Action and support: the muscles and skeleton

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Action and support: the muscles and skeleton. Chapter 40, pages 774-791. Muscles and Skeleton Work Together. Animalsjellyfish, earthworms, crabs, horses, and peoplemove using the same fundamental mechanism: - PowerPoint PPT Presentation



  • Muscles and Skeleton Work Together Animalsjellyfish, earthworms, crabs, horses, and peoplemove using the same fundamental mechanism:

    Contracting muscles exert forces on the skeleton and cause the body to change shape

    A body with muscles but no skeleton would not have coordinated movement

    A skeleton without muscles remains in one position

  • Types of SkeletonsTypes of skeletons

    Hydrostatic skeletons Exoskeletons Endoskeletons

    Coordinated movement is produced by alternating contractions of antagonistic muscles Antagonistic muscles act on each type of skeleton to provide movement

  • Hydrostatic Skeleton Worms, cnidarians and many mollusks (snails, octopuses)

    A hydrostatic skeleton is a sac or tube filled with a liquid

    Hydrostatic means to stand with water, which is how hydrostatic skeletons function

    A water-filled balloon stands up because it contains water, but if punctured it collapses The volume of the balloon is fixed, but you can change its shape by squeezing

  • Earthworm MovementAn animal with a hydrostatic skeleton controls the overall shape of its body using two sets of antagonistic muscles -circular and longitudinal

    For an earthworm to move forward it uses wavelike, alternating contractions of longitudinal and circular muscles Setae hold the front of the worm in placeThe worm first contracts its longitudinal muscles in its front end, so it becomes shorter and fatter Other longitudinal muscles in the middle and tail contract, making it shorter

    Earthworm Locomotion

  • The worm contracts circular muscles in its front half, making that half longer and thinner When the worm is fully extended, longitudinal muscles in the head contract again, fattening and anchoring the head As the wave of circular muscle contraction moves down the worm, the tail gets thin Longitudinal muscle contraction in the back half of the worm pulls the tail up toward the head This cycle is repeated over and over as the worm crawls through the soil

  • Hydrostatic Skeleton (a) Hydrostatic skeletonCircular musclescontractLongitudinalmuscles relaxCircular musclesrelaxliquidliquidLongitudinalmuscles contract

  • ExoskeletonArthropods (spiders, crustaceans) and insects, have rigid exoskeletons outside skeletons

    Movement occurs at joints of the legs, mouthparts, antennae, base of the wings, and body segments

    Thin, flexible tissue joins stiff sections of exoskeleton

    Antagonistic muscles attach to opposite sides of the inside of a joint, contraction causes movement

    Contraction of a flexor muscle bends a joint; contraction of an extensor muscle straightens a joint

    Alternating contraction of antagonistic muscles moves the joints

  • Exoskeleton (b) ExoskeletonFlexor musclecontractsExtensor musclecontractsExtensor musclerelaxesFlexor musclerelaxes

  • Molting

    The exoskeleton cannot expand, an arthropod molt its exoskeleton so that it can grow (27 times in up to 3 yrs)

  • EndoskeletonRigid structures found inside the bodies of echinoderms and chordates

    Movement also occurs primarily at joints, where two parts of the skeleton are attached to one another

    Biceps - a flexor and triceps extensor attach on opposite sides of the outside of a joint and move the joint back and forth, or rotate them in one direction or the other

  • Endoskeleton (c) EndoskeletonFlexor muscle(biceps) contractselbowExtensor muscle(triceps) relaxesFlexor musclerelaxesExtensor musclecontracts

  • Functions of Vertebrate Skeleton Provides a rigid framework that supports the body and protects its internal organs

    Allows locomotion

    Participates in sensory function

    Bones produce red blood cells, white blood cells, and platelets in red bone marrow

    Store calcium and phosphorus

  • Skeletal CategoriesThe axial skeleton, which includes the bones of head, vertebral column, and rib cage

    The appendicular skeleton pectoral, pelvic girdles and the appendages attached to them

