The Animal Body and How it Moves

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The Animal Body and How it Moves

• Chapter 42

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Outline

• Characteristics of Epithelial Tissue
• Tissue Types
• Types of Skeletons
• The Structure of Bone
• Types of Joints
• Actions of Skeletal Muscles
• Sliding Filament Mechanism of Contraction
• Control of Muscle Contraction
• Types of Muscle Fibers
• Modes of Animal Locomotion

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Organization of the Body

• Bodies of all vertebrates are basically a tube
  within a tube.
• all vertebrate bodies supported by internal
  skeleton
• Four levels of organization
• cells
• tissues
• organs
• organ systems

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Organization of the Body

• Tissues
• Groups of cells similar in structure and function
  are organized into tissues.
• Early in development, embryo cells differentiate
  into three germ layers.
• endoderm
• mesoderm
• ectoderm

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Tissues

• Adult vertebrates have four primary tissues
• epithelial
• connective
• muscle
• nerve

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Organization of the Body

• Organs and organ systems
• Organs are body structures composed of several
  different tissues that form a structural and
  functional unit.
• An organ system is a group of organs that operate
  to perform the major activities of the body.

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Characteristics of Epithelial Tissue

• Epithelium covers every major surface of the
  vertebrate body.
• derived from all three germ layers
• can provide a barrier that can impede the passage
  of some substances while facilitating the passage
  of others
• remarkable regenerative powers

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Characteristics of Epithelial Tissue

• Types of epithelial tissues
• simple - one layer thick
• squamous - lining of lungs
• cuboidal - lining of kidney tubules
• columnar - lining of stomach
• stratified - several cell layers thick and named
  according to features of their uppermost layers

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Characteristics of Epithelial Tissue

• Glands of vertebrates are derived from
  invaginated epithelium.
• exocrine glands - connection between the gland
  and the epithelial membrane is maintained as a
  duct
• endocrine glands - ductless glands - connections
  with the epithelium, from which they are derived,
  are lost during development
• secrete hormones

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Connective Tissue Proper

• Connective tissues are divided into
• connective tissue
• divided into loose and dense connective tissues
• special connective tissues
• include cartilage, bone, and blood
• extracellular material generically known as matrix

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Connective Tissue Proper

• Loose connective tissue
• cells scattered within amorphous mass of proteins
  that form a ground substance
• strengthened by collagen, elastin and reticulin -
  secreted by fibroblasts
• adipose cells found in loose connective tissue

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Connective Tissue Proper

• Dense connective tissue
• regular
• collagen fibers lined up in parallel
• tendons and ligaments
• irregular
• collagen fibers have many orientations
• organ coverings - capsules
• muscle coverings - epimysium
• nerve coverings - perineurium
• bone covering - periosteum

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Special Connective Tissues

• Cartilage
• specialized connective tissue in which fibers are
  laid down along the lines of stress in long,
  parallel arrays
• firm and flexible
• chondrocytes - cartilage cells that live within
  spaces (lacunae) within cartilage matrix

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Cartilage
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Special Connective Tissues

• Bone
• Many bones are first modeled in cartilage. The
  cartilage matrix calcifies at particular
  locations, thus chondrocytes are no longer able
  to obtain oxygen and nutrients through diffusion.

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The Structure of Bone

• New bone is formed by osteoblasts that secrete
  collagen organic matrix in which calcium
  phosphate is later deposited.
• cells then encased in spaces called lacunae in
  the calcified matrix
• Bone is constructed in thin, concentric layers or
  lamellae, laid down around Haversian canals that
  run parallel to the length of the bone.
• contain nerve fibers and blood vessels

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The Structure of Bone

• Bone formation
• flat bones - Osteoblasts located in a web of
  dense connective tissue produce bone within that
  tissue.
• long bones - bone first modeled in cartilage
• ends and interior composed of spongy bone

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Bone
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Special Connective Tissues

• Blood
• classified as connective tissue because it
  contains plasma and platelets
• erythrocytes - contain hemoglobin
• leukocytes - have nuclei and mitochondria, but
  lack hemoglobin
• neutrophils, eosinophils, and basophils
• lymphocytes and monocytes

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Muscle Tissue

• Muscle cells are the motors of the vertebrate
  body.
• three types smooth - skeletal - cardiac
• Skeletal and cardiac muscles are striated because
  their cells have transverse stripes when viewed
  in longitudinal section.
• Contraction of skeletal muscle is under voluntary
  control, whereas contraction in cardiac and
  smooth muscle is generally involuntary.

