The actions that muscles perform are listed in Table 7–2 and some are shown in Fig. 7–7. Most are in pairs as antagonistic functions.
After the brief summaries of the muscles of each body area that follow, the major muscles are shown in Fig. 7–8. They are listed, according to body area, in Tables 7–3 through 7–7, with associated Figs. 7–9 through 7–13, respectively. When you study the dia- grams of these muscles, and the tables that accompany them, keep in mind the types of joints formed by the bones of their origins and insertions. Muscles pull bones to produce movement, and if you can remember the joints involved, you can easily learn the locations and actions of the muscles.
The name of the muscle may also be helpful, and again, many of the terms are ones you have already learned. Some examples: “abdominis” refers to an abdominal muscle, “femoris” to a thigh muscle,
“brachii” to a muscle of the upper arm, “oculi” to an
eye muscle, and so on. Other parts of muscle names may be words such as “longus” or “maximus” that tell you about size, or “flexor” that tells you about function.
Muscles that are sites for intramuscular injections are shown in Box 7–5.
BOX7–5 COMMON INJECTION SITES Intramuscular injectionsare used when rapid absorption is needed, because muscle has a good blood supply. Common sites are the but- tock (gluteus medius), the lateral thigh (vastus lat- eralis), and the shoulder (deltoid). These sites are shown; also shown are the large nerves to be avoided when giving such injections.
Box Figure 7–A Sites for intramuscular injections.
Posterior view of right side of body.
150 The Muscular System
MUSCLES OF THE HEAD AND NECK
Three general groups of muscles are found in the head and neck: those that move the head or neck, the mus- cles of facial expression, and the muscles for chewing.
The muscles that turn or bend the head, such as the sternocleidomastoids (flexion) and the pair of splenius capitis muscles (extension), are anchored to the skull and to the clavicle and sternum anteriorly or the ver- tebrae posteriorly. The muscles for smiling or frown- ing or raising our eyebrows in disbelief are anchored to the bones of the head or to the undersurface of the skin of the face. The masseter is an important chewing muscle in that it raises the mandible (closes the jaw).
Flexion
Flexion
Extension
Extension
Abduction Adduction Abduction
Adduction
Figure 7–7. Actions of muscles.
QUESTION:Crossing the arm in front of the chest would be which of these actions?
Table 7–2 ACTIONS OF MUSCLES
Action Definition
Flexion Extension Adduction Abduction Pronation Supination Dorsiflexion Plantar flexion Rotation
Most are grouped in pairs of antagonistic functions.
• To decrease the angle of a joint
• To increase the angle of a joint
• To move closer to the midline
• To move away from the midline
• To turn the palm down
• To turn the palm up
• To elevate the foot
• To lower the foot (point the toes)
• To move a bone around its longitudinal axis
MUSCLES OF THE TRUNK
The muscles of the trunk cannot be described with one or two general functions. Some form the wall of the trunk and bend the trunk, such as the rectus abdo- minis (f lexion) and the sacrospinalis group (exten- sion). The trapezius (both together form the shape of a trapezoid) is a large muscle that can raise (shrug) the shoulder or pull it back, and can help extend the head.
Other muscles found on the trunk help move the arm at the shoulder. The pectoralis major is a large muscle of the chest that pulls the arm across the chest (flexion and adduction). On the posterior side of the trunk, the latissimus dorsi pulls the arm downward and behind the back (extension and adduction). These muscles have their origins on the bones of the trunk, the ster- num, the or vertebrae, which are strong, stable anchors. Another set of muscles forms the pelvic floor, where the muscles support the pelvic organs and assist with urination and defecation. Yet another category is the muscles that are concerned with breathing. These are the intercostal muscles between the ribs and the diaphragm that separates the thoracic and abdominal cavities (see Fig. 15–6).
MUSCLES OF THE SHOULDER AND ARM
The triangular deltoid muscle covers the point of the shoulder like a cap, and can pull the humerus to the
side (abduction), forward (flexion), or backward (extension). You already know the functions of the biceps brachii and triceps brachii, the muscles that form the bulk of the upper arm. Other muscles par- tially in the upper arm help bend the elbow (flexion).