  • Structure of Vertebrate Skeletons Three types of connective tissuecartilage, bone, and ligamentmake up the skeleton All are living cells embedded in a matrix of collage protein, with various other substances included in the matrix

    Bone - larger amounts of minerals composed mostly of calcium and phosphate, and is hard and rigid

    Cartilage contains large amounts of glycoproteins and includes elastic fibers, which make some cartilages flexible

    Ligaments hold bones together at joints and have small amounts of elastic fibers

  • Cartilage plays many rolesProvides flexible support and connections In some fishes (sharks and rays) the entire skeleton is composed of cartilage

    During embryonic development, the skeleton (except for skull and collarbone) is first formed as cartilage, and later replaced by bone

  • Skeletal Development

  • More Cartilage FunctionsCovers the ends of bones at joints

    Supports the flexible portions of the nose and external ear

    Provides the framework for the larynx, trachea, and bronchi of the respiratory system

    Forms the tough, shock-absorbing intervertebral discs between the vertebrae of the backbone

  • Cartilage StructureChondrocytes are the living cellsSecrete the glycoproteins and collagen that make up the matrix No blood vessels penetrate cartilage To exchange wastes and nutrients, chondrocytes rely on diffusion of materials through the collage matrix Cartilage cells have low metabolic rate, damaged cartilage repairs itself slowly, if at all

  • BoneHard outer shell of compact bone encloses spongy bone Compact bone is dense and strong, provides an muscle attachment site Develops as small tubes called osteons with collagen and calcium phosphate surrounding a central canal containing blood vessels

    Spongy bone is an open network of bony fibers Porous, lightweight, rich in blood vessels Red bone marrow is found in the cavities of spongy bone

  • Cartilage and Bone compactbonespongybone(containsmarrow)cartilagechondrocytescollagenmatrixosteonosteocytescentralcanalblood vessels

  • Bone CellsThere are three types of bone cells: Osteoblastsbone-forming cells Osteocytesmature bone cells Osteoclastsbone-dissolving cells

    Early in development, when bone replaces cartilage in the skeleton, osteoclasts invade and dissolve the cartilage Ostoblasts secrete a hardened matrix of bone and gradually become entrapped within it

  • As bones mature, the trapped osteoblasts mature into osteocytes Not capable of enlarging a boneEssential to bone health because they rework the calcium phosphate deposits, preventing excessive crystallization that would make the bone brittle

  • Bone Remodeling Allows skeletal repair and adaptation to stressEach year, 5% -10% of your bone is dissolved.

    Replaced by the coordinated activity of osteoclasts that secrete acid and dissolve small amounts of bone, and osteoblasts that secrete new bone This process allows the skeleton to alter its shape in response to demands placed on it Bones that carry heavy loads or are subjected to extra stress become thicker, providing more strength and support

  • Bone remodeling varies with age Early in life, the activity of osteoblasts outpaces that of osteoclasts, allowing bones to become larger and thicker as a child grows

    In the aging body, however, the balance shifts to favor osteoclasts, and bones become more fragile as a result Although both sexes lose bone mass with age, this is typically more pronounced in women

  • Broken Bone RepairThe ultimate bone remodeling occurs after a fracture healing takes about 6 weeksTypically, the ends of the broken bone are put back into proper alignment

    A clot is formed surrounding the broken endsCartilage replaces the clotBone replaces the cartilageCompleted when mature bone completely replaces cartilage, etc.

  • Bone Repair Blood fromruptured bloodvessels forms aclot surroundingthe ends of thebroken bone1 Healing beginswhen a callus ofcartilage replacesthe clot2 Bone gradually replaces thecartilage in thecallus3 When maturebone completelyreplaces the callusand the originalshape of the bonehas been mostlyrestored, thefracture is healed4largebloodclotcompact bonespongy bone

  • Muscles produce force by contracting A muscle can only contract or not contract

    Muscle lengthening is passive, occurring when muscles relax and are stretched by other forces such as: contractions of other musclesweight of a limbpressure from food

    Coordinated movement is produced by alternating contractions of muscles with opposing actions by antagonistic muscles

