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The Muscular System Functions Gross Structure of Skeletal Muscle Muscles Working Together Shapes of Muscles Naming Muscles Muscles act through Levers Functions of Muscle Movement Stability Energy source Heat source Food source Structure of Muscles at the Gross Level Muscles must be attached at two sites (tendinous origin and insertion) The origin is defined as the attachment which is less mobile on contraction The insertion is defined as the attachment that is more mobile on contraction The origin is also called the head of the muscle; the thicker, fleshy part is the belly Muscles do not work individually to control movement Synergists: work together to cause a movement example: biceps brachii and the brachialis flex forearm Antagonists: muscles working in opposition to movement caused by synergists example: the triceps is an antagonist to the biceps brachii Prime Mover: the main synergist resposible for an action example: brachialis Muscles do not work individually to control movement Fixator: stabilizes a joint which is crossed by a prime mover example: muscles controlling wrist extension stabilize the wrist so that flexors of the fingers can act Shapes of Muscles Pennate (feather-like) Parallel Convergent Shapes of Muscles Geometric Shapes Multiple Heads Naming of Muscles Muscles are named for: - their location (pectoralis; brachialis) - their size (major, minor, maximus, minimus, longus, brevis, etc.) - their shape (deltoid, teres, quadratus) - orientation (oblique, rectus) - origin & insertion (sternocleidomastoid, brachioradialis) - number of heads (biceps, triceps, quadriceps) - function (abductor, adductor, flexor, extensor, etc) Muscles act through Levers Muscles act by causing a pulling force across a lever A lever is a rigid shaft which moves across a pivot point (fulcrum) against resistance (weight) In the body, the shaft is bone and the fulcrum is a joint There are three classes of levers, which differ by the relative location of the pulling force, fulcrum, and weight along the shaft Each class has different capabilities: how much weight is moved, and how far Types of Levers: Class I In a Class I lever, the fulcrum is located between the pulling force (tendon attachment) and the weight being lifted. Example: seesaw easily move a small amount of weight a small distance fulcrum weight force Types of Levers: Class I Example in the body: atlanto-occipital joint Types of Levers: Class II In a Class II lever, the weight is located between the fulcrum and the force. Example: wheelbarrow Able to lift a large amount of weight a short distance Weight Force Fulcrum Types of Levers: Class II Example in the body: lifting the body by plantarflexion Types of Levers: Class III In a Class III lever, the force is located between the fulcrum and the weight Most common type of lever in the body Example: lifting dirt in a shovel Less weight can be lifted, but lifted a greater distance Types of Levers: Class III Example in the body: flexion of the forearm Next Lecture... Histology of Skeletal Muscle