Special Characteristics of the Skull PDF

## Chapter 7: Skeletal System: Axial Skeleton ### 7.7 Special Characteristics of the Skull #### Objective - Describe the following special features of the skull: sutures, paranasal sinuses, and fontanels. - **The nasal septum** is a vertical structure in the skull that divides the nasal cavity i...

## Chapter 7: Skeletal System: Axial Skeleton ### 7.7 Special Characteristics of the Skull #### Objective - Describe the following special features of the skull: sutures, paranasal sinuses, and fontanels. - **The nasal septum** is a vertical structure in the skull that divides the nasal cavity into a left and right side. - It is composed of bone and cartilage. - The three components are the **vomer,** the **septal cartilage,** and the **perpendicular plate of the ethmoid bone.** - The anterior border of the vomer articulates with the septal cartilage, which is hyaline cartilage. Together, they form the anterior portion of the septum. - The superior border of the vomer articulates with the perpendicular plate of the ethmoid bone to form the rest of the nasal septum. - The term “broken nose” usually refers to damage to the septal cartilage, rather than a fracture of the nasal bones. **Clinical Correlation** - **Deviated Nasal Septum** - A deviated nasal septum is one that does not project along the midline of the nasal cavity. It is bent (deviated) to one side. - A blow to the nose can easily damage or break this delicate bony septum, and displace and damage the cartilage. - Often, when a fractured nasal septum heals, the bones and cartilage deviate to one side or the other. - This deviated septum can block airflow on the restricted side of the nose, making it difficult to breathe on that side. - Deviation usually occurs at the union of the vomer bone with the septal cartilage. - Septal deviations can also be caused by developmental anomalies. - If the deviation is severe, it can block the nasal passages completely; even partial blockage can lead to infection. - Inflammation can cause nasal congestion, sinus blockage, chronic headaches, and nosebleeds. - This condition can be corrected or improved with surgery. **The Orbits** - **The Orbits** are formed by seven cranial bones: - The frontal bone - The sphenoid bone - The ethmoid bone - The palatine bone - The zygomatic bone - The lacrimal bone - The maxilla bone - They are also known as **orbital cavities**. - Each orbit contains the eyeball and associated structures. - There are five openings associated with each orbit: - The **optic canal** is located at the junction of the roof and the medial wall of the orbit. - The **superior orbital fissure** is located at the superior lateral angle of the apex. - The **inferior orbital fissure** is located at the junction of the lateral wall and the floor. - The **supraorbital foramen** is located on the medial side of the supraorbital margin of the frontal bone. - The **lacrimal fossa** is located on the lacrimal bone. **Foramina** - **Foramina** are openings that allow blood vessels, nerves, and ligaments to pass. - Foramen location and associated anatomy are described throughout this chapter. **Table 7.3: Major Foramina of the Skull** - **Feature** | **Location** | **Associated Anatomical Anatomy** --- | --- | --- - **Carotid Canal** | Petrous portion of the temporal bone | Internal carotid artery, sympathetic nerves for the eyes - **Hypoglossal Canal** | Base of occipital condyles | Hypoglossal nerve (XII), branch of the pharyngeal artery - **Infraorbital Foramen** | Maxilla | Infraorbital nerve and vessels, a branch of the maxillary division of the trigeminal nerve (V) - **Jugular Foramen** | Between petrous temporal bone and occipital bone | Internal jugular vein; glossopharyngeal (IX), vagus (X), and accessory (XI) nerves - **Lacerum (anterior)** | Bounded by sphenoid, temporal, and occipital bones | Branch of the pharyngeal artery - **Magnum Foramen** | Occipital bone| Medulla oblongata and its membranes (meninges), accessory nerve (XI), vertebral and spinal arteries - **Mandibular Foramen** | Medial surface of mandibular ramus | Inferior alveolar nerve and blood vessels - **Mastoide** | Posterior border of the mastoid process | Emissive vein to the transverse sinus, a branch of the occipital artery to the dura mater - **Mental Foramen** | Mandible | Mental nerve, blood vessels - **Olfactory** | Cribriform plate of the ethmoid bone | Olfactory nerve - **Optic Canal** | Greater wing of the sphenoid bone | Optic nerve (II), ophthalmic artery - **Oval** | Greater wing of the sphenoid bone | Mandibular division of the trigeminal nerve (V) - **Rotundum** | Between the anterior and medial parts of the sphenoid bone | Maxillary division of the trigeminal nerve (V) - **Stylomastoid** | Between the styloid and mastoid processes | Facial nerve (VII), stylomastoid artery - **Supraorbital** | Supraorbital margin of the frontal bone | Supraorbital artery and nerve **Unique Features of the Skull** - **Sutures** are immovable joints that hold together most of the cranial bones. - They are found throughout the skull, but four are most prominent: - The **coronal suture** joins the frontal and parietal bones. - The **sagittal suture** joins the parietal bones. - The **lambdoid suture** joins the two parietal bones to the occipital bone. - The **squamous sutures** join the parietal and temporal bones. - **Paranasal Sinuses** are air-filled cavities within some cranial and facial bones near the nasal cavity. - They enlarge and become more visible during a sagital cut. - They are lined by mucous membranes that drain into the nasal cavity. - **Fontanels** are mesenchyme-filled spaces between cranial bones that are present at birth. - As cranial bones ossify during development, fontanels shrink and close. - Fontanels allow the fetal skull to deform during childbirth. - They also provide space for the skull to expand as the brain grows. **Clinical Correlation** - **Sinusitis** - Sinusitis is inflammation of the mucous membrane lining one or more sinuses. - It can be caused by microbial infection (bacterial, viral, or fungal), allergic reactions, nasal polyps, a deviated nasal septum, or a combination of these factors. - If the inflammation or an obstruction blocks drainage of the mucus from the sinus to the nasal cavity, pressure builds up within the sinus, resulting in pain. - This can also cause nasal congestion, a loss of sense of smell, fever, and cough. - **Fontanels** - Fontanels are soft spots on the skull. - They are present at birth to allow the skull to deform during childbirth and for the brain to grow. - The fontanels usually close by the time a child is 2 years old. - There are six fontanels, each named for its location: - **Anterior** - **Posterior** - **Anterolateral** - **Posterolateral** - **Sphenoidal** - **Mastoid** The anterior fontanel is the largest of the fontanels. It is located between the two parietal bones and the frontal bone. It usually closes by the time a child is 18 to 24 months old. The posterior fontanel is located between the two parietal bones and the occipital bone. It usually closes by the time a child is 2 months old. The anterolateral and posterolateral fontanels are located on the sides of the skull. They are much smaller than the anterior and posterior fontanels, and each usually closes by the time a child is 3 months old. The sphenoidal and mastoid fontanels are located at the base of the skull. They are very small and usually close by the time a child is 6 to 8 weeks old. The size of the fontanel at birth can help to assess the health of the newborn infant. If the fontanel is too large, it may indicate that the brain is not growing properly. If the fontanel is too small, it may indicate that the skull is not growing properly. The fontanel can also be used as a landmark for performing certain medical procedures, such as lumbar punctures.