308
UNIT TWO
Doctors diagnose TMJ syndrome using an
electromyograph, in which electrodes record
muscle activity in four pairs of head and neck
muscle groups. One treatment is transcutane-
ous electrical nerve stimulation (TENS), which
stimulates the facial muscles for up to an hour.
Another treatment is an orthotic device fitted
by a dentist. Worn for three to six months, the
device fine-tunes the action of jaw muscles to
form a more comfortable bite. A dentist can
use bonding materials to alter shapes of certain
teeth to provide a more permanent treatment
for TMJ syndrome.
syndrome, tensing a muscle in the forehead can
cause a headache, or a spasm in the muscle that
normally opens the auditory tubes during swal-
lowing can impair ability to clear the ears.
Many cases of TMJ can be treated without
medical intervention if a cause is identified.
Getting enough sleep, drinking enough water,
and learning relaxation techniques to combat
stress can help. Massaging affected muscles
can alleviate symptoms. Posture is sometimes
the culprit—sitting for long hours in one posi-
tion in front of a computer screen can cause or
worsen TMJ.
F
acial pain, headache, ringing in the ears,
a clicking jaw, insomnia, teeth sensitive
to heat or cold, backache, dizziness, and
pain in front of the ears are aches and pains that
may all result from temporomandibular joint
(TMJ) syndrome. A misaligned jaw or grinding or
clenching the teeth can cause TMJ by stressing
the temporomandibular joint, the articulation
between the mandibular condyle of the man-
dible and the mandibular fossa of the temporal
bone. Loss of coordination of these structures
affects the nerves that pass through the neck
and jaw region, causing the symptoms. In TMJ
9.3
CLINICAL APPLICATION
TMJ Syndrome
The
medial pterygoid
(ter
ı
˘-goid) extends back and
downward from the sphenoid, palatine, and maxillary bones
to the ramus of the mandible. It closes the jaw (±
g. 9.25
c
)
and moves it from side to side.
The ± bers of the
lateral pterygoid
extend forward from
the region just below the mandibular condyle to the sphe-
noid bone. This muscle can open the mouth, pull the man-
dible forward to make it protrude, and move the mandible
from side to side (±
g. 9.25
c
).
Muscles That Move the Head and
Vertebral Column
Paired muscles in the neck and back fl ex, extend, and rotate
the head and hold the torso erect (
f
gs. 9.26
and 9.28 and
table 9.5
). They include the following:
Sternocleidomastoid
Semispinalis capitis
Splenius capitis
Quadratus lumborum
Erector spinae
The
sternocleidomastoid
(ster
no-kli
do-mas
toid) is
a long muscle in the side of the neck that extends upward
from the thorax to the base of the skull behind the ear. When
arch to the mandible. The masseter raises the jaw, but it can
also control the rate at which the jaw falls open in response
to gravity (±
g. 9.25
a
).
The
temporalis
(tem-po-ra
lis) is a fan-shaped muscle
located on the side of the skull above and in front of the
ear. Its fibers, which also raise the jaw, pass downward
beneath the zygomatic arch to the mandible (± g. 9.25
a
and
b
). Tensing this muscle is associated with temporomandibu-
lar joint syndrome, discussed in Clinical Application 9.3.
TABLE
9.4
|
Muscles of Mastication
Muscle
Origin
Insertion
Action
Nerve Supply
Masseter
Lower border of zygomatic arch
Lateral surface of mandible
Elevates mandible
Trigeminal n.
Temporalis
Temporal bone
Coronoid process and anterior ramus of mandible
Elevates mandible
Trigeminal n.
Medial pterygoid
Sphenoid, palatine, and maxillary
bones
Medial surface of mandible
Elevates mandible and moves it
from side to side
Trigeminal n.
Lateral pterygoid
Sphenoid bone
Anterior surface of mandibular condyle
Depresses and protracts mandible
and moves it from side to side
Trigeminal n.
When two dentists examined an eyeless cadaver’s skull from an
unusual perspective, they discovered a then-unknown muscle.
Named the sphenomandibularis, the muscle extends about an inch
and a half from behind the eyes to the inside of the jawbone and may
assist chewing movements. In traditional dissection from the side,
the new muscle’s origin and insertion are not visible, so it may have
appeared to be part of the larger and overlying temporalis muscle.
Although the sphenomandibularis inserts on the inner side of the
jawbone, as does the temporalis, it originates differently, on the
sphenoid bone.
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