Muscles

Types of Mucles Cardiac Muscle Branched Intercalated disc Myogenic – does not need a nerve impulse to contract Smooth Muscle Spindle shaped Involuntary Striated Muscle- Skeletal Muscle Multinucleated Voluntary Striated

Vertebrate Skeletal Muscle Skeletal Muscle is also called striated muscle Sarcomere: repeating unit of muscle tissue or functional unit of muscle contraction Z lines ~ sarcomere border I band~only actin protein A band~actin & myosin protein overlap H zone~central sarcomere; only myosin

Sliding-filament model Theory of muscle contraction Sarcomere length reduced Z line length becomes shorter Actin and myosin slide past each other (overlap increases)

Steps of Muscle Contraction 1. A motor neuron will release acetylcholine at the synapse of the neuromuscular junction. 2. Acetylcholine binds to receptors on the muscle fiber and causes depolarization of the muscle fiber. 3. This creates an action potential along the T-Tubules (transverse tubules) to the sarcoplasmic reticulum (E.R.) 4. Calcium ions are released from the sarcoplasmic reticulum.

5. Calcium ions bind to troponin and cause it to move off of the actin, exposing the myosin binding sites. 6. Myosin cross-bridges form with the actin and pull the actin towards the center of the sarcomere. This requires ATP. 7. Ca++ is removed by active transport back into the SR after the action potential ends.

8. Tropomyosin blockage of the myosin binding sites is restored and the contraction ends and the muscle fiber lengthens (relaxes)

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Types of Skeletons Hydrostatic – consists of fluid held under pressure in a closed body compartment Hydra Nematodes Annelids Exoskeleton – hard encasements on the outer surface of the animal such as insects and lobsters. Endoskeleton – hard supporting elements buried inside the soft tissues of the animal – bony skeleton