L2.pdf

The SKULL (2) Dr. Firas Al-Hameed M.B.CH.B C.A.B.S MRCS(ENT)(England) Thi-Qar Medical School  Cribriform plate Perpendicular plate Ethmoidal labyrinth.  The cribriform plate Forms the roof of the nasal cavity. Pierced by numerous olfactory nerve fibres, which...

The SKULL (2) Dr. Firas Al-Hameed M.B.CH.B C.A.B.S MRCS(ENT)(England) Thi-Qar Medical School  Cribriform plate Perpendicular plate Ethmoidal labyrinth.  The cribriform plate Forms the roof of the nasal cavity. Pierced by numerous olfactory nerve fibres, which innervate the nasal cavity with the sense of smell. Crista galli: Projects superiorly from the cribriform plate which provides an attachment point for the falx cerebri (sheet of dura mater that separates the two cerebral hemispheres).  Perpendicular plate: descends from the cribriform plate. It forms the superior two-thirds of the nasal septum. The ethmoid bone contains two ethmoidal labyrinths which contain the ethmoidal air cells (sinuses). Superior and middle concha  Temporal bone Contributes to the lower lateral walls of the skull. It contains the middle and inner portions of the ear and surround external auditory canal. Crossed by the majority of the cranial nerves. The temporomandibular joint of the jaw. Five constituent parts: The squamous, tympanic and petromastoid parts, with the zygomatic and styloid processes projecting outwards  Petromastoid part Can be split into a mastoid and petrous parts. Mastoid part: mastoid process, an inferior projection of bone, palpable just behind the ear Mastoid process mastoid air cells. These are hollowed out areas within the temporal bone. They act as a reservoir of air, equalising the pressure within the middle ear The petrous part is pyramidal shaped, and lies at the base of temporal bone. It contains middle and inner ear. Separate the middle from posterior fossa Attached muscles Muscle Site of Attachment Description Temporalis Originates from the lower part of squamous Muscle of mastication Masseter Lateral zygomatic surface Muscle of mastication Superficial muscle of the neck. Involved in rotation of head and flexion of Sternocleidomastoid Mastoid process neck. Important landmark for the anterior and posterior cervical triangles. Posterior belly of digastric Mastoid process A suprahyoid muscle. Involved in processes such as swallowing. Strap-like muscle in the back of the neck. Involved in movements such as Splenius capitis Mastoid process shaking the head.  Occipital Bone Unpaired trapezoidal bone Main bone of back of the skull (occiput). It entirely houses the cerebellum. Articulates: Parietal bones. The cervical spine (only cranial bone ) Sphenoid Petrous Parts: Basilar part (1) Condylar part (2) Squamous part (3) The squamous part The largest; it lies posterior to foramen magnum The external occipital protuberance.. …attachment for the trapezius muscle Three curved lines (nuchal lines) Highest, superior and inferior Medial nuchal line The internal surface : marked by grooves due to venous cranial sinuses: The superior sagittal sinus The transverse sinuses The sigmoid sinus  The basilar part Anterior to the foramen magnum and adjacent to the petrous part of the temporal bone. Clivus: anterior most part of basilar part that fuses with sphenoid bone. The condylar parts (occipital condyle, Condylus occipitalis) Two kidney-shaped prominences. Lateral to the foramen magnum. Articulate with the first cervical vertebra (atlanto- occipital joint). Hypoglossal canal pierces through the condylar part of the occipital bone. The jugular foramen lies between the occipital bone and petrous part of the temporal bone Inner surface Median internal occipital crest Internal occipital protuberance Groove for the transverse sinus runs from each side of the protuberance. Groove for sigmoid sinus  The pterion ‘H-shaped’ junction between temporal, parietal, frontal and sphenoid bones. The thinnest part of the skull. A fracture here can lacerate the middle meningeal artery (anterior branch), resulting in an extradural haematoma.  Sutures of the Skull Unique to the skull. Immovable junctions between bones, and fuse completely around the age of 20. Clinical importance: they can be points of potential weakness in both childhood and adulthood. 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. In neonates, the incompletely fused suture joints give rise to membranous gaps between the bones, known as fontanelles. Frontal fontanelle (located at the junction of the coronal and sagittal sutures) Occipital fontanelle (located at the junction of the sagittal and lambdoid sutures).