The Muscular System

1. The Muscular System The Skeletal Muscles

2. Types of Muscle • Smooth - lines blood vessels and other organs (ex. Stomach) (involuntary) • Cardiac - found in heart (involuntary) • Skeletal - attached to skeleton to create movement (voluntary)

3. Functions of skeletal muscle • Movement • Posture • Stabilize joints • Generate heat

4. Origin and Insertion Origin* - Attachment to less moveablebone *Muscles are attached to bones by tendons Insertion* - point of attachment to moveable bone

5. Flexors and Extensors • Flexor - decreases angle between bones at a joint (ex.curling forearm towards upper arm) • Extensor - increases angle between bones at a joint (ex. straightening arm)

6. Prime mover/Agonist vs. Antagonist • Prime movers are muscles that produce the most force for a give movement • Antagonists oppose the force of the prime mover, but are not activated during the movement

7. Types of Muscle Contractions • Isometric - muscle contracts, but does not shorten or lengthen • Isotonic - muscle contracts, and either shortens or lengthens • Concentric - muscle contracts as it shortens • Eccentric - muscle contracts as it lengthens

8. Muscle Contraction • Muscle contraction is stimulated by motor neurons • Motor neurons are nerve cells that stimulate skeletal muscle • Each muscle is innervated by at least one motor nerve • A motor neuron and the muscle fibers it controls are called a motor unit

9. Motor Units • Motor units are activated during contraction • To exert more force (i.e. moving a heavy weight or moving very quickly) more motor units must be recruited

10. Parts of a Muscle Fiber (a.k.a. muscle cell) • Sarcolemma - cell membrane of muscle fiber • Sarcoplasm - cytoplasm of muscle fiber • Sarcoplasmic reticulum - endoplasmic reticulum of muscle fiber (stores Ca2+ ions) • T-tubules - folding in of the sarcolemma (allows nerve impulses to reachinto the interior of a fiber)

11. Muscle Contraction (cellular level) • Motor neuron sends nerve impulse to muscle fibers • Impulse travels along sarcolemma of fiber and down T-tubules • Calcium ions are released from the sarcoplasmic reticulum • Ca2+ allow myosin heads to attach to actin binding sites forming a cross-bridge • Using the energy of ATP, myosin pulls on actin, causing the muscle to shorten along its length

12. Sarcomere - smallest contractile unit of skeletal muscle • A Band - area occupied by myosin filaments (dark) • H zone - area between actin filaments • Z disk - proteins marking the beginning and end of the sarcomere • I band - area where there is no mysoin (light)