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					Chapter 49, pg. 1063-1068: Muscular/Skeletal System
   Skeletal functions: (1) Support, (2) Protection for soft tissues, and (3) Movement, by giving
     muscles something firm to work against
   Three diff. kinds of skeletons
  1. Hydrostatic skeleton = fluid held under pressure by a closed body compartment
           a. Muscles used to change the shape of the compartments and to move forward
           b. Cushions internal organs from shock, supports crawling in terrestrial animals, good
                for aquatic animals
           c. Cnidarians (gastrovascular cavity), flatworms/planarians (body walls), nematodes
                (pseudocoeloms)
           d. Annelids: fluid in coelom divided by their septa  segmentation
                      i. Segmentation used for peristalsis: contraction of longitudinal muscles
                          thickens and shortens the worm while contraction of circular muscles
                          constricts and elongates it, causing movement
  2. Exoskeleton = hard encasement deposited on the surface of an animal
           a. Mollusks (calcium carbonate shells) and bivalves (muscles to close their
                exoskeletons)
           b. Arthropods – exoskeleton is their cuticle (coat secreted by epidermis) w/ knobs and plates attached to muscles (shell must be
                molted as animals grow larger)
                      i. Chitin fibrils and protein matrix create strong and flexible exoskeleton that is hardened with proteins where needed
                          or thin where necessary
  3. Endoskeleton = Hard supporting elements buried under soft tissues
           a. Sponges have hard spicules, echinoderms have endoskeletons of ossicle plates
           b. Chordates – endoskeleton consisting of cartilage, bone, and the combo of this w/ 200+ bones fused together or connect by
                joints (ligaments) for free movement
                      i. Axial skeleton = skull, vertebral column (backbone), and rib cage
                     ii. Appendicular skeleton = limb bones and pectoral and pelvic girdles
           c. Ball-and-socket joints (circular rotation), hinge joints (singular plane movement), pivot joints (elbows and head)
   Body posture (position of legs relative to main body) is skeletal feature that allows for the support of an animal’s body weight
           o Tendons = connective tissue that joins muscles to bone – work w/ muscles to carry body weight
   Muscles contract passively. Muscles are attached to skeleton in antagonistic pairs, which wach muscle working against each other –
     Biceps contracted, triceps relaxed vs. Triceps contracted, Biceps relaxed.
   Skeletal muscle = attached to the bones and responsible for skeletal
     movement
           o Consists of longitudinal fibers (a single cell w/ multiple nuclei)
                parallel to the muscle’s length
           o Longitudinal fibers are made up of myofibrils, which are made up
                of myofilaments (thin and thick filaments) – thick filaments made
                up of two actin strands and one regulatory protein strand coiled
                around each other, and thick filaments are staggered myosin
                molecules
           o Skeletal muscle = striated muscle b/c myofilaments create pattern
                of light and dark bands Form sacromeres (basic contractile unit of
                the muscle) bordered by Z lines
           o Z lines connected to thin filaments at the center of sacromere, w/ thick filaments in btw thick filaments
                       I Band = area near sacromere’s edge where there are only thin filaments
                       A band = area near center of sacromere that is length of thick filaments, w/ an H zone in the middle w/ only thick
                           filaments
   Sliding-filament model of muscle contraction: sacromere shortens and the filaments slide past each other longitudinally, producing an
     overlap btw thin and thick filaments so that I band and H zone shrink
   Myosin molecule consists of globular head (center of bioenergetic reactions and powers muscle contractions by hydrolyzing ATP) and
     long tail that adheres to other tails to form thick filaments
           o Hyrdolysis of ATP  mysonin head binds to actin, which forms cross-bridge andpulls thin filament to sacromere’s center
                 new ATP binds to mysonin head  hydrolysis repeats and mysonin head attaches to another actin farther along thin
                filament  breaking and building of cross-bridges drive filaments past each other
           o Creatine phosphate and glycogen sustain energy needed for muscle contractions  glycolysis and aerobic respiration
Skeletal/Muscular Systems Chapter 49, pages 1068-1074
    o The Role of Calcium and Regulatory Proteins
          Muscle fiber contracts when stimulated by motor neuron
          Muscle fiber at rest  myosin-binding sites on thin filament are blocked by regulatory protein tropomyosin
          Muscle fiber contracts when binding sites uncovered (Ca2+ bind to another set of regulatory proteins, troponin complex
