Chapter 40 Action and Support The Muscles and Skeleton Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Despite enormous differences in body form and structure nearly all animals jellyfish earthworms crabs horses and people move using the same fundamental mechanism Contracting muscles exert forces on the structure that supports the body called a skeleton and cause the body to change shape A body with its full complement of muscles but no skeleton would not have coordinated movement A skeleton without muscles would remain in one position unless someone else moved it Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Muscles produce force by contracting A muscle can only contract or not contract Coordinated movement of an animal s body is produced by alternating contractions of muscles with opposing actions called antagonistic muscles which can make the digestive tract thinner or fatter or move appendages back and forth Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement The animal kingdom has three types of coordinated systems of skeletons and muscles Animal skeletons come in three different forms Hydrostatic skeletons Exoskeletons Endoskeletons Antagonistic muscles act on each type of skeleton to provide movement Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Worms cnidarians jellyfish anemones and their relatives and many mollusks snails octopuses and their relatives have a hydrostatic skeleton which is basically a sac or tube filled with a liquid Hydrostatic means roughly to stand with water which is what hydrostatic skeletons do A water filled balloon stands up because it contains water but if it is punctured it collapses The volume of the balloon is fixed but you can change its shape by squeezing it in various places Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Hydrostatic skeleton continued An animal with a hydrostatic skeleton controls the overall shape of its body by using two sets of antagonistic muscles in its body wall one circular the other longitudinal For an earthworm to move forward through its burrow it uses wavelike alternating contractions of longitudinal and circular muscles Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement The bodies of arthropods such as spiders crustaceans and insects are encased by rigid exoskeletons outside skeletons Movement of an exoskeleton typically only occurs at joints in the legs mouthparts antennae bases of the wings and body segments where thin flexible tissue joins stiff sections of exoskeleton Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Exoskeleton continued Antagonistic muscles attach to opposite sides of the inside of a joint Contraction of a flexor muscle bends a joint contraction of an extensor muscle straightens a joint Alternating contraction of the antagonistic muscles moves joints back and forth allowing the animal to walk fly or spin a web Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Because the exoskeleton cannot expand arthropods must periodically molt its exoskeleton so that it can grow Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 1 How Do Muscles and Skeletons Work Together to Provide Movement Endoskeletons internal skeletons are rigid structures found inside the bodies of echinoderms sea stars and their relatives and chordates animals with a notochord most of which are vertebrates In animals with endoskeletons movement also occurs primarily at joints where two parts of the skeleton are attached to one another firmly but flexibly Antagonistic muscles such as the biceps a flexor and the triceps an extensor attach on opposite sides of the outside of a joint and move the joint back and forth or rotate them in one direction or the other Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 2 What Are the Structures of Vertebrate Muscles Vertebrates have three types of muscle skeletal cardiac and smooth All work on the same basic principles but differ in function appearance and control Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 2 What Are the Structures of Vertebrate Muscles Skeletal muscle Skeletal muscle so named because it moves the skeleton appears striped when viewed through a microscope and is often referred to as striated Nearly all skeletal muscle is under voluntary or conscious control Skeletal muscles produce contractions ranging from quick twitches to powerful sustained tension Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 2 What Are the Structures of Vertebrate Muscles Cardiac muscle Cardiac muscle which is also striated is located only in the heart It is spontaneously active it initiates its own contractions but it is also influenced by the nervous system and by hormones Cardiac muscle is usually not under voluntary control although biofeedback training allows many people to regulate their heartbeat to a limited extent Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 2 What Are the Structures of Vertebrate Muscles Smooth muscle Smooth muscle is not striated It surrounds large blood vessels and most hollow organs producing slow sustained contractions that cannot be controlled voluntarily Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle Cardiac muscle powers the heart Cardiac muscle like skeletal muscle is striated due to its regular arrangement of sarcomeres with their alternating thick and thin filaments The fibers of cardiac muscle are branched smaller than most skeletal muscles cells and possess only a single nucleus Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 40 4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle Cardiac muscle powers the heart continued Because cardiac muscles must contract around 70 times each minute and
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