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CHAPTER 5: THE SKELETON (SKULL)
ANATOMY AND PHYSIOLOGY
ETHMOID BONE
An anterior cranial bone found between the eyes. It contributes
to the medial wall of the orbit, the roof and walls of the nasal
cavity, and the nasal septum. Very porous, delicate bone.
Contains 3 major portions.
Parts of the Ethmoid
1. PERPENDICULAR PLATE:
Vertical, thin plate of bone that forms the superior 2/3s of nasal
septum. (lower part formed by vomer bone). The septum divides the
nasal cavity into right and left air spaces called the NASAL FOSSAE.
The septum is often curved (deviated) toward one nasal fossa or the
other.
2.CRIBRIFORM PLATE:
Horizontal, forms roof of nasal
cavity. It contains a crest called
the CRISTA GALLI, an
attachment point for the
meninges that enclose the
brain. The CRIBRIFORM
FORAMINA is on either side of
crista. A pair of olfactory bulbs
of the brain, concerned with
smell, rest in these depressions,
and the foramina allow passage
for olfactory nerves from the
nasal cavity to the bulbs.
3. LABYRINTH:
Large mass on each side of
perpendicular plate. It is
named this due to the internal
maze of air spaces called the
ETHMOIDAL CELLS.
Collectively, these constitute
the ETHMOID SINUS. The
lateral surface of the labyrinth
is a smooth, slightly concave
ORBITAL PLATE seen on the
medial wall of the orbit. The
medial surface of the labyrinth
gives rise to 2 curled, scrolllike plates of bone called the
SUPERIOR AND MIDDLE
NASAL CONCHAE. The
inferior nasal conchae is a
facial bone. These project into
the nasal fossa from its lateral
wall toward the septum.
These nasal conchae together occupy most of the space in the nasal cavity.
By filling space and creating turbulence in the flow of inhaled air, they ensure
that the air contacts the mucous membranes that cover these bones, which
cleanse, humidify, and warm the inhaled air before it reaches the lungs. The
superior concha and adjacent part of the nasal septum also bear the sensory
cells of smell. In studying an intact skull, all that can be seen of the ethmoid is
the perpendicular plate, by looking into the nasal cavity; the orbital plate, by
looking at the medial wall of the orbit; and the crista galli and cribriform plate,
viewed from within the cranial cavity.
Injury to the ethmoid bone: it is very delicate and easy to injure by a
sharp upward blow to the nose, such as a person might suffer by
striking an automobile dashboard in a collision. The blow can drive
bone fragments through the cribriform plate into the meninges or
brain tissue. Detection is by seeing leakage of cerebral fluid into the
nasal cavity, followed by the spread of infection from the nasal cavity
to the brain. Blows to the head can also shear off the olfactory
nerves that pass through the ethmoid bone and cause anosmia, an
irreversible loss of the sense of smell and a great reduction in the
sense of taste (most of which depends on smell).
FACIAL BONES (14 FACIAL BONES)
All are paired up except for the MANDIBLE and VOMER bones. The
MAXILLAE, ZYGOMATICS, NASALS, LACRIMALS, PALATINES, and
INFERIOR NASAL CONCHAE are paired bones.
As a rule, men’s facial bones are more
elongated than that of women;
therefore, women’s faces are rounder
and less angular.
Facial bones
have no direct
contact with the
brain or
meninges. They
provide
attachment for
the muscles of
facial
expression.
1. MANDIBLE (single)
V-shaped, lower jaw,
largest, strongest bone of
the face.
The “body” of the
mandible forms the chin;
the 2 rami (“Y” shaped at
top) are upright meeting
the body at the
MANDIBULAR ANGLE.
2 processes at top of
ramus are separated by
the MANDIBULAR
NOTCH.
CORONOID PROCESS –
attachment point for jaw
muscles to move jaw up
and down
ALVEOLAR MARGIN is the area where teeth are located.
MANDIBULAR FORAMEN is located on each ramus, permit nerves responsible for
tooth sensation to pass to teeth in lower jaw. This is where dentist inject
Novocain to work on lower teeth with no pain.
MENTAL FORAMINA – found on mandibular body – allows blood vessels and
nerves to pass to chin and lower lip
MANDIBULAR SYMPHYSIS(Protuberance) – as fetus, your mandible is 2 bones.
As you develop they fuse to form this joint.
2. MAXILLAE or maxillary bones (pair)
Upper jaw, central portion of face
All facial bones (except mandible)
articulate with maxillae – KEYSTONE
BONE OF THE FACIAL SKELETON.
As a fetus, the maxillae is actually 2 bones
and fuses to form one bone at the
INTERMAXILLARY SUTURE.
These bones fuse at 12 weeks gestation but failure of this will
result in a “CLEFT PALATE” / “CLEFT LIP”.
This will cause nursing to be difficult until corrected surgically.
Our palate allows us to breath as we chew our food. The
PALATINE BONES form the rest of the hard palate.
3. PALATINE BONES (pair)
Form the rest of hard palate, part of nasal cavity wall, part
of floor of orbit.
PALATINE PROCESSES form roof of mouth and floor of nasal
cavity. ALVEOLAR MARGINS hold upper teeth in place.
ALVEOLI (sockets) contain the roots of the teeth.
4. ZYGOMATIC BONES (pair)
Irregularly shaped.
Also known as
“malar bones”.
Give us our cheek
bones along with the
zygomatic processes
of the temporal
bones and the
zygomatic processes
of the maxillae.
5. NASAL BONES (pair)
Thin, rectangular
shape
Fused medially to
form bridge of nose.
Inferiorly, they attach
to the cartilage plates
that form the lower
skeleton of nose.
6. LACRIMAL BONES (pair)
Form part of
medial wall of each
orbit.
Fingernail shaped
LACRIMAL FOSSA
– a depression that
houses the
lacrimal sac which
collect tears from
the eye and drain
into the nasal
cavity.
7. VOMER BONE (single)
Slender, plow-shaped;
Name means “plowshare”
Located within nasal cavity
forming part of nasal
septum.
8. INFERIOR NASAL CONCHAE (pair)
Three of these in nasal cavity (superior and middle conchae are part of
the ethmoid bone). The INFERIOR NASAL CONCHAE is the largest of
the three. Thin, curved bones projecting from the lateral walls of the
nasal cavity. Form part of the lateral walls of the nasal cavity.
THE EYE ORBITS ON SKULL: 7 bones make up each orbit
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FRONTAL
SPHENOID
ZYGOMATIC
MAXILLA
PALATINE
LACRIMAL
ETHMOID
BONES ASSOCIATED WITH SKULL
Some bones closely associated with skull but not considered part of it:
AUDITORY
OSSICLES –
found in middle
ear cavity; deal
with hearing
1. malleus (hammer)
2. incus (anvil)
3. stapes (stirrup)
HYOID BONE
Slender bone between chin and larynx. Doesn’t articulate with
ANY other. Suspended from styloid process in the mid-neck
region like a hammock. Serves as attachment of several
muscles that control the mandible, tongue, larynx. Helps with
swallowing and speech. Forensic pathologists look for a
fractured hyoid as evidence of strangulation.
PARANASAL SINUSES
5 skull bones contain mucosa-lined, air-filled sinuses that cause
these bones to look rather moth-eaten in an X-ray.
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Frontal
Sphenoid
Ethmoid
Paired
maxillary
bones
Help with resonance of voice. Small openings connect sinuses to
nasal cavity. Air enters the sinuses from the nasal cavity and mucus
formed by the sinus mucosae drains into the nasal cavity. The
mucosa of the sinus also helps to warm and humidify inspired air.