46 - 46.1 Muscles have to pull against something to cause changes that result in movement Three types of skeletal systems hydrostatic skeletons

46 - 46.1 Muscles have to pull against something to cause...

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46.1 Muscles have to pull against something to cause changes that result in movement. Three types of skeletal systems: hydrostatic skeletons, endoskeleton, exoskeleton. Hydrostatic skeletons: use water pressure inside a body wall. Found primarily in soft-bodied terrestrial invertebrates (slugs or earthworms) or soft-bodied aquatic invertebrates (squids or jellyfish). Musculoskeletal action in earthworms: a fluid filled central cavity is encompassed by two sets of muscles in the body wall: circular (repeatedly run the length of the worm) and longitudinal (oppose the action of the circular). Muscles act on the fluid center space in the body (is the hydrostatic skeleton) As locomotion begins, the anterior circular muscles contract pushing against the inner fluid and thinning the front of the worm as the body wall pushes forward o On the underside of the worms body there are short bristle-like structures called the chaetae. When circular muscles act, the chaetae are moved toward the body and loose contact with the ground. o Circular muscle activity is passed backward segment after segment to create a wave of contraction. As the wave continues the circular muscles relax and the longitudinal muscles take over thickening the front allowing the chaetae to regain contact with the ground. o The chaetae attach to the ground not allowing the worm to slip backward. o The motion proceeds forward as waves of circular muscle contraction are followed by longitudinal muscle effects. Exoskeletons are rigid skeletons on the exterior bodies of arthropods primarily made of the polysaccharide chitin (also found in the cell walls of fungi and some protists). A chitin exoskeleton resists bending and provides a framework for the body, it also allows muscles attach sites and protects organs inside. Muscles are in the exoskeleton casing. In order to grow the animal must molt periodically, shedding the exoskeleton. o During molting the animal is vulnerable to predators until a new exoskeleton forms. Crabs/lobsters usually hide until this process passes. o Chitin exoskeletons are not as strong as internal skeletons. The respiratory system of insects (they breathe through tubes) does not allow an insect to go beyond a certain size with the exoskeleton. Endoskeletons: rigid internal structures that form the body’s framework and allow for muscles to attach to them. o Echinoderms, sea urchins and sand dollars, have endoskeletons made of calcite a crystalline form of calcium carbonate. o Bone is composed of calcium phosphate. The vertebrate endoskeleton is composed of fibrous dense connective tissue with surrounding rigid special connective tissue, bone or cartilage. Cartilage is strong and slightly flexible, important for padding when bones connect at places in a joint.
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