How Animals Move

1
How Animals Move

• Chapter 32

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Skeleton

• A medium or structural element against which
  contractile cells can act
• Three types
• Hydrostatic
• Exoskeleton
• Endoskeleton

exoskeleton
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Endoskeleton

• All vertebrates have endoskeletons
• Fins or limbs attach to skeleton at pectoral and
  pelvic girdles

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Human Skeleton
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Functions of Bone

• Interact with muscle to enable movement
• Support and anchor muscles
• Enclose and protect internal organs
• Store calcium and phosphorus
• Produce blood cells

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Long Bone Structure

• Compact bone
• Spongy bone
• Central cavity contains yellow marrow

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Compact Bone Structure

• Mature compact bone consists of many cylindrical
  Haversian systems

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Bone Marrow

• Yellow marrow
• Fills the cavities of adult long bones
• Is largely fat
• Red marrow
• Occurs in spongy bone of some bones
• Produces blood cells

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Long Bone Formation
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Bone Remodeling

• In adults, bone building and bone breakdown
  continue constantly
• Osteoblasts deposit bone
• Osteoclasts secrete enzymes that degrade it
• Remodeling adjusts bone strength and helps
  maintain blood calcium levels

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Bone Density

• Exercise can increase bone density
• Osteoporosis is a decrease in bone density
• May occur when the action of osteoclasts outpaces
  that of osteoblasts
• May also occur as a result of inability to absorb
  calcium

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Joints

• Areas of contact or near contact between bones
• Fibrous joints
• Short connecting fibers join bones
• Synovial joints
• Move freely ligaments connect bones
• Cartilaginous joints
• Straps of cartilage allow slight movement

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Skeletal Muscle

• Bundles of striped muscle cells
• Attaches to bone
• Often work in opposition

biceps
triceps
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Tendons Attach Muscle to Bone
muscle
tendon
bursae
synovial cavity
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Human Skeletal Muscles
TRICEPS BRACHII
BICEPS BRACHII
PECTORALIS MAJOR
DELTOID
TRAPEZIUS
SERRATUS ANTERIOR
EXTERNAL OBLIQUE
LATISSIMUS DORSI
RECTUS ABDOMINUS
GLUTEUS MAXIMUS
ADDUCTOR LONGUS
BICEPS FEMORIS
SARTORIUS
QUADRICEPS FEMORIS
GASTROCNEMIUS
TIBIALIS ANTERIOR
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Skeletal Muscle Structure

• A muscle is made up of muscle cells
• A muscle fiber is a single muscle cell
• Each fiber contains many myofibrils

myofibril
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Sarcomere
A myofibril is made up of thick and thin
filaments arranged in sarcomeres
sarcomere
sarcomere
sarcomere
sarcomere
Z band
Z band
Z band
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Muscle Microfilaments

• Thin filaments
• Like two strands of pearls twisted together
• Pearls are actin
• Other proteins in grooves in filament

• Thick filaments
• Composed of myosin
• Each myosin molecule has tail and a double head

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Sliding-Filament Model

• Sarcomere shortens because the actin filaments
  are pulled inward, toward the sarcomere center

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Sliding-Filament Model

• Myosin heads attach to actin filaments
• Myosin heads tilt toward the sarcomere center,
  pulling actin with them

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Role of Calcium in Contraction

• T tubules in the sarcoplasmic reticulum relay
  signal
• Calcium ions are released

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Nervous System Controls Contraction

• Signals from nervous system travel along spinal
  cord, down a motor neuron
• Endings of motor neuron synapse on a muscle cell
  at a neuromuscular junction

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Contraction Requires Energy

• Muscle cells require huge amounts of ATP energy
  to power contraction
• The cells have only a very small store of ATP
• Three pathways supply ATP to power muscle
  contraction

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ATP for Contraction
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Motor Unit

• One neuron and all the muscle cells that form
  junctions with its endings
• When a motor neuron is stimulated, all the muscle
  cells it supplies are activated to contract
  simultaneously
• Each muscle consists of many motor units

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Twitches and Tetanus
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Muscle Tension

• Mechanical force a contracting muscle exerts on
  an object
• For a muscle to shorten, muscle tension must
  exceed the load that opposes it
• The load may be the weight of an object or
  gravitys pull on the muscle

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Two Main Types of Contraction

• Isotonic contraction
• Muscle visibly shortens moves a load
• Tension remains constant as the muscle changes
  length
• Isometric contraction
• Muscle does not change length
• Tension is insufficient to move load

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Muscle Fatigue

• An inability to maintain muscle tension
• Occurs after a period of tetanic contraction
• Different types of muscle show different fatigue
  patterns

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Muscular Dystrophies

• A class of genetic disorders where muscles
  progressively weaken and degenerate
• Duchenne muscular dystrophy is the most common
  among children
• Myotonic muscular dystrophy is the most common
  among adults

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Aging Muscles

• Over time, the number and size of muscle fibers
  decreases

32
Clostridium

• Clostridium botulinum causes botulism, stopping
  the release of acetylcholine, a neurotransmitter
  that enables muscle contraction
• Clostridium tetani causes tetanus, blocking the
  neurotransmitters GABA and glycine, which leads
  to uninhibited muscle contraction