cle that adducts (movement caused) the thigh; and the quadriceps
(4 heads) femoris muscle follows the course of the femur.
Of the muscles
illustrated in Figure 10.2, the one with the parallel arrangement (sartorius)
could shorten to the greatest degree. Te stocky bipennate (rectus femoris)
and multipennate (deltoid) muscles would be most powerful because they
pack in the most ﬁbers.
Tird-class levers are the fastest levers.
that operates at a mechanical advantage allows the muscle to exert less
force than the load being moved.
John was using the frontal belly of his
epicranius to raise his eyebrows and the orbicularis oculi muscles to wink
±o make a sad clown’s face you would contract your platysma,
depressor anguli oris, and depressor labii inferioris muscles.
has a broad origin. When only its anterior ﬁbers contract, it ﬂexes and
medially rotates the humerus. When only its posterior ﬁbers contract, it ex-
tends and laterally rotates the humerus.
Te opponens pollicis does not
have an insertion on the bones of the thumb.
Review Questions 1.
(1)e, (2)c, (3)g, (4)f, (5)d;
Case Study 1.
A prime mover is a muscle that has primary or major re-
sponsibility for producing a speciﬁc movement. A synergist is a muscle
that supports or helps the action of a prime mover by adding extra force,
or providing stability so that the prime mover can perform its action.
An antagonist is a muscle that opposes, resists, or reverses a particular
movement. By mimicking the action of an antagonist, the therapist can
test the strength of the agonist muscle and compare it with the same mus-
cle in the other limb.
Ideally, the therapist would assess each muscle
individually. In reality, these assessments usually measure the function of
a group of muscles because multiple muscles are o²en involved in similar
actions. (a) Tis assessment focuses on the thigh adductors (magnus,
longus, brevis), pectineus, and gracilis. Speciﬁcally, the adductor magnus
is innervated by the damaged sciatic nerve. (b) Tis assessment addresses
Mrs. ±anner’s ability to dorsiﬂex her foot. Dorsiﬂexion involves all of the
muscles in the anterior compartment of the lower leg: the tibialis anterior,
extensor digitorum longus, ﬁbularis (peroneus) tertius, and extensor hal-
lucis longus. (c) Tis assessment addresses the function of the muscles of
the posterior compartment of the thigh. Te hamstrings (biceps femoris,
semitendinosus, semimembranosus) are the prime movers involved in
±o assess these muscles, the therapist would apply resis-
tance to the natural action of these muscles. (a) Te extensor hallucis lon-
gus inserts on the distal phalanx of the great toe. Te therapist can apply
resistance to the top of the toe and ask Mrs. ±anner to extend the toe.
(b) Te ﬁbularis longus is involved in eversion of the foot and plantar
ﬂexion. Te therapist can apply resistance to the lateral aspect of the foot
and ask Mrs. ±anner to evert (turn out) her ankle. In addition, resistance
can be applied to the bottom of the foot and Mrs. ±anner asked to push
against that resistance. (c) Te gastrocnemius, along with the soleus, is a
powerful plantar ﬂexor. Te therapist can (1) ask Mrs. ±anner to raise her
body up on her toes using her right foot, or (2) apply pressure to the bot-
tom of the foot and ask Mrs. ±anner to push against that resistance.
Check Your Understanding 1.
Integration involves processing and inter-
preting sensory information, and making a decision about motor output.
Integration occurs primarily in the CNS.
(a) Tis “full stomach” feeling
would be relayed by the sensory (aﬀerent) division of the PNS (via its vis-
ceral aﬀerent ﬁbers). (b) Te somatic nervous system, which is part of the
motor (eﬀerent) division of the PNS, controls movement of skeletal mus-
cle. (c) Te autonomic nervous system, which is part of the motor (eﬀer-
ent) division of the PNS, controls the heart rate.
Astrocytes control the
extracellular environment around neuron cell bodies in the CNS, whereas
satellite cells perform this function in the PNS.