The muscles that form the bulk of the forearm are the flexors and extensors of the hand and fingers. You can demonstrate this yourself by clasping the middle of your right forearm with your left hand, then moving your right hand at the wrist and closing and opening a fist; you can both feel and see the hand and finger muscles at work.
MUSCLES OF THE HIP AND LEG
The hip muscles that move the thigh are anchored to the pelvic bone and cross the hip joint to the femur.
Among these are the gluteus maximus (extension), gluteus medius (abduction), and iliopsoas (flexion).
The muscles that form the thigh include the quadri- ceps group anteriorly and the hamstring group posteriorly. For most people, the quadriceps is stronger than the hamstrings, which is why athletes more often have a “pulled hamstring” rather than a
“pulled quadriceps.” Movement of the knee joint depends on thigh muscles and lower leg muscles.
Movement of the foot depends on lower leg muscles such as the gastrocnemius (dorsiflexion or flexion) and the tibialis anterior (plantar flexion or extension).
152
Brachioradialis Biceps
brachii Brachialis Triceps brachii
Latissimus dorsi
External oblique Gluteus medius
Gluteus maximus
Vastus lateralis Biceps femoris Semitendinosus
Soleus
A
Achilles tendon
Trapezius Deltoid
Infraspinatus Teres major
Triceps brachii
Brachioradialis
Adductor magnus
Gracilis
Semimembranosus
Gastrocnemius
Figure 7–8. Major muscles of the body. (A) Posterior view.
B
Pectineus Masseter
Sternocleidomastoid
Deltoid Pectoralis major
Brachialis Biceps brachii
Brachioradialis
Gastrocnemius Tibialis anterior
Soleus
Vastus medialis Vastus lateralis Gracilis
Rectus femoris Adductor longus
Sartorius Iliopsoas
Rectus abdominis External oblique Triceps
brachii
Figure 7–8. Major muscles of the body. (B) Anterior view.
QUESTION:Find a muscle named for: shape, size, location, a bone it is near, and function.
153
154
Levator labii superioris
Zygomaticus
Orbicularis oris
Mentalis
Platysma
Anterior—left lateral view
Orbicularis oculi
Temporalis
Buccinator Masseter Sternohyoid Sternocleidomastoid
Trapezius Frontalis
Epicranial aponeurosis
Figure 7–9. Muscles of the head and neck in anterior, left-lat- eral view.
QUESTION:In what way are both orbicularis muscles similar?
Table 7–3 MUSCLES OF THE HEAD AND NECK
Muscle Function Origin Insertion
Frontalis Orbicularis oculi Orbicularis oris Masseter Buccinator
Sternocleidomastoid Semispinalis capitis
(a deep muscle) Splenius capitis
Raises eyebrows, wrinkles skin of forehead
Closes eye Puckers lips Closes jaw
Pulls corners of mouth laterally Turns head to opposite side
(both—flex head and neck) Turns head to same side (both—
extend head and neck) Turns head to same side (both—
extend head)
• epicranial aponeurosis
• medial side of orbit
• encircles mouth
• maxilla and zygomatic
• maxilla and mandible
• sternum and clavicle
• 7th cervical and first 6 thoracic vertebrae
• 7th cervical and first 4 thoracic vertebrae
• skin above supraorbital margin
• encircles eye
• skin at corners of mouth
• mandible
• orbicularis oris
• temporal bone (mastoid process)
• occipital bone
• occipital bone
155 Table 7–4 MUSCLES OF THE TRUNK
Muscle Function Origin Insertion
Trapezius
External intercostals Internal intercostals Diaphragm Rectus abdominis External oblique Sacrospinalis group
(deep muscles)
Raises, lowers, and adducts shoulders
Pull ribs up and out (inhalation) Pull ribs down and in (forced
exhalation)
Flattens (down) to enlarge chest cavity for inhalation Flexes vertebral column, com-
presses abdomen
Rotates and flexes vertebral col- umn, compresses abdomen Extends vertebral column
• occipital bone and all thoracic vertebrae
• superior rib
• inferior rib
• last 6 costal cartilages and lumbar vertebrae
• pubic bones
• lower 8 ribs
• ilium, lumbar, and some thoracic vertebrae
• spine of scapula and clavicle
• inferior rib
• superior rib
• central tendon
• 5th–7th costal cartilages and xiphoid process
• iliac crest and linea alba
• ribs, cervical, and thoracic vertebrae External oblique
Internal oblique
Transversus abdominis
Rectus abdominis
Trapezius
Pectoralis major Serratus anterior
Trapezius
Splenius capitis Deltoid
Teres major Infraspinatus
Rhomboideus major
Gluteus maximus
Latissimus dorsi External oblique
B
Figure 7–10. Muscles of the trunk. (A) Anterior view. (B) Posterior view.
