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Osteology Skull Foramina Cavities joints Surface markings The cervical vertebrae BAAB 16/05/2016 The head skeleton is formed of the skull The neck skeleton is formed of the cervical vertebrae of the vertebral column. SKULL: The skull is a bony structure that forms the skeleton of the head in most vertebrates. ◦ Therefore, a human skull is the bony structure whose bones are forming through intramembranous ossification that forms the head in the human skeleton ◦ It supports the structures of the face and forms a cavity for the brain; Like the skulls of other vertebrates, it protects the brain from injury. The skull consists of two parts there of different embryological origin ◦ the neurocranium (or braincase) forms the protective cranial cavity that surrounds and houses the brain and brainstem. This is also subdivided into skullcap or cranial roof known as calvarium, and the cranial base. ◦ The facial skeleton (viscerocranium) is formed by the bones supporting the face including the mandible. Except for the mandible, all other bones of the skull are joined together by sutures—synostosis (synarthrodial or immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as wormian bones or sutural bones. The mandible forms a temporomandibular synovial double condylar variety. Cranial skull: ◦ The cranium (also known as the neurocranium), is formed by the superior aspect of the skull. It encloses and protects the brain, meninges and cerebral vasculature. ◦ 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. The base provides an articulation point for the 1st cervical vertebra (atlas), as well as the facial bones and the mandible (jaw bone). ◦ The base is divided into anterior, middle and posterior cranial fossae. Facial skeleton: ◦ also known as the viscerocranium supports the soft tissues of the face. In essence, they determine our facial appearance. ◦ It consists of 14 individual bones, which fuse to house the orbits of the eyes, tympanocochlea apparatus, nasal and oral cavities, as well as the sinuses. ◦ The frontal bone, typically a bone of the calvaria, is sometimes included as part of the facial skeleton. ◦ 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 Inferior nasal conchae (2) – Located within the bridge of the nose. nasal cavity, they increase the surface area of the nasal cavity, thus increasing the amount of inspired air that contact with the nasal cavity walls. Palatine (2) – Situated at the rear roof 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). JOINTS OF THE SKULL: ◦ Joints of the skull are mostly the suture variety of fibrous joint. ◦ They are immovable, and fuse completely around the age of 20. Fig – The major fontanelles and sutures of the skull Sutures are of clinical importance, as 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. The two major fontanelles are the frontal fontanelle (located at the junction of the coronal and sagittal sutures) and the occipital fontanelle (located at the junction of the sagittal and lambdoid sutures) Others (minor) are sphenoidal fontanelles (located at the junction of the suture between frontal, parietal, sphenoidal and zygomatic bones. This is a future pterion) and the mastoid fontanelle (located at the junction of the suture of temporal, parietal and occipital bones) Skull injury and fracture: The majority of skull fractures result from blunt force or penetrating trauma, and can produce numerous signs and symptoms. The clinical features may be obvious, such as visible injuries and bleeding. There are also subtle signs of fracture, such as clear fluid draining from the ears and nose (cerebrospinal fluid leak indicative of base of skull fracture), poor balance and confusion, slurred speech and a stiff neck. There are certain areas of the skull that are natural points of weakness: 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. Anterior cranial fossa: Depression of skull formed by frontal, ethmoid and sphenoid bones. Middle cranial fossa: Depression formed by sphenoid, temporal and parietal bones. Posterior cranial fossa: Depression formed by squamous and mastoid temporal bone, plus occipital bone. There are four major types of cranial fracture: ◦ Depressed – A fracture of the bone with depression of the bone inwards. They occur as a result of a direct blow, causing skull indentation, with possible underlying brain injury. ◦ Linear – The simple break in the bone, traversing its full thickness. They have