              [controls position of tropomyosin on thin filament; exposes myosinbinding sites on thin filament]
          Stimulus: action potential in motor neuron that makes synapse
          Synaptic terminal releases neurotransmitter  depolarizes muscle fiber  produces action potential  spreads deep into
              interior of muscle fiber along infoldings of plasma mebrane called transverse (T) tubules  make contact with sarcoplasmic
              reticulum (SR) specialized endoplasmic reticulum
               When muscle fiber at rest, SR membrane pumps Ca2+ from cytosol to interior of SR
               When muscle fiber produces action potential, Ca2+ channels open in SR = Ca2+ enters cystosol
                   o Calcium binds to troponin complex = contraction of muscle fiber
                   o Contraction stops when SR pumps Ca2+ back out of cytosol
          Diseases that cause paralysis: amyotrophic lateral sclerosis (ALS) a.k.a. Lou Gehrig’s disease  motor neurons in spinal cord
              and brainstem degenerate; Botulism  result from consumption of exotoxin from bacterium in foods = muscle paralysis 
              used in “Botox” treatments; Myasthenia  autoimmune disease
    o Neural Control of Muscle Tension
          Action potential releases acetylecholine  muscle fiber twitches
          Graded contractions = voluntary
               Produced by varying number of muscle fibers that contract and varying rate at which muscle fibers are stimulated
          Motor unit: consiss of single motor neuron and all muscle fibers it controls
          More motor units activated = more strength used  process of recruitment
          Some muscles always partially contracted, prolonged contraction = fatigue b/c of depletion of ATP, dissipation of ion gradients
              required for normal electrical signaling, and accumulation of lactate
          Reducing fatigue  switch activation among motor units in a muscle = take turns with prolonged contraction
          Tetanus: maximal, sustained contraction of a skeletal muscle, caused by fast frequency of action potentials elicited by continual
              stimulation
          Increase in tension during summation and tetanus occurs b/c muscle fibers not directly attached to bones, but connected by
              tendons and connective tissues
          When muscle fiber contracts, stretches tendons and tissues = tension to the bones
               During summation, greater stretching of elastic structures
               During tetanus, elastic structures fully stretched
    o Types of Muscle Fibers
          Speed of contraction [due to rate in which myosin heads hydrolyze ATP] = classify muscle fibers as either fast or slow
               Fast fibers  brief, rapid, powerful contractions
               Slow fibers  sustain long contractions [less SR and slower calcium pumps]
          Another way to classify fibers is metabolic pathway used for producing ATP
               Oxidative fibers  rely on aerobic respiration (steady supply of energy, many mitochondria, rich blood supply, large
                   amount of oxygen-storing protein called myoglobin, fast or slow)
               Glycolytic fibers  rely on glycolysis (fast)
          In conclusion, fast oxidative, slow oxidative, fast glycolytic (see Table 49.1 on pg. 1072)
               Fast glycolytic fibers can develop into fast oxidative fibers
 Other Types of Muscle
    o Cardiac muscle: the heart, striated; have ion channels in plasma membrane that cause rhythmic depolarizations = action potentials
         without input from nervous system (last 20 times longer than skeletal muscle fibers)
    o Intercalated disks: plasma membranes of adjacent cardiac muscle cells interlock here
    o Smooth muscle: found in walls of hollow organs e.g. blood vessels, digestive tract, lack striations b/c thick filaments scattered
         throughout cytoplasm; don’t have troponin complex or T tubules, SR is not well developed; contract relatively slow
    o Invertebrates have muscle cells similar to vertebrate skeletal and smooth muscle cells
    o Arthropod skeletal muscles nearly identical to vertebrate skeletal muscles, but flight muscles capable of independent, rhythmic
         contraction
    o Evolutionary adaptation  paramyosin (helps muscles remain contracted with low energy rate of consumption) in clam muscles to
         hold shells closed
Concept 49.7 Locomotion requires energy to overcome friction and gravity
 Locomotion: active travel from place to place
 Swimming: Sleek, fusiform shape is common adaptation of fast swimmers; diff. ways to swim: use legs, jet-propelled, moving body
    from side to side or up and down
 Locomotion on Land: Leg muscles work against gravity, inertia, friction; common adaptation = strong muscles, e.g. kangaroo’s legs;
    balance, e.g. kangaroo’s tail
 Flying: Wings develop enough lift to overcome gravity, key to flight = wing shape, flying animals light, structural adaptations that
    reduce body mass
 Comparing Costs of Locomotion: depends on the mode of locomotion and environment; use of energy determines how much energy in
    food it consumes

				
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