the alimentary canal, blood vessels, respiratory passages, and urinary and reproductive ducts and cavitiesUsually slow acting and can maintain prolonged contractions with little energy use Normally controlled by the autonomic nervous system, hormones and local regulatory systems Animal Movement

Animal MovementSmooth muscle contractions are involuntary and unconscious; function by sustained contractions and relaxationsMost smooth muscles push material through a tube like the intestines or regulate tube diameter during blood flow or air flowTypes of invertebrate muscles include variations of smooth, striated, and oblique striated musclesStriated muscles are found in a variety of cnidarians and arthropodsGiant barnacles and Alaskan king crabs have giant muscle fibers that 3 mm wide by 6 cm long

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29-*Bivalve molluscan muscle fibers are of two types- striated and smooth musclesScallops use fast striated muscle fibers to close valves during swimming actions as these can contract rapidlyA slower smooth muscle is able to sustain long-lasting contraction for hours or days Slow adductors use very little energy and require very little neural stimulation to remain contractedThe contracted state resembles a catch mechanism with low rate of cross-bridge cycling between contractile proteins within the muscle fibers

Animal Movement

29-*Insect flight muscles can beat their wings more than 1,000 beats per secondThis fibrillar muscle contracts at frequencies much faster than any vertebrate muscle but has limited extensibilityThe wing leverage system is arranged so the muscles shorten very little during each downbeat; both muscles and wings operate as a rapidly oscillating system in an elastic thoraxMuscles recoil elastically, are activated by stretch during flight, and require excitatory neural signals periodically with one signal per 20 to 30 contractionsAnimal Movement

29-*Structure of striated muscle is from the periodic bands visible under the light microscopeEach cell or fiber is a multinucleated tube with many myofibrils packed together and surrounded by a cell membrane called the sarcolemma Myofibrils contains two filaments of proteins called myosin and actinActin extends in parallel filaments from a dense protein complex called the Z lineSarcomere is the functional unit of myofibrils, extending between successive Z linesAnimal Movement

29-*Myosin filament is composed of myosin molecules packed together in a bundleEach myosin molecule consists of two polypeptide chains, each with a club-shaped head regionTwo myosin bundles are held end-to-end at the center of each sarcomereThe double heads of each myosin molecule face outward from the center of the filament and point towards the Z lineThe heads act as binding sites for ATP and form molecular cross bridges that interact with the actin filaments during muscle contractionAnimal Movement

29-*Figure 29.15 Molecular structure of actin and myosin filaments of skeletal muscle A, The myosin molecule. B, The myosin filament extended towards actin filaments. C, The actin filament.

29-*Actin filaments are made of a backbone of double stranded actin twisted into a double helix and two actin-binding proteins called tropomyosin and troponinEach tropomyosin is a double helix that lies near the grooves between the actin strandsTroponin is a complex of three globular proteins located at intervals along the actin filament that act as a calcium-dependent switch that control contraction Actin filament complexes extend outward from both sides of the Z line and overlap myosin bundles towards the sarcomereAnimal Movement

Animal MovementNebulin regulates actin length and the elastic protein titin support and anchor the myosin to the middle of the sarcomere at the M lineSliding filament model of muscle contraction was independently proposed in the 1950s by A.F. Huxley and H.E Huxley to explain contractionThe actin and myosin filaments link together by molecular cross bridges and then act as levers to pull the filaments past each other

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29-*The club shaped heads of the myosin filaments form cross bridges that snap rapidly back and forth, attaching and releasing from special receptor sites on the actin filamentsThis ratcheting action draws the actin past the myosin and pulls the Z lines together All sarcomere units shorten together as the muscle contractsRelaxation is passive: when the cross bridges between the filaments release, the sarcomeres are free to lengthenThis requires some force, usually supplied by recoil of elastic fibers within the muscle, and by antagonistic muscles or by gravity

Animal Movement

29-*Figure 29.16 Sliding-filament hypothesis, showing how actin and myosin filaments interact during contraction. A, Muscle relaxed. B, Muscle contracted.

