Generality
The occipital bone is the uneven skull bone and resembles a shallow cooking dish, which, located in the occiput, provides protection to the occipital lobes of the brain and the cerebellum.
Bordering on the parietal bones (superiorly), the temporal bones (laterally) and the sphenoid bone (anteriorly), the occipital bone can be divided into 4 main parts, which in a front-back sense are: the basilar part, the lateral parts and the scaly part.
Among the numerous anatomical elements present on the occipital bone, the occipital or foramen magnum hole is also present; the latter is the opening through which the medulla is passed before entering the vertebral canal and becoming spinal cord.
What is Occipital bone?
The occipital bone is the uneven bone of the posterior-inferior portion of the skull, occupying the region of the occiput and placed to protect the occipital lobes of the brain and the hemispheres of the cerebellum.
The occipital bone represents one of the 8 bones of the so-called neurocranium, ie the upper skeletal complex of the skull.
Short anatomical review
- The skull of the human being can be divided into two main skeletal complexes: the aforementioned neurocranium and the splancnocranium .
In addition to the occipital bone, the neurocranium includes: the frontal bone, the two temporal bones, the two parietal bones, the sphenoid bone and the ethmoid bone.
To the splancnocranium, on the other hand, belong 14 bones, which are: the two zygomatic bones, the two tear bones, the two nasal bones, the two palatine bones, the two lower nasal horns, the two maxillary bones, the vomer and the mandible.
- Occiput is the anatomical term indicating the posterior region of the head, the one in which the occipital lobe of the brain and the occipital bone reside.
Anatomy
Similar in the contours of a trapezoid, the occipital bone has an internal convexity (that is, on the side of the brain), which makes it look very much like a shallow kitchen dish ; this particular convexity is justified by the need to better accommodate the occipital lobe of the brain.
The occipital bone belongs to the category of flat bones ; the latter are bones typically developed in length and width, but not in thickness (so they are fine).
To make the description of the occipital bone easier, the anatomists divide the latter into 4 main parts, which, proceeding in the opposite direction of the head-back of the head, are: the so-called basilar part, the so-called two lateral parts and the so-called scaly part.
The basic part: is the section of occipital bone closest to the forehead; morphologically similar to a quadrilateral, it takes place in front of the occipital hole (or foramen magnum ), that is the characteristic opening present on the occipital bone and which will be the object of further study in a separate chapter.
The side parts: moving away from the front, are the two sections immediately following the basic part; in fact, they are the components of the occipital bone that make up the sides of the occipital hole.
The scaly part: is the section of occipital bone furthest from the forehead; subsequently localizes to the lateral parts, therefore it is posterior to the occipital hole. It is the largest part of the occipital bone and the one that gives it the most convex aspect.
Did you know that ...
Because of their composition and shape, flat bones like the occipital bone are very resistant .
Relations of occipital bone
The occipital bone has relationships with as many as 5 bones of the skull; to be precise, it borders on:
- The two parietal bones, above;
- The temporal bones, latero-inferior;
- The sphenoid bone, anteriorly.
Fundamental structural elements of the occipital bone
The most classic structural descriptions of the occipital bone recognize in the latter the existence of:
- Two surfaces, the outer surface and the inner surface ;
- The occipital hole;
- Four corners, the upper corner, the lower corner and the two side corners ;
- Two edges, the upper edge and the lower edge .
OUTER SURFACE
The outer surface of the occipital bone is the latter's surface closely related to the skin of the head.
From the anatomical point of view, the scaly part and the two lateral parts are particularly relevant to this surface; on the scaly part, in fact, it is possible to notice:
- A central prominence, called the external occipital protuberance, whose culminating point is called inion ;
- A crest, called external occipital crest or medial nuchal line, which runs from the inion to the occipital hole and on which the so-called nuchal ligament is inserted;
- Three pairs of detected and symmetrical lines, placed at the sides of the external occipital protuberance and of the occipital crest, and with an orientation almost perpendicular to the latter. Placed one on top of the other, these pairs of lines are called nuchal lines and are the seat of attachment for different muscles and ligaments.
