The mandible pdf - Head and Neck

Basic Anatomy

forms the spiral organ of Corti and contains

membrane

The highly specialized epithelium that lies on the

ductus reuniens.

and is connected to the saccule by the

is triangular in cross section

duct of the cochlea

The

semicircular ducts.

is detected in the sensory receptors in the ampullae of the

to that of the walls of the semicircular ducts. This change

semicircular ducts changes its speed of movement relative

the head accelerates or decelerates, the endolymph in the

begins or ceases to move, or whenever a movement of

so that all three planes are represented. Whenever the head

figuration. They are arranged at right angles to each other

diameter than the semicircular canals, have the same con

although much smaller in

semicircular ducts,

The

tation of the head to gravity or other acceleration forces.

cialized sensory receptors, which are sensitive to the orien

Located on the walls of the utricle and saccule are spe

face of the petrous part of the temporal bone.

(Fig. 11.30). This lies beneath the dura on the posterior sur

saccus endolymphaticus

end in a small blind pouch, the

being joined by the ductus utriculosaccularis, passes on to

as described previously. The ductus endolymphaticus, after

is globular and is connected to the utricle,

saccule

The

ductus utriculosaccularis.

lymphaticus by the

indirectly connected to the saccule and the ductus endo

is the larger of the two vestibular sacs. It is

utricle

The

All these structures freely communicate with one another.

the duct of the cochlea, which lies within the bony cochlea.

lar ducts, which lie within the bony semicircular canals; and

which are lodged in the bony vestibule; the three semicircu

rounded by perilymph. It consists of the utricle and saccule,

labyrinth (Fig. 11.30). It is filled with endolymph and sur

The membranous labyrinth is lodged within the bony

Membranous Labyrinth

fenestra cochleae.

middle ear by the secondary tympanic membrane at the

The perilymph in the scala tympani is separated from the

stapes and the anular ligament at the fenestra vestibuli.

tibuli is separated from the middle ear by the base of the

below. The perilymph within the scala ves

scala tympani

above and the

scala vestibuli

the cochlear canal into the

the spiral lamina to the outer bony wall, thus dividing

stretches from the free edge of

basilar membrane

it. The

jects into the interior of the canal and partially divides

winds around the modiolus and pro

spiral lamina,

rated by branches of the cochlear nerve. A spiral ledge,

the bottom of the internal acoustic meatus. It is perfo

The modiolus has a broad base, which is situated at

wall of the middle ear.

lea is responsible for the promontory seen on the medial

base faces posteromedially. The first basal turn of the coch

structure is conical. The apex faces anterolaterally and the

successive turn is of decreasing radius so that the whole

low bony tube makes two and one half spiral turns. Each

around which a hol

modiolus,

sists of a central pillar, the

anterior part of the vestibule (Fig. 11.30). Basically, it con

resembles a snail shell. It opens into the

cochlea

The

the mastoid antrum, above the facial nerve canal.

zontal position, and it lies in the medial wall of the aditus to

axis of the petrous bone. The lateral canal is set in a hori

569

-
-

the

-
-

basilar

the sensory receptors for hearing. For a detailed

ion

descript

of the spiral organ, a textbook of histology should be
consulted.

sion on the base, on either side of the symphysis menti

is a small, roughened depres

digastric fossa

The

The lower border of the body of the mandible is called

roots of the teeth.

in the adult, it contains 16 sockets for the

alveolar part;

The upper border of the body of the mandible is called

part of the mylohyoid line (Fig. 11.32).

for the sublingual gland, lies above the anterior

gual fossa,

sublin

below the posterior part of the mylohyoid line. The

superficial part of the submandibular salivary gland, lies

for the

submandibular fossa,

the third molar tooth. The

the area of the mental spines to an area below and behind

as an oblique ridge that runs backward and laterally from

can be seen

mylohyoid line

muscles below (Fig. 11.31). The

gin to the genioglossus muscles above and the geniohyoid

these give ori

mental spines;

the median plane are seen the

On the medial surface of the body of the mandible in

alveolar nerve and vessels.

