Skull Anatomy PDF

10/4/24, 11:58 AM Anatomy and Function of the Skull 🏰 The Skull: A Functional Castle 🏰 The skull can be considered as consisting of two parts: the facial skeleton and the brain case. Facial Sk...

10/4/24, 11:58 AM Anatomy and Function of the Skull 🏰 The Skull: A Functional Castle 🏰 The skull can be considered as consisting of two parts: the facial skeleton and the brain case. Facial Skeleton The facial skeleton includes large flat bones and landmarks that we should know about. It is responsible for respiration and chewing. Brain Case The brain case, also known as the neurocranium in some medical textbooks, is the region surrounding the brain. It is responsible for protecting precious tissues inside. “"The brain case is like a castle, protecting the treasure inside."” Bones of the Skull The skull has a total of 22 bones, some of which are paired (left and right) and some of which are unpaired (one in the middle). Bone Description Frontal Bone Unpaired bone in the front of the skull Sphenoid Bone Unpaired bone with two sets of wings, resembling a butterfly Zygomatic Bone Paired bone, shaped like the state of Texas, in the cheekbone area Maxillary Bone Paired bone, holds the upper teeth Lacrimal Bone Small bone with a sulcus for the nasolacrimal duct Nasal Bone Paired bone, where eyeglasses would sit Mandible Unpaired bone, the lower jaw Parietal Bone Paired bone, covering the top of the skull https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 1/13 10/4/24, 11:58 AM Anatomy and Function of the Skull Bone Description Temporal Bone Paired bone, related to time, named after the place that turns gray first Vomer Unpaired bone, medial wall of the nasal cavity, resembling a plow Ethmoid Bone Paired bone, superior half of the medial septum Nasal Conchae Paired bones, bony curtains in the nasal cavities Joints of the Skull The skull has many joints, including sutures, which are the common type of joints. Clinical Correlates Skull fractures are an important topic, and we will discuss special types of fractures that you should be able to recognize. Fossae of the Brain Case The brain case is divided into three fossae: anterior, middle, and posterior cranial fossa. Basic Cranium and Palate The basic cranium is the bottom of the skull, where it meets the neck. The palate is the roof of the mouth area. Lecture Objectives Understand the structure and function of the skull Identify the bones of the skull Recognize special types of skull fractures Understand the clinical correlates of the skull## 🦴 Facial Bones and Landmarks Independent Bones https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 2/13 10/4/24, 11:58 AM Anatomy and Function of the Skull The inferior nasal concha is an independent bone, not part of the maxilla. It's also known as the maxilloturbinels. “"The inferior nasal concha is a separate bone that is not fused to the maxilla, unlike other bones in the face."” Supraorbital and Infraorbital Features The supraorbital notch or foramen is located above the orbit. The infraorbital foramina are located below the orbit. The mental foramina are located near the chin region of the mandible. Feature Location Description Supraorbital Above the orbit Passage for the supraorbital nerves, notch/foramen arteries, and veins Infraorbital foramina Below the orbit Passage for the infraorbital nerves, arteries, and veins Mental foramina Near the chin region of the Passage for the mental nerves, arteries, mandible and veins Nerves and Blood Vessels The trigeminal nerve is a major nerve that branches into smaller nerves, including the supraorbital, infraorbital, and mental nerves. The supraorbital nerves, infraorbital nerves, and mental nerves are branches of the trigeminal nerve. Frontal Bone The frontal bone is an unpaired bone that fuses from two separate bones in juveniles. https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 3/13 10/4/24, 11:58 AM Anatomy and Function of the Skull The metopic suture is the suture region where the two halves of the 🦴 Posterior Skull frontal bone fuse. Bones of the Posterior Skull The parietal bones are large, dome-like bones. The occipital bone is an unpaired bone located at the back of the skull. The temporal bones are located on the sides of the skull. Landmarks of the Posterior Skull The external occipital protuberance is a bony projection at the back of the skull. The inion is another name for the external occipital protuberance. The lambda is the point where the parietal bones meet the occipital bone. 🦴 Bone Remodeling and Variation Bone remodeling is the process of bone deposition and resorption that occurs throughout life. Humans have a unique pattern of bone remodeling that results in a flatter face compared to other primates. There is variation in bone remodeling between males and females, with males tend to have more prominent features such as brow ridges and the mastoid process. 🦴 Complex Bones Temporal Bone The temporal bone is a synostosis of multiple bones. https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 4/13 10/4/24, 11:58 AM Anatomy and Function of the Skull It has several parts, including the squamosal, mastoid, tympanic, and styloid process. The petrosal part is a rocky, medial part of the temporal bone. Sphenoid Bone The sphenoid bone has a complex shape, with a body, lesser wings, greater wings, and feet. It is often compared to a bat or butterfly in shape.