How many foramina in the skull

Learning Objectives Describe the purpose of foramina in the skull. Key Points A foramen plural: foramina is an opening inside the body that allows key structures to connect one part of the body to another.

The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital. There are 21 foramina in the human skull. Key Terms foramina : The openings inside the body that typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body to another. Parents may worry that their infant may be more prone to injury at the fontanelles.

In fact, although they may colloquially be called soft spots, the membrane covering the fontanelles is extremely tough and difficult to penetrate. The fontanelles allow the infant brain to be imaged using ultrasonography. Once they are closed, most of the brain is inaccessible to ultrasound imaging because the bony skull presents an acoustic barrier. Privacy Policy. Skip to main content.

Skeletal System: Parts of the Skeleton. Search for:. The Skull. General Features and Functions of the Skull The human skull is the part of the skeleton that supports the structures of the face and forms a cavity for the brain. Learning Objectives Describe the parts of the skull. Key Takeaways Key Points The adult human skull consists of two regions of different embryological origins: the neurocranium and the viscerocranium.

The neurocranium is a protective shell surrounding the brain and brain stem. The viscerocranium or facial skeleton is formed by the bones supporting the face. Except for the mandible, all skull bones are joined together by sutures —synarthrodial immovable joints. The skull contains air-filled cavities called sinuses. Their functions are debatable, but may be related to lessening skull weight, contributing to voice resonance, and warming and moistening inspired air.

Key Terms viscerocranium : The skeleton that supports facial structure. Cranial Bones The neurocranium is comprised 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 Points The eight bones of the neurocranium form major portions of the skull and protect the brain.

The neurocranium consists of two temporal bones situated to the base and side of the skull, and two parietal bones that make up the roof of the skull.

A single occipital bone forms the base of the skull, and the frontal bone forms the forehead. The sphenoid and ethmoid bones located to the front of the skull form parts of the orbital sockets and nasal cavity; they also support and protect key organs found in the skull. Key Terms neurocranium : The part of the skull that encloses and protects the brain and brain stem.

Facial Bones The viscerocranium face includes these bones: vomer, 2 inferior nasal conchae, 2 nasals, maxilla, mandible, palatine, 2 zygomatics, and 2 lacrimals. Learning Objectives List the facial bones of the viscerocranium.

Key Takeaways Key Points The several bones of the viscerocranium are joined by sutures to each other and the neurocranium, except for the mandible, which articulates with the temporal bones.

The hyoid bone, ethmoid bone, and sphenoid bones are sometimes included in the viscerocranium. Key Terms viscerocranium : The facial skeleton that is formed by the bones of the anterior and lower skull, which are derived from branchial arches.

Orbits The orbit is the cavity or socket of the skull in which the eye and its appendages are situated. Learning Objectives Locate the orbits in the skull. Key Takeaways Key Points The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point backwards.

To the rear of the orbit the optical foramen opens into the optic canal, which transmits the optic nerve and opthalmic artery. The orbit protects the eye from mechanical injury and provides access for the optic nerve to the brain.

Key Terms optic canal : The canal that transmits the optic nerve and ophthalmic artery into the orbital cavity. Foramina The human skull has numerous holes known as foramina through which cranial nerves, arteries, veins, and other structures pass. Learning Objectives Describe the purpose of foramina in the skull. Key Takeaways Key Points A foramen plural: foramina is an opening inside the body that allows key structures to connect one part of the body to another.

The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital. There are 21 foramina in the human skull. Key Terms foramina : The openings inside the body that typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body to another. Sutures A suture is a type of fibrous joint or synarthrosis that only occurs in the skull or cranium.

Learning Objectives List the sutures of the skull. Key Takeaways Key Points It is normal for many of the bones of the skull to be unfused at birth. This allows a tiny amount of movement at the sutures, which contributes to the compliance and elasticity of the skull. Sutures become fused as individuals age; thus, examining sutures can provide an estimate of age postmortem.

There are 17 named sutures on the human skull. Key Terms suture : A fairly rigid joint between two or more hard elements, such as the bony plates of the skull. Paranasal Sinuses The paranasal sinuses four, paired, air-filled spaces surround the nasal cavity, and are located above and between the eyes, and behind the ethmoids. Learning Objectives Describe the structure and function of the paranasal sinuses.

