Animal Skeletons. Earthworm peristaltic movement. Hydrostatic Skeletons

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1 Animal Skeletons The Musculo-Skeletal System Functions: Support Protection Movement all movement results from: muscle working against a skeleton 3 Types of skeletons hydrostatic exoskeleton endoskeleton Hydrostatic Skeletons A hydrostatic skeleton fluid held under pressure in a closed body compartment typical of cnidarians flatworms nematodes annelids Earthworm peristaltic movement

2 Exoskeleton Hard encasement deposited on outside of animal Typical of mollusca arthropoda Thigh bone connected to the... The mammalian skeleton is built from more than 200 bones Some fused together and others connected at joints by ligaments that allow freedom of movement are bones alive? osteoblasts, osteocytes Endoskeleton Hard supporting elements deposited on inside of animal Typical of sponges echinoderms chordates Do you know your bones?

3 Types of joints in the appendicular skeleton

4 Vertebrate Skeletal Muscle Muscles move the skeleton What is always the action of muscle cells? Skeletal muscles are attached to the skeleton in antagonistic pairs Contraction Vertebrate Skeletal Muscle Vertebrate Skeletal Muscle

5 Vertebrate Skeletal Muscle Sliding filament theory Mechanism of contraction? thick and thin filaments... slide past one another. Mechanism of sliding filaments? Interaction between... actin and myosin: The head of a myosin molecule binds to an actin filament Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere Sliding filament theory Sliding filament theory ATP binds to myosin head Head releases from actin site Energized by phosphoryllation of ATP, Myosin head now able to bind to actin site

6 Sliding filament theory Sliding filament theory Binding to actin site releases ADP + Phosphate Myosin head bends into low E config Sliding filament theory The Role of Calcium and Regulatory Proteins If ATP available, why doesn t muscle just keep contracting? Regulation Contraction stimulated by: a motor neuron At rest, myosin-binding sites blocked by: tropomyosin (regulatory protein) Actin Tropomyosin Ca 2+ -binding sites Troponin complex (a) Myosin-binding sites blocked

7 The Role of Calcium and Regulatory Proteins What do calcium ions (Ca 2+ ) do? Bind to the troponin complex, which uncovers myosin-binding sites Myosin- binding site Ca 2+ The Role of Calcium and Regulatory Proteins Where does Ca 2+ come from? How do Ca 2+ ions get released? Action potential (AP) in a motor neuron that synapses w/ the muscle fiber releases acetylcholine (n.t.) depolarizes the muscle and causing it to produce an AP causes the sarcoplasmic reticulum (SR) to release Ca 2+ SR? = modified ER (b) Myosin-binding sites exposed Neural Control of Muscle Tension Contraction of a whole muscle is graded Which means that we can voluntarily alter the extent and strength of its contraction

8 There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles the number of fibers that contract the rate at which muscle fibers are stimulated In a vertebrate skeletal muscle Each branched muscle fiber is innervated by only one motor neuron Each motor neuron May synapse with multiple muscle fibers Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Muscle Figure Tendon Muscle fibers A motor unit Consists of a single motor neuron and all the muscle fibers it controls Recruitment of multiple motor neurons Results in stronger contractions A twitch Results from a single action potential in a motor neuron More rapidly delivered action potentials Produce a graded contraction by summation Tetanus Tension Summation of two twitches Single twitch Figure Action potential Pair of action potentials Time Series of action potentials at high frequency

9 Tetanus is a state of smooth and sustained contraction Produced when motor neurons deliver a volley of action potentials Types of Muscle Fibers Slow-twitch vs Fast twitch? white meat vs dark meat muscle that needs energy for prolonged contraction/ exercise needs more Oxygen = more myglobin, more pigment, darker Skeletal muscle fibers are classified as slow oxidative, fast oxidative, and fast glycolytic Based on their contraction speed and major pathway for producing ATP Types of skeletal muscles Other Types of Muscle Cardiac muscle, found only in the heart Consists of striated cells that are electrically connected by intercalated discs Can generate action potentials without neural input

10 In smooth muscle, found mainly in the walls of hollow organs The contractions are relatively slow and may be initiated by the muscles themselves In addition, contractions may be caused by Stimulation from neurons in the autonomic nervous system