  • Structures of Vertebrate Muscles The muscles of all animals have striking similarities in both the cellular components that produce contractions and in the structural arrangement of these components The details of muscle structure and function, however, show a tremendous range of adaptations For example, clams possess a special type of muscle that holds their shells tightly closed for hours using very little energy Some flies have flight muscles that can contract 1,000 times per second

  • Types Vertebrate MuscleSkeletal, cardiac, and smooth

    All work on the same basic principles but differ in function, appearance, and control

  • Skeletal muscle Moves the skeletonCells are striated MultinucleateVoluntary or conscious control Contractions range from quick twitches to powerful, sustained tension Many nuclei located just beneath the cells plasma membrane; largest fibers have several thousand nuclei

  • Cardiac muscle StriatedOne nucleus per cellBranched cellsLocated only in the heart

    Initiates its own contractions, but is influenced by nervous system and hormones Biofeedback training allows some people to regulate their heartbeat

  • Smooth muscle Not striated

    Spindle shaped

    One nucleus per cell

    Surrounds large blood vessels and most hollow organs, producing slow, sustained contractions Involuntary Control

  • Skeletal Muscle Cell StructureHighly organized, repeating structures Skeletal muscle consists of a series of nested, repeating parts

    Skeletal muscles are encased in connective tissue sheaths and attached to the skeleton by tendons Within the muscles outer sheath, individual muscle cells called muscle fibers are grouped into bundles by further coverings of connective tissue

  • More Details Blood vessels and nerves pass through the muscle in the spaces between the bundles

    Each individual muscle fiber has its own thin connective tissue wrapping These multiple connective tissue coverings, each connected to the others, provide the strength needed to keep the muscle from bursting apart during contraction

    Muscle cells are among the largest cells in the human body, ranging from 10 - 100 micrometers in diameter and some run the entire length of a muscle, so they can be over 30 centimeters long

  • Skeletal Muscle Structure tendon (connectsto bone)skeletal muscleconnective tissuenerves andblood vesselsbundle of muscle cellsmuscle fiber(muscle cell)myofibril

  • Individual muscle fibers contain many parallel cylinders called myofibrils

    Each myofibril is surrounded by a specialized type of endoplasmic reticulum called a sarcoplasmic reticulum

    SR is flattened, membrane-enclosed compartments filled with fluid containing a high concentration of calcium ions

  • The plasma membrane that surrounds each muscle fiber tunnels deep into the inside of the cell at regular intervals, producing tubes called T tubules T tubules encircle the myofibrils, running between and closely attached to segments of the SR Each myofibril has repeating subunits called sarcomeres that are aligned end to end along the length of the myofibril, connected to one another by protein discs or Z lines Within each sarcomere is a precise arrangement of thin and thick protein filaments Each thin filament is anchored to a Z line at one end Suspended between the thin filaments are thick filaments

  • Animation: Muscle Structure

  • Thin and thick filaments of myofibrils are composed of actin and myosin, they interact to contract the muscle fiber A myofibril also contains smaller amounts of other proteins hold the fibril together, attach the thin filaments to the Z lines, and regulate contraction Dystrophin binds thin filaments to proteins in the plasma membrane, which is are attached to extracellular proteins that surround the muscle fiber Dystrophin helps to distribute the forces generated during muscle contraction so the fiber doesnt tear itself apart

  • Individual actin proteins are nearly spherical A thin filament consists of two strands of actin proteins wound about each otherAccessory proteins that regulate contraction called troponin and tropomyosin lie atop the actin A myosin protein is shaped like a hockey sticka head attached at an angle to a long shaft The myosin head is hinged to the shaft and can move back and forth

  • A thick filament consists of a bundle of myosin proteins with a shaft in the middle of the bundle and the heads protruding out The heads of the two ends of the thick filament are oriented in opposite directions

  • (b) A sarcomere(c) Thick and thin filaments(a) Cross-section of a musclefibermyofibrilT tubulesplasmamembranesarcoplasmicreticulumsarcomeremyofibrilthick filamentthin filamentZ linesmyosinthin filamentthick filamenttroponintropomyosinmyosin headsactinaccessoryproteinsmuscle fiberA Skeletal Muscle Fiber