QUESTION:Which muscles of the trunk move the arm? Why are they on the trunk?
156 The Muscular System
Deltoid
Biceps
Brachialis
Extensor carpi radialis longus
Extensor carpi radialis longus
Brachioradialis Flexor carpi radialis Extensor carpi radialis brevis Abductor pollicis brevis
Abductor pollicis
Triceps
Palmaris longus
Flexor pollicis longus
Deltoid
Brachialis
Brachioradialis
Extensor carpi radialis brevis
Extensor digitorum
A B
Flexor digitorum superficialis
Abductor pollicis longus
Extensor pollicis brevis Anconeus
Flexor carpi ulnaris
Extensor carpi ulnaris
Extensor digiti minimi
Figure 7–11. Muscles of the arm. (A) Anterior view. (B) Posterior view.
QUESTION:Where are the muscles that flex the fingers located? How did you know?
Table 7–5 MUSCLES OF THE SHOULDER AND ARM
Muscle Function Origin Insertion
Deltoid Pectoralis major Latissimus dorsi Teres major Triceps brachii Biceps brachii Brachioradialis
Abducts the humerus Flexes and adducts the
humerus
Extends and adducts the humerus Extends and adducts
the humerus Extends the forearm Flexes the forearm Flexes the forearm
• scapula and clavicle
• clavicle, sternum, 2nd–6th costal cartilages
• last 6 thoracic vertebrae, all lum- bar vertebrae, sacrum, iliac crest
• scapula
• humerus and scapula
• scapula
• humerus
• humerus
• humerus
• humerus
• humerus
• ulna
• radius
• radius
Table 7–6 MUSCLES OF THE HIP AND LEG
Muscle Function Origin Insertion
Iliopsoas Gluteus maximus Gluteus medius
Quadriceps femoris group:
Rectus femoris Vastus lateralis Vastus medialis Vastus intermedius Hamstring group
Biceps femoris Semimembranosus Semitendinosus Adductor group Sartorius Gastrocnemius Soleus Tibialis anterior
Flexes femur Extends femur Abducts femur
Flexes femur and extends lower leg
Extends femur and flexes lower leg
Adducts femur
Flexes femur and lower leg Plantar flexes foot
Plantar flexes foot Dorsiflexes foot
• ilium, lumbar vertebrae
• iliac crest, sacrum, coccyx
• ilium
• ilium and femur
• ischium
• ischium and pubis
• ilium
• femur
• tibia and fibula
• tibia
• femur
• femur
• femur
• tibia
• tibia and fibula
• femur
• tibia
• calcaneus (Achilles tendon)
• calcaneus (Achilles tendon)
• metatarsals
158
Sartorius
Rectus femoris
Vastus lateralis
Peroneus longus Tibialis anterior
Extensor digitorum brevis Extensor digitorum longus
Extensor hallucis brevis Iliopsoas
Pectineus
Adductor longus Adductor magnus
Gracilis
Semitendinosus Vastus medialis Semimembranosus
Gastrocnemius
Soleus
A
B
Flexor
digitorum longus Peroneus brevis Extensor hallucis longus
Gluteus maximus
Vastus lateralis
Plantaris
Peroneus longus Biceps femoris
Figure 7–12. Muscles of the leg. (A) Anterior view. (B) Posterior view.
QUESTION:How does the gastrocnemius compare in size to the tibialis anterior? What is the reason for this difference?
Clitoris Urethra Vagina Ischium Central tendon Anus Gluteus maximus Anococcygeal
ligament
Coccyx
Ischiocavernosus Bulbospongiosus
Transverse perineus Levator ani
External anal sphincter Coccygeus
Figure 7–13. Muscles of the female pelvic floor.