On the lateral parts, instead, one on the right and one on the left of the occipital hole, are the two so-called occipital condyles, whose role will be discussed later.
Did you know that ...
The three pairs of nuchal lines include: the supreme nuchal lines, which are those located higher up, the upper nuchal lines, which are those located just below the supreme nuchal lines, and finally the inferior nuchal lines, which are those placed more in bass.
INTERNAL SURFACE
The inner surface of the occipital bone is the surface of the latter located on the side of the occipital lobe of the brain.
From the anatomical point of view, all its constituent parts are important for this surface; Here because:
- In the two lateral parts (ie the lateral regions to the occipital hole) reside the two hypoglossal channels (in which the right hypoglossal cranial nerve and the left hypoglossal cranial nerve run ) and the two jugular holes ;
- In the basilar part, it locates the clivus, a not very deep and smooth depression, placed anteriorly to the occipital hole and designed to receive the Varolio bridge just before becoming elongated marrow .
- In the scaly part, they take place: the internal occipital crest (coincides with the inside of the external occipital crest), the internal occipital protuberance (corresponds to the inside of the internal occipital protuberance), the two pits each hosting one of the two occipital lobes of the brain ( cerebral pits ), the two welcoming pits each one of the two hemispheres of the cerebellum ( cerebellar pits ) and the two grooves with lateral course with respect to the internal occipital protuberance, in which the so-called transverse sinuses flow (they are the venous vessels that drain the poor blood of oxygen from the back of the head).
Short study of cerebral and cerebellar pits
The cerebral pits of the occipital bone lie in the portion of the inner surface and this explains why they are also called superior pits .
The cerebellar pits of the occipital bone, on the other hand, reside in the lower portion of the inner surface and this is why they are also called lower pits .
OCCITAL HOLE
The most often mentioned occipital hole is the characteristic opening of the occipital hole between:
- The lateral parts of the occipital bone, right and left;
- The basilar part of the occipital bone, anteriorly (closer to the forehead);
- The scaly part of the occipital bone, posteriorly (farther from the forehead).
The occipital hole owes its notoriety to the fact of being the fissure of the skull through which the medulla oblong transits just before entering the vertebral canal and becoming spinal marrow, and through which other important anatomical structures pass, such as the vertebral arteries, the accessory nerve ( XI cranial nerve ), the tectoria membrane and the anterior and posterior spinal arteries .
Elongated marrow and Varolio bridge
The elongated medulla and the Varolio bridge mentioned above constitute, together with the midbrain, an important structure of the central nervous system: the brainstem .
These three elements are connected to each other, with the midbrain superimposed on the Varolio bridge, which, in turn, resides above the elongated medulla.
UPPER ANGLE, LOWER CORNER AND SIDE CORNERS
The upper corner of the occipital bone is the portion of the latter bordering and in union, by means of a joint, with the occipital corners of the two parietal bones, located above.
The inferior angle of the occipital bone is the structural element of the latter bordering and in union, by means of another articulation, with the sphenoid bone, placed anteriorly.
Finally, the lateral corners of the occipital bone are the right and left portions of the latter, located at the end of the groove of the aforementioned transverse sinuses (inner surface) and adjacent as well as in union with the mastoid angle of the parietal bones and the mastoid angle of temporal bones (NB: clearly, the right lateral angle borders the mastoid angle of the parietal bone and the right temporal bone, while the left lateral angle with the mastoid angle of the parietal bone and left temporal bone).
Did you know that ...
In the skull of the fetus and the newborn child, the upper corner of the occipital bone is in the immediate vicinity of the posterior fontanel.
UPPER EDGE AND LOWER EDGE
The edges of the occipital bone are, in fact, the elements of the latter that mark its thickness ; the edges are anatomically important, because they are the true creators of the joints between the occipital bone and the other cranial bones.
Entering each individual edge, the upper edge comprises the entire thickness of the upper corner and of the side corners side more contiguous to the aforementioned upper corner. The lower edge, on the other hand, includes the entire thickness of the lower corner and of the side angles closest to the lower corner mentioned above.
