Covering, Support, and Movement of the Body
the biceps brachii muscle of the arm (Figure 10.2c). However,
some authorities classify spindle-shaped muscles into a sepa-
rate class as
. Tis is the approach we use
here in Figure 10.2.
āt) pattern, the fascicles (and muscle ﬁbers)
are short and they attach obliquely (
feather) to a cen-
tral tendon that runs the length of the muscle. Pennate muscles
come in three forms:
, 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
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?
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
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
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
Te fascicular pattern is
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
(“squeezers”). Examples are the orbicularis muscles surround-
ing the eyes and the mouth.
muscle has a broad origin, and its fascicles
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).
arrangement, the length of the fascicles runs par-
allel to the long axis of the muscle. Such muscles are either
like the sartorius muscle of the thigh (Figure 10.2d),
with an expanded belly (midsection), like
Patterns of fascicle arrangement in muscles.