Skull: Structure and Function

OPTOMETRY · SEMESTER 1

Human Anatomy and Physiology

START READING NOTES

SKULL-STRUCTURES AND FUNCTIONS

bony

that its hape.
 Skull is the

framework, gives the head, characteristic s

function of the

protect
and the
tissues of
rly the
The
skull is to the soft vital

the head, particula brain.

the

The Skull

consists of Cranium bony box housing the brain) and face.

of

in
cranium
the
The skull is
composed
22 bones,
the
and 14 in
face.

The Eight bones

(1) Frontal

(2) Occipital (3) Sphenoid (4) Ethmoid

of
the
Cranium
are
:-

(5) Two Parietal

bones

(6) Two Temporal bones

(i) FRONTAL : The

frontal bone forms the forehead , the anterior (front) part of the cranial vault and the roof of the orbits (eye sockets).

Inside the bone,
just
behind the eyebrows are
the frontal sinuses.

two air spaces called

(ii) OCCIPITAL : The

occipital bone forms the posterior (back) part of the floor and vault of the cranium. It is the bone which supports the head upon the spinal column.

The spinal cord leaves the cranium through an opening in the

occipital bone called the foramen magnum

(iii) SPHENOID : The

sphenoid bone is the central part of the base of the cranium. It forms part of the orbits, transmits the optic nerve and supports the posterior part of the maxilla.

The sphenoid air sinuses lie in this bone. The pituitary gland lies in a bony socket called the sella turcica, located on the superior aspect of the sphenoid bone.

Dental Tip: When a patient is seated in the dental chair, the headrest

should support the occipital bone and thereby support the entire head.

(iv) ETMOID : The

Ethmoid bone lies between the eyes and extends from the frontal bone to the sphenoid bone. It forms the anterior part of the skull, the medial wall of each orbit, part of the nasal

septum and the roof
of the nose.
It transmits the olfactory
smell)

nerve (nerve of

(v) PARIETAL : The

Parietal bones forms large part of the
a
cranial
extend frontal
vault and
from the bone to the
occipital bone. The
two bones join at the midline on the top of the cranium and form the saggital suture.
From this suture, these bones
extend down and
out to about the level of the top of the external ear

where they meet the temporal bones.

(vi) TEMPORAL :

Temporal bones complete the sides and part of the base of the cranium. These bones contain organs of hearing and equilibrium.

The external acoustic meatus
in the side of each bone
forms a passage from the external ear to the middle ear

which lies within each bone.

There are 14 bones in the

(i) Mandible (1)
(ii) Maxillae (2)
(iii) Zygomatic Bones (2)
(iv) Lacrimal Bones (2)
(v) Nasal Bones (2)
(vi) Inferior conchae (2)
(vii) Palatine Bones (2)
(viii) Vomer (1)

face.

(i) ZYGOMATIC : The

right and left zygomatic bones form the lower and outer edges of each orbit and that part of each zygomatic arch nearest the eye.

The Zygomatic bone and Zygomatic
process of the
temporal bone form the Zygomatic arch. The anterior edge
of the zygomatic bone joins the maxilla.

That part of the maxilla which joins the zygomatic bone is called the zygomatic process.

(ii) LACRIMAL :

The paired (right and left) Lacrimal bones form small parts of the
medial walls
the orbits.
of
The lacrimal bones transmits
the naso-lacrimal duct from

the eye to the nose or nasal fossa.

(iii) NASAL : The

nasal bones (right and left) are long, thin pieces of bone that form the upper part of the bridge of the nose.

The anterior lower part
cartilage

of the nasal septum is composed of

(iv) INFERIOR

CONCHAE: The inferior nasal conchae (right
and left) are scroll like bones lying horizontally
along the lateral walls of the nasal cavity.
The bony elements of the middle
and superior conchae are

extensions of the lateral parts of the ethmoid bones.

(v) PALATINE: The

palatine bones (right and left) join in the midline to form the posterior
part of the
palate .
hard
Palatine bones also form part
of the floor and lateral walls

of the nasal cavity and part of the floor of the orbits.

(vi) VOMER: The

vomer forms the inferior part of the nasal septum, the

vertical partition separating the right and left nasal cavities.

(vii) MAXILLA: The

right and left maxillary bones forms the upper jaw and palate
of
the
mouth.
The two halves are fused
form the upper jaw.
at

the intermaxillary suture to

(viii) MANDIBLE:

The horse shoe- shaped bone forming the lower jaw, articulating with the skull at the temporomandi – -bular joint.

Mandible is the largest, strongest
face.

and lowest bone in the

External Surface of Cranial Base

The external aspect of the cranial base or basicranium features…….

The alveolar arch of the maxillae (supporting the maxillary teeth),

The palatine processes of the maxillae,
The palatine,
Sphenoid,
Vomer,
Temporal

Occipital bones.

Skull: Structure and Function

The hard palate (bony palate) is formed by the palatine processes of the maxillae anteriorly and the horizontal plates of the palatine bones posteriorly.

Skull: Structure and Function

Depressions in the squamous part of the temporal bone, called the mandibular fossae,accommodate the heads of the mandible when the mouth is closed.

The cranial base is formed posteriorly by the occipital bone, which articulates with the sphenoid anteriorly.

CT

The parts of the occipital bone encircle the large foramen magnum.

On the lateral parts of the occipital bone are two large protuberances, the occipital condyles, by which the cranium articulates with the vertebral column.

The large opening between the occipital bone and the petrous part of the temporal bone is the jugular foramen.

Internal Surface of Cranial Base

The internal surface of the cranial base has three large depressions that lie at different levels o The anterior

o The middle

o Posterior cranial fossae, which form the bowl-shaped floor of the cranial cavity

The Anterior Cranial Fossa

The anterior cranial fossa is formed by the frontal bone anteriorly, the ethmoid bone centrally, and the body and lesser wings of the sphenoid posteriorly.

The butterfly-shaped middle cranial fossa has a central part composed of the sella turcica (Turkish saddle) on the body of the sphenoid and large depressed lateral parts on each side.

The Middle Cranial Fossa

The bones forming the larger, lateral parts of the middle cranial fossa are the greater wings of the sphenoid, squamous parts of the temporal bones laterally, and petrous parts of the temporal bones posteriorly.

The Posterior Cranial Fossa

The largest and deepest of the cranial fossae contains the cerebellum, pons, and medulla oblongata. Its formed by 2 temporal bones and 1 occipital bone

Boundaries

Anteromedial – dorsum sellae of the sphenoid bone (large projection of bone superiorly that arises from the body of the sphenoid).

Anterolateral – superior border of the petrous part of the temporal bone.

Posterior – internal surface of the squamous part of the occipital bone.

Floor – mastoid part of the temporal bone and the squamous, condylar and basilar parts of the occipital bone.

Function of the Skull

The cranium protects the delicate tissue of the brain
Protects the eyes in the bony eye sockets
Temporal bone protects the delicate structures of the ear

Chewing of the food by movable mandible (jaw bone)

5. Facilitate breathing by bone of nasal cavities

6. Maxilla and mandible provide alveolar ridges in which the teeth are embedded 7. Some bones of the face and the base of the skull give resonance to voice because they have cavities called sinuses