The Bones of the Head
The skull contains all the bones of the head and is a shell for the brain and the origins of the central nervous system. A first glance shows that this is one large mass of detailed and irregular bone.
Upon closer inspection however, it seems that it is intricately constructed of many smaller bone fragment pairs, all unique in shapes and sizes, that bilaterally make up this hollow, three dimensional ovoid shaped structure. Because of its complexity, the first step to approach to the anatomy of the skull is to begin with its regional and topographic overview.
Neurocranium: occipital bone, temporal bones (2), parietal bones (2), sphenoid bone, ethmoid bone, frontal bone
Viscerocranium: vomer, nasal conchae (2), nasal bones (2), maxilla, mandible, palatine bones (2), zygomatic bones (2), lacrimal bones (2)
(1) Region of the cranium, subregions:
- cranial vault - upper portion of the skull
- cranial base - inferior portion of the skull
- cranial cavity - interior of the skull (subregions: anterior, middle, posterior cranial fossae)
- facial skeleton - bones that make up the face
- acoustic skeleton - ear ossicles(2) Region of the mandible
|Clinical relations||Fractures, osteoporosis, osteoradionecrosis, osteomalacia, osteomyelitis, pneumatization, circumstantial bone resorption|
This article gives a general overview of the most complicated bony structure in the entire human body.
The term 'the skull' includes all the bones of the head, face and jaws. Within this capacity, there are twenty eight individual bones. Of these twenty eight bones, eleven of them are paired, to form a bilaterally symmetrical three dimensional structure and six of them are single, unique bones.
In some cases sutural bones, also known as wormian bones may grow between the sutures of two bones. These occur naturally and are not counted among the primary cranial bones.
The skull bones are categorized into regional and development bones.
When done by region, the skull is classified by its two main parts: the cranium and the mandible.
These two structures are not attached when there are no tendons or muscles holding them together. The mandible is one entire bone but the cranium is further divided into subcategories of bones, including the cranial vault or upper portion of the skull, the cranial base which is the inferior portion of the skull, the cranial cavity, also known as the interior of the skull, the bones that make up the face and are called the facial skeleton and lastly, the acoustic skeleton or ear ossicles.
Developmentally, the skull is separated into the viscerocranium and the neurocranium. These are the areas of the skull that take part in digestion and respiration and also those which guard the central nervous system and the organs of taste, touch, smell, hearing and site respectively.
The Cranial Cavity is divided into three different sections. These borders are marked on the skull by specific structures, but also by which part of the brain they house.
- The frontal lobe of the brain fills the anterior cranial fossa
- The middle cranial fossa holds the temporal lobe of the brain
- The last fossa, named the posterior cranial fossa, contains the cerebellum.
Finally, it is to be noted that there a several different views of the skull, that when separate from the body in its entirety, are possible without hindrance from other structures. These five views are the anterior view or norma frontalis, the lateral view or norma lateralis, the posterior view or norma occipitalis, the inferior view or norma basalis and finally the superior view or norma verticalis.
The most important function of the skull is to protect the brain and the central nervous system. It also protects the organs that control special senses. These five senses and their corresponding organs are:
- Olfaction or sense of smell which is accommodated by the nasal cavity;
- Vision which is hosted by the eye;
- Taste which is regulated by the oral cavity;
- Vestibular function and auditory function, simply known as movement or touch and hearing. The Ear encompasses these two senses.
The pathology of the skull is complex, however the main reasons for a health disturbance are trauma and bone disease.
The most probable cause for trauma to the skull is a car accident, violence and then sports injuries, in that order. The fractures that occur due to these traumas can occur in certain areas of the skull and are named according to the these areas in a list seen below:
- Frontobasal fractures cause injury to the forehead and the base of the skull in the occipital bone;
- Blow-out fractures damage the floor of the orbit;
- lateral and midfacial fractures harm the frontal and lateral areas of the face;
- Mandibular fractures occur anywhere on the mandible, with the most common area being the condyle;
- Le Fort fractures occur in three areas range from the maxilla (Le Fort I), the midface (Le Fort II), to the border of the viscerocranium and the neurocranium (Le Fort III) and incorporate various facial bones.
Clinically, fractures of the face can present with severe pain, mobility, hematomas and lacerations.
Bone diseases include osteoporosis, osteoradionecrosis, osteomalacia, osteomyelitis, pneumatization and circumstantial bone resorption to name but a few. Depending on whether the disorder is chronic or acute, bacterial or substance related and congenital or acquired, their a various treatments and medications prescribed by surgeons and dentists alike.