Bellwork: Why are skeletons important?

Movement and Support Section 28.2

How do animals move? In order to move animals must generate physical force, and they must apply that force against air, water and land in order to push or pull themselves Movement is facilitated by rigid body parts Legs, wings, flippers Each is supported by some sort of skeleton There are three main types of skeletons Hydrostatic, Exoskeletons and Endoskeletons

How does a hydrostatic skeleton work? Fluids held in a gastro vascular cavity that can alter an animal’s body shape drastically This is done by opening and closing the mouth When the mouth is closed, water trapped in the body causes the body to elongate When the mouth is open, water is released and it becomes shorter

What does an exoskeleton do? Many arthropods and mollusks have exoskeleton A hard body covering made of either chitin (Arthropod) or shell (Calcium carbonate – mollusk) Jointed exoskeletons allow arthropods to move and live in a variety of ways Also provides protection But – there can be issues Growing is not straightforward Need to break out of old exoskeleton and build a new one – molting Exoskeletons are also heavy – can cause issues

How does an Endoskeleton work? Echinoderms and Vertebrates have Endoskeletons Acts as a structural support system within a body Sea stars and echinoderm have endoskeleton made of calcified plates Support and protect, and give a bumpy texture Vertebrate endoskeletons are made of cartilage, or cartilage and bone Sharks and other fishes mainly cartilage Vertebrates bone is most common Some four limb vertebrates have limb girdles – support limbs and allow animal movement All provide strong lightweight support, and can grow with the animal

What is the importance of joints? Without joints animals cannot move A joint is a place where parts of a skeleton are held together in ways that enable them to move in respect to one another In vertebrates ligaments connect bones at joints Most joints are a combination of ligaments, cartilage and lubricating fluid

How do muscles enable movement? Muscles are specialized tissues that produce force by contracting when stimulated But muscles can not actively get longer. Force is only generated in one direction What problem does this cause, how do our bodies address this? In most animals muscles work together in pairs or groups attached to different parts of a skeleton Tendons attach muscles to bones around joints Tendons pull on bones when muscles contract

So how do the muscular and skeletal system work together? There is widespread variation amongst vertebrates In fish and snakes, muscles are arranged in blocks along opposite sides of the backbone The blocks contract in waves, bending the body from one side to another Thurst is generated, Many amphibians look like they are doing pushups, but sideways movement of backbone moves limbs forewards and backwards Mammal limbs have evolved to enable different kinds of movement

Variation explained Ultimately, the widespread variation to vertebrate musculoskeletal systems allows vertebrates to inhabit a wide range of habitats, and live in a variety of different ways

Key Points Questions What body structures generate force? What are the main advantages and disadvantages of an exoskeleton? Are endoskeletons always made of bone? Why are the largest land animals vertebrates? What characteristics do the skeletons of all vertebrates share? What connects bones to bones? What connects bones to joints?