General Features and Functions of the Skull

The human skull is the component of the skeleton the supports the structures of the face and forms a cavity because that the brain.

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Key Takeaways

Key PointsThe adult person skull is composed of two regions of different embryological origins: the neurocranium and the viscerocranium.The neurocranium is a protective shell neighboring the mind and brain stem.The viscerocranium (or facial skeleton) is created by the bones sustaining the face.Except because that the mandible, every skull bones space joined with each other by sutures —synarthrodial (immovable) joints.The skull has air-filled cavities referred to as sinuses. Their functions are debatable, yet may be concerned lessening skull weight, contributing to voice resonance, and warming and moistening influenced air.Key Termsviscerocranium: The skeleton that supports face structure.sutures: A relatively rigid joint in between bones the the neurocranium.neurocranium: The protective vault surrounding the mind and mind stem.

The skull supports the musculature and structures that the face and forms a security cavity because that the brain. The skull is formed of numerous bones which, with the exemption of the mandible, space joined with each other by sutures—synarthrodial (immovable) joints.

Composition the the Skull

The adult human being skull is comprised of twenty-two bones i beg your pardon are separated into two components of differing embryological origin: the neurocranium and also the viscerocranium.

Neurocranium

The neurocranium develops the cranial cavity the surrounds and also protects the mind and brainstem. The neurocranium is formed from the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones; they are all joined in addition to sutures.


Components that neurocranium: Neurocranium consists of 8 parts: frontal, sphenoid, ethmoid, occipital, 2 temporal, and also 2 parietal bones.


Viscerocranium

The viscerocranium bones type the anterior and lower regions of the skull and include the mandible, i m sorry attaches through the just truly motile joint found in the skull. The facial skeleton consists of the vomer, 2 nasal conchae, two nasal bones, 2 maxilla, the mandible, two palatine bones, 2 zygomatic bones, and also two lacrimal bones.


Components of viscerocranium : The confront is made of 2 nasal, 2 lacrimal, 2 palantine, 2 inferior sleep concha, 2 zygomatic, 2 maxilla, 1 mandible, and also 1 vomer.


Other Features

The skull additionally contains the sinuses. These are air-filled caries that add to lessening the weight of the skull with a minimal palliation in strength. They add to resonance that the voice and assist in the warming and moistening of wait inhaled via the nose.


Cranial Bones

The neurocranium is made up of eight bones: occipital, two temporal bones, two parietal bones, sphenoid, ethmoid, and the frontal bone.


Learning Objectives

Differentiate the bones of the neurocranium


Key Takeaways

Key PointsThe eight skeletal of the neurocranium form major parts of the skull and protect the brain.The neurocranium consists of two temporal bones located to the base and side that the skull, and also two parietal bones that consist of the roof that the skull.A solitary occipital bone forms the base of the skull, and also the frontal bone develops the forehead.The sphenoid and also ethmoid bones located to the front of the skull form parts the the orbit sockets and also nasal cavity; they likewise support and also protect an essential organs discovered in the skull.Key Termsneurocranium: The part of the skull the encloses and also protects the brain and brain stem.

The neurocranium creates the cranial cavity the surrounds and protects the brain and brainstem. The neurocranium is composed of the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid, and also frontal bones—all room joined along with sutures.

Evolutionary,it is the development of the neurocranium the has promoted the growth of the mind and its associated developments.


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Neurocranium: A lateral view reflecting the skeletal that framework the neurocranium.


Occipital Bone

The occipital bone forms the base of the skull in ~ the behind of the cranium. That articulates with the first vertebra the the spinal cord and also contains the foramen magnum, the huge opening the the ability through which the spinal cord passes as it enters the vertebral column. The occipital bone borders the parietal bones with the heavily serrated lambdoidal suture, and additionally the temporal bones through occipitomastoid suture.

Temporal Bones

The temporal bones are located at the base and sides of the skull, lateral to the temporal lobes the the brain. The temporal skeletal consist of 4 regions the squamous, mastoid, petrous and tympanic regions.