lar tooth; it transmits the terminal branches of the inferior

can be seen below the second premo

mental foramen

The

symphysis menti.

two halves during development at the

midline, has a faint ridge indicating the line of fusion of the

on its external surface in the

body of the mandible,

The

(Fig. 11.32).

angle of the mandible

on each side at the

The body of the mandible meets the ramus

rami.

a pair of

body

The mandible consists of a horseshoe-shaped

mandibular joint.

of the face, and it articulates with the skull at the temporo

The mandible or lower jaw is the largest and strongest bone

organ of Corti.

spiral

branches of this nerve pass from the ganglion to the

modiolus in the base of the spiral lamina. The peripheral

that is lodged in a canal winding around the

ganglion

spiral

glion of this nerve takes the form of an elongated

foramina at the base of the modiolus. The sensory gan

divides into branches, which enter

cochlear nerve

The

the saccule, and the ampullae of the semicircular ducts.

the membranous labyrinth, where they supply the utricle,

end of the internal acoustic meatus and gain entrance to

The branches of the nerve then pierce the lateral

ganglion.

vestibular

is expanded to form the

vestibular nerve

The

lear portions (Fig. 11.28).

(see page 613), the nerve divides into vestibular and coch

On reaching the bottom of the internal acoustic meatus

Vestibulocochlear Nerve

The Mandible

and

the

the base.

(Fig. 11.32). It is in these fossae that the anterior bellies of

On the lateral surface of the ramus are markings for the

(Fig. 11.32).

mandibular notch

the two processes are separated by the

head;

process,

condyloid

and a posterior

coronoid process

an anterior

is vertically placed and has

ramus of the mandible

The

the digastric muscles are attached.

attachment of the masseter muscle. On the medial

e is

surfac

for the inferior alveolar nerve and

mandibular foramen

the

570

CHAPTER 11

The Head and Neck

of pharynx

medial pterygoid

lateral pterygoid

stylomandibular ligament

mandibular foramen

temporalis

lingula

sphenomandibular

ligament
superior constrictor

sublingual fossa

mental spines

digastric fossa

anterior belly of digastric

geniohyoid

genioglossus

submandibular fossa

mylohyoid muscle

mylohyoid line

neck

masseter

ramus

angle

buccinator

body

base of body

platysma

depressor anguli oris

mental foramen

alveolar part of body

depressor

labii

inferioris

mentalis

incisor teeth

canine tooth

premolar teeth

molar teeth

coronoid process

mandibular notch

condyloid process (head)

medial aspect (left side)

lateral aspect (right side)

greater horn (cornu)

stylohyoid

ligament

lesser horn (cornu)

body

hyoglossus

middle constrictor

stylohyoid ligament

geniohyoid

mylohyoid

omohyoid

sternohyoid

digastric and stylohyoid

thyrohyoid

right aspect

anterosuperior aspect

FIGURE 11.32

ligament

sphenomandibular

for the attachment of the

vessels. In front of the foramen is a projection of bone, called

Hyoid bone.

Mandible. B.

the lingula,

(Figs. 11.32 and 11.33). The foramen leads into the

mandibular canal,

which opens on the lateral surface of the

(see above). The

mental foramen

body of the mandible at the

mandible are shown in Figure 11.32.

The important muscles and ligaments attached to the

(Fig. 11.32).

neck

is a short

head,

process,

condyloid

attachment of the temporalis muscle. Below the

receives on its medial surface the

coronoid process

The

canal beyond the mental foramen and below the incisor teeth.

is a continuation forward of the mandibular

incisive canal

Fractures of the Mandible

The mandible is horseshoe shaped and forms part of a bony

ring with the two temporomandibular joints and the base of

the skull. Traumatic impact is transmitted around the ring,

causing a single fracture or multiple fractures of the mandible,

often far removed from the point of impact.

