Cranial Bones, Sinuses, and Associated Structures: Anatomy & Physiology Study Notes

Cranial and Facial Bones

Inferior Nasal Conchae

The inferior nasal conchae are thin, curved bones that form part of the lateral walls of the nasal cavity. They play a role in conditioning inhaled air by increasing surface area and creating turbulence.

• Location: Lateral walls of the nasal cavity

• Function: Help filter, warm, and moisten incoming air

• Structure: Separate bones, not part of the ethmoid bone (unlike the superior and middle nasal conchae)

Hyoid Bone

The hyoid bone is a unique, U-shaped bone located in the anterior neck. It does not articulate directly with any other bone.

• Location: Suspended in the neck, anchored by ligaments to the styloid processes of the temporal bones

• Function: Serves as an attachment site for tongue and neck muscles involved in swallowing and speech

• Special Feature: Only bone in the body that does not articulate with another bone

Orbits (Eye Sockets)

Orbital Bones

The orbits are bony cavities in the skull that house and protect the eyes. Each orbit is formed by contributions from seven different bones.

• Movements: Muscles attached to the orbits allow for eye movements (e.g., rolling your eyes)

• Bones forming the orbit:

  1. Frontal bone

  2. Sphenoid bone

  3. Zygomatic bone

  4. Maxilla

  5. Palatine bone

  6. Lacrimal bone

  7. Ethmoid bone

Example: The frontal bone forms the superior part of the orbit, while the maxilla forms the floor.

Nasal Cavity

Nasal Septum

The nasal septum divides the nasal cavity into right and left halves. It is composed of both bone and cartilage.

• Bony part: Formed by the perpendicular plate of the ethmoid bone and the vomer

• Cartilaginous part: Formed by hyaline cartilage

Function: Supports the nose and directs airflow.

Paranasal Sinuses

Sinus Locations and Functions

Paranasal sinuses are air-filled spaces within certain skull bones. They are lined with mucous membranes and connect to the nasal cavity.

• Functions:

  • Lighten the weight of the skull

  • Enhance resonance of the voice

  • Produce mucus to moisten the nasal cavity

• Major Sinuses and Locations:

  • Frontal sinus: Located above the eyes, within the frontal bone

  • Ethmoid sinus: Located between the nose and the eyes, within the ethmoid bone

  • Sphenoid sinus: Located behind the ethmoid sinuses, within the sphenoid bone

  • Maxillary sinus: Located within the maxilla, lateral to the nasal cavity (largest paranasal sinus)

Sinus	Location	Drains Into
Frontal	Above eyes, frontal bone	Nasal cavity
Ethmoid	Between nose and eyes, ethmoid bone	Nasal cavity
Sphenoid	Behind ethmoid, sphenoid bone	Nasal cavity
Maxillary	Lateral to nasal cavity, maxilla	Nasal cavity

Example: The maxillary sinus is the largest and is located on either side of the nose.

Fontanelles ("Soft Spots")

Definition and Types

Fontanelles are areas of fibrous membranes between the cranial bones of a fetal skull. They allow for flexibility during birth and brain growth during infancy.

• Anterior fontanel: Located between the frontal and parietal bones

• Posterior fontanel: Located between the occipital bone and parietal bones

Function: Permit molding of the fetal head during passage through the birth canal and accommodate rapid brain growth.