Anatomy/Head and neck
The Skull
The skull describes the structure of the bones that constitute the human head. Not only humans, this description suits the explanation of the skull for all vertebrates. The skull is not just a skeletal frame, it performs the function of protection to the brain, brainstem and it supports the face.
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The Skull
[edit | edit source]Structure: The adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility.
Eight bones form the neurocranium (brain case), a protective vault of bone surrounding the brain and brain stem. Fourteen bones form the splanchnocranium, which comprises the bones supporting the face. Encased within the temporal bones are the six auditory ossicles (3 ossicles in each ear) of the middle ear. The hyoid bone, supporting the larynx, is usually not considered as part of the skull, as it is the only bone that does not articulate with other bones of the skull.
The skull also contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium, which also lines the large airways. The exact functions of the sinuses are debatable; they contribute to lessening the weight of the skull with a minimal reduction in strength, they contribute to resonance of the voice, and assist in the warming and moistening of air drawn in through the nasal cavities.
The meninges are three layers of connective tissue surrounding structures of the central nervous system. From outermost to innermost layer, they are the dura mater, the arachnoid mater, and the pia mater. Each layer adds important protective and physiologic functions.
The anatomical position for the skull is the Frankfurt plane, where the lower margins of the orbits and the upper borders of the ear canals are all in a horizontal plane. This is the position where the subject is standing and looking directly forward. The Frankfurt plane may also be used to study the brains of other specifies, notably primates and hominids. However, this does not always equate to a natural posture in life.
The 21 immovable bones include: A. 8 paired bones (right and left): parietal, temporal, zygomatic, lacrimal, maxillary, nasal, palatine, inferior concha. B. 5 unpaired bones: frontal, ethmoid, sphenoid, occipital, vomer.
Parts of the skull: 1. Cranium: The upper & post. part which encloses the brain. 2. Facial Skeleton: The ant. part of the skull which includes an upper fixed part and the mandible.
Different aspects of the skull: 1. Anterior aspect (Norma Frontalis) 2. Superior aspect (Norma Verticalis) 3. Lateral aspect (Norma Lateralis) 4. Posterior aspect (Norma Occipitalis) 5. Inferior aspect (Norma Basalis) 6. Interior of Skull (Cranial Cavity) Tarek Karim Jan 08:55, 8 December 2007 (UTC)
Individual Bones of the Skull
[edit | edit source]Before describing individual bones of the cranium, It is appropriate to categorize them under 1) Neurocranium 2) Viscerocranium. Although, viscerocranium is further subdivided into membranous viscerocranium and cartilaginous viscerocranium, primarily the consideration of the former one is more relevant in the study of anatomy.