radiating (stellate) fracture lines away from the point of impact. The most common type of cranial fracture. ◦ Basal skull – Affects the base of the skull. They characteristically present with bruising behind the ears, known as Battle’s sign (mastoid ecchymosis) or bruising around the eyes/orbits, known as Raccoon eye’s. ◦ Diastatic – A fracture that occurs along a suture line, causing a widening of the suture. They are most often seen in children. Fig - Skull showing depressed fracture of the frontal bone, a linear fracture marked A Facial Fractures: Are common and generally trauma related, i.e. road traffic collisions, fights and falls. They are often associated with clinical features such as profuse bleeding, swelling, deformity and anaesthesia of the skin. ◦ The nasal bones are most frequently fractured, due to their prominent position at the bridge of the nose. ◦ A maxillofacial fracture is one that affects the maxillae bones. This requires a trauma with a large amount of force. Facial fractures affecting the maxillary bones can be identified using the Le Fort classification, depending on the bones involved, ranging from 1 to 3 (most serious). A Le Fort fracture of the skull Classification and external resources LeFort I (red), II (blue), and III (green) fractures ANATOMICAL LAND MARKS: These are on the outer and inner surfaces of the skull. The point at which the frontal bone and the two parietal bones meet is known as "Bregma“ The point at which the two parietal and occipital bones meet is known as "Lambda". these landmarks indicate the fontanelle in newborns, also act as reference points in medicine and surgery. The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, numerous furrows for the lodgement of branches of the meningeal vessels. a middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. A groove is crossed in front by the coronal suture and behind by the lambdoid suture, while the sagittal suture lies in the medial plane between the parietal bones. FORAMINA: The foramen magnum (Latin: great hole) is a large oval opening in the occipital bone. It is one of the several oval or circular openings (foramina) in the base of the skul l The spinal cord, an extension of the medulla, passes through the foramen magnum as it exits the cranial cavity Also other structures pass through. These are the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membranes and alar ligaments. Other foramina, bones and contents are: BONE Frontal Frontal Ethmoid FOSSA Anterior cranial - FORAMEN VESSELS NERVE supraorbital Supraorbital supraorbital Foramen caecum emmissary Cribriform plate - Olfactory nerve bundle Ethmoid Anterior cranial Anterior ethimoid Anterior ethimoid Anterior ethimoid Ethmoid Anterior cranial Posterior ethimoid Posterior ethimoid Posterior ethimoid Sphenoidal Sphenoidal Middle cranial Optical canal - Optic nerve II Sup. Orbital fissure Sup. and inf. orbital veins Oculomotor, Trochlea, Ophthalmic and Abducent sphenoid Foramen rotundum maxillary Maxilla - sphenopalatine nasopalatine Incisive foramen/canal palatine - Greater palatine Greater palatines Greater palatine Palatine and maxilla - Lesser palatine Lesser palatines Lesser palatine Sphenoid and maxilla - Inf. Orbital fissure Inf. Ophthalmic vv infraorbitals Zygomatic, infraorbital of maxillary n. orbital branches of pterygopalatine maxilla - infraorbital infraorbitals infraorbital Sphenoidal Middle cranial Foramen ovale accessory meningeal aa. Mandibular, lesser petrosal Sphenoidal Middle cranial Foramen rotundum Meningeal br. of mandibular Middle meningeal aa Sphenoid Middle cranial Foramen lacerum Internal carotid aa, artery of pterygoid canal Nerve of pterygoid canal Temporal Middle cranial Internal acoustic meatus Labyrinthine aa. Facial and vestibulocochlear Temporal Posterior cranial Jugular Inf. Petrosal sinus and sigmoid sinus Glossopharyn geal, vagus and accessory occipital Posterior cranial hypoglossal - hypoglossal Occipital Posterior cranial Foramen magnum Ant. And post. Medulla Spinal aa. and oblongata vertebral aa. Temporal Posterior cranial stylomastoid Stylomastoid artery Facial The opisthion is the midpoint on the posterior margin of the foramen magnum and is a cephalometric landmark. Another landmark is the basion located at the midpoint on the anterior margin of the foramen magnum. The foramen magnum is a very important feature in bipedal mammals. Studies on the foramen magnum position have shown a connection to the functional influences of