29-*Muscles contract in response to nerve control and stimulationIf a nerve to a muscle is severed, the muscle atrophies or wastes awaySkeletal muscles are innervated by motor neurons whose cell bodies are located in the central nervous system (brain and spinal cord)Each cell body leads to a motor axon that leaves the brain and spinal cord, travels through the peripheral nerve trunk, and branches to many terminal points on a muscleEach terminal branch innervates a single muscle fiber, while a single motor axon may innervate a few fibers for precise control like the eyeAnimal Movement

29-*Large muscle groups like the leg can have single motor axons controlling up to 2,000 muscle fibersA motor neuron and all of the muscle fibers it innervates are called a motor unitWhen a motor neuron fires, the action potential passes simultaneously to all motor units and each is contracted simultaneouslyThe total force of muscle contraction depends on the number of motor units activatedPrecise control of movement requires varying number of motor units activated at one timeMotor unit recruitment is a steady increase in muscle tension by increasing motor unitsAnimal Movement

29-*The neuromuscular (myoneural) junction is the place where the motor axon terminates on a muscle fiber At this junction, there is a synaptic cleft, which separates the nerve terminal from the muscle fiberNeuron stores acetylcholine in small synaptic vesicles near the synaptic cleftWhen the nerve signal or action potential reaches the synapse, the acetylcholine is released and acts as chemical neurotransmitterAcetylcholine causes depolarization of the muscle fiber membrane by binding to receptor sites and induces muscle contraction

Animal Movement

29-*Synapse provides a chemical bridge that couples the nerve impulse and muscle fibersVertebrate skeletal muscles have elaborate conduction system that carries the depolarization from the neuromuscular junction to the densely packed filaments of the muscle fiberNumerous invaginations on the sarcolemma surface project into muscle fibers called T-tubulesT-tubule system is continuous with the sarcoplasmic reticulum (specialized endoplasmic reticulum) that runs parallel to the actin and myosin filaments, where it releases calcium to enable muscle contraction

Animal Movement

29-*Figure 29.17 Section of vertebrate skeletal muscle showing a nerve-muscle synapse (neuromuscular or myoneural junction)

29-*Excitation-contraction coupling occurs when electrical depolarization of the sarcolemma and t-tubules activate the contractile systemIn resting muscle, contraction does not occur since the tropomyosin strands around the actin filaments block the myosin heads from attaching to actinWhen muscle is stimulated, the action potential is transmitted down the t-tubulesElectrical depolarization causes Ca+2 to be released from sarcoplasmic reticulum; it then binds with troponinAnimal Movement

Animal MovementTroponin changes shape, shifts the tropomyosin out of its blocking position, and allows active sites on actin filaments to be exposed Myosin heads binds to active site and form cross bridges between the adjacent myosin and actin filamentsMuscle action follows a series of attach-pull-release cycle or cross-bridge cycling Release of bond energy from ATP activates the myosin head that swings 45 degrees and releases a molecule of ADPThis power stroke pulls the actin filament about 10 nanometers in distance

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29-*Movement stops when another ATP molecule binds to the myosin head and thus freeing it from the active siteShortening continues as long as nerve action potential arrive at the neuromuscular junction and that free calcium remains availableThe cross-bridge cycling can repeat 50100 times per second in pulling actin and myosin filaments past each otherEach sarcomere shortens a very small distanceThis distance is multiplied by the thousands of sarcomeres lying end-to-end in muscle fiber, such that strongly contracting muscle may shorten by one-third of its length

Animal Movement

29-*When stimulation stops, calcium is pumped back into sarcoplasmic reticulumTroponin resumes its original configuration and tropomyosin moves back to its blocking position on the actin, leading to muscle relaxationLarge amounts of energy is needed for muscle contractionATP is the immediate source of energy and is normally present at constant levelsAerobic metabolism catabolizes glucose that is transported through the blood to produce ATPAnimal Movement

29-*Figure 29.18 Excitation-contraction coupling in vertebrate skeletalmuscle. Step 1: An action potential spreads along the sarcolemma Step 2: Myosin forms cross bridges Step 3: Using ATP, the myosin head swings toward the center of the sarcomere Step 4: The myosin head binds another ATP Step 5: The myosin head splits ATP, retaining the energy.