## 🦴 Sphenoid Bone and Skull Anatomy The sphenoid bone has several important features, including the pterygoid processes and the spine of the sphenoid. The spine of the sphenoid is a small, bony projection that is often confused with the pterygoid processes. Development of the Skull The skull develops from multiple ossification centers, which eventually fuse together to form the adult skull. This process involves the replacement of cartilage with bone, and is an example of endochondral ossification. “"Endochondral ossification is the process by which cartilage is replaced by bone tissue, resulting in the formation of the adult skeleton."” The skull has around 800 ossification centers at birth, which eventually fuse together to form around 200 bones in the adult skeleton. 🤝 Joints of the Skull There are several types of joints found in the skull, including: Synarthrosis: a joint where there is no motion allowed Amphiarthrosis: a joint where there is limited motion allowed Diarthrosis: a joint where there is free movement allowed https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 5/13 10/4/24, 11:58 AM Anatomy and Function of the Skull Types of Synarthrosis There are several types of synarthrosis joints found in the skull, including: Type Description Suture A joint where two bones are connected by a fibrous joint, with a wavy line where the bones meet Gomphosis A joint where a tooth inserts into a socket in the bone Synchondrosis A joint where two bones are connected by cartilage, which is fused between them Synostosis A joint where two bones are connected by a bony bridge, which is formed by the fusion of two independent ossification centers Examples of Synarthrosis Joints The coronal suture is an example of a suture joint, where the frontal bone meets the parietal bone. The lambdoidal suture is an example of a suture joint, where the parietal bone meets the occipital bone. The sphenoidal fontanelle is an example of a synchondrosis joint, where the sphenoid bone meets the parietal bone. 🤝 Amphiarthrosis Joints Amphiarthrosis joints are joints where there is limited motion allowed. Examples of amphiarthrosis joints in the skull include: Syndesmosis: a joint where two bones are connected by a fibrous joint, with some motion allowed Symphysis: a joint where two bones are connected by fibrocartilage, with some motion allowed Examples of Amphiarthrosis Joints https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 6/13 10/4/24, 11:58 AM Anatomy and Function of the Skull The interosseous membrane is an example of a syndesmosis joint, where the tibia and fibula bones meet. The pubic symphysis is an example of a symphysis joint, where the two pubic bones meet. 🤝 Diarthrosis Joints Diarthrosis joints are joints where there is free movement allowed. Examples of diarthrosis joints in the skull include: The temporomandibular joint is an example of a diarthrosis joint, where the mandible bone meets the temporal bone. 📚 Sutures of the Skull There are several sutures found in the skull, including: Coronal suture: a suture where the frontal bone meets the parietal bone Lambdoidal suture: a suture where the parietal bone meets the occipital bone Squamosal suture: a suture where the squamosal part of the temporal bone meets the parietal bone Sphenoidal suture: a suture where the sphenoid bone meets the parietal bone 📚 Fontanelles Fontanelles are soft spots in the skull where the bones have not yet fused together. Examples of fontanelles include: Anterior fontanelle: a fontanelle where the frontal bone meets the parietal bone https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 7/13 10/4/24, 11:58 AM Anatomy and Function of the Skull Posterior fontanelle: a fontanelle where the parietal bone meets the occipital bone Sphenoidal fontanelle: a fontanelle where the sphenoid bone meets the parietal bone Asterion: a fontanelle where the temporal, parietal, and occipital bones meet## 🤕 Skull Fractures and Landmarks 🤕 Maxillofacial Fractures Maxillofacial fractures are types of fractures that separate the facial skeleton from the brain case. They do not involve the brain case and are important to know about and to be able to stage or identify the type. All maxillofacial fractures involve some kind of fracture of the pterygoid plates of the sphenoid bone. To diagnose a LaForte fracture, a CT scan must show a fracture to the pterygoid plates. LaForte Fractures LaForte fractures are a type of maxillofacial fracture that can be classified into four types. Type Description Diagnostic Feature LaForte Type 1 Floating palate Palate moves when front teeth are pulled LaForte Type Floating maxilla Palate and nose move when front teeth are pulled 2 LaForte Type Craniofacial Face moves when front teeth are pulled 3 separation LaForte Type Non-diastatic fracture Fracture through the frontal bone, but not along the 4 suture https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 8/13 10/4/24, 11:58 AM Anatomy and Function of the Skull Skull Landmarks The human skull is unique in that it is a bent tube, unlike other animals which have a straight tube-like brain case. This bending creates three cranial fossae. Cranial Fossae The three cranial fossae are: Anterior Cranial Fossa: Located at the front of the brain case, it contains structures related to the sense of smell. Middle Cranial Fossa: Located in the middle of the brain case, it contains structures related to the sense of sight. Posterior Cranial Fossa: Located at the back of the brain case, it contains structures related to the sense of hearing and balance. Structures in the Cranial Fossae Cranial Fossa Structures Anterior Cranial Crista galli, cribiform plate, lesser wing of sphenoid, anterior