The squamous region is the largest and also most superior region. Inferior to the squamous is the mastoid region, and fused in between the squamous and mastoid areas is the petrous region. Finally, the small and worse tympanic an ar lies anteriorly to the mastoid.

There room two procedures that originate indigenous the temporal bone:

The zygomatic procedure that projects from the reduced squamous region and articulates with the zygomatic bone the the cheek.The styloid procedure projects downwards indigenous the internal of the temporal bone and provides attachment for numerous muscles connected with the tongue.

The temporal skeletal have 4 borders:

The occipitomastoid suture the end the occipital bone and also mastoid section of temporal bone.The squamosal suture separates the parietal bone and also squama section of temporal bone.The sphenosquamosal suture the end the sphenoid bone and also squama part of temporal bone.The zygomaticotemporal suture off the zygomatic bone and also zygomatic procedure of temporal bone.

Parietal Bones

The two big parietal bones are connected and make up part of the roof and sides that the human being skull. The two bones articulate to form the sagittal suture. In the front, the parietal bones kind the coronal suture with the frontal bone, and in the rear, the lambdoid suture is developed by the occipital bone. Finally, the squamosal suture separates the parietal and also temporal bones.

Sphenoid Bone

The sphenoid bone is located in the middle of the skull towards the front and forms the behind of the orbit. It has actually been described as the same, similar thing a butterfly as result of its wing-like processes. The sphenoid bone is divided into several parts: the human body of the bone, two greater wings, two lesser wings, and the pterygoid processes.

The sphenoid bone is one of the most facility in the body due to its interactions with numerous facial bones, ligaments, and muscles. The human body that creates the center of the sphenoid bone articulates through the ethmoid and also occipital bone and also forms a crucial part that the nasal cavity; it also contains the sphenoidal sinuses.

The greater wings kind the floor the the center cranial fossa that residences the frontal lobes and pituitary gland, and likewise the posterior wall of the orbit. The lesser wings task laterally and form the floor of the anterior cranial fossa and the premium orbital fissure v which several vital optical nerves pass.

Ethmoid Bone

The ethmoid bone is a tiny bone in the skull the separates the nasal cavity native the brain. It is lightweight because of its spongy, air-filled construction and is situated at the roof the the nose and also between the 2 orbits.

The ethmoid bone forms the medial wall of the orbit, the roof that the sleep cavity, and also due to its central location it articulates with many bones of the viscerocranium. Within the neurocranium it articulates through the frontal and also sphenoid bones.

Frontal Bone

The frontal bone forms the front of the skull and also is split into 3 parts:

Squamous: This component is huge and flat and forms the main an ar of the forehead.Orbital: This component lies inferiorly and forms the exceptional border the the orbit.Nasal: this component is smaller and articulates v the sleep bones and maxilla to contribute to the roof the the nose.

The frontal bone borders two other neurocranial bones—the parietal bones through the coronal sutures and also the sphenoid bone v the sphenofrontal suture. It likewise articulates v the zygomatic and also nasal bones and the maxilla.


Facial Bones

The viscerocranium (face) consists of these bones: vomer, 2 inferior nasal conchae, 2 nasals, maxilla, mandible, palatine, 2 zygomatics, and 2 lacrimals.


Key Takeaways

Key PointsThe numerous bones that the viscerocranium space joined by sutures to each other and the neurocranium, except for the mandible, i beg your pardon articulates with the temporal bones.The hyoid bone, ethmoid bone, and also sphenoid bones are sometimes included in the viscerocranium.Key Termsviscerocranium: The facial skeleton that is created by the skeleton of the anterior and lower skull, i m sorry are derived from branchial arches.

The Viserocranium

The viscerocranium or face bones supports the soft organization of the face. The viscerocranium is composed of 14 separation, personal, instance bones that fuse together. However, the hyoid bone, ethmoid bone, and also sphenoid bones space sometimes contained in the viscerocranium.

Zygomatic Bones

The 2 zygomatic bones form the cheeks and contribute to the orbits. Lock articulate through the frontal, temporal, maxilla, and sphenoid bones.

Lacrimal Bones

The two lacrimal bones type the medial wall surface of the orbit and articulate with the frontal, ethmoid, maxilla, and also inferior sleep conchae. The lacrimal bones room the two smallest bones located in the face.

