The Muscular System

The Skeletal Muscles

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)

Functions of skeletal muscle Movement Posture Stabilize joints Generate heat

Insertion* - point ofattachment to moveable bone

Origin* - Attachment to less moveablebone

Origin andInsertion

*Muscles areattached to bones bytendons

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)

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

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

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

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

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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)

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

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)

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