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Muscle Tissue

• Smooth muscle - found in organs of internal
  environment (viscera)
• Skeletal muscle - usually attached to tendons or
  bones, so when muscles contract causes bones to
  move at joints
• made up of long muscle fibers that contract by
  myofibrils
• made up of highly ordered arrays of actin and
  myosin filaments

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Muscle Tissue

• Cardiac muscles
• composed of smaller, interconnected cells, each
  with a single nucleus
• interconnections appear as dark lines called
  intercalated disks
• enable cardiac muscles to form single functioning
  unit - myocardium

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Nerve Tissue

• Cells include neurons and neuroglia (supporting
  cells).
• Neurons are specialized to produce and conduct
  electrochemical impulses.

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Nerve Tissue

• Neuroglia do not conduct electrical impulses but
  instead support and insulate neurons and
  eliminate foreign materials in and around
  neurons.
• myelin sheath - insulating covering of neuroglia
  cells wrapped around axons
• nodes of Ranvier separate adjacent neuroglia cells

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Nerve Tissue

• Nervous system is divided in the central nervous
  system (CNS) which includes the brain and spinal
  cord, and the peripheral nervous system (PNS)
  which includes nerves and ganglia.
• Nerves consist of axons in the PNS bundled
  together.
• Ganglia are collections of neuron cell bodies.

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Types of Skeletons

• Hydrostatic skeletons - fluid-filled cavity
  encircled by muscle fibers
• As the muscles contract, fluid in the cavity
  moves and changes cavity shape.
• Exoskeletons - surround the body as a rigid, hard
  case
• must be periodically shed
• limits body size as exoskeleton has to grow
  increasingly thicker and heavier

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Types of Skeletons

• Endoskeletons - rigid internal skeleton to which
  muscles are attached
• composed of cartilage or bone
• vertebrate skeleton
• axial skeleton - forms axis of body and supports
  organs of the head, neck, and chest
• appendicular skeleton - includes bones of the
  limbs, pectoral and pelvic girdles

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Exoskeleton and Endoskeleton
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Types of Joints
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Types of Joints
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Types of Joints
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Actions of Skeletal Muscles

• Skeletal muscles produce movement of the skeleton
  when they contract.
• attachment to bones made by tendons
• origin remains stationary during contraction
• insertion attached to bone that moves during
  contraction

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Actions of Skeletal Muscles

• Synergists - muscles that cause same action at a
  joint
• Antagonists - muscles that produce opposing
  actions
• Isotonic contraction - muscle and all fibers
  shorten in length thus force of contraction
  remains relatively constant
• Isometric contraction - tension is absorbed by
  tendons and other elastic tissue, and muscle does
  not change in length

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Flexor and Extensor Muscles
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Sliding Filament Mechanism of Contraction

• Each skeletal muscle contains numerous muscle
  fibers.
• Each muscle fiber encloses 4-20 myofibrils.
• Each myofibril composed of thick and thin
  myofilaments.
• Thick myofilaments produce A bands.
• Thin myofilaments produce I bands.
• Each I band divided in half by disc of protein (Z
  band).

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Skeletal Muscle Organization
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Sliding Filament Mechanism of Contraction

• Sarcomere - structure of myofibril from Z line to
  Z line
• smallest subunit of muscle contraction
• A muscle contracts and shortens because its
  myofibrils contract and shorten.
• Myofilaments do not shorten, but slide deeper
  into the A band.

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Sliding Filament Mechanism of Contraction

• Electron micrographs reveal cross-bridges that
  extend from the thick to thin filaments.
• Each thick filament composed of many myosin
  proteins packed together, and every myosin
  molecule has a head region.
• Each thin filament consists primarily of many
  globular actin proteins twisted in a double helix.

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Sliding Filament Mechanism of Contraction

• Before the myosin heads bind to the actin of the
  thin filaments, they act as ATPase, splitting ATP
  into ADP and Pi.
• activates heads
• Once a myosin head binds to actin, it undergoes a
  shape change, pulling the thin filament toward
  the center of the sarcomere.
• allows head to detach from actin and continue
  cross-bridge cycle

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Control of Muscle Contraction

• Role of Ca in contraction
• When a muscle is relaxed the myosin head cannot
  bind to actin because the attachment sites are
  physically blocked by tropomyosin.
• In order to contract a muscle, troponin must move
  tropomyosin away from the binding site.
• complex regulated by calcium ion concentration

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Control of Muscle Contraction

• When Ca concentration of the muscle cell
  cytoplasm is low, tropomyosin inhibits
  cross-bridge formation and the muscle is relaxed.
• When Ca concentration is raised, Ca binds to
  troponin.
• When a muscle fiber is stimulated to contract, an
  electrical impulse travels into the muscle fiber
  down transverse tubules.
• triggers release of Ca from sarcoplasmic
  reticulum

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Control of Muscle Contraction

• Nerves stimulate contraction
• Somatic motor neurons stimulate skeletal muscles.
• Axon extends from neuron cell body and branches
  to make synapses with a number of muscle fibers.