Nasal Bones

The 2 slender nasal bones located in the midline that the confront fuse to form the leg of the noise and also articulate v the frontal, ethmoid and maxilla bones. The inferior sleep conchae are located within the sleep cavity. They room spongy and curled in shape; their primary function is to increase the surface area that the nasal cavity, which likewise increases the lot of air that contacts the mucous membranes and cilia of the nose, thus filtering, warming, and humidifying the air before it start the lungs. At the basic of the sleep cavity is the tiny vomer bone which forms the sleep septum.

Maxilla Bones

The maxilla skeletal fuse in the midline and form the top jaw. They administer the bed for the top teeth, the floor that the nose, and also the basic of the orbits. The maxilla articulates v the zygomatic, nasal, lacrimal, and also palatine bones.

Palatine Bones

The palatine bones fuse in the midline to kind the palatine, situated at the ago of the nasal cavity that creates the roof the the mouth and the floor that the orbit.

The Mandible

Finally, the mandible develops the reduced jaw that the skull. The joint in between the mandible and the temporal skeletal of the neurocranium, well-known as the temporomandibular joint, forms the only non-sutured share in the skull.


Facial bones: There space fourteen face bones. Some, like the lacrimal and also nasal bones, are paired. Others, like the mandible and vomer, are singular.


Key Takeaways

Key PointsThe orbits room conical or four-sided pyramidal cavities, i beg your pardon open right into the midline the the confront and allude backwards.To the rear of the orbit the optical foramen opens into the optic canal, i beg your pardon transmits the optic nerve and opthalmic artery.The orbit protects the eye from mechanically injury and provides accessibility for the optic nerve come the brain.Key Termsoptic canal: The canal the transmits the optic nerve and also ophthalmic artery right into the orbital cavity.orbit: The bony cavity containing the eyeball; the eye socket.

The orbit, or eye socket, is the cavity situated in the skull in i m sorry the eye and also its associated appendages are housed. The orbits are conical, sometimes explained as four-sided pyramidal, cavities that open up in the midline that the confront and point backwards. To the rear of the orbit, the optic foramen opens right into the optical canal through which the optic nerve and ophthalmic artery pass.

The primary functions of the orbit encompass protection of its delicate materials and, with muscle attachment and also a smooth coating fascia, to additionally promote the smooth, vulnerable movements of the eye.

Structure that the Orbit

The orbit cavity is developed from seven bones. The frontal bone develops the exceptional border the the orbit rim and also the superior wall (roof) the the orbit surface.

The zygomatic bone develops the lateral (and half of the basal) border of the orbit rim, and additionally the lateral wall of the orbit surface—this is the thickest region of the orbit as it is most exposed to external trauma.

Completing the basal and medial border that the orbit rim is the maxillary bone, which likewise forms the inferior wall (floor) the the orbital surface.

The lacrimal and ethmoid bones add to the medial wall of the orbit and additionally to the medial wall surface of the orbital canal. The small palatine bone contributes to the floor the the orbit.

Finally, the sphenoid bone forms the posterior wall of the orbit and also contributes come the development of the optic canal.


Foramina

The human being skull has plenty of holes known as foramina through which cranial nerves, arteries, veins, and other structures pass.


Key Takeaways

Key PointsA foramen (plural: foramina ) is an opened inside the body that allows an essential structures to connect one part of the human body to another.The skull bones that contain foramina encompass the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital.There room 21 foramina in the human being skull.Key Termsforamina: The openings within the body that typically allow muscles, nerves, arteries, veins, or various other structures to attach one part of the human body to another.

In anatomy, a foramen is any kind of opening. Foramina within the body of humans and also other animals typically allow muscles, nerves, arteries, veins, or other structures to attach one part of the body v another.

The person skull has countless foramina with which cranial nerves, arteries, veins, and other structures pass. The skull bones the contain foramina incorporate the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and also occipital lobes.

Key foramina in the skull include:

Supraorbital foramen: located in the frontal bone, it enables passage of the supraorbital vein, artery, and nerve right into the orbit.Optic foramen: situated in the sphenoid, it allows the i of the ophthalmic artery and nerve native the optic canal into the orbit.Foramen magnum: located in the occipital bone, it enables the passage of the spinal and vertebral arteries and also the spinal cord to pass from the skull into the vertebral column.Foramina of cribriform plate: located in the ethmoid bone, it allows the i of the olfactory nerve.Foramen rotundum: located in the sphenoid bone, it permits passage the the maxillary nerve.

Sutures

A suture is a kind of fibrous joint (or synarthrosis) that just occurs in the skull (or cranium).


Key Takeaways

Key PointsIt is normal for countless of the bones of the skull to it is in unfused in ~ birth. This allows a tiny amount of movement at the sutures, i beg your pardon contributes to the compliance and also elasticity that the skull.Sutures end up being fused as people age; thus, evaluating sutures can administer an estimate of age postmortem.There space 17 named sutures on the person skull.Key Termssuture: A reasonably rigid joint between two or more hard elements, such as the bony key of the skull.

A suture is a type of fibrous share (or synarthrosis) that only occurs in the skull. The bones are bound with each other by Sharpey’s fibers, a matrix of connective organization which provide a firm joint.

A small amount of activity is permitted through this sutures that contributes to the compliance and also elasticity the the skull. The joint between the mandible and the cranium, recognized as the temporomandibular joint, develops the only non-sutured joint in the skull. Most sutures are named for the bones that they articulate.

At birth, many of the skeleton of the skull remain unfused come the soft spots explained as fontanelle. The bones fuse reasonably rapidly through a process known together craniosynotosis, back the loved one positions that the bones can proceed to change through life. In old age the cranial sutures might ossify completely, reduce the quantity of elasticity present in the skull. Together such, the level of ossification can be a useful tool in determining period postmortem.


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Lateral view of a skull reflecting sutures: The dotted red lines indicate the location of skull sutures.


Sutures primarily visible native the side include:

Coronal suture: Located between the frontal and parietal bones.Lambdoid suture: Located between the parietal, temporal and occipital bones.Occipitomastoid suture.Parietomastoid suture.Sphenofrontal suture.Sphenoparietal suture.Sphenosquamosal suture.Sphenozygomatic suture.Squamosal suture: Located in between the parietal and also the temporal bone.Zygomaticotemporal suture.Zygomaticofrontal suture.

Sutures mostly visible native front or over include:

Frontal suture or metopic suture: Located between the two frontal bones, before the fusion of the two into a solitary bone.Sagittal suture: located along the midline, in between the parietal bones.

Sutures mostly visible from listed below or inside include:

Frontoethmoidal suture.Petrosquamous suture.Sphenoethmoidal suture.Sphenopetrosal suture.

Paranasal Sinuses

The paranasal sinuses (four, paired, air-filled spaces) surround the nasal cavity, and also are located over and in between the eyes, and also behind the ethmoids.


Key Takeaways

Key PointsThe sinuses are called for the facial bones the they are located behind.There are four sinuses; the maxillary, frontal, ethmoid, and also sphenoid.Paranasal sinuses kind developmentally through excavation the bone through air-filled sacs from the nasal cavity.This procedure begins prenatally and continues with the food of an individual’s lifetime.The biological function of the sinuses is debated, but a number of possible functions have to be proposed: decreasing load of the face; increasing resonance that voice; buffer versus blows; insulating sensitive structures from rapid temperature fluctuations; and humidifying and heating the inhaled air.Key Termsparanasal sinuses: A team of four, paired, air-filled spaces that surround the nasal cavity (maxillary sinuses), over the eyes (frontal sinuses), between the eye (ethmoid sinuses), and also behind the eyes (sphenoid sinuses).
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Paranasal sinuses space a team of four, paired, air-filled spaces that surround the sleep cavity (maxillary sinuses), above the eye (frontal sinuses), between the eyes (ethmoid sinuses), and behind the eyes (sphenoid sinuses). The sinuses are called for the face bones that they are located behind.

