Animal Support System

• To move, muscles must work in concert with
a skeleton.
• The skeleton provides a rigid structure to
which muscles are attached.
• Muscles exert force only during contraction.
Moving a body part back & forth requires
two muscles attached to the same section
of the skeleton.
• These two muscles are known as an
antagonistic pair, which functions
cooperatively. The nervous system
coordinates these muscles.

The main function of a
skeleton
• Support
• Protection
– In many animals, the skeleton protects soft
tissue.
– For example, the vertebrate skull protects the
brain whilst the ribs of terrestrial vertebrates
forms a cage around the heart, lungs and other
internal organs.
• Movement

Types of skeletons
• There are three types of skeletons, namely:
– A Hydrostatic skeleton
– An Exoskeleton , and
– An Endoskeleton

Hydrostatic skeletons
• Consists of fluid held under pressure in a
closed body compartment.
• Examples of animals containing a
hydrostatic skeleton:
– Cnidarians
– Flatworms
– Nematodes
– Annelids

• Movement and form is
controlled by using muscles
to change the shape of the
fluid filled compartment.
• A Hydra, for example,
elongates by closing its
mouth by using contractile
cells in its body wall. This
results in the constriction of
its central gastro-vascular
cavity.
• By decreasing the diameter
of the cavity, the cavity is
forced to become longer.

Body structure of a
Hydra

• In planarians & other flatworms, the
interstitial fluid is kept under pressure &
functions as the main hydrostatic skeleton.
• Planarian movement results mainly from
muscles in the body wall exerting localized
forces against the hydrostatic skeleton.

• Nematodes hold fluid in their body
cavity, which is a pseudocoelom.
• Contractions of longitudinal muscles
move the animal forward by
undulations (wavelike) motions, of
the body.
• In earthworms and other annelids the
coelomic fluid functions as a
hydrostatic skeleton. The coelomatic
cavity in many annelids is divided by
the septa between the segments;
allowing the animal to change the
shape of each segment individually,
using both circular and longitudinal
muscles.
• Annelids use their hydrostatic
skeleton for peristalses (movement
produced by rhythmic waves of
muscle contractions passing from
front to back).

Movement of a
Nematode
• Nematode Movement.

• Well suited for live in an
aquatic environment.
• Cushion internal organs
from shocks, provide
support for crawling and
burrowing (in terrestrial
animals).
• Cannot support terrestrial
activities in which an
animal’s body is held off
the ground, thus walking
and running for example.

Exoskeletons
• Hard, encasement
deposited on an animal’s
surface; for example, most
molluscs (slugs and snails)
are enclosed in a calcium
carbonate shell secreted
by the mantle (sheet like
extension of the body
wall).
• As the animal grows, it
enlarges its shell by adding
to the outer edge.

Exoskeleton
• Jointed exoskeleton arthropods have a cuticle,
which is secreted by the epidermis. Muscles are
attached to knobs and plates of the cuticle that
extend into the interior of the body.
• 30 – 50% of the cuticle consist of chitin, a
polysaccharide similar to cellulose. Fibrils of
chitin is embedded in a protein matrix, which
forms a composite material that combines
strength and flexibility.

Exoskeletons
• For example, crustaceans (like
lobsters) harden portions of
their exoskeleton by adding
calcium salts.
• In leg joints, where the cuticle
is thin and flexible, cross
linking of proteins and
inorganic salt decomposition
occurs.
• With each growth spurt, an
arthropod must shed its
exoskeleton to produce a
larger one, thus they molt.

Endoskeletons
• Consist of hard, supporting
elements, such as bones which is
buried within the soft tissue of
animals.
• Sponges are reinforced by hard,
needle like structures of inorganic
materials, or by softer fibres made
of protein.
• Echinoderms have an endoskeleton
of hard plates called ossicles
beneath their skin.
• Ossicles are composed of
magnesium carbonate, calcium
carbonate crystals and are usually
bound together by protein fibres.

Endoskeletons
• Ossicles of sea urchins are tightly bound whilst
ossicles of sea stars are more loosely linked. This
allows the sea star to change the shape of its arms.
• A chordate’s skeleton consits out of caritlage, bone or
a combination of both.
• Mammalian skeletons are built from more than 200
bones; some are fused together, others are
connected at joints by ligaments that allow freedom
of movement.

Internal Structure of a
Long Bone

Name those Bones …
• Name those Bones …

Joints present in an
endoskeleton
• Three types of joints
can be distinguished in
endoskeletons, namely:

– Ball-and-socket joints
– Hinge joints
– Pivot joints

Ball-and-socket joints
• These joints are present where:
– The humerus contacts the shoulder girdle
– The femur contacts the pelvic girdle
• Enable us to rotate our arms and legs.
• Also allows for us to move our arms and legs
in several planes.