both posture and locomotion. Opisthion shown in red Basion shown in red Superior orbital fissure; List the contents: ◦ superior and inferior divisions of oculomotor nerve (III) ◦ trochlear nerve (IV) ◦ lacrimal, frontal and nasociliary branches of ophthalmic nerve (V1) ◦ abducens nerve (VI) ◦ superior and inferior divisions of ophthalmic vein. Inferior division also passes through the inferior orbital fissure. ◦ sympathetic fibers from cavernous plexus Skull basal cranial fossae Anterior cranial fossa: Anterior limit by the posterior wall of the frontal sinus. Posterior limit by the anterior clinoid processes and the planum sphenoidale formed by the roof of the sphenoid sinus. lateral boundaries by the frontal bone.The frontal bone houses the supraorbital foramina, which, along with the frontal sinuses, form 2 important surgical landmarks during approaches involving the anterior skull base. Middle cranial fossa: The anterior limit by the greater wing of the sphenoid The posterior limit is the clivus. The lateral limit by the greater wing of the sphenoid as it extends laterally and upward from the sphenoid body to meet the squamous portion of the temporal bone and the anteroinferior portion of the parietal bone. ◦ The greater wing of the sphenoid forms the anterior floor of the fossa. ◦ The anterior aspect of the petrous temporal bone forms the posterior floor of the middle cranial fossa. ◦ The body of the sphenoid makes up the central portion of the middle fossa and houses the sella turcica. Posterior cranial fossa: The posterior skull base consists of primarily the occipital bone, with contributions from the sphenoid and temporal bones. The anterior portion by the basal portion of the occipital bone (the basiocciput) and the basisphenoid. These 2 regions combine to form the midline clivus. The lateral wall by the posterior surface of the petrous temporal bone and the lateral aspect of the occipital bone. The occipital bone also fuses with the mastoid portion of the temporal bone to form the occipitomastoid suture. The petrous portion of the temporal bone and the greater wings of the sphenoid bone are particularly important for identifying structures. The overlying tentorium cerebelli separates the cerebellum from the cerebral hemispheres above, whereas the occipital bone form the lateral walls and floor. Vertebral column in general ◦ The vertebral column usually consists of 33 vertebrae: 24 presacral vertebrae (7 cervical, 12 thoracic, and 5 lumbar) followed by the sacrum (5 fused sacral vertebrae) and the coccyx (4 frequently fused coccygeal vertebrae). ◦ The adult vertebral column presents four anteroposterior curvatures: thoracic and sacral, both concave anteriorly, and cervical and lumbar, both concave posteriorly. Fig: The vertebral column indicating the curvetures Parts of a Vertebra. ◦ A typical vertebra consists of (1) a body and (2) a vertebral arch, which has several processes (articular, transverse, and spinous) for articular and muscular attachments. ◦ Between the body and the arch is the vertebral foramen ◦ the sum of the vertebral foramina constitutes the vertebral canal, which houses the spinal cord ◦ Between the vertebrae of the spine are thin regions of cartilage known as the intervertebral discs. ◦ Intervertebral discs are made of an outer shell known as the annulus fibrosus (bone binder) and a soft, pulpy region known as the nucleus pulposus (shock absorber) in the middle. The body is the main weight-bearing region of a vertebra, making up the bulk of the bone’s mass. Extending from the body, the transverse processes are thin columns of bone that point out to the left and right sides of the body. The spinous process extends from the ends of the transverse processes in the posterior direction. Between the body, transverse processes and spinous process is the vertebral foramen, a hollow space that contains the spinal cord and meninges. The bars joining a body to the transverse process are The bars joining the transverse processes and continuous backward to spinous processes are laminae. pedicles. Features of a typical vertebral bone Cervical Vertebrae, the skeleton of the neck The seven vertebrae of the neck are characterized by an opening in each transverse process known as a foramen transversarium. The upper six pairs of foramina transversaria transmit the vertebral artery. The C1 vertebra, which supports the skull, is termed the atlas after the Greek titan who held the Earth on his shoulders. The C2, which serