322
UNIT 2
Covering, Support, and Movement of the Body
10
the biceps brachii muscle of the arm (Figure 10.2c). However,
some authorities classify spindle-shaped muscles into a sepa-
rate class as
fusiform muscles
. Tis is the approach we use
here in Figure 10.2.
Pennate
In a
pennate
(pen
9
āt) pattern, the fascicles (and muscle fibers)
are short and they attach obliquely (
penna
5
feather) to a cen-
tral tendon that runs the length of the muscle. Pennate muscles
come in three forms:
Unipennate
, in which the fascicles insert into only one side of
the tendon, as in the extensor digitorum longus muscle of the
leg (Figure 10.2g).
Check Your Understanding
1.
The term “prime mover” is used in the business world to
indicate people that get things done—the movers and
shakers. What is its physiological meaning?
2.
What criteria are used in naming each of the following
muscles? Iliacus, adductor brevis, quadriceps femoris.
For answers, see Appendix H.
Muscle Mechanics: Importance
of Fascicle Arrangement
and Leverage
Name the common patterns of muscle fascicle arrangement
and relate them to power generation.
Define lever, and explain how a lever operating at a
mechanical advantage differs from one operating at a
mechanical disadvantage.
Name the three types of lever systems and indicate the
arrangement of effort, fulcrum, and load in each. Also note
the advantages of each type of lever system.
We discussed most factors contributing to muscle force and
speed (load, fiber type, etc.) in Chapter 9 with two important
exceptions—fascicle arrangement and lever systems. We attend
to these factors next.
Arrangement of Fascicles
All skeletal muscles consist of fascicles (bundles of fibers), but
fascicle arrangements vary, resulting in muscles with different
shapes and functional capabilities. Te most common patterns
of fascicle arrangement are circular, convergent, parallel, and
pennate
(Figure 10.2)
.
Circular
Te fascicular pattern is
circular
when the fascicles are ar-
ranged in concentric rings (Figure 10.2a). Muscles with this ar-
rangement surround external body openings, which they close
by contracting. A general term for such muscles is
sphincters
(“squeezers”). Examples are the orbicularis muscles surround-
ing the eyes and the mouth.
Convergent
A
convergent
muscle has a broad origin, and its fascicles
con-
verge
toward a single tendon of insertion. Such a muscle is tri-
angular or fan shaped like the pectoralis major muscle of the
anterior thorax (Figure 10.2b).
Parallel
In a
parallel
arrangement, the length of the fascicles runs par-
allel to the long axis of the muscle. Such muscles are either
straplike
like the sartorius muscle of the thigh (Figure 10.2d),
or
spindle shaped
with an expanded belly (midsection), like
(f) Bipennate
(rectus femoris)
(a)
(b)
(c)
(f)
(g)
(e)
(d)
(a) Circular
(orbicularis oris)
(b) Convergent
(pectoralis major)
(d) Parallel
(sartorius)
(c) Fusiform
(biceps brachii)
(g) Unipennate
(extensor digitorum
longus)
(e) Multipennate
(deltoid)
Figure 10.2
Patterns of fascicle arrangement in muscles.
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