C L I N I C A L N O T E S

Basic Anatomy

571

articular
tubercle

zygomatic

arch (cut)

zygomatic
process

tendon of

temporalis

coronoid

process

mandible

head of
mandible

ramus of
mandible

neck of
mandible

angle of
mandible

external

carotid

artery

temporal fascia

temporalis

mandibular
fossa

sternocleido-
mastoid

external
auditory
meatus

mandibular
notch

The temporomandibular joint is synovial. The articular disc

Type of Joint

are covered with fibrocartilage.

dible below (Figs. 11.33 and 11.34). The articular surfaces

bone above and the head (condyloid process) of the man

anterior portion of the mandibular fossa of the temporal

Articulation occurs between the articular tubercle and the

Articulation

Temporomandibular Joint

divides the joint into upper and lower cavities (Fig. 11.35).

side of the joint (Fig. 11.33). It is a thin band that is

lies on the medial

sphenomandibular ligament

The

direction and thus protects the external auditory meatus.

ligament limits the movement of the mandible in a posterior

lateral surface of the neck of the mandible (Fig. 11.33). This

backward from the tubercle on the root of the zygoma to the

lateral aspect of the capsule, and its fibers run downward and

strengthens the

lateral temporomandibular ligament

The

Ligaments

fossa and below to the neck of the mandible.

the articular tubercle and the margins of the mandibular

The capsule surrounds the joint and is attached above to

Capsule

external auditory
meatus

tympanic
plate

mastoid
process

styloid process

stylomandibular
ligament

capsule

temporomandibular
ligament

articular tubercle

capsule

styloid
process

sphenomandibular
ligament

spine of
sphenoid

stylomandibular
ligament

FIGURE 11.33

Temporomandibular joint as seen from the

lateral (A) and medial (B) aspects.

FIGURE 11.34

ve been

A dissection of the left temporomandibular joint. The capsule and lateral temporomandibular ligament ha

of the mandible. The articular disc is present within the joint cavity on the upper surface of the head of the mandible.

removed to reveal the interior of the joint. Note the articular tubercle and mandibular fossa of the temporal bone and the head

572

CHAPTER 11

The Head and Neck

articular
disc

articular
cartilage

mandibular
fossa

articular tubercle

lateral
pterygoid
muscle

head
of mandible

synovial
membrane

temporalis

lateral pterygoid

medial pterygoid

digastric
(anterior belly)

sternohyoid

omohyoid
(superior belly)

thyrohyoid

masseter

digastric
(posterior belly)

neck of mandible

FIGURE 11.35

Temporomandibular joint with mouth closed

ular disc so that the latter moves onto the articular tubercle

which pulls forward the neck of the mandible and the artic

plished by the contraction of the lateral pterygoid muscle,

muscle, the mandible is pulled forward. This is accom

essarily on the parotid gland and the sternocleidomastoid

tal axis. To prevent the angle of the jaw impinging unnec

on the undersurface of the articular disc around a horizon

As the mouth is opened, the head of the mandible rotates

contact.

slightly apart. On closure of the jaws, the teeth come into

position of rest, the teeth of the upper and lower jaws are

retracted. Rotation can also occur, as in chewing. In the

The mandible can be depressed or elevated, protruded or

Movements

dibular nerve

Auriculotemporal and masseteric branches of the man

Nerve Supply

joint (Fig. 11.35).

This lines the capsule in the upper and lower cavities of the

Synovial Membrane

the lower surface is concave to fit the head of the mandible.

shape of the articular tubercle and the mandibular fossa;

the disc is concavoconvex from before backward to fit the

tion and retraction of the mandible. The upper surface of

backward with the head of the mandible during protrac

ble. These bands ensure that the disc moves forward and

muscle and by fibrous bands to the head of the mandi

also attached in front to the tendon of the lateral pterygoid

lage that is attached circumferentially to the capsule. It is

lower cavities (Fig. 11.35). It is an oval plate of fibrocarti

divides the joint into upper and

articular disc

The

(Fig. 11.33).

apex of the styloid process to the angle of the mandible

of thickened deep cervical fascia that extends from the

to the joint and some distance from it. It is merely a band

lies behind and medial

stylomandibular ligament

The

remains of the first pharyngeal arch in this region.

to the lingula of the mandibular foramen. It represents the

attached above to the spine of the sphenoid bone and below

arrows

tion to the mandible. The

The attachment of the muscles of mastica

the mandible and articular disc in relation to the articular tubercle in each case.

(A) and with the mouth open (B). Note the position of the head of

indicate the direction of their actions.

Depression of the Mandible

-
-

(Fig. 11.35). The forward movement of the disc is limited

disc to the temporal bone posteriorly.

pulled backward by the fibroelastic tissue, which tethers the

the posterior fibers of the temporalis. The articular disc is

goids. The head of the mandible is pulled backward by

tion of the temporalis, the masseter, and the medial ptery

Elevation of the mandible is brought about by contrac

and then the head rotates on the lower surface of the disc.

First, the head of the mandible and the disc move backward,

The movements in depression of the mandible are reversed.

mandible forward.

the lateral pterygoids play an important role by pulling the

tion of the digastrics, the geniohyoids, and the mylohyoids;

Depression of the mandible is brought about by contrac

disc to the temporal bone posteriorly.

by the tension of the fibroelastic tissue, which tethers the

Elevation of the Mandible

-
-

Basic Anatomy

The muscles of mastication are summarized in

in unison.

cles responsible on both sides work alternately and not

place, a certain amount of rotation occurs, and the mus

retracting the mandible on each side. For this to take

These are accomplished by alternately protruding and

Lateral Chewing Movements

about by contraction of the posterior fibers of the temporalis.

backward into the mandibular fossa. Retraction is brought

The articular disc and the head of the mandible are pulled

Retraction of the Mandible

cles of both sides, assisted by both medial pterygoids.

brought about by contraction of the lateral pterygoid mus

lower teeth are drawn forward over the upper teeth, which is

takes place in the upper cavity of the joint. In protrusion, the

carrying the head of the mandible with it. All movement thus

The articular disc is pulled forward onto the anterior tubercle,

Protrusion of the Mandible

573

Table 11.4. See also Figure 11.35.

nerve and artery (Fig. 11.36)

The mandibular notch and the masseteric

Anteriorly:

Important Relations of the Temporomandibular Joint

■

Muscles of the Head

T A B L E 1 1 . 4

Muscle

Origin

Insertion

Nerve
Supply

Action

Muscle of Scalp
Occipitofrontalis

Occipital belly

Frontal belly

Highest nuchal line of

occipital bone

Skin and superficial fascia

of eyebrows

Epicranial aponeurosis

Facial nerve Moves scalp on skull and raises

eyebrows

Muscles of Facial Expression
Orbicularis oculi

Palpebral part

Medial palpebral ligament

Lateral palpebral raphe

Facial nerve Closes eyelids and dilates lacrimal

sac

Orbital part

See Table 11.5

Wrinkles skin of nose

Vertical wrinkles of forehead, as in

Medial palpebral ligament

and adjoining bone

Loops return to origin

Facial nerve Throws skin around orbit into folds

to protect eyeball

Corrugator supercilii

Superciliary arch

Skin of eyebrow

Facial nerve

frowning

Compressor nasi

Frontal process of maxilla

Aponeurosis of bridge

of nose

Facial

nerve

Compresses mobile nasal

cartilages

Dilator naris

Maxilla

Ala of nose

Facial nerve Widens nasal aperture

Procerus

Nasal bone

Skin between eyebrows

Facial nerve

Orbicularis oris

Maxilla, mandible, and skin Encircles oral orifice

Facial nerve Compresses lips together

Dilator Muscles of Lips
Levator labii superioris

alaeque nasi

Levator labii superioris

Zygomaticus minor

Zygomaticus major

Levator anguli oris

Risorius

Depressor anguli oris

Depressor labii inferioris

Mentalis

Buccinator

Platysma

Arise from bones and fas-

cia around oral aperture

and insert into substance

of lips

Outer surface of alveolar

margins of maxilla and

mandible and ptery-

gomandibular ligament

Facial nerve

Separate lips

Compresses cheeks and lips

against teeth

(continued)