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Control of Muscle Contraction

• Somatic motor neuron stimulates contraction
• releasing acetylcholine neurotransmitter (ACh).
• impulses spread along membrane and carried into
  the muscle fibers through the T tubules
• T tubules conduct impulse toward the sarcoplasmic
  reticulum, which releases Ca
• Excitation-contraction coupling

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Control of Muscle Contraction

• Motor units and recruitment
• set of muscle fibers innervated by all axonal
  branches is defined as a motor unit
• division of muscle into motor units allows
  muscles strength of contraction to be finely
  graded
• most muscles contain motor units in a variety of
  sizes
• recruitment - nervous systems use of increased
  numbers and sizes of motor units to produce a
  stronger contraction

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Number and Size of Motor Units
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Types of Muscle Fibers

• Muscle fiber twitches
• muscle stimulated with a single electric shock
• A second electrical shock delivered immediately
  after the first will produce a second twitch that
  may partially piggyback on the first (summation).
• At a particular frequency of stimulation, there
  is no visible relaxation between successive
  twitches (tetanus).

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Summation
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Types of Muscle Fibers

• Skeletal muscle fibers can be divided on the
  basis of their contraction speed
• Type I slow-twitch fibers
• rich capillary supply, numerous mitochondria, and
  high concentration of myoglobin pigment (red
  fibers)
• Type II fast-twitch fibers
• fewer capillaries and mitochondria and not as
  much myoglobin (white fibers)

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Types of Muscle Fibers

• Muscle metabolism during rest and exercise
• Skeletal muscles at rest obtain energy from
  aerobic respiration of fatty acids.
• Skeletal muscles respire anaerobically for the
  first 45-90 seconds of moderate to heavy
  exercise.
• Maximum rate of oxygen consumption in the body is
  called maximal uptake or aerobic capacity.

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Types of Muscle Fibers

• Muscle fatigue and physical training
• Muscle fatigue refers to the use-dependent
  decrease in the ability of a muscle to generate
  force.
• usually correlated with the production of lactic
  acid by the exercising muscles
• also related to depletion of muscle glycogen

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Types of Muscle Fibers

• Endurance-trained athletes have a high aerobic
  capacity, and thus can perform more exercise
  before lactic acid production and glycogen
  depletion cause muscle fatigue.
• Weight training (resistance training) causes
  muscle fibers to become thicker as a result of
  increased size and number of myofibrils.
• cause skeletal muscles to grow by hypertrophy

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Modes of Animal Locomotion

• In large animals, active locomotion is almost
  always produced by appendages that oscillate
  (appendicular locomotion) or by bodies that
  undulate, pulse, or undergo peristaltic waves
  (axial locomotion).

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Modes of Animal Locomotion

• Locomotion in water
• Buoyancy reduces the influence of gravity.
• The primary force retarding forward movement is
  frictional drag.
• Swimming uses the body or its appendages to push
  against the water.

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Locomotion in Water
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Modes of Animal Locomotion

• Locomotion on land
• Mollusks slide along a path of mucus.
• Vertebrates and arthropods have a raised body and
  move forward by pushing the ground with a series
  of jointed appendages.
• Vertebrates have four limbs, while arthropods
  have six or more.
• basic walking pattern of all tetrapod vertebrates
  LH LF RH RF

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Locomotion on Land

• Both arthropods and vertebrates achieve faster
  gaits by overlapping leg movements.
• The highest running speeds of tetrapod
  vertebrates are obtained with asymmetrical gaits.
• galloping horse never supported by more than two
  legs, occasionally by none
• reduces friction against ground
• Many vertebrates use peristaltic locomotion.
• Most snakes employ serpentine locomotion.

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Modes of Animal Locomotion

• Locomotion in air
• Flight has evolved four times
• insects, pterosaurs, birds,and bats
• propulsion achieved by pushing down against the
  air with wings
• Raising and lowering wings is achieved by
  alternate contraction of extensor muscles and
  flexor muscles.

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Modes of Animal Locomotion

• In some insect orders, flight muscles are not
  attached to the wings, but rather to the stiff
  wall of the thorax.

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Summary

• Characteristics of Epithelial Tissue
• Tissue Types
• Types of Skeletons
• The Structure of Bone
• Types of Joints
• Actions of Skeletal Muscles
• Sliding Filament Mechanism of Contraction
• Control of Muscle Contraction
• Types of Muscle Fibers
• Modes of Animal Locomotion

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