Skull-Structure And Functions

SKULL-STRUCTURES AND FUNCTIONS

bony

• that its hape.
•  Skull is the

Framework that gives the head its characteristic shape

function of the

• protect
• and the
• tissues of
• rly the
• The

skull is protective to the soft vital structures/organs of the head, particularly brain.

the

The Skull

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

of

• in
• cranium
• the
• The skull is
• composed
• 22 bones,
• in cranium
• 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.It is bat-shaped bone 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) ETHMOID : 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
• passes through cribriform plate

Nerve that

(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 sagittal 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.

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 Functions

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 (atlas).

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 (fossae) 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 CRANIAL FOSSAE

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.

SCALP

The scalp consists of skin and subcutaneous tissue that covers the neurocranium form the uperior nuchai lines on the occipital bone to the supraorbital margins of the frontal bone.

• The scalp consists of five layers:
• Skin-contains many sweat and sebaceous glands and hair follicles
• Connective tissue-forming the thick, dense, richly vascularized, subcutaneous layer

Aponeurosis (epicranial aponeurosis)-strong tendinous sheet that covers the calvaria Loose connective tissue-a sponge –like layer, has potential spaces this layer allows free movement Pericranium-a dense layer of connective tissue, forms the external Periosteum of the neurocranium

SCALP

STRUCTURE OF SCALP

Blood and nerve supply of scalp

Functions 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)
• Facilitate breathing by bone of nasal cavities

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