QUESTION:In women, what organs are directly supported by this “floor” of muscles?
Table 7–7 MUSCLES OF THE PELVIC FLOOR
Muscle Function Origin Insertion
Levator ani
Coccygeus
Ischiocavernosus Bulbospongiosus Transverse perineus
(superficial and deep) External anal sphincter
Supports pelvic organs, especially dur- ing defecation, urination, coughing, and forced exhalation; constricts anus, urethra, and vagina
Supports pelvic organs, especially dur- ing defecation, urination, coughing, and forced exhalation
Erection of clitoris in female, penis in male
Assists urination; erection in female;
erection and ejaculation in male Assists urination in female; urination and
ejaculation in male Closes anus
• pubis and ischium
• ischium
• ischium and pubis
• central tendon of perineum
• ischium
• anococcygeal ligament
• coccyx, anal canal, urethra
• coccyx and sacrum
• clitoris or penis
• fasciae, pubic arch, clitoris, or penis
• central tendon of perineum
• central tendon of perineum
STUDY OUTLINE
Organ Systems Involved in Movement 1. Muscular—moves the bones.
2. Skeletal—bones are moved, at their joints, by mus- cles.
3. Nervous—transmits impulses to muscles to cause contraction.
4. Respiratory—exchanges O2 and CO2 between the air and blood.
5. Circulatory—transports O2to muscles and removes CO2.
Muscle Structure
1. Muscle fibers (cells) are specialized to contract, shorten, and produce movement.
2. A skeletal muscle is made of thousands of muscle fibers. Varying movements require contrac-
tion of variable numbers of muscle fibers in a muscle.
3. Tendons attach muscles to bone; the origin is the more stationary bone, the insertion is the more movable bone. A tendon merges with the fascia of a muscle and the periosteum of a bone; all are made of fibrous connective tissue.
Muscle Arrangements
1. Antagonistic muscles have opposite functions. A muscle pulls when it contracts, but exerts no force when it relaxes and it cannot push. When one mus- cle pulls a bone in one direction, another muscle is needed to pull the bone in the other direction (see also Table 7–2 and Fig. 7–1).
2. Synergistic muscles have the same function and alternate as the prime mover depending on the position of the bone to be moved. Synergists also stabilize a joint to make a more precise movement possible.
3. The frontal lobes of the cerebrum generate the impulses necessary for contraction of skeletal mus- cles. The cerebellum regulates coordination.
Muscle Tone—the state of slight contraction present in muscles
1. Alternate fibers contract to prevent muscle fatigue;
regulated by the cerebellum.
2. Good tone helps maintain posture, produces 25%
of body heat (at rest), and improves coordination.
3. Isotonic exercise involves contraction with move- ment; improves tone and strength and improves cardiovascular and respiratory efficiency (aerobic exercise).
• Concentric contraction—muscle exerts force while shortening.
• Eccentric contraction—muscle exerts force while lengthening.
4. Isometric exercise involves contraction without movement; improves tone and strength but is not aerobic.
Muscle Sense—proprioception: knowing where our muscles are without looking at them
1. Permits us to perform everyday activities without having to concentrate on muscle position.
2. Stretch receptors (proprioceptors) in muscles respond to stretching and generate impulses that the brain interprets as a mental “picture” of where
the muscles are. Parietal lobes: conscious muscle sense; cerebellum: unconscious muscle sense used to promote coordination.
Energy Sources for Muscle Contraction 1. ATP is the direct source; the ATP stored in muscles
lasts only a few seconds.
2. Creatine phosphate is a secondary energy source; is broken down to creatine ⫹ phosphate ⫹ energy.
The energy is used to synthesize more ATP. Some creatine is converted to creatinine, which must be excreted by the kidneys. Most creatine is used for the resynthesis of creatine phosphate.
3. Glycogen is the most abundant energy source and is first broken down to glucose. Glucose is broken down in cell respiration:
Glucose ⫹O2→CO2⫹H2O ⫹ATP ⫹heat ATP is used for contraction; heat contributes to body temperature; H2O becomes part of intracellu- lar fluid; CO2is eventually exhaled.
4. Oxygen is essential for the completion of cell res- piration. Hemoglobin in red blood cells carries oxygen to muscles; myoglobin stores oxygen in muscles; both of these proteins contain iron, which enables them to bond to oxygen.
