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* - Attachment to less moveable bone
Origin and
Insertion
Origin* - Attachment to less moveable bone
*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 reach into 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)