Cranial Bones

Cranial Bones

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Head Bones and Their Functions

The bones of the head form a protective and immovable cavity around the brain. These bones, a total of 22, are divided into two main categories: the cranium and the facial skeleton. The cranium encloses and protects the brain, while the facial skeleton provides support to facial soft tissues. Nerves and blood vessels enter and exit the cranium through the cranial foramina.

The cranium can be further divided into the calvarium and the cranial base. The calvarium, made up of the frontal, occipital and two parietal bones, is the top part of the cranium. The cranial base, which is made up of the frontal, sphenoid, ethmoid, occipital, parietal and temporal bones, articulates with the first cervical vertebra and the mandible to form the temporomandibular joint.

The mandible, the largest and strongest bone of the face, forms the lower jaw and is where the lower teeth are inserted. The sphenoid bone is shaped like a butterfly and consists of a body, as well as upper and lower wings. It contains the sphenoid sinuses. The ethmoid bone forms the roof of the nasal cavity, and fibers from the olfactory nerve (CN1) pass through it allowing for the sense of smell. The temporal bone, located laterally, supports the temporal lobes and also houses the middle and inner parts of the ear.

The bones of the head also create the bony orbits, symmetrical cavities that surround and protect the eyes and associated structures. The head bones also give rise to the bony component of the nasal skeleton.

Joints of the Head Bones

The bones of the head meet at immovable joint lines called sutures. These are fibrous joints. Additionally, the cranium articulates with the first cervical vertebra and the mandible to form the temporomandibular joint. This joint is responsible for some of the movements of the mandible, and for allowing the lower jaw to open, close, and side-to-side. It is also known as the TMJ joint.

The TMJ joint is a complex joint composed of two bones and an articular disc. The two bones of the TMJ joint are the condyle, which is part of the mandible, and the temporal bone of the skull. The articular disc distributes load and helps limit the mandible’s movement.

Cranial Nerves and Muscles

The cranium is responsible for protecting and providing its contents, namely, the brain and its cranial nerves. The cranial nerves are 12 pairs of nerves that come out of the brainstem, through the foramina of the skull, and branch off towards different parts of the body. The cranial nerves are responsible for vision, hearing, taste, smell, the muscles of the face and neck, and other functions.

The muscles of the head and neck are also responsible for the many movements that the head is capable of, such as turning, tilting, and nodding. These muscles are mostly made of up of the eight cranial nerves, and the two branches of the cervical plexus.

  • Oculomotor nerve (CN3) - Responsible for movement of the eye
  • Trochlear nerve (CN4) - Moves the eyeball downward and inward
  • Trigeminal nerve (CN5) - Facilitates facial sensation and movement of the jaw
  • Abducens nerve (CN6) - Moves the eyeball to the side
  • Facial nerve (CN7) - Moves facial muscles and carries taste sensation
  • Vestibulocochlear nerve (CN8) - Carries hearing and balance information
  • Glossopharyngeal nerve (CN9) - Responsible for movement and sensation of the throat
  • Vagus nerve (CN10) - Responsible for the movement of the larynx and the sensation of the chest, abdomen and organs
  • Accessory nerve (CN11) - Moves muscles of the shoulder and neck
  • Hypoglossal nerve (CN12) - Controls the tongue muscles

The two branches of the cervical plexus are the spinal accessory nerve (CN11) and the hypoglossal nerve (CN12). The spinal accessory nerve (CN11) moves the muscles of the shoulder and neck, and the hypoglossal nerve (CN12) moves the tongue muscles.


The bones of the head are an integral part of the body. The head bones form a protective cavity around the delicate brain, allowing it to stay safe and healthy. The joints of the head bones, the cranial nerves, and the muscles attached to the head bones all work together to keep the head functioning properly and performing its many tasks. The bones of the head are one of the most important parts of the body, providing essential protection and support.

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