clinoid process Fossa Middle Cranial Greater wing of sphenoid, foramen spinosum, groove for middle meningeal Fossa artery, foramen lacerum Posterior Cranial Petrosal part of temporal bone, squamosal part of temporal bone Fossa Bone Relationships The parietal bone covers the back of the skull. The frontal bone covers the front of the skull. The sphenoid bone is located in the middle of the brain case, with the lesser wing forming the anterior cranial fossa and the greater wing https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 9/13 10/4/24, 11:58 AM Anatomy and Function of the Skull forming the middle cranial fossa. The petrosal part of the temporal bone is located between the sphenoid bone and the occipital bone. “"The macaroni model is your imagination guide, and we're gonna talk about what you would see at the very front of this tube."## Sphenoid Bone 🌀” The sphenoid bone is a complex bone located in the skull. It has several important features, including: Foramen rotundum: a circular opening in the greater wing of the sphenoid bone Foramen ovale: an oval-shaped opening in the greater wing of the sphenoid bone Sella turcica: a saddle-shaped region in the sphenoid bone that houses the pituitary gland Hypophyseal fossa: a depression in the sella turcica that contains the pituitary gland “"The sella turcica is called a Turkish saddle because of its shape, which resembles a saddle used by Turkish horsemen."” Cavernous Sinus 🌀 The cavernous sinus is a venous sinus located in the sphenoid bone. It is a complex structure that contains several important nerves and blood vessels. Mnemonic: Oh, Tomcat O: Ocular motor nerve T: Trochlear nerve O: Ophthalmic branch of trigeminal nerve https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 10/13 10/4/24, 11:58 AM Anatomy and Function of the Skull M: Maxillary branch of trigeminal nerve C: Carotid artery (internal carotid artery) A: Abducens nerve 🌀 T: Trochlear nerve (again, from medial to lateral) Posterior Fossa The posterior fossa is a region of the skull that contains several important structures, including: Occipital bone: a bone that forms the back and base of the skull Clivus: a bony ridge in the occipital bone that forms a "water slide" for the brain stem Internal acoustic meatus: a hole in the petrosal part of the temporal bone that contains the facial nerve and vestibulocochlear nerve Jugular foramen: a hole between the petrosal part of the temporal bone and the occipital bone that contains the internal jugular vein and several cranial nerves Cranial Nerves 🌀 The following cranial nerves are associated with the jugular foramen: Cranial Nerve Function Glossopharyngeal nerve (CN IX) Swallowing, taste, and sensation in the throat Vagus nerve (CN X) Parasympathetic functions, including heart rate and digestion Accessory nerve (CN XI) Movement of the neck and shoulder muscles Skull-Based Fractures 🌀 https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 11/13 10/4/24, 11:58 AM Anatomy and Function of the Skull Skull-based fractures are fractures that occur in the cranial fossa. Warning signs of a skull-based fracture include: Raccoon eyes: ecchymosis or bruising around the orbits Battle sign: bruising and possibly a CSF leak behind the ear Landmarks of the Skull 🌀 The following are important landmarks of the skull: Zygomatic arches: arches on the sides of the skull formed by the temporal process of the zygomatic bone and the zygomatic process of the temporal bone Vomer: a bone that forms the posterior part of the hard palate of the skull Sphenoid bone: a complex bone located in the skull that contains several important features, including the sella turcica and cavernous sinus## 🗿️ Temporal Bone Landmarks The mandibular fossa, also known as the glenoid fossa, is the area where the mandible fits. Fissures and Foramina The squamous tympanic fissure is a small crack between the tympanic part of the petrosal bone and the squamous part of the temporal bone. The petrotympanic fissure is a fissure located inside the squamous tympanic fissure, through which the chorda tympani branch of the facial nerve emerges. Processes The styloid process is a small, pointed projection of bone, similar to a stylus used for writing on a personal digital assistant. https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 12/13 10/4/24, 11:58 AM Anatomy and Function of the Skull The mastoid process is a larger, more prominent projection of bone 🚪 Foramina of the Skull located behind the styloid process. Foramen Location Description Carotid canal Petrosal part of temporal bone A hole for the internal carotid artery Foramen lacerum Between petrosal and occipital A hole between two bones bones Foramen magnum Occipital bone A large hole in the occipital bone Jugular foramen Between occipital and petrosal A hole between two bones bones Foramen Sphenoid bone A hole for the middle meningeal spinosum artery Foramen ovale Sphenoid bone A hole for the mandibular nerve 👀 Sphenoid Bone and Palate The greater wings of the sphenoid have two foramina: the greater palatine foramen and the lesser palatine foramen. The hard palate is the front part of the skull, with a intermaxillary suture running down the middle. The incisive foramina are located at the anterior end of the hard palate. 🐦 Landmarks on the Skull The superior nuchal line is a landmark on the skull that resembles the wings of a bird. The internal choanae or internal nares are the openings of the nasal cavities into the throat. https://www.turbolearn.ai/content/265d9513-2fc1-440e-a6cc-2f442f4d6b52 13/13