Bio250-6 Skull

Axial Skeleton

  • Skull:

    • Cranial Bones: Comprises 8 bones - frontal, parietal (2), temporal (2), occipital, sphenoid, and ethmoid, collectively protecting the brain and supporting the structures of the face.

    • Facial Bones: 14 bones - nasal, zygomatic (2), maxilla (2), palatine (2), vomer, lacrimal (2), and mandible, which form the front structure of the skull and house the dental arches and nasal cavity.

  • Vertebral Column:

    • Divided into regions: 7 cervical (C1-C7), 12 thoracic (T1-T12), and 5 lumbar (L1-L5), totaling 24 individual vertebrae.

    • The vertebral column includes the sacrum (5 fused vertebrae) and coccyx (4 fused vertebrae), providing support and protection for the spinal cord while allowing for flexibility and movement.

  • Thoracic Cage:

    • Composed of 12 pairs of ribs and the sternum, providing a protective enclosure for the heart and lungs while aiding in the mechanics of breathing. The ribs (true ribs - 7 pairs, false ribs - 3 pairs, floating ribs - 2 pairs) articulate with thoracic vertebrae.

  • Hyoid Bone:

    • A unique U-shaped bone located in the neck, it does not articulate with any other bone and serves as a crucial anchorage for tongue muscles and support for the larynx during phonation and swallowing.

  • Auditory Ossicles:

    • Comprising 6 small bones (3 on each side) - malleus, incus, and stapes, situated within the middle ear, they play a pivotal role in the transmission of sound vibrations from the eardrum to the inner ear.

Major Sutures

  • Coronal Suture:

    • A fibrous joint separating the frontal bone from the parietal bones, playing a significant role in the growth and development of the skull.

  • Sagittal Suture:

    • The joint that unites the two parietal bones along the midline, crucial for skull stability.

Cranial Structures

  • Frontal Bone:

    • Contains the frontal sinus, contributes to the formation of the forehead and orbits, and supports the structures of the face.

  • Parietal Bones:

    • These paired bones are situated at the superior and lateral aspects of the skull, forming the sides and roof of the cranial cavity.

  • Occipital Bone:

    • Found at the posterior aspect of the skull, it contains the foramen magnum, allowing the spinal cord to connect with the brain, and articulates with C1 allowing for nodding motion.

  • Temporal Bones:

    • Situated near the ears, these bones house structures for hearing and balance; notable features include the zygomatic process, mastoid process, and the external acoustic meatus.

  • Sphenoid Bone:

    • A complex bone located at the base of the skull; it contributes to the formation of the eye socket and contains key structures for the passage of nerves.

  • Ethmoid Bone:

    • Located between the nasal cavity and the orbits, it features the crista galli and cribiform plate, crucial for olfactory function and the structure of the nasal cavity.

Temporal Bone Functions

  • Key for hearing and equilibrium, the temporal bones house the auditory ossicles and contain features like the auditory canal and semicircular canals, which are essential for balance.

Ethmoid Bone Features

  • Crista Galli:

    • An upward projection providing attachment for the dura mater (protective covering of the brain).

  • Cribriform Plate:

    • Contains olfactory foramina, allowing for the passage of olfactory nerve fibers, crucial for the sense of smell.

  • Ethmoid Sinuses:

    • Air-filled spaces aiding in humidifying and filtering air entering the nasal cavity.

  • Nasal Conchae:

    • Superior and middle structures within the nasal cavity, facilitating airflow and trapping particulate matter.

  • Perpendicular Plate:

    • Contributes to the septum dividing the nasal cavity into right and left halves.

Sphenoid Bone Structures

  • Sella Turcica:

    • A saddle-shaped depression housing the pituitary gland, vital for hormonal regulation.

  • Optic Foramen:

    • Allows the passage of the optic nerve (CN II) from the eye to the brain.

  • Superior Orbital Fissure:

    • A space allowing passage for nerves controlling eye movements and the ophthalmic vein.

Occipital Bone Details

  • Foramen Magnum:

    • The large opening at the base of the skull allowing the spinal cord to merge with the brain stem.

  • Occipital Condyles:

    • Articulate with the first cervical vertebra enabling nodding movements of the head.

  • Jugular Foramen:

    • A critical passage for cranial nerves (CN IX, X, XI) and the internal jugular vein, vital for venous drainage from the brain.

Facial Structures

  • Maxillary Bone:

    • Forms the upper jaw and part of the hard palate, playing a role in mastication.

  • Palatine Bones:

    • Contributes to the hard palate and part of the nasal cavity, ensuring separation between the nasal and oral cavities.

  • Zygomatic Bones:

    • Known as cheekbones, they provide structure to the face and contribute to the orbit.

  • Vomer Bone:

    • Forms the lower part of the nasal septum, separating the left and right nasal passages and ensuring efficient airflow.

Hyoid Bone Functionality

  • Acts as a base for the tongue, facilitating speech and swallowing, and providing structural support to the larynx.

Dentition Overview

  • Teeth Count:

    • 20 primary (baby) teeth that eventually fall out, replaced by 32 permanent adult teeth.

  • Molars:

    • 12 (3 on each side of the jaw), designed for grinding food.

  • Premolars/Bicuspids:

    • 8 in total (2 on each side), serving to grasp and tear food.

  • Canines:

    • 4 pointed teeth, crucial for piercing and tearing.

  • Incisors:

    • 8 sharp-edged teeth used for cutting food.

Infantile Skull Characteristics

  • At birth, the skull is not fully ossified, featuring fontanels (soft spots) that allow for cranial flexibility and growth during the birthing process. These fontanels gradually close as the child matures, providing structure as the brain grows.