Human Anatomy: Skull and C1 + C2

These flashcards cover the anatomy of the skull, its subdivisions, development, clinical conditions like craniosynostosis, major bones, muscles of expression and mastication, and the C1 and C2 vertebrae.

Viscerocranium

The group of skull bones that form the skeleton of the face and the mandible.

Neurocranium

The group of bones that form the walls of the cranial cavity, which houses the brain.

Calvaria

The dome-shaped roof of the neurocranium, primarily composed of the frontal, parietal, and temporal bones.

Basicranium

The floor of the neurocranium, also known as the cranial base.

Cranial Fossa

Three depressions in the floor of the neurocranium (Anterior, Middle, and Posterior) that contain different parts of the brain.

Endochondral Ossification

The process by which bone tissue is produced for most of the cranial base, including the ethmoid and portions of the frontal, sphenoid, temporal, and occipital bones.

Intramembranous Ossification

The process by which the bones of the face (viscerocranium) and all bones of the calvaria are formed.

Sutures

Narrow seams of fibrous connective tissue that act as interlocking fibrous joints between the flat bones of the skull.

Fontanelles

Fibrous connective tissue filled gaps located at the corners of parietal bones in a neonatal skull, allowing for deformation during birth and brain growth.

Anterior Fontanelle

The largest and most clinically important fontanelle, with an average size of $2.1\,\text{cm}$ and a median closure time of $13.8$ months.

Craniosynostosis

An anomaly of development involving premature suture fusion that results in a deformation of the calvarial shape.

Scaphocephaly

A long, narrow, wedge-shaped calvaria caused by the premature fusion of the sagittal suture.

Brachycephaly

A wider and shorter than normal skull resulting from the premature fusion of bilateral coronal sutures.

Pterion

A thin region of bone where several sutures meet, overlying the anterior division of the middle meningeal artery.

Ethmoid Bone

An unpaired bone that separates the nasal cavity from the brain and contains the cribriform plate for olfactory nerves.

Sella Turcica

A saddle-shaped depression in the sphenoid bone consisting of the hypophyseal fossa and dorsum sellae, which houses the pituitary gland.

Zygomatic Bone

The cheekbone or malar bone that forms the prominence of the cheeks and contributes to the structure of the orbit.

Foramen Magnum

The large opening in the occipital bone through which the spinal cord and vertebral arteries pass.

Orbicularis Oris

A sphincter muscle around the oral cavity that seals the lips and prevents drooling.

Buccinator

A muscle of facial expression that compresses the cheek against the teeth to keep food on the occlusal surfaces during chewing.

Occipitofrontalis

A muscle consisting of frontal and occipital bellies joined by the epicranial aponeurosis, used to move the scalp and elevate eyebrows.

Temporomandibular Joint (TMJ)

The articulation between the mandibular condyle and the mandibular fossa of the temporal bone, covered by fibrocartilage.

Masseter

A muscle of mastication that spans the space between the zygomatic arch and the mandible's ramus, functioning to elevate the mandible.

Atlas (C1)

The first cervical vertebra, which lacks a vertebral body and contains lateral masses that articulate with the occipital condyles.

Axis (C2)

The second cervical vertebra, characterized by the dens (odontoid process) which acts as a pivot for rotation.

Dens (Odontoid Process)

A tooth-like bony protrusion of the Axis that represents the fused body of the C1 vertebra.

Alar Ligaments

Ligaments extending from the dens to the lateral margins of the foramen magnum that prevent excessive rotation of the head.