5. Oxygen debt (recovery oxygen uptake): Muscle fibers run out of oxygen during strenuous exercise, and glucose is converted to lactic acid, which causes fatigue. Breathing rate remains high after exercise to deliver more oxygen to the liver, which converts lactic acid to pyruvic acid, a simple carbohydrate (ATP required).
Muscle Fiber—microscopic structure
1. Neuromuscular junction: axon terminal and sar- colemma; the synapse is the space between. The axon terminal contains acetylcholine (a neurotrans- mitter), and the sarcolemma contains cholinesterase (an inactivator) (see Fig. 7–2).
2. Sarcomeres are the contracting units of a muscle fiber. Myosin and actin filaments are the contract- ing proteins of sarcomeres. Troponin and tropo- myosin are proteins that inhibit the sliding of myosin and actin when the muscle fiber is relaxed (see Figs. 7–3 and 7–5).
3. The sarcoplasmic reticulum surrounds the sarco- meres and is a reservoir for calcium ions.
4. Polarization (resting potential): When the muscle fiber is relaxed, the sarcolemma has a (⫹) charge 160 The Muscular System
1. Name the organ systems directly involved in movement, and for each state how they are involved. (p. 138)
2. State the function of tendons. Name the part of a muscle and a bone to which a tendon is attached.
(p. 138)
3. State the term for: (pp. 138–139) a. Muscles with the same function b. Muscles with opposite functions
c. The muscle that does most of the work in a movement
4. Explain why antagonistic muscle arrangements are necessary. Give two examples. (p. 138) 5. State three reasons why good muscle tone is
important. (p. 140)
6. Explain why muscle sense is important. Name the receptors involved and state what they detect.
(p. 141)
7. With respect to muscle contraction, state the functions of the cerebellum and the frontal lobes of the cerebrum. (p. 140)
8. Name the direct energy source for muscle con- traction. Name the two secondary energy sources.
Which of these is more abundant? (p. 141) 9. State the simple equation of cell respiration and
what happens to each of the products of this reac- tion. (p. 142)
10. Name the two sources of oxygen for muscle fibers. State what the two proteins have in com- mon. (p. 142)
11. Explain what is meant by oxygen debt. What is needed to correct oxygen debt, and where does it come from? (p. 142)
12. Name these parts of the neuromuscular junction:
(p. 142)
a. The membrane of the muscle fiber b. The end of the motor neuron
c. The space between neuron and muscle cell State the locations of acetylcholine and cholin- esterase.
13. Name the contracting proteins of sarcomeres, and describe their locations in a sarcomere. Where is the sarcoplasmic reticulum and what does it con- tain? (p. 142)
REVIEW QUESTIONS
outside and a (⫺) charge inside. Na⫹ions are more abundant outside the cell and K⫹ ions are more abundant inside the cell. The Na⫹and K⫹pumps maintain these relative concentrations on either side of the sarcolemma (see Table 7–1 and Fig.
7–4).
5. Depolarization: This process is started by a nerve impulse. Acetylcholine released by the axon termi- nal makes the sarcolemma very permeable to Na⫹ ions, which enter the cell and cause a reversal of charges to (⫺) outside and (⫹) inside. The depo- larization spreads along the entire sarcolemma and initiates the contraction process. Folds of the sar- colemma called T tubules carry the depolarization into the interior of the muscle cell.
Contraction—the sliding filament mecha- nism (see Fig. 7–5)
1. Depolarization stimulates a sequence of events that enables myosin filaments to pull the actin fila-
ments to the center of the sarcomere, which short- ens.
2. All of the sarcomeres in a muscle fiber contract in response to a nerve impulse; the entire cell con- tracts.
3. Tetanus is a sustained contraction brought about by continuous nerve impulses; all our movements involve tetanus.
4. Paralysis: Muscles that do not receive nerve impulses are unable to contract and will atrophy.
Paralysis may be the result of nerve damage, spinal cord damage, or brain damage.
Responses to Exercise—maintaining homeo- stasis
See section in chapter and Fig. 7–6.
Major Muscles
See Tables 7–2 through 7–7 and Figs. 7–7 through 7–13.