NS-L16

Which of the following bones does not articulate with the cranial base? - Atlas - Axis - Facial bones - Mandible

- Axis [Axis, or C2 vertebrae, does not articulate with the cranial base.]

Anatomically, the cranium can be subdivided into a roof (known as the calvarium), and a base:

- Calvarium: Comprised of the frontal, occipital and two parietal bones. - Cranial base: Comprised of six bones - the frontal, sphenoid, ethmoid, occipital, parietal and temporal bones. These bones are important as they provide an articulation point for the 1st cervical vertebra (atlas), as well as the facial bones and the mandible (jaw bone).

Sutures primarily visible from the side of the skull (norma lateralis) include:

- Coronal suture: between the frontal and parietal bones; - Lambdoid suture: between the parietal, temporal, and occipital bones; - Occipitomastoid suture; - Parietomastoid suture; - Sphenofrontal suture; - Sphenoparietal suture; - Sphenosquamosal suture; - Sphenozygomatic suture; - Squamosal suture: between the parietal and the temporal bone; - Zygomaticotemporal suture; - Zygomaticofrontal suture

The main sutures in adulthood are:

- Coronal suture: which fuses the frontal bone with the two parietal bones. - Sagittal suture: which fuses both parietal bones to each other. - Lambdoid suture: which fuses the occipital bone to the two parietal bones.

Which of the following describes a fracture occurring along a suture? - Depressed fracture - Diastatic fracture - Linear fracture - Basal skull fracture

- Diastatic fracture

Sutures primarily visible from front of the skull (norma frontalis) or above the skull (norma verticalis) include:

- Frontal suture / Metopic suture: between the two frontal bones, prior to the fusion of the two into a single bone; - Sagittal suture: along the midline, between parietal bones.

Sutures primarily visible from below the skull (norma basalis) or inside the skull include:

- Frontoethmoidal suture; - Petrosquamous suture; - Sphenoethmoidal suture; - Sphenopetrosal suture.

Which of the following bones does not contribute to the calvarium of the cranium? - Parietal bone - Frontal bone - Sphenoid bone - Occipital bone

- Sphenoid bone [The sphenoid forms part of the cranial base.]

In neonates, the incompletely fused suture joints give rise to membranous gaps between the bones, known as fontanelles. The two major fontanelles are:

- The frontal fontanelle [Anterior] : (located at the junction of the coronal and sagittal sutures) - The occipital fontanelle [Posterior] : (located at the junction of the sagittal and lambdoid sutures)

What is the thinnest part of the skull? - Floor of the anterior cranial fossa - Lateral wall of the posterior cranial fossa - Floor of the middle cranial fossa - The pterion

- The pterion

The facial bones are:

- Zygomatic (2) - Forms the cheek bones of the face, and articulates with the frontal, sphenoid, temporal and maxilla bones. - Lacrimal (2) - The smallest bones of the face. They form part of the medial wall of the orbit. - Nasal (2) - Two slender bones, located at the bridge of the nose. - Inferior nasal conchae (2) - Located within the nasal cavity, these bones increase the surface area of the nasal cavity, thus increasing the amount of inspired air that can come into contact with the cavity walls. - Palatine (2) - Situated at the rear of oral cavity, and forms part of the hard palate. - Maxilla (2) - Comprises part of the upper jaw and hard palate. - Vomer - Forms the posterior aspect of the nasal septum. Mandible (jaw bone) - Articulates with the base of the cranium at the temporomandibular joint (TMJ).

The Pterion:

A 'H-shaped' junction between temporal, parietal, frontal and sphenoid bones. The thinnest part of the skull. A fracture here can lacerate an underlying artery (the middle meningeal artery), resulting in a extradural haematoma.

Middle cranial fossa:

Depression formed by sphenoid, temporal and parietal bones. [ It is said to be "butterfly shaped", with a middle part accommodating the pituitary gland and two lateral parts accommodating the temporal lobes of the brain]

Posterior cranial fossa:

Depression formed by squamous and mastoid temporal bone, plus occipital bone.