Joints
In describing the angles and then the edges, this article on the occipital bone spoke of joints.
Such joints are examples of cranial joints or, as would be better to call them, cranial sutures .
The cranial suture that joins the upper corner of the occipital bone to the parietal bones the so-called lambdoid suture .
The cranial sutures that connect the lateral corners of the occipital bone to the mastoid corners of temporal bones and parietal bones are the so - called occipito-mastoid sutures .
The cranial suture that joins the lower corner of the occipital bone to the sphenoid bone is the so - called spheno-occipital suture .
Cranial sutures, however, not only the only joints with which the occipital bone is attached; the latter, in fact, also presents the so - called atlo-occipital joint, a diarthrosis (that is, a mobile joint ) which has the fundamental task of joining the skull to the vertebral column.
The atlo-occipital joint sees the union of the two occipital condyles of the occipital bone with the upper articular facet of the first cervical vertebra of the vertebral column, vertebra whose name is atlas.
Curiosity
Due to some genetic diseases (eg: Crouzon syndrome ), the lambdoid suture of the occipital bone may be subject to craniostenosis, ie premature fusion .
The premature fusion of the lambdoid suture - as well as of other cranial sutures - can affect the normal development of the brain, with repercussions in terms of intellectual capacity.
Fetal and post-natal development
The process of occipital bone formation, during fetal development, occurs with different times and methods, depending on the part of bone considered:
- The scaly part results from the contribution of 6 ossification centers, 4 of which are activated at the second month of fetal life and the remaining 2 at the third month of fetal life; initially, the scaly part is separated into two, but from the third month of fetal life onwards (therefore when the last two ossification centers are also activated) it becomes a unique piece;
- The lateral parts result from the work of an ossification center for each part, which is activated at the eighth week of fetal life;
- The basic part is the result of the action of 2 ossification centers, which operate starting from the sixth week of fetal life.
AFTER THE BIRTH
At birth, the various parts that form the occipital bone are separated from each other (ie they are distinct elements). This situation remains unchanged until the fourth year of life, when the scaly part and the lateral parts begin to merge with each other; next to the 6th year of life, then, the fusion between the scaly part and the lateral parts is added to the fusion between the side parts and the basic part.
Ultimately, from the sixth year of life, the occipital bone is a single bone, for which the division into parts is only ideal and serves to simplify its description.
ADULT LIFE
When adulthood is reached, when the brain has grown properly, the occipital bone is founded on the other cranial bones that border it.
Specifically, between the ages of 18 and 25, it enters into fusion with the sphenoid bone placed anteriorly, while, between 26 and 40 years, it enters into fusion with the parietal bones located above.
Function
The occipital bone is one of the bones of the skull involved in the formation of the cranial vault, ie the skeletal structure responsible for enclosing and protecting the encephalon (NB: the brain is the set of brain, cerebellum, diencephalon and brainstem). Specifically, due to the position it occupies, the occipital bone constitutes the area of the cranial vault designed to protect: the occipital lobes of both the cerebral hemispheres and the two hemispheres of the cerebellum.
The functions of the occipital bone, however, do not end with the protection of the brain; because of its contribution to the formation of the aforementioned atlo-occipital joint, the bone in question is a fundamental element of conjunction between the head and the vertebral column.
The functions of the atlo-occipital joint
The atlo-occipital joint allows the head to flex, the extension movement and a moderate lateral bending movement (lateral bending).
diseases
The occipital bone is a resistant bone, however, like all the other bones of the human body, it can be subject to fracture, if subjected to traumas of a certain size.
In addition to the problem of fractures, there is also the possibility of involvement of the occipital bone in genetic diseases, which alter its morphology, such as Edwards syndrome and Beckwith-Wiedemann syndrome .
Fracture of the occipital bone
The occipital bone is particularly susceptible to fractures in its basilar part, where the so-called posterior occipital fossa is located.
Morphological alterations of the occipital bone
Genetic diseases such as Edwards syndrome and Beckwith-Wiedemann syndrome induce a morphological alteration of the occipital bone, such that the head is particularly prominent in the occipital region.