  • Skeletal Muscle ContractionContraction happens through interaction between thin and thick filaments The molecular architecture of thin and thick filaments allows them both to grip and to slide past one another, shortening the sarcomeres and producing muscle contraction by what is called the sliding filament mechanism Each spherical actin protein has a binding site for the myosin head In a relaxed muscle cell, however, these binding sites on actin are covered by tropomyosin, which prevents the myosin heads from attaching

  • When a muscle contracts, tropomyosin moves aside, exposing the binding sites on the active proteins The myosin head binds to these sites, temporarily linking the thick and thin filaments The myosin heads flex, pulling on the thin filaments and causing them to slide a tiny distance along the thick filament The myosin heads on the two ends of each thick filament pull the thin filaments toward the middle of the sarcomere

  • Because thin filaments are attached to the Z lines at the ends of the sarcomere, this movement shortens the sarcomere All of the sarcomeres of the entire muscle fiber shorten simultaneously, so the whole muscle fiber contracts a little

    The myosin heads release the thin filament, extend, reattach farther along the thin filament, and flex again, shortening the muscle fiber a little more, much like a sailor hauling in a long anchor line a little at a time, hand over hand

    The cycle repeats as long as the muscle is contracting

  • Author Animation: Fiber Structure

  • ATPADPthin filamentmyosin (part of a thick filament)myosinheadbinding sitesmyosinheadactintroponintropomyosin Tropomyosin coversthe binding sites, so themyosin head cannotattach1 When the bindingsites of actin are exposed, the myosinhead attaches to abinding site2 The myosin head flexes,pulling the thin filament pastthe thick filament andshortening the sarcomere3 Using energyfrom ATP, themyosin headdetaches from theactin, extends, andthen attaches toanother actinbinding site fartheralong on the thinfilament4The Sliding Filament Mechanism of Muscle Contraction

  • Filament Sliding Shortens Sarcomeres

  • Muscle contraction requires ATPContracting muscles require a lot of energy One might think that the energy is used to flex the myosin head and pull the thin filament along

    The energy of ATP is used not to flex the myosin head, but to extend it and store the energy in this stretched position

    When the head binds to actin, the stored energy flexes the myosin head and pulls the thin filament toward the center of the sarcomere

  • There is another crucial role for ATP in muscle contraction Picture a sailor hauling in an anchor line When he has pulled the line as far as he can with one arm, he must release the rope before he can move this arm further down and grasp the rope again for another pull Similarly, when a myosin head has flexed and pulled on the thin filament, the head must release the actin before the head can extend and bind again at a second location a little further along on the thin filament

  • When ATP binds to a myosin head, it causes the head to release actin

    Only then can the energy of ATP be used to extend the head, storing that energy to use during the next pull on the thin filament

  • A skeletal muscles reserves of ATP are used up after only a few seconds of high-intensity exercise Skeletal muscles also stock a supply of creatine phosphate, an energy-storage molecule that can donate a high-energy phosphate to ADP, thus regenerating ATP However, creatine phosphate is also depleted rapidly During brief, high-intensity exertion, muscle cells generate a bit more ATP using glycolysis, which does not require oxygen but is also not very efficient For prolonged or low-intensity exercise, muscle cells produce ATP from glucose and fatty acids using cellular respiration, which requires a continuous supply of oxygen delivered to the muscles by the cardiovascular system

  • Nervous SystemThe nervous system controls contraction of skeletal muscles Skeletal muscle contraction is voluntaryWe have already seen that moving the accessory proteins away from the binding sites on actin begins the cycle of myosin head movements that cause skeletal muscle fibers to contract What links activity in the nervous system and the position of the accessory proteins?

