The Muscular System

Chapter 11

Please Note:

• The muscular system includes all the skeletal muscles that can be controlled voluntarily.

• There are about 700 identified skeletal muscles in the human body.

I. Organization of Skeletal Muscle Fibers

A. Factors that determine the effects of a muscle contraction:

1. The anatomical arrangement of the muscle fibers

2. The way the muscle attaches to the bones of the skeletal system

B. Fascicles- bundles of muscle fibers within a skeletal muscle.

C. 4 Patterns of Fascicle Organization

1. Parallel Muscles- fascicles are parallel to the long axis of the muscle.

a. Most common type.

b. Some are flat bands.

c. Some are spindle-shaped w/ a central body (aka belly or gaster)

d. Ex. biceps brachii

2. Convergent Muscles- fascicles are based over a broad area, but unite at a common attachment site.

a. Fan- or triangle-shaped

b. Ex. pectoralis group (chest muscles)

3. Pennate Muscles- fascicles form a common angle with the tendon.

a. Unipennate- Fibers go off in one direction Ex. extensor digitorum

b. Bipennate- Fibers go off in two directions Ex. rectus femoris

c. Multipennate- Fibers go off in many directions

Ex. deltoid

4. Circular Muscles (aka sphincter)- fibers are concentrically arranged around an opening or recess.

a. Contracting decreases the diameter of the opening.

b. Guard entrances and exits of internal passageways.

c. Ex. orbicularis oris (mouth)

(a review from physical science…)

Levers are:– simple machines

– structures that move on a fixed point called a fulcrum.

– When effort force is applied, a lever moves about the fulcrum, overcoming the resistance.

II. 3 Classes of Levers in the Body

A. First Class Levers

1. The fulcrum lies between the applied force (AF) and the resistance (R)

2. Ex.a. Teeter-totter

b. scissors

B. Second Class Levers

1. The resistance is located between the applied force and the fulcrum.

2. Ex.a. Wheelbarrowb. Hinged doors

C. Third Class Levers1. The applied force is between the resistance and

the fulcrum.

2. This is the most common type of lever in the body.

3. Ex.a. Sweeping

b. Shoveling

III. Muscle Terminology

A. Muscle Attachment1. Origin- where a muscle begins

a. Generally remains stationaryb. Generally proximal

2. Insertion- where a muscle endsa. Generally moveableb. Generally distal

3. Contraction results in the shortening of the distance between the origin & insertion, which causes movement at the insertion end.

Actions (review)

• Flexion• Rotation• Adduction• Pronation• Protraction• Inversion• Lateral Flexion• Depression

• Extension• Circumduction• Abduction• Supination• Retraction• Eversion• Opposition • Elevation

IV. Grouping Muscles According to their Primary Actions:

A. Prime Mover / Agonist- muscle whose contraction is chiefly responsible for producing a particular movement.

– Ex. biceps brachii

B. Antagonists- muscle that opposes agonist.– Ex. triceps brachii

C. Synergist- assists the prime mover

D. Fixator- stabilizes agonist to prevent movement.

V. Naming Skeletal Muscle

A. Fascicle Organization:1. Rectus- “straight”- parallel muscles whose

fibers run along the long axis of the body

2. Transversus- muscles whose fibers run across the long axis of the body

3. Obliquus- muscles whose fibers run at an angle to the long axis of the body

B. Relative Position:1. Externus- visible at body surface

2. Superficialis- visible at body surface

3. Internus- found beneath the surface

4. Profundus- found beneath the surface

5. Extrinsic- superficial muscles that stabilize an organ

6. Intrinsic- muscles located entirely within the organ

C. Structure:1. Ex. biceps brachii (2 tendons of origin) 2. Ex. quadriceps group (4 tendons of origin)

D. Size:1. Longus / Brevis - long / short muscles2. Major / Minor - large / small muscles

E. Shape:1. Ex. Trapezius- trapezoid-shaped2. Ex. Rhomboideus- rhomboid-shaped

F. Origin & Insertion:1. Ex. genioglossus

a. Origin: chin “geneion”

b. Insertion: tongue “glossus”

G. Action:1. Flexor

2. Extensor

3. …