Muscular System: Anatomy of a Muscle............

I). Functions of Skeletal Muscle

	Movement
	Posture
	Stabilizes joints
	Heat
	Protects organs

II). Terms

	Excitability
	Contractility
	Extensibility
	Elasticity

origin & insertion	direct & indirect attachments

III). Attachments

A). Insertion: moves the bone.
B). Origin:  does not move or is less movable.
C). Direct attachments: the connective tissue fuses to the bone.
D). Indirect attachments: outer connective tissue forms a tendon that connects to the bone

IV). Muscle Structure

A). Muscle
B). Fascicle
C). Muscle Fiber: Cell
                   sarcolemma  =  plasma membrane
D). Myofibril: Organelle
E). Sarcomere: Contractile unit

F). Myofilaments

Actin
Myosin

V). Bands of the Muscle Fiber

A).  Muscle fiber:

1). Dark A bands: The thick myosin filaments extend the length of the A band.
2). Light I bands: The thin actin filaments extend the length of the I band & part of the A band

B). Myofibril

1). A band

a). H zone: Lighter stripe
b). M line: bisects the H zone

2). I band

a). Z disc midline

Sarcomere is the area between 2 Z discs.

During muscle contractions the I band shortens

 and the Z discs move closer together.

VII). Myofilament Composition

A). Thick filament (MYOSIN)

The 2 heads  contain ATP binding sites & link the actin and myosin together during contraction.

B). Thin Filaments (ACTIN)

	Binds to the myosin heads.
	Active sites are blocked when the muscle is relaxed.