  • Muscle fibers can fire action potentials, much like neurons Action potentials in muscle fibers cause the fibers to contract The role of the nervous system is to trigger action potentials in muscle fibers Motor neurons, mostly in the spinal cord, send axons out to the skeletal muscles These axons innervate muscle fibers at specialized synapses called neuromuscular junctions

  • All vertebrate neuromuscular junctions use the neurotransmitter acetylcholine Each action potential in a motor neuron releases enough acetylcholine to produce a huge excitatory postsynaptic potential in the muscle fiber, bringing its membrane potential above threshold and triggering an action potential

  • The muscle fibers action potential moves down the T tubules to the SR, where it causes calcium ions (Ca2+) to be released from the SR into the cytoplasmic fluid surrounding the thin and thick filaments Ca2+ binds to the smaller accessory protein, troponin, causing it to pull the larger accessory protein, tropomyosin, off the actin binding sites With tropomyosin out of the way, myosin heads can bind to actin The myosin heads repeatedly attach, flex, extend, and reattach to actin, pulling the thin filament toward the center of each sarcomere

  • Animation: Fiber Function

  • Activity in a Motor Neuron Stimulates Contraction of a Skeletal Muscle Fiber

  • A single action potential in a muscle fiber causes all of its sarcomeres to shorten simultaneously, slightly shortening the fiber What makes the fiber stop contracting? When the action potential in the muscle fiber is over, the SR stops releasing Ca2+ Active transport proteins in the membrane of the sarcoplasmic reticulum pump Ca2+ back into the SR Ca2+ leaves the accessory proteins, which move back over the active binding sites Therefore, the myosin head can no longer attach to actin, and contraction stops within a few hundredths of a second

  • Regulating the intensity of contraction To control the force, distance, and duration of muscle contraction, you must be able to control how many muscle fibers in a single muscle contract, how they contract, and how long they contract How does this work? First, a single motor neuron typically synapses with several muscle fibers in a single muscle A motor neuron and all the muscle fibers that it innervates are called a motor unit

  • Motor units vary in size In muscles used for fine control, such as those that move the eyes or fingers, motor units are small A single motor neuron may synapse on just a few muscle fibers In muscles used for large-scale movements, such as those of the thigh and buttocks, motor units are large A single motor neuron may synapse on dozens or even hundreds of muscle fibers

  • Second, the nervous system controls the strength of muscle contraction by varying both the number of muscle fibers stimulated and the frequency of action potentials in each fiber Because motor neurons synapse on multiple muscle fibers in a given muscle, and because the muscle fibers are attached to one another and to the muscles tendons, a single action potential in a single motor neuron will cause some contraction of the entire muscle

  • The contractions caused by a single motor neuron firing multiple action potentials in rapid succession add up to a larger contraction Firing multiple motor neurons that innervate fibers in the same muscle will also cause a larger contraction of the muscle Finally, rapid firing of all the motor neurons that innervate all of the fibers in the muscle will cause a maximal contraction

  • Muscle Fibers are SpecializedSpecialized for different types of activity Two basic types, slow twitch and fast twitch

    Slow-twitch and fast-twitch fibers have different forms of myosin, causing them to contract slowly or more rapidly

  • Slow-twitch FibersContract with less power, but can keep on contracting for a very long time Have lots of mitochondria and a plentiful blood supply that provides oxygen for cellular respiration in the mitochondria

    Slow-twitch fibers are thin Thin fibers packed with mitochondria have fewer myofibrils, but they trade the resulting decreased power for rapid diffusion of oxygen in and wastes out Thus, slow-twitch fibers produce abundant ATP and have fewer filaments to use it up, so they resist fatigue

  • 40.3 How Do Skeletal Muscles Contract? Fast-twitch fibers, on the other hand, contract more powerfully They have a smaller blood supply, fewer mitochondria, and a larger diameter Thick fibers with relatively few mitochondria have more myofibrils and are therefore more powerful The extreme versions of fast-twitch fibers use mostly glycolysis for energy production, which does not require oxygen but supplies a lot less ATP than cellular respiration does Fast-twitch fibers fatigue more rapidly than do slow-twitch fibers

  • 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle? Although all muscle cells are built on the same general principlesfilaments of actin and myosin attaching and sliding past one anothercardiac and smooth muscles differ significantly from skeletal muscles

