Key Functions and Clinical Importance of the Sphenoid Bone
The sphenoid bone or the Wasp bone is an unpaired bone that is situated in the skull or the cranium of the human head. The prime location of the sphenoid bone is in the frontal side of the brain, just before the occipital bone. There are eight bones that construct the entire cranium of the head and sphenoid bone is one of them.
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It can be described as the superior section of the skull that is responsible for the protection of the brain. The name sphenoid comes from the Greek term ‘sphenoeides’ which translates to ‘wedge-shaped’. It is a central unit in the skull and has a pretty complex shape consisting of the main body as well as two sets of wings along with the pterygoid process.
Sphenoid Bone Anatomy
The structure of the sphenoid bone is shaped somewhat like a butterfly. The main parts of the sphenoid bone consist of the body, greater wings, pterygoid process, and the lesser wings.
Situated centrally along the skull’s midline is the body of the sphenoid bone. There are wings on either side of the body and the structure is quite complicated. The portion that faces the front helps in creating the nasal cavity. The sides of the body contribute to the creation of the optic canal.
The sella turcica in the sphenoid bone is formed by the upper surface of the structure. It is created with the hypophyseal fossa (a small depression meant to hold the pituitary gland), the dorsum sellae, and tuberculum sellae. The sphenoid bone sella turcica has 2 anterior clinoid processes surrounding it along with 2 other bony protrusions. On the rear end, there are 2 eminences known as the posterior clinoid processes. These result in the deepened structure of the sella turcica.
The lesser wings in the sphenoid bones rise from the frontal section and move to the sides. These wings have a triangular shape. The lower borders present in the lesser winds help in the creation of the orbits that hold the eyes. The upper borders create the cranial cavity which holds some parts of the brain.
Situated behind the lesser wings, the greater winds run to the extreme sides. The shape of the greater wings is triangular as well and these run laterally to the sphenoid bone body. The sides of the greater wings create the infratemporal surfaces. These surfaces move backwards to join the sides and have a convex shape. The portions in the front help in the formation of the orbit’s sidewalls. Each of the wings has three different openings known as the foramen spinosum, foramen rotundum, and foramen ovale. These openings allow the passage of vessels and nerves such as the maxillary and the mandibular nerves.
Essentially known as the extensions of the sphenoid bone’s body, the pterygoid processes are a very important part of the sphenoid bone anatomy. These processes have 2 different protrusions that emerge from the backside of the body and move downward. There are two canals in the processes known as the palatovaginal and the pterygoid canals. These canals also allow the passage of nerves and each canal has a hamulus, projecting the shape of a hook.
Sphenoid Bone Location
The location of the sphenoid bone is in the central section of the skull that is a part of the midline. This structure separates the occipital and the frontal bone. Aside from that, the sphenoid bone also articulates and connects to other bones that run along the side. Some examples of such bones include the ethmoid bone, parietal bone, temporal bone, vomer bone, and palatine bone, and zygomatic bone. These connections help provide a stable structure to the skull and help in holding the brain in its place.
Sphenoid Bone Function
Working together with the orbital floor in the skull, the sphenoid bone helps in the formation of the sides and base of the human skull. Some major components of the sphenoid bone also result in the formation of the facial skeleton. Since it is centrally placed in the skull, the bone also provides the skull with proper rigidity and assists in the protection of the nerve structures as well as the brain. The rear sections of the sphenoid bone act as attachment locations for muscles that play a role in talking or chewing. The foramina that are present in the sphenoid bone allow the important vessels and nerves to pass in and out the skull. The cavity present in the sphenoid bone further allows the formation of the sphenoid sinus which is connected to the nasal cavity.
Conclusion
According to sphenoid bone radiology, it is centrally located in the base of the skull and is considered to be one of the most complex structures of the human body. It creates the major boundary between the extracranial and intracranial structures and also acts as a conduit for different cranial nerves. The foramina extending from the sphenoid bones help in extending the orbits, hence making the structure extremely important for the functioning of the body.
FAQs on Sphenoid Bone Anatomy: Complete Student Guide
1. Why is the sphenoid bone often called the 'keystone' of the skull?
The sphenoid bone is called the 'keystone' of the skull because it is the only cranial bone that articulates with all other cranial bones. Much like a keystone in an architectural arch, it locks the other bones in place, providing crucial stability and rigidity to the entire cranial structure. Its central location and extensive connections are vital for maintaining the skull's integrity.
2. Where is the sphenoid bone located in the human skull?
The sphenoid bone is an unpaired bone situated in the middle of the skull base, towards the front. It lies posterior to the frontal bone and anterior to the occipital bone. It acts as a central anchor, forming parts of the floor of the middle cranial fossa, the sidewalls of the skull, and the walls of the orbits (eye sockets).
3. What are the four main parts of the sphenoid bone?
The complex, butterfly-shaped structure of the sphenoid bone consists of four primary parts:
- Body: The central, cubical part which contains the sphenoidal sinuses.
- Greater Wings: Two large wings that project sideways from the body, forming part of the cranial floor and the sides of the skull.
- Lesser Wings: Two smaller, triangular wings located superior to the greater wings, which form the upper border of the superior orbital fissure.
- Pterygoid Processes: Two processes that extend downwards from the junction of the body and greater wings, serving as attachment sites for chewing muscles.
4. What is the importance of the sella turcica on the sphenoid bone?
The sella turcica, which means 'Turkish saddle', is a critical saddle-shaped depression located on the superior surface of the sphenoid bone's body. Its primary importance is that it houses and protects the pituitary gland, which is the master gland of the endocrine system responsible for regulating numerous vital bodily functions.
5. How does the sphenoid bone contribute to both the cranium and the facial skeleton?
The sphenoid bone has a dual role, contributing to both structures. For the cranium, it forms a significant part of the cranial floor, directly protecting the base of the brain. For the facial skeleton, its greater wings form the posterior walls of the orbits (eye sockets), and its pterygoid processes help form the walls of the nasal cavity and provide attachment points for muscles essential for mastication (chewing).
6. What is the function of the various foramina, or openings, in the sphenoid bone?
The foramina of the sphenoid bone serve as vital passageways for critical neurovascular structures. Their main function is to allow cranial nerves (such as the optic, maxillary, and mandibular nerves) and major blood vessels to pass between the cranial cavity and the orbits, face, and other regions. For example, the optic canal transmits the optic nerve, and the foramen rotundum allows passage for the maxillary nerve.
7. What is a common misconception about the sphenoid bone's role in the nose?
A common misconception is that the sphenoid bone is located inside the nose. In reality, the sphenoid bone is situated posterior (behind) and superior (above) the nasal cavity. However, it is related to the nose in two key ways: it forms the rearmost part of the roof of the nasal cavity, and its hollow body contains the sphenoidal sinuses, which are air-filled spaces that drain into the nasal cavity.
8. What is sphenoid sinusitis and how is it related to the bone's structure?
Sphenoid sinusitis is the inflammation or infection of the sphenoidal sinuses, the air-filled cavities within the body of the sphenoid bone. Due to the bone's deep location, this condition can be serious. The sinuses are very close to critical structures like the optic nerves, pituitary gland, and internal carotid arteries. An infection here can lead to severe headaches, vision problems, or spread to become a more dangerous intracranial infection.