Schwann cells form myelin sheaths in the CNS and PNS, respectively.
restorative process, the so-called EPOC. Although jogging is primarily
an aerobic exercise, there is always some anaerobic respiration that oc-
curs as well—the amount depends on exercise intensity. As fatigue oc-
curs, potassium ions accumulate in the ± tubules, and lactic acid and
phosphate ions accumulate in the muscle cells.
Factors that inﬂuence
muscle contractile force include muscle ﬁber size, the number of muscle
ﬁbers stimulated, the frequency of stimulation, and the degree of muscle
stretch. Factors that inﬂuence velocity of contraction include muscle
ﬁber type, load, and the number of motor units contracting.
colytic ﬁbers would provide for short periods of intense strength needed
to li² and move furniture.
±o increase muscle size and strength,
anaerobic exercise is best. Muscle endurance is enhanced by aerobic ex-
Both skeletal and smooth muscle ﬁbers are elongated cells, but
unlike smooth muscle cells, which are spindle shaped, uninucleate, and
nonstriated, skeletal muscle cells are very large cigar-shaped, multinucle-
ate, striated cells.
Calcium binds to troponin on the thin ﬁlaments
in skeletal muscle cells. In smooth muscle cells, it binds to a cytoplasmic
protein called calmodulin.
Hollow organs that have smooth muscle
cells helping to form their walls o²en must temporarily store the organ’s
contents (urine, food residues, etc.), an ability ensured by the stress-
During development of skeletal muscle ﬁbers,
the myoblast cells join together, forming multinucleate myotubes.
Te connective tissue in muscles increases with age, causing the
muscles to get stringier.
Regular exercise and strength training help
to defer the loss in strength and muscle wasting that tends to occur with
age, and improve neuromuscular function.
Review Questions 1.
(1)b, (2)a, (3)b, (4)a, (5)b, (6)a;
(1)a, (2)a, c, (3)b, (4)c, (5)b, (6)b;
Case Study 1.
Te ﬁrst reaction to tissue injury is the initiation of the in-
ﬂammatory response. Te inﬂammatory chemicals increase the permea-
bility of the capillaries in the injured area, allowing white blood cells, ﬂuid,
and other substances to reach the injured area. Te next step in healing
involves the formation of granulation tissue, in which the vascular supply
for the injured area is regenerated and collagen ﬁbers that knit the torn
edges of the tissue together are formed. Skeletal muscle does not regener-
ate well, so the damaged areas of Mrs. DeStephano’s muscle tissue will
probably be repaired primarily by the formation of ﬁbrous tissue, creating
Healing is aided by good circulation of blood within the
injured area. Vascular damage compromises healing because the supply
of oxygen and nutrients to the tissue is reduced.
Under normal circum-
stances, skeletal muscles receive electrical signals from the nervous system
continuously. Tese signals help to maintain muscle tone and readiness.
Severing of the sciatic nerve removes this continuous nervous input to the
muscles and will lead to muscle atrophy. Immobility of muscles will lead
to a replacement of contractile muscle tissue with noncontractile ﬁbrous
connective tissue. Distal to the point of transection, the muscle will begin
to decrease in size within 3–7 days of becoming immobile. Tis process
can be delayed by electrically stimulating the tissues. Passive range-of-
motion exercises also help prevent loss of muscle tone and joint range,
and improve circulation in the injured areas.
Mrs. DeStephano’s phy-
sician wants to supply her damaged tissues with the necessary building
materials to encourage healing. A high-protein diet will provide plenty of
amino acids to rebuild or replace damaged proteins, carbohydrates will
provide the fuel molecules needed to generate the required A±P, and
vitamin C is important for the regeneration of connective tissue.
Check Your Understanding 1.
Te term “prime mover” refers to the mus-
cle that bears the most responsibility for causing a particular movement.
Te iliacus overlies the iliac bone; the adductor brevis is a small (size) mus-