Locomotion

• Movement in animals differs based on the type of skeleton they have
• Hydrostatic skeletons depend on constant volume and incompressible fluids, contraction of a muscle results in a decrease in one dimension of the body which in turn results in an increases in another dimension
• Polyp cnidarians use their gastrovascular cavity as their hydrostatic skeleton. Medusa cnidarians have a ring of muscle around the bottom of their bell which is full of water, when they contract the muscle it shoots the water out and propels them forward
• Annelids and nematodes use skeletal muscles on the outside of the body to produce motion. Longitudinal muscles allow for side-to-side motion, longitudinal and circular muscles allow for peristatic motion.
• Echinoderms have an endoskeleton but they do not use it for locomotion, instead they use their water vascular system and tube feet which function as a hydraulic system. Tube feet have little suction cups on the end which have ampulla where water is squeezed in and out to protract and retract the foot, muscle in the tube foot bends allowing it to take a step
• Muscles must act over joints in a skeleton to produce movement in all animals.
    * In arthropods muscles attach to apodemes in the exoskeleton.
    * In vertebrates muscles attach to the bones with tendons
• Muscles work by contracting and pulling on a bone or attachement to an exoskeleton
• Flexion and extension of a limb are the result of the contraction of antagonistic sets of muscles
• All types of locomotion must deal with gravity and/or friction
• Because water is a dense medium most fish and marine mammals use axial locomotion to swim, using the body muscles to produce propulsion
• Frogs, turtles, waterfowl, and mammals swim using appendicular locomotion, using their limbs
• Flying animals must be able to create lift to counteract gravity and move themselves through the air

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