Key Takeaways Key Points The sinuses are named for the facial bones that they are located behind. There are four sinuses; the maxillary, frontal, ethmoid, and sphenoid. Paranasal sinuses form developmentally through excavation of bone by air-filled sacs from the nasal cavity.

The biological role of the sinuses is debated, but a number of possible functions have been proposed: decreasing weight of the face; increasing resonance of voice; buffer against blows; insulating sensitive structures from rapid temperature fluctuations; and humidifying and heating of inhaled air. Key Terms paranasal sinuses : A group of four, paired, air-filled spaces that surround the nasal cavity maxillary sinuses , above the eyes frontal sinuses , between the eyes ethmoid sinuses , and behind the eyes sphenoid sinuses.

Learning Objectives Identify the evolutionary purpose of skull fontanelles. At birth, the skull features a small posterior fontanelle an open area covered by a tough membrane where the two parietal bones adjoin the occipital bone at the lambda ; it usually closes in the first two to three months of life through intramembranous ossification. This article discusses each of the aforementioned fossae and their associated foramina. For more information on the bones of the skull, see the Geeky Medics article here.

The anterior fossa is the most shallow of the three recesses and surrounds the anteroinferior aspects of the frontal lobes of the cerebrum. Inferior to the anterior fossa lie the nasal cavities, and the orbits. The anterior fossa is comprised of three bones :. This forms part of the ethmoid bone and contains multiple foramina allowing the passage of olfactory nerves from the nasal cavity into the olfactory bulb and then on to the olfactory areas entorhinal cortex and piriform cortex, among others within the cerebrum via the olfactory tract.

Trauma resulting in fracture of the cribriform plate can very commonly result in cerebrospinal fluid CSF rhinorrhoea. The CSF moves away on the paper, whereas the blood moves closer inwards, resulting in two rings on the paper target or halo sign. This leakage of CSF can, in rare cases, put such patients at risk of serious complications including meningitis , encephalitis or brain abscess. Fracture of the cribriform plate can also result in anosmia due to the shearing of the olfactory nerves running through the perforations within the plate.

Bounded superiorly by the lesser wing of sphenoid, and inferiorly by the greater wing of sphenoid, the superior orbital fissure allows transmission from the cavernous sinus into the orbit, of:.

The above are listed in order going from superior to inferior as they pass through the fissure. It can be appreciated that this includes nerves supplying motor innervation to the eyes. The temporal bones surround the temporal lobes laterally within the middle fossa, and the sphenoid bone sits more centrally. This is a centrally located deep depression within the sphenoid bone. The most inferior part of the sella turcica, the hypophyseal fossa , contains the pituitary gland.

Transmits maxillary division of the trigeminal nerve [ V 2 ]. Transmits mandibular division of the trigeminal nerve [ V 3 ]. This is filled with cartilage and lies at the intersection between temporal, sphenoid and occipital bones. This foramen transmits the middle meningeal artery as well as the middle meningeal vein , and a branch of the mandibular division of the trigeminal nerve [V].

The internal carotid artery runs through the carotid canal before continuing to form the middle cerebral artery and running across the circle of Willis to supply blood to the brain.

The middle meningeal artery , a branch of the maxillary artery , enters the middle cranial fossa via the foramen spinosum. It ultimately splits into anterior and posterior divisions.

It is the anterior division that runs anterolaterally along the greater sphenoid wing until it eventually passes under the pterion and giving off its terminal branches. The pterion is the site of a junction between four bones , and is the weakest point in the skull:. A fracture in this region can result in damage to the middle meningeal artery and subsequent extradural haemorrhage.

The pterion is also a common neurosurgical approach to access the middle cranial fossa for a range of procedures. The posterior fossa or the cranial cavity is the deepest of the three recesses that comprise the three cranial fossae. This fossa surrounds the cerebellum and the brainstem , and is made up of three bones :. This opening lies within the posterior component of the petrous portion of the temporal bone and comprises the start of a bony canal linking the posterior fossa to the inner ear.

Two cranial nerves pass through the internal acoustic meatus :. This foramen is superiorly bordered by the petrous portion of the temporal bone, and inferiorly by the occipital bone.