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Effectors. Organs of Response. Effectors. enable animals to respond to information include internal organs that maintain homeostasis organs that interact with the environment organs of movement. Effectors. organs that interact with the environment nematocysts of cnidarians

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Effectors l.jpg

Effectors

Organs of Response


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Effectors

  • enable animals to respond to information

  • include

    • internal organs that maintain homeostasis

    • organs that interact with the environment

    • organs of movement


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Effectors

  • organs that interact with the environment

    • nematocysts of cnidarians

    • chromatophores of several groups

    • exocrine glands

    • electric organs



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Effectors

  • organs of movement

    • microtubules

      • chromosomal movements

      • axon growth

      • cilia & flagella

    • microfilaments (+ myosin)

      • cytokinesis

      • endocytosis

      • amoeboid movement


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Organs of Movement

  • muscles are universal among animals

    • mediate whole tissue contractions

    • due to interactions of actin and myosin filaments


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Organs of Movement

  • vertebrate muscles are of three types

    • smooth muscle

      • provides autonomic control of internal organs

      • long, spindle-shaped uni-nucleate cells

      • sheets of cells in direct electrical contact through gap junctions

      • cells depolarize in response to stretching

      • membrane polarity is altered by autonomic neurotransmitters


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smooth muscleFigure 47.1


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Organs of Movement

  • vertebrate muscles are of three types

    • cardiac muscle

      • uninucleate branched cells resist tearing

      • intercalated discs provide intercellular reinforcement

      • sheets of cells are in electrical contact

      • pacemaker cells produce myogenic beat

      • responds to autonomic neurotransmitters


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cardiac muscleFigure 47.1


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Organs of Movement

  • vertebrate muscles are of three types

    • skeletal muscle

      • mediates voluntary movements

      • multinucleate fibers develop from the fusion of many cells

      • muscles consist of bundles of muscle fibers

      • actin/myosin arrangement gives a striated appearance



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Organs of Movement

  • skeletal muscle

    • muscle fiber contains myofibrils

    • myofibrils contain many ordered assemblies of actin & myosin

    • thick myosin filaments are clusters of myosin molecules with free heads

    • six thin actin filaments surround each myosin filament

    • ends of actin filaments overlap ends of myosin filaments




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structure of a myofibril

  • overlapping actin & myosin filaments produce a repeating pattern in muscle fibers

    • bipolar myosin filaments are anchored by the M band within the H zone and titin filaments

    • oppositely directed actin filaments are joined at the Z line within the I band

    • A band encompasses the entire myosin filament

    • sarcomere extends between two Z lines



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Organs of Movement

  • skeletal muscle

    • contraction occurs as actin filaments slide past myosin filaments

    • sarcomeres decrease in length during contractions

      • myosin head binds to actin

      • myosin head changes position

      • myosin head hydrolyzes ATP, releases actin and resets



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Organs of Movement

  • skeletal muscle

    • contractions are initiated by action potentials

    • each motor neuron activates many muscle fibers (motor units)

      • action potential depolarizes motor end plate

      • depolarization causes plasma membrane to fire action potential

      • action potential spreads over surface of plasma membrane and down T tubules



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Organs of Movement

  • skeletal muscle

    • action potential releases Ca2+ from sarcoplasmic reticulum

    • in unstimulated muscle, tropomyosin blocks myosin binding sites & no contraction occurs

    • released Ca2+ binds troponin, exposing myosin binding sites & contraction occurs


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Ca2+ stimulates muscle contractionFigure 47.6


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Organs of Movement

  • muscle contraction

    • sum of contractions of individual fibers

      • spatial summation

        • sum of contractions of several fibers

      • temporal summation

        • sum of sequential contractions of a fiber

    • tetanus - maximum muscle tension

    • tonus - low, resting level of muscle tension


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summation of twitchesFigure 47.7

tetanus


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Muscle strength & performance

  • Fiber types determine endurance & strength

    • Slow twitch & fast twitch

  • Strength is related to length

  • Exercise increases strength& endurance

  • Fuel supply limits performance


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Skeletal Systems

  • work with muscles to produce movement

  • hydrostatic skeletons are found in soft-bodied animals

    • muscular fluid-filled body

      • contraction in one direction causes body to expand in another direction


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alternate radial & longitudinal contraction against an earthworm’s hydrostatic skeletonFigure 47.11


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Skeletal Systems

  • exoskeletons

    • external shells of various compositions

      • provide points of attachment for internal muscles

      • joints allow relative mobility of skeletal segments


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chitinousinsect exoskeleton


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Skeletal Systems

  • endoskeletons

    • internal body scaffolding

    • provide points of attachment for muscles

    • joints allow relative mobility of adjacent bones

    • skeleton consists of two extracellular matrices

      • cartilage - largely collagen

      • bone - collagen + calcium phosphate


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Skeletal Systems

  • endoskeletons

    • bone is constantly being broken down and reformed

      • osteoclasts erode bone

      • osteoblasts form new bone

      • osteocytes are osteoblasts trapped in solid matrix


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bones are dynamicFigure 47.13

osteoblasts

osteoclasts


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Skeletal Systems

  • human skeleton

    • 206 bones

      • axial skeleton

        • head, spinal column, ribs

      • appendicular skeleton

        • pectoral girdle

        • pelvic girdle

        • bones of the limbs


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human skeletonFigure 47.12


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Skeletal Systems

  • human skeleton

    • bone may be

      • cancellous

      • compact

        Haversian systems


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cancellous, compact boneFigure 47.15



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Skeletal Systems

  • human skeleton

    • muscles move bones around joints

      • bone attaches to bone by ligaments

      • muscle attaches to bone by tendons

    • muscles work in opposed pairs

      • flexor muscles bend the joint

      • extensor muscles straighten the joint



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Skeletal Systems

  • the force exerted by a joint depends on its construction

    • the length of the moving bone (load arm) relative to the insertion of the flexor on it (power arm) determines its maximum force


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power arm to load arm ratio determines maximum forceFigure 47.18