574

CHAPTER 11

The Head and Neck

Muscles of the Head (continued )

T A B L E 1 1 . 4

Laterally:

parotid gland

tory meatus (Fig. 11.33) and the glenoid process of the

The tympanic plate of the external audi

Posteriorly:

Tuberosity of maxilla and

Temporalis

Muscle

Origin

Insertion

Nerve
Supply

Action

Muscles of Mastication
Masseter

Zygomatic arch

Lateral surface

ramus of mandible

Mandibular

division of

trigeminal

nerve

Elevates mandible to occlude teeth

Floor of temporal fossa

Coronoid process of

mandible

Mandibular

division of

trigeminal

nerve

Anterior and superior fibers

elevate mandible; posterior

fibers retract mandible

Lateral pterygoid (two

heads)

Greater wing of sphenoid

and lateral pterygoid

plate

Neck of mandible and

articular disc

Mandibular

division of

trigeminal

nerve

Pulls neck of mandible forward

Medial pterygoid (two

heads)

lateral pterygoid plate

Medial surface of angle

of mandible

Mandibular

division of

trigeminal

nerve

Elevates mandible

■

The parotid gland, fascia, and skin (see Fig. 11.85)

lotemporal nerve

The maxillary artery and vein and the auricu

Medially:

■

Clinical Significance of the Temporomandibular

of the temporomandibular joint may

articular disc

Joint

The temporomandibular joint lies immediately in front of the

external auditory meatus. The great strength of the lateral

temporomandibular ligament prevents the head of the mandi-

ble from passing backward and fracturing the tympanic plate

when a severe blow falls on the chin.

The

become partially detached from the capsule, and this results

in its movement becoming noisy and producing an audible

click during movements at the joint.

Dislocation of the Temporomandibular Joint

Dislocation sometimes occurs when the mandible is

depressed. In this movement, the head of the mandible and

the articular disc both move forward until they reach the sum-

mit of the articular tubercle. In this position, the joint is unsta-

ble, and a minor blow on the chin or a sudden contraction of

the lateral pterygoid muscles, as in yawning, may be sufficient

C L I N I C A L N O T E S

(continued)

to pull the disc forward beyond the summit. In bilateral cases,

lateral margins of the aponeurosis are attached to

occipitofrontalis muscle (Figs. 11.37 and 11.38). The

sheet that unites the occipital and frontal bellies of the

poneurosis (epicranial), which is a thin, tendinous

arteries, and a free anastomosis takes place between them.

arteries are branches of the external and internal carotid

Numerous arteries and veins are found in this layer. The

aponeurosis of the occipitofrontalis muscle (Fig. 11.37).

the fibrous septa uniting the skin to the underlying

onnective tissue beneath the skin, which is fibrofatty,

numerous sebaceous glands

kin, which is thick and hair bearing and contains

layer of the scalp.

to denote the

the scalp, use each letter of the word

To assist one in memorizing the names of the five layers of

intimately bound together and move as a unit (Fig. 11.37).

The scalp consists of five layers, the first three of which are

dislocation is easily achieved by pressing the gloved thumbs

the mouth is fixed in an open position, and both heads of the

mandible lie in front of the articular tubercles. Reduction of the

downward on the lower molar teeth and pushing the jaw back-

ward. The downward pressure overcomes the tension of the

temporalis and masseter muscles, and the backward pressure

overcomes the spasm of the lateral pterygoid muscles.

The Scalp

Structure

SCALP

■