29-*Glycogen is stored within the muscles to supply glucose for ATP productionIt is a polysaccharide chain of glucose molecules that is stored in the liver and musclesAbundant as more than three-fourths of all glycogen is stored in musclesCan be mobilized quickly to provide energy in both aerobic and anaerobic conditionsMuscles also have an energy reserve called creatine phosphate that is a high-energy phosphate compound stored during restCreatine phosphate releases stored bond energy to convert ADP to ATP

Animal Movement

29-*Different muscle types, like slow and fast oxidative fibers, rely heavily on glucose and oxygen transported by bloodIf muscle contraction is not too vigorous or prolonged, glucose is completely oxidized to CO2 and water by aerobic respirationDuring prolonged heavy exercise, blood flow cannot provide enough oxygen for complete oxidation of glucoseMuscles must then rely on energy from anaerobic glycolysisAnaerobic glycolysis is not as efficient as aerobic respiration but is needed for all forms of heavy muscular exertion

Animal Movement

29-*Fast glycolytic fibers rely exclusively on anaerobic glycolysis for energyAnaerobic glycolysis degrades glucose to lactic acid to release energy Lactic acid accumulates in the muscle and diffuses rapidly into general circulationContinued muscular exertion causes a buildup of lactic acid that leads to muscle fatigue that was initially thought to be due to decreased pH and enzyme inhibitionRecent evidence suggests that muscle fatigue in muscles relying on creatine phosphate may be due to accumulation of inorganic phosphate

Animal Movement

29-*Anaerobic pathway is self-limiting; continued heavy exertion leads to exhaustionMuscles incur an oxygen debt because accumulated lactic acid must be converted to pyruvic acid, which can be fed into the Krebs Cycle via conversion to Acetyl-CoALactic acid is then oxidized by extra oxygen as the oxygen debt gets repaid via increased oxygen consumption, even after muscle exertion has ended Oxygen replenishment continues until all lactic acid has been oxidized in the body and glycogen is resynthesized

Animal Movement

29-*Muscle performance depends on the type of muscle fiber Slow oxidative fibers (red muscle fibers) are specialized for slow, sustained contractions without fatigue These fibers function in postural musclesContain extensive blood supply (red color), a high density of mitochondria for constant ATP supply, and abundant stored myoglobin that supplies additional stored oxygenTwo kinds of fast fibers capable of fast, powerful contractions but with different energy production pathways

Animal Movement

29-*Fast glycolytic fibers (white muscles) lack efficient blood supply, have low density of mitochondria and myoglobin, and thus fatigue easily when usedUsually pale in color and function anaerobically, as exemplified by the white meat of chicken breast and running muscles of catsDuring a chase, such muscles rapidly develop an oxygen debt in less than a minute Cheetahs must rest 3040 minutes after a chaseHuman weight lifters favor these muscles and can not sustain lifting heavy objects for long periods of timeAnimal Movement

29-*Fast oxidative fibers have extensive blood supply and high density of mitochondria and myoglobin Functions aerobically and is used for rapid, sustained activities since the muscles are fatigue resistantMigratory birds, like geese and swans, dogs, and ungulates have limb muscles with a high percentage of fast oxidative fibers capable of active locomotion for long periodsMost muscles possess a mixture of the three different types of muscle fibers to permit a wide range of activities

Animal Movement

29-*Importance of tendons in energy storage is due to stored elastic strain energy during walking and runningThe Achilles tendon is stretched by the combination of downward force of the body and the contraction of the calf musclesAs tendon recoils, this extends the foot while the muscle is still contracted and propels the leg forwardKangaroo uses the recoil energy in tendons to bounce along called the bouncing ball principleAnimal Movement

Animal MovementThis bouncing ball type of movement uses far less energy than would be required if every step relied solely on alternate muscle contraction and relaxationElastic storage of energy also occurs in the legs of grasshoppers and fleas, wing hinges of flying insects, hinge ligaments of bivalve molluscs, and the dorsal ligament (ligamentum nuchae) that supports the head of hoofed mammals during running29-*

29-*Figure 29.19 Energy storage in the Achilles tendon of human and kangaroo legs.