Animal Locomotion

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Animal Locomotion

• Skeletal Muscular Systems

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Learning Objectives (3/11/09)

1. Describe the types of skeletons that support and
   enable movement in animals, with examples.
2. Describe how muscles exert force against skeletal
   elements to maintain posture and produce
   movement.
3. Compare the structure and function of the three
   types of muscle tissue.
4. Differentiate between whole muscle contraction
   and contraction of a single muscle cell,
   including the sliding filament theory of muscle
   contraction.

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Musculoskeletal Machines

• The skeleton and muscles work together in lever
  systems
• Muscles can only shorten by contraction, they
  cannot actively elongate.
• An external force is needed to stretch a muscle
  back to its resting length.
• Opposing muscle sets provide this external force.
  

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Hydrostatic Skeletons
How do soft-bodied animals like worms and other
forms that lack rigid skeletons operate opposing
muscles?
p. 1046

• Fluid held in internal compartments as a
  hydraulic fluid transfers force between opposing
  muscle sets.
• As muscles contract, internal volume remains the
  same, so the opposing muscle set must stretch.
• This stretch creates the potential to do work

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Hydrostatic Skeleton
Sea anemones (Phylum ?) have cylindrical
fluid-filled bodies that function as a
hydrostatic skeleton.
They have both circular and longitudinal muscle
that contract against the fluid in their
gastrovascular cavity.
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Sea Anemone Body Shapes
How can this animal change so dramatically in
volume?
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Nematode Worms
See p. 694

• Roundworms have only longitudinal muscles,
  innervated by two nerve cords, and use a
  hydrostatic skeleton.
• Their body can assume curved and S-shaped
  configurations to help them move through soil and
  other media.

Name the closed, water-filled body cavity that
acts as the hydroskeleton.
nematode locomotion
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Annelid Worms

• Each segment in the worm body can act as an
  independent hydrostatic skeleton.
• This permits much more complex changes in body
  shape.
• The head is extended forward by contraction of
  circular muscles.
• A wave of contraction of longitudinal muscles
  then anchors the segments near the head.

earthworm locomotion
See p. 724
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Polychaete Worms
Contraction of longitudinal muscles on one side
of a segment stretches the longitudinal muscles
on the other side.
Parapodia act like paddles to push each segment
toward the rear of the animal.
See p. 724
polychaete worm swimming
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Exoskeletons
Exoskeletons are hardened outer surfaces to which
internal muscles are attached.
Increased leg length allows greater speed and
power in locomotion (simple lever
systems). Multiple, long legs create a potential
problem of tripping over ones legs. Centipedes
and crustaceans have staggered activity in their
legs to prevent tripping. More advanced forms
(e.g. crustaceans and insects) fuse segments and
reduce the number of legs.
p. 1046
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Endoskeletons
Endoskeletons are internal, articulated systems
of rigid supports consisting of bone and
cartilage to which muscles are attached.
What are some of the advantages associated with
endoskeletons, over exoskeletons? How could you
improve the efficiency of the lever system for
arm flexion? ?
p. 1046
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Lever Systems

• Muscles and bones work together around joints as
  systems of levers.
• Lever systems of muscles and skeletons can be
  designed either for power or speed.
• The ratio of load arm (resistance) to power arm
  (effort) determines the power.
• A low load arm to power arm ratio provides high
  power but low speed
• A high load arm to power arm ratio provides high
  speed but lower power.

Power LP 2
Speed LP 5
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What is stored within cisternae of muscle cells?
What is a myofibril?
p. 1072
Internal organization of a muscle cell
What is the functional unit of contraction in a
muscle fiber? Circle and/or label one in this
diagram.
Each t-tubule is an extension of the
________________.
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Organization of Myofilaments in a Sarcomere
A sarcomere within a myofibril
p. 1070
myofibril
actin
myosin
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Events at the NMJ
p. 1072
Is the release of neurotransmitter active
transport or passive transport? Is the influx of
Na ions by active transport or passive
transport? How does the influx of Na ions change
the transmembrane electrochemical potential?
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Are the calcium channels in cisternae
voltage-gated or chemically-gated? Besides Ca2,
what must also be present in order for myosin to
bind to actin?