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THE MUSCULAR SYSTEM
Chapter 11
CHAPTER SUMMARY
This chapter describes in detail how the skeletal muscles of the body produce specific movements of the body. Specific
movements occur as a consequence of a number of characteristics including the origin and insertion of a muscle, lever
systems and leverage, the arrangement of fascicles, and the coordinated actions of groups of muscles acting cooperatively.
The characteristics used in the naming of individual muscles are concisely explained. The principal skeletal muscles are
presented in groups and each individual muscle is described according to the following criteria: name, origin, insertion,
and action. This chapter concludes with a thorough study outline, an excellent self-quiz, critical thinking questions, and
answers to questions that accompany chapter figures.
STUDENT OBJECTIVES
1. Describe the relationship between bones and skeletal muscles in producing body movements.
2. Define a lever and a fulcrum and compare the three types of levers on the basis of location of the fulcrum, effort, and
resistance.
3. Identify the various arrangements of muscle fibers in a skeletal muscle, and relate the arrangements to the strength of
contraction and range of motion.
4. Explain how the prime mover, antagonist, synergist, and fixator in a muscle group work together to produce
movements.
5. Explain seven characteristics used in naming skeletal muscles.
6. Identify the principal skeletal muscles in different regions of the body by name, origin, insertion, action
LECTURE OUTLINE
A. How Skeletal Muscles Produce Movement: (p. 289)
1. Origin and Insertion
i. Contractions of skeletal muscles produce movements by exerting a pulling force on tendons, which in
turn pull on bones (or other structures, such as skin).
ii. Most muscles extend across at least one joint and are attached to the articulating bones that form the
joint.
iii. When such a muscle contracts, one bone remains relatively stationary while the other (movable) bone
is pulled toward it.
a. The attachment of a muscle tendon to the stationary bone is the origin (it is usually the
proximal attachment).
b. The attachment of the other muscle tendon to the movable bone is the insertion (it is usually
the distal attachment).
iv. During most contractions, the insertion is pulled toward the origin resulting in the observed movement.
v. The fleshy portion of the muscle located between the tendons is called the belly (gaster).
2. Lever Systems and Leverage (p. 290)
i. To produce a body movement, bones act as levers and joints function as the fulcrums of these levers.
ii. A lever is acted on at two different points by two different forces:
a. effort, which is the force exerted to achieve a movement
b. load or resistance, which is the weight that opposes movement.
iii. Leverage is the mechanical advantage, or disadvantage, gained by a lever; it is largely responsible for a
muscle’s strength and range of motion, i.e., the maximum ability to move the bones of a joint through
an arc. Strength and range of motion vary inversely.
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iv. Levers are classified into three types:
a. first-class levers have the fulcrum between the effort and resistance (EFL)
b. second-class levers have the fulcrum at one end, the effort at the opposite end, and the
resistance between them (FLE)
- most authorities believe that there are no second-class levers in the body
c. third-class levers have the fulcrum at one end, the resistance at the opposite end, and the effort
between them (FEL); these are the most common levers in the body.
3. Effects of Fascicle Arrangement (p. 291)
i. Skeletal muscle fibers are arranged within a muscle in bundles called fascicles.
ii. Within each fascicle the fibers are arranged in a parallel fashion, but the arrangement of fascicles with
respect to the tendons may take one of several characteristic patterns (see Table 11.1):
a. parallel
b. fusiform
c. circular
d. triangular
e. pennate
- unipennate
- bipennate
- multipennate
iii. Fascicular arrangement affects the power of a muscle and its range of motion.
4. Coordination within Muscle Groups (p. 292)
i. Most movements require several muscles acting cooperatively in groups rather than individually; in
addition, most skeletal muscles are arranged in opposing (antagonistic) pairs at joints.
ii. A prime mover or agonist is a muscle that causes a desired action.
iii. An antagonist is a muscle whose effect is opposite to that of the prime mover; an antagonist must relax
in order to permit the agonist to cause the desired action.
iv. A synergist is a muscle that serves to prevent unwanted movements at intermediate joints or helps the
prime mover function more efficiently.
v. Some muscles in a group also act as fixators, which stabilize the origin of a prime mover so that the
prime mover can act more efficiently.
vi.