Hinge joints
• Found between the humerus and the head
of the ulna.
• Restricts movement to a single plane.

Pivot joints
• Allows us to rotate our forearm at the
elbow.
• Movement of head from side to side.

Locomotion
• Requires that an animal expend energy to
overcome two forces that tend to keep an
organism stationary.
• These forces are:
– Friction, and
– Gravity.
• By exerting a force, energy is required which
is produced during consuming cellular work.

Types of locomotion
• Locomotion can be accomplished by means
of three methods, namely:
– Swimming,
– Locomotion on land, and
– Flying.

Swimming as locomotive
tool
• Overcoming gravity is easier in water, than it
is for species who live on land. But, friction
is a major problem for aquatic animals.
• A common adaptation for fast swimmers is a
sleek, fusiform (torpedo like) shape.

Swimming as locomotive
tool – diverse
adaptations
• Insects and four-legged vertebrates use their
legs as oars to push against the water.
• Squids, scallops and some cnidarians are jet-
propelled; they take in water and squirt it
out in bursts in order to move.
• Sharks and bony fish swim by moving their
body and tail from side to side.
• Whales and dolphins move by undulating
their body and tail up and down.

Locomotion on land
• Walking, running, hopping and crawling animals must be able to
support themselves and move against gravity. Air poses relatively little
resistance at moderate speeds.
• When a land animal walks, runs, or hop, its leg muscles expend energy
not only to propel the animal, but also to keep it from falling down.
With each step the leg muscles must overcome inertia by accelerating a
leg from a standing start.
• Strong skeletal support and powerful muscles are important.

Locomotion on land -
diverse adaptations
• Kangaroos have large, powerful
muscles in their hind legs which is
suitable for locomotion by hopping.
• As a kangaroo lands after each leap,
tendons in its hind legs momentarily
store energy. The farther the animal
hops, the more energy the tendons
store.
• Analogous to energy in a compressed
spring, the energy stored in the
tendons is available for the next jump
and reduces the total amount of
energy the animal must expend to
travel.

diverse adaptations
• Legs of an insect, dog and human also retain
some energy during walking and running,
but in a smaller share.
• Another important prerequisite for walking,
running and hopping is to maintain balance.
• A kangaroo’s large tail help balance its body
during leaps and also forms a stable tripod
with its hind legs when the animal sits and
moves slowly.

diverse adaptations
• Bipedal animals (such as humans and birds)
keep part of at least one foot on the ground
when walking.
• When running:
– All four feet (or both for bipeds) may be off the
ground briefly, but at running speeds it is
momentum more than foot contact that keeps
the body upright.

diverse adaptations
• When crawling:
– Much of the body is in contact
with the ground, a crawling
animal must exert
considerable effort to
overcome friction.
– Earthworms crawl by means of
peristalsis.
– Many snakes crawl by
undulating their entire body
from side to side; assisted by
large, moveable scales on its
underside. When the snake’s
body pushes against the
ground, its scales tilt forward
and then push backward
against the ground.

Flying as locomotive
tool
• For flying animals, gravity is a
major problem since the
animal’s wings must develop
enough lift to overcome
gravity’s downward force.
• The animal’s wing shape is
important.
– All types of wings have airfoils
(structures whose shape
alters air currents in a way
that helps animals stay aloft).
– The body usually have a
fusiform shape help reduce
the drag in air as it does in
water.

tool
• Flying animals are relatively light.
• Body masses range from less to a gram to
about 20 kg (largest flying birds).

tool -adaptations
• Many structural adaptations contribute to a
lower body mass.
• For example:
– Birds have no urinary bladder or teeth, they have
relatively large bones with air filled regions.
– This lessen the bird’s weight.

Worksheets
• Complete the following worksheets for
homework:
– Diagram of the Human Skeleton
– Fill in the missing words
– Crossword one
– Crossword two

References
• Campbell, N. A., & Reece, J. B. (2008). Biology (8th ed.). San Francisco,
California, United States of America: Benjamin Cummings.
• Google images
• Skeletal System Cloze (n.d.). Available from:
http://www.bogglesworld.esl.com/skeletalsystem.htm
(Accessed 29 April 2012)
• Skeletal System Crossword 1 (n.d.). Available from:
• Skeletal System Crossword 2 (n.d.) Available from:
• Skeletal System Diagram (n.d.). Available from:
• You tube

Animal Support System

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