petrous temporal bone

Examples of petrous temporal bone in the following topics:

• Abducens (VI) Nerve

  • At the tip of the petrous temporal bone, it makes a sharp turn forward to enter the cavernous sinus.
  • For example, fractures of the petrous temporal bone can selectively damage the nerve, as can aneurysms of the intracavernous carotid artery.
  • Mass lesions that push the brainstem downward can damage the nerve by stretching it between the point where it emerges from the pons and the point where it hooks over the petrous temporal bone.

• Facial (VII) Nerve

  • The motor and sensory parts of the facial nerve enter the petrous temporal bone into the internal auditory meatus (intimately close to the inner ear), then runs a tortuous course (including two tight turns) through the facial canal, emerges from the stylomastoid foramen, and passes through the parotid gland, where it divides into five major branches.

• Cartilaginous Joints: Synchodroses

  • Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint.
  • This type of joint also forms the growth regions of immature long bones and the intervertebral discs of the spinal column.
  • A temporary form of joint called an epiphyseal (growth) plate, is one where the cartilage is converted into bone before adult life.
  • Such joints are found between the epiphyses and diaphyses of long bones, between the occipital and the sphenoid bones, and during the early years of life, between the petrous portion of the temporal and the jugular process of the occipital bone.
  • The epiphyseal plate is a hyaline cartilage plate in the metaphysis at each end of a long bone.

• Cranial Bones

  • The neurocranium is comprised of eight bones: occipital, two temporal bones, two parietal bones, sphenoid, ethmoid, and the frontal bone.
  • The temporal bones are situated at the base and sides of the skull, lateral to the temporal lobes of the brain.
  • The temporal bones consist of four regions the squamous, mastoid, petrous and tympanic regions.
  • Inferior to the squamous is the mastoid region, and fused between the squamous and mastoid regions is the petrous region.
  • The squamosal suture separates the parietal bone and squama portion of temporal bone.

• Facial Bones

  • The hyoid bone, ethmoid bone, and sphenoid bones are sometimes included in the viscerocranium.
  • They articulate with the frontal, temporal, maxilla, and sphenoid bones.
  • The lacrimal bones are the two smallest bones located in the face.
  • The joint between the mandible and the temporal bones of the neurocranium, known as the temporomandibular joint, forms the only non-sutured joint in the skull.
  • There are fourteen facial bones.

• General Features and Functions of the Skull

  • The skull is formed of several bones which, with the exception of the mandible, are joined together by sutures—synarthrodial (immovable) joints.
  • The adult human skull is comprised of twenty-two bones which are divided into two parts of differing embryological origin: the neurocranium and the viscerocranium.
  • The neurocranium is formed from the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones; they are all joined together with sutures.
  • The facial skeleton contains the vomer, two nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, and two lacrimal bones.
  • Neurocranium consists of 8 parts: frontal, sphenoid, ethmoid, occipital, 2 temporal, and 2 parietal bones.

• Sutures

  • The bones are bound together by Sharpey’s fibers, a matrix of connective tissue which provide a firm joint.
  • Most sutures are named for the bones that they articulate.
  • At birth, many of the bones of the skull remain unfused to the soft spots described as fontanelle.
  • The bones fuse relatively rapidly through a process known as craniosynotosis, although the relative positions of the bones can continue to change through life.
  • Frontal suture or metopic suture: Located between the two frontal bones, prior to the fusion of the two into a single bone.

• Fontanels

  • The ossification of the bones of the skull causes the fontanelles to close over a period of 18 to 24 months; they eventually form the sutures of the neurocranium.
  • The cranium of a newborn consists of five main bones: two frontal bones, two parietal bones, and one occipital bone.
  • 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).
  • The mesenchymal connective tissue turns into bone tissue.
  • The more anterior one is the sphenoidal (between the sphenoid, parietal, temporal, and frontal bones), while the more posterior one is the mastoid (between the temporal, occipital, and parietal bones) .

• Sutures

  • Frontal suture / Metopic suture: between the two frontal bones, prior to the fusion of the two into a single bone
  • In adults, the skull bones are closely opposed and fibrous connective tissue fills the narrow gap between the bones.
  • The fusion of the skull's bones at birth is known as craniosynostosis.
  • At some sutures, the connective tissue will ossify and be converted into bone, causing the adjacent bones to fuse to each other.
  • This fusion between bones is called a synostosis (joined by bone).

• Foramina

  • The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital lobes.
  • Supraorbital foramen: Located in the frontal bone, it allows passage of the supraorbital vein, artery, and nerve into the orbit.
  • Foramen magnum: Located in the occipital bone, it allows the passage of the spinal and vertebral arteries and the spinal cord to pass from the skull into the vertebral column.
  • Foramina of cribriform plate: Located in the ethmoid bone, it allows the passage of the olfactory nerve.
  • Foramen rotundum: Located in the sphenoid bone, it allows passage of the maxillary nerve.