Under different conditions, i.e., depending on the movement, many muscles may act, at various
times, as prime movers, antagonists, synergists, or fixators.
vii.
In the limbs, a compartment is a group of muscles (along with their associated blood vessels and
nerves) that have a common function.
B. How Skeletal Muscles Are Named (p. 293)
1. The names of most of the nearly 700 skeletal muscles are based on a number of different characteristics (see
Table 11.2):
i. direction of muscle fibers, such as:
a. rectus (e.g., rectus abdominis)
b. transverse (e.g., transversus abdominis)
c. oblique (e.g., external oblique)
ii. size, such as:
a. maximus (e.g., gluteus maximus)
b. minimus (e.g., gluteus minimus)
c. longus (e.g., adductor longus)
d. brevis (e.g., peroneus brevis)
iii. shape, such as:
a. deltoid
b. trapezius
c. serratus (e.g., serratus anterior)
d. rhomboideus (e.g., rhomboideus major)
iv. action, such as:
a. flexor (e.g., flexor carpi radialis)
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b. extensor (e.g., extensor carpi ulnaris)
c. abductor (e.g., abductor pollicis brevis)
d. adductor (e.g., adductor longus)
e. levator (e.g., levator scapulae)
f. depressor (e.g., depressor labii inferioris)
g. supinator
h. pronator (e.g., pronator teres)
i. sphincter (e.g., external anal sphincter)
j. tensor (e.g., tensor fasciae latae)
k. rotator (e.g., obturator externus)
v. number of origins, such as:
a. biceps (e.g., biceps brachii)
b. triceps (e.g., triceps brachii)
c. quadriceps (e.g., quadriceps femoris)
vi. location (e.g., frontalis, tibialis anterior)
vii. origin and insertion (e.g., sternocleidomastoid, stylohyoid)
C. Principal Skeletal Muscles (p. 297)
1. Every principal muscle in the body is described according to the following criteria:
i. name accompanied by phonetic pronunciation and derivation
ii. origin
iii. insertion
iv. action
v. innervation
2. The actions of muscles are more easily understood if the naming of muscles is mastered.
3. The muscles are divided into groups according to the part of the body on which they act; as each group of
muscles is studied, students should note how each group is related to all other groups.
4. The figures that accompany the exhibits contain superficial and deep, anterior and posterior, or medial and
lateral views to show each muscle’s position as clearly as possible.
5. The groups of muscles are presented in the following sequence:
Exhibit 11.1 Muscles of Facial Expression
Exhibit 11.2 Muscles That Move the Eyeballs - Extrinsic Eye Muscles
Exhibit 11.3 Muscles That Move the Mandible (Lower Jaw Bone)
Exhibit 11.4 Muscles That Move the Tongue - Extrinsic Tongue Muscles
Exhibit 11.5 Muscles of the Anterior Neck
Exhibit 11.6 Muscles That Move the Head
Exhibit 11.7 Muscles of the Larynx (Voice Box)
Exhibit 11.8 Muscles of the Pharynx (Throat)
Exhibit 11.9 Muscles That Act on the Abdominal Wall
Exhibit 11.10 Muscles Used in Breathing
Exhibit 11.11 Muscles of the Pelvic Floor
Exhibit 11.12 Muscles of the Perineum
Exhibit 11.13 Muscles That Move the Pectoral (Shoulder) Girdle
Exhibit 11.14 Muscles That Move the Humerus (Arm Bone)
Exhibit 11.15 Muscles That Move the Radius and Ulna (Forearm Bones)
Exhibit 11.16 Muscles That Move the Wrist, Hand, Thumb, and Fingers
Exhibit 11.17 Intrinsic Muscles of the Hand
Exhibit 11.18 Muscles That Move the Vertebral Column (Backbone)
Exhibit 11.19 Muscles That Move the Femur (Thigh Bone)
Exhibit 11.20 Muscles That Act on the Femur (Thigh Bone) and Tibia and Fibula (Leg)
Exhibit 11.21 Muscles That Move the Foot and Toes
Exhibit 11.22 Intrinsic Muscles of the Foot