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Muscular System
I. Muscle tissue
A. Skeletal muscles
1. Composed of contractile cells bundled in muscle fibers.
2. Muscle Fibers – bundles of elongated cells made up of
alternating light and dark stripes know as striations.
3. Fascicles are dense bundles of muscle fibers bound
together by connective tissue.
4. Most skeletal muscle contractions can be controlled and
are called voluntary muscles.
B. Smooth muscle
1. differs from skeletal muscle:
- fewer nuclei in cells
- spindle shaped cells
- found in wall of internal organs and blood vessels
2. Smooth muscle contractions are not consciously
controlled and are known as involuntary muscles
II. Muscle Structure
A. Muscles are made up of hundreds to thousands of muscle
fibers, connective tissue, and blood vessels.
B. One muscle fiber contains bundles of small myofibrils.
C. Each myofibril contains two types of protein filamentsmyosin and actin.
D. The arrangement of actin and myosin in a myofibril give
muscles their striated appearance.
III. Muscle Contractions
A. Sarcromeres are the basic repeating unit of a myofibril –
they are the contraction unit of a muscle.
B. Sarcromeres begin and end at Z-lines: this is where the actin
is anchored.
C. Actin has a golfball like head on it.
D. Myosin is golf club like.
E. During contraction they each shorten and stick together
side-to-side and end-to-end.
F. This action happens in each sarcromere of a muscle causing
the whole muscle to contract or shorten.
G. The energy for muscle contraction comes in the form of ATP
H. ATP is used each time a myosin detaches from an actin.
I. If we didn’t have ATP, myosin would never release from the
actin, and the result would be permanent contraction.
IV. Muscle Movements
A. Muscles are attached to bones through tendons.
B. Point where muscle attaches to a stationary bone is known as
the origin.
C. The point where muscle attaches to a moveable bone is
known as the insertion.
D. Most skeletal muscles are arranged in opposing pairs- each
pulls the limb in a different direction.
E. Flexor -the muscle that bends a joint (bicep).
F. Extensor- the muscle that straightens a limb (tricep).
G. One muscle of the pair contracts while the other relaxes.
V. Muscle Fatigue