334
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE GALLERY
Table 10.3
Muscles of the Anterior Neck and Throat: Swallowing
(Figure 10.9)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
SUPRAHYOID MUSCLES
(soo
0
prah-hi
9
oid)
Muscles that help form floor of oral cavity, anchor tongue, elevate hyoid, and move larynx superiorly during
swallowing; lie superior to hyoid bone
Digastric
(di-gas
9
trik)
(
di
5
two;
gaster
5
belly)
Consists of two bellies
united by an intermediate
tendon, forming a V shape
under the chin
O—lower margin of
mandible (anterior belly)
and mastoid process of
temporal bone (posterior
belly)
I—by a connective tissue
loop to hyoid bone
Open mouth and depress
mandible
; acting in
concert, the digastric
muscles elevate hyoid
bone and steady it during
swallowing and speech
Mandibular branch
of trigeminal nerve
(cranial V) for anterior
belly; facial nerve
(cranial VII) for
posterior belly
Stylohyoid
(sti
0
lo-hi
9
oid)
(also see Figure 10.8)
Slender muscle below angle
of jaw; parallels posterior
belly of digastric muscle
O—styloid process of
temporal bone
I—hyoid bone
Elevates and retracts
hyoid
, thereby elongating
floor of mouth during
swallowing
Facial nerve
Mylohyoid
(mi
0
lo-hi
9
oid)
(
myle
5
molar)
Flat, triangular muscle just
deep to digastric muscle;
this muscle pair make a
sling that forms the floor of
the anterior mouth
O—medial surface of
mandible
I—hyoid bone and
median raphe (a median
strip of connective tissue
between the mylohyoid
muscles)
Elevates hyoid bone and
floor of mouth
, enabling
tongue to exert backward
and upward pressure that
forces food into pharynx
Mandibular branch of
trigeminal nerve
Geniohyoid
(je
9
ne-o-hi
0
oid)
(also see Figure 10.8)
(
geni
5
chin)
Narrow muscle in contact
with its partner medially;
runs from chin to hyoid
bone deep to mylohyoid
O—inner surface of
mandibular symphysis
I—hyoid bone
Pulls hyoid bone
superiorly and anteriorly
,
shortening floor of
mouth and widening
pharynx to receive food
First cervical spinal
nerve via hypoglossal
nerve (cranial XII)
INFRAHYOID MUSCLES
Straplike muscles that depress the hyoid bone and larynx during swallowing and speaking (see also
Figure 10.10c)
Sternohyoid
(ster
0
no-hi
9
oid)
(
sterno
5
sternum)
Most medial muscle of
the neck: thin; superficial
except inferiorly,
where covered by
sternocleidomastoid
O—manubrium and
medial end of clavicle
I—lower margin of hyoid
bone
Depresses larynx and
hyoid bone if mandible is
fixed
; may also flex skull
Cervical spinal nerves
1–3 (C
1
–C
3
) through
ansa cervicalis (slender
nerve root in cervical
plexus)
Sternothyroid
(ster
9
no-thi
9
roid)
(
thyro
5
thyroid cartilage)
Lateral and deep to
sternohyoid
O—posterior surface of
manubrium of sternum
I—thyroid cartilage
Pulls larynx and hyoid
bone inferiorly
As for sternohyoid
Omohyoid
(o
0
mo-hi
9
oid)
(
omo
5
shoulder)
Straplike muscle with
two bellies united by an
intermediate tendon;
lateral to sternohyoid
O—superior surface of
scapula
I—hyoid bone, lower
border
Depresses and retracts
hyoid bone
As for sternohyoid
Thyrohyoid
(thi
0
ro-hi
9
oid)
(also see Figure 10.8)
Appears as a superior
continuation of
sternothyroid muscle
O—thyroid cartilage
I—hyoid bone
Depresses hyoid bone or
elevates larynx if hyoid
is fixed
First cervical nerve via
hypoglossal nerve
The sternocleidomastoid muscle divides the neck into two triangles
(anterior and posterior; Figure 10.9a). In this table, we consider the
muscles of the
anterior
triangle, which are divided into
suprahyoid
and
infrahyoid muscles
(above and below the hyoid bone,
respectively). Most of these muscles participate in swallowing.
Swallowing begins when the tongue and buccinator muscles of the
cheeks squeeze the food back along the roof of the mouth toward
the pharynx. A rapid series of sequential muscular movements in the
posterior mouth and pharynx complete the process:
1.
The
suprahyoid muscles
pull the hyoid bone superiorly and
anteriorly toward the mandible, which widens the pharynx to
receive the food (Figure 10.9c). The larynx is also pulled superiorly
and anteriorly under the cover of the flaplike epiglottis, a maneuver
that closes off the respiratory passageway (larynx) so that food is not
inhaled into the lungs.
2.
Small muscles that elevate the soft palate close off the nasal
passages to prevent food from entering the superior nasal cavity.
(These muscles, the
tensor
and
levator veli palatini
, are not described
in the table but are illustrated in Figure 10.9c.)
3.
The
pharyngeal constrictor muscles
in the wall of the pharynx
propel food inferiorly into the esophagus.
4.
The
infrahyoid muscles
pull the hyoid bone and larynx to their
more inferior positions as swallowing ends.
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