Anterior cranial fossa:

Depression of skull formed by frontal, ethmoid and sphenoid bones.

Anterior cranial fossa boundaries:

The anterior cranial fossa consists of three bones: the frontal bone, ethmoid bone and sphenoid bone. Its boundaries are as follows: - Anteriorly and laterally it is bounded by the inner surface of the frontal bone. - Posteriorly and medially it is bounded by the limbus of the sphenoid bone. The limbus is a bony ridge that forms the anterior border of the prechiasmatic sulcus (a groove running between the right and left optic canals). - Posteriorly and laterally it is bounded by the lesser wings of the sphenoid bone (these are two triangular projections of bone that arise from the central sphenoid body). - The floor consists of the frontal bone, ethmoid bone and the anterior aspects of the body and lesser wings of the sphenoid bone

Middle cranial fossa boundaries:

The middle cranial fossa consists of three bones - the sphenoid bone and the two temporal bones. Its boundaries are as follows: - Anteriorly and laterally it is bounded by the lesser wings of the sphenoid bone. These are two triangular projections of bone that arise from the central sphenoid body. - Anteriorly and medially it is bounded by the limbus of the sphenoid bone. The limbus is a bony ridge that forms the anterior border of the chiasmatic sulcus (a groove running between the right and left optic canals). - Posteriorly and laterally it is bounded by the superior border of the petrous part of the temporal bone. - Posteriorly and medially it is bounded by the dorsum sellae of the sphenoid bone. This is a large superior projection of bone that arises from the sphenoidal body. - The floor is formed by the body and greater wing of the sphenoid, and the squamous and petrous parts of the temporal bone.

Posterior cranial fossa boundaries:

The posterior cranial fossa is comprised of three bones: the occipital bone and the two temporal bones. It is bounded as follows: - Anteriorly and medially it is bounded by the dorsum sellae of the sphenoid bone. This is a large superior projection of bone that arises from the body of the sphenoid. - Anteriorly and laterally it is bounded by the superior border of the petrous part of the temporal bone. - Posteriorly it is bounded by the internal surface of the squamous part of the occipital bone. - The floor consists of the mastoid part of the temporal bone and the squamous, condylar and basilar parts of the occipital bone.

Anterior cranial fossa Contents + Quiz:

http://teachmeanatomy.info/head/areas/anterior-cranial-fossa/

Middle cranial fossa Contents + Quiz:

http://teachmeanatomy.info/head/areas/middle-cranial-fossa/

Posterior cranial fossa Contents + Quiz:

http://teachmeanatomy.info/head/areas/posterior-cranial-fossa/

Useful links:

http://teachmeanatomy.info/head/osteology/skull/ http://teachmeanatomy.info/head/areas/anterior-cranial-fossa/ https://www.youtube.com/watch?v=FC67CJ4hLuQ https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/joints-8/fibrous-joints-1372/sutures-510-8650/ [https://www.youtube.com/watch?v=9CRKHG1ARks]

Sutures nomenclature:

Most sutures are named for the bones they articulate, but some have special names of their own.

The frontal (Anterior) fontanelle closure point become:

Bregma

The occipital (Posterior) fontanelle closure point become:

Lambda

The skull is a bony structure that supports the face and forms a protective cavity for the brain. It is comprised of many bones, formed by intramembranous ossification, which are joined together by:

Sutures

Type of joint in sutures:

(Fibrous joints) = Immovable joints [These joints fuse together in adulthood, thus permitting brain growth during adolescence.]

How many individual bones contribute to the facial skeleton? - Ten - Eleven - Thirteen - Fourteen

- Fourteen

Which cranial suture joins the two parietal bones? - Coronal suture - Sagittal suture - Lambdoid suture - Frontal fontanelle

- Sagittal suture