Skeletal and muscular systems
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There are different kinds of skeletons in the animal kingdom.
The hydrostatic skeleton That is inside of the animal, is a fluid that provides the animal with support and allows movement. It is found in worms and mollusks as well as some other invertebrates. The exoskeleton is a non-living structure made up of proteins that is replaced as the animal grows. It protects the organism as an armour or carcass. It is found in arthropods. The endoskeleton found in vertebrates, is made of a hard tissue that provides support, protection and movement. The human skeleton also stores minerals and produces blood cells inside the long bones.
Muscles help on keeping body shape and posture, movement and production of heat as they contract.
Muscle cells have the property of contraction and expansion due to their elasticity that allows them to recover their original shape after a contraction.
The Skeletal Muscle is made of striated fibers. Each cell is multinucleated and has the ability to contract as their structure slides using the energy of their mitochondria. It is attached to the bones by tendons. Its movement is voluntary.
The cardiac muscle is found only in the heart. It is made of uninucleated cells that have the ability of contracting faster and regularly because they contain many mitochondria to provide energy. It is involuntary and is not under the nervous system control. The nervous system only maintains the pulse rate.
The Smooth Muscle is made of spindle-shaped non striated fibers with uninucleated cells that work in response to hormones and nervous stimuli. It is found inside of the organs of the digestive system, the urinary bladder, the uterus and the blood vessels. It is also found in the muscles of the eyes.
The lever doesn't work without a fulcrum...