  • 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle? Cardiac muscle powers the heart Cardiac muscle, like skeletal muscle, is striated due to its regular arrangement of sarcomeres with their alternating thick and thin filaments The fibers of cardiac muscle are branched, smaller than most skeletal muscles cells, and possess only a single nucleus

  • 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle? Cardiac muscle powers the heart (continued) Because cardiac muscles must contract around 70 times each minute, and sometimes much faster, for your whole life, cardiac muscle fibers have enormous numbers of mitochondria, which occupy as much as 25% of the volume of the fibers Unlike skeletal muscle fibers, cardiac muscle fibers can initiate their own contractions This ability is particularly well developed in the specialized cardiac muscle fibers of the hearts pacemaker

  • 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle? Cardiac muscle powers the heart (continued) Action potentials from the pacemaker spread rapidly through gap junctions in the intercalated discs that interconnect cardiac muscle fibers Strong cell-to-cell attachments in the intercalated discs, called desmosomes, hold cardiac muscle fibers firmly to one another, preventing the forces of contraction from pulling them apart

  • 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle? Smooth muscle produces slow, involuntary contractions Smooth muscle surrounds blood vessels and most hollow organs, including the uterus, bladder, and digestive tract Smooth muscle cells are not striated because the thin and thick filaments are scattered throughout the cells Like cardiac muscle fibers, smooth muscle fibers each contain a single nucleus

  • Smooth muscle fibers are directly connected to one another by gap junctions, allowing the cells to contract in synchrony

    Smooth muscle contraction is either slow and sustained (such as the constriction of arteries that elevates blood pressure during times of stress) or slow and wavelike (such as the waves that move food through the digestive tract)

  • Smooth muscle stretches easily, as can be observed in the bladder, the stomach, and the uterus

    Smooth muscle contraction is involuntary and can be initiated by stretching, hormones, signals from the autonomic nervous system, or by a combination of stimuli

  • Almost all animals move by the action of pairs of antagonistic muscles working on a skeleton Not all joints are movable; for example, immobile joints called sutures join the bones of the skull In movable joints, however, the portion of each bone that forms the joint is coated with a layer of cartilage; its smooth, resilient surface allows the bone surfaces to slide past one another with relatively little friction Joints are held together by ligaments that are strong and flexible but usually not very elastic Tendons attach muscles to the bones

  • tendon: insertionof quadricepsfemurkneecapcartilageligament: kneecapto tibiatibiaBiceps femoris(flexor): bendsthe legtendon: insertionof biceps femorisligament: femurto fibulafibulaQuadriceps(extensor):straightensthe legThe Human Knee

  • How Do Muscles Move the Skeleton? When one of a pair of antagonistic muscle contracts, it moves the bone around its joint and simultaneously stretches the relaxed opposing muscle Antagonistic muscles can cause a remarkable range of motions depending on the configuration of a joint, including moving bones back and forth, moving them side to side, or rotating them

  • Hinge JointsElbows, knees, and fingers

    These joints move in only two dimensions The antagonistic muscle pairthe flexor and extensor muscleslies in roughly the same plane as the joint

    The tendon at one end of each muscle, called the origin, is fixed to a bone that remains stationary while the other end, the insertion, is attached to the bone on the far side of the joint, which is moved by the muscle

  • When the flexor muscle contracts, it bends the joint; when the extensor muscle contracts, it straightens the joint Contraction of the biceps femoris (the flexor) bends the leg at the knee, while contraction of the quadriceps (the extensor) straightens it Alternating contractions of flexor and extensor muscles cause the lower leg bones to swing back and forth at the knee joint

  • A Hinge Joint humerusradiusulnahinge joint(elbow)(a) A hinge joint

  • Ball-and-socket Joints Hip and shoulderThe round end of one bone fits into a hollow depression of another Ball-and-socket joints allow movement in several directions The range of motion in ball-and-socket joints is made possible by at least two pairs of antagonistic muscles oriented at angles to each other to move the joint in three dimensions

  • A Ball-and-Socket Joint pelvisball-and-socket joint (hip)femur(b) A ball-and-socket joint


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