Sample Material of Our Online Coaching Programme
Subject: General Science
Topic: Muscular and Skeletal System
The single-celled protozoan ancestors of animals had their
weight supported by water and were able to move by cilia or other simple
organelles. The evolution of large and more complex organisms (animals)
necessitated the development of support and locomotion systems. Animals use
their muscular and skeletal systems for support, locomotion, and maintaining
SKELETAL SYSTEMS OF VARIOUS ANIMALS
(i) Movement is a major characteristic of animals. This
movement is a result of contraction of muscles. The skeleton helps transmit that
movement. Skeletons are either a fluid-filled body cavity, exoskeletons, or
(ii) Hydrostatic skeletons consist of fluid-filled closed chambers. Internal
pressures generated by muscle contractions cause movement as well as maintain
the shape of the animals, such as the sea anemone and worms. The sea anemone has
one set of longitudinal muscles in the outer layer of the body, and a layer of
circular muscles in the inner layer of the body. The anemone can elongate or
contract its body by contracting one or the other set of muscles.
(iii) Exoskeletons are characteristic of the Phylum Arthropoda. Exoskeletons are
hard segments that cover the muscles and visceral organs. Muscles for movement
attach to the inner surface of the exoskeleton Exoskeletons restrict the growth
of the animal, thus it must shed its exoskeleton (or molt) to form a new one
that has room for growth. The bulk and weight of the exoskeleton and associated
mechanical problems limits the size a animals can attain.
Note : Spiders use a combination of an exoskeleton for protection and
fluid pressure for movement. Vertebrates have developed an internal mineralized
(in most cases) endoskeleton composed of bone and/or cartilage. Muscles are on
the outside of the endoskeleton.
Cartilage and bone are types of connective tissue.
- Sharks, and rays have skeletons composed entirely of cartilage; other
vertebrates have an embryonic cartilage skeleton progressively replaced by
bone as they mature and develop.
- Some areas of the human body, however, retain cartilage in the adult: in
joints and flexible structures such as the ribs, trachea, nose and ears.
THE SKELETON AND MUSCLES
- The skeleton and muscles function together as the musculoskeletal
system. This system (often treated as two separate systems, the muscular,
and skeletal) plays an important homeostatic role: allowing the animal to
move to more favorable external conditions.
- Certain cells in the bones produce immune cells as well as important
cellular components of the blood.
- Bone also helps regulate blood calcium levels, serving as a calcium
sink. Rapid muscular contraction is important in generating internal heat,
another homeostatic function.