THE MUSCULOSKELETAL SYSTEM

Animals often respond to a stimulus with movement, which is made possible by the musculoeskeletal system. Movement can take place without changing position, like closing eyelids, or it can lead to a change in position, like flying. This system consists of two structures: the skeleton and the muscles.

ANIMAL SKELETONS

The skeleton is the passive part of the musculoeskeletal system. It gives the body its shape, protects internal organs and serves as a support or anchor for the muscles 

TYPES OF SKELETONS 

-Hydroskeleton.

Features: closed body cavities filled with fluid and surrounded by muscles.

Examples: most echinoderms, cnidaria, flatworms, annelids 

-Exoskeleton

Features: in molluscs, it is rigid and grows with the animal. In arthropods, it is articulated and shed during moulting.

Examples: molluscs and arthropods

-Endoskeleton

Features: an internal skeleton formed by hard cartilage, bone or both. It grows with the animal.

Example. vertebrates

ANIMAL MUSCLES

Muscles are the active part of the musculoeskeletal system. They contract and relax, changing in length. There are three types: 

·Skeletal muscle. Rapid, voluntary contractions. It interacts with the skeleton and enables movement. The muscles are attached to the skeleton by tendons

·Smooth muscle. Slow, involuntary contractions. It covers the walls of hollow organs like blood vessels. It helps to move substances like food through body.

·Cardiac muscle. Rhythmic, involuntary contractions. It pumps blood through the body.