The maxillary sinuses (also referred to as the maxillary antrechea, the biggest of the paranasal sinuses) are located under the orbits in the maxillary bones.The frontal sinuses space superior to the orbits and are in the frontal bone.The ethmoid sinuses are formed from several discrete air cells within the ethmoid bone in between the nose and the orbits.The sphenoid sinuses space in the sphenoid bone in ~ the center of the skull basic under the pituitary gland.The paranasal sinuses space lined through respiratory epithelium.

The paranasal sinuses form developmentally with excavation of bone by air-filled sacs (pneumatic diverticula) native the sleep cavity. This procedure begins prenatally and continues v the food of one individual’s lifetime.

Function of the Paranasal Sinuses

The biological duty of the sinuses is debated, however a variety of possible features have to be proposed. This include:

Decreasing the relative weight that the front of the skull, and also especially the skeletal of the face.Increasing resonance the the voice.Providing a buffer against blows to the face.Insulating perceptible structures like dental roots and also eyes from fast temperature fluctuations in the nasal cavity.Humidifying and also heating the inhaled air due to the fact that of sluggish air sales in this region.Regulation that intranasal and serum gas pressures.Immunological defense.

Fontanelles

A fontanelle is one anatomical feature on an infant’s skull that allows its plates to be flexible to pass with the bear canal.


Key Takeaways

Key PointsFontanelles are soft spots on a baby’s head that, during birth, enable the bony plates of the skull come flex and permit the child’s head come pass v the birth canal.At birth, the skull functions a tiny posterior fontanelle (an open up area spanned by a difficult membrane) wherein the 2 parietal bones adjoin the occipital bone (at the lambda); it typically closes in the first two to 3 months of life v intramembranous ossification.The much larger, diamond-shaped anterior fontanelle—where the 2 frontal and two parietal skeletal join—generally remains open up until the son is about two years of age.Two smaller sized fontanelles are located on every side of the head. The an ext anterior one is the sphenoidal (between the sphenoid, parietal, temporal, and frontal bones), if the an ext posterior one is the mastoid (between the temporal, occipital, and parietal bones).Key Termsfontanelle: A fontanelle is a soft membraneous spot on the head the a baby because of incomplete blend of the cranial bones.

Fontanelles are soft point out on a baby’s head that, during birth, permit the bony plates of the skull come flex and allow the child’s head to pass v the birth canal. The ossification of the skeletal of the skull reasons the fontanelles come close end a duration of 18 to 24 months; lock eventually form the sutures of the neurocranium.

The cranium the a newborn is composed of 5 main bones: two frontal bones, two parietal bones, and also one occipital bone. These room joined by fibrous sutures that allow movement that facilitates childbirth and brain growth.

At birth, the skull attributes a little posterior fontanelle (an open up area covered by a tough membrane) where the 2 parietal skeletal adjoin the occipital bone (at the lambda). This fontanelle commonly closes during the first two to 3 months of an infant’s life. This is referred to as intramembranous ossification. The mesenchymal connective tissue turns into bone tissue.

The much larger, diamond-shaped anterior fontanelle—where the two frontal and also two parietal bones join—generally remains open until a kid is about two years old. The anterior fontanelle is useful clinically, together examination of an infant consists of palpating the anterior fontanelle.

Two smaller sized fontanelles are situated on every side the the head. The much more anterior one is the sphenoidal (between the sphenoid, parietal, temporal, and frontal bones), if the an ext posterior one is the mastoid (between the temporal, occipital, and also parietal bones).



The fontanelle may pulsate. Return the specific cause that this is not known, the is perfect normal and also seems come echo the heartbeat, probably via the arterial pulse in ~ the brain vasculature, or in the meninges. This pulsating action is exactly how the soft spot got its name: fontanelle means little fountain.

Parents may worry that your infant may be an ext prone come injury at the fontanelles. In fact, back they might colloquially be called soft spots, the membrane extending the fontanelles is extremely hard and daunting to penetrate.

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The fontanelles allow the infant mind to be imaged making use of ultrasonography. As soon as they are closed, many of the brain is inaccessible to ultrasound imaging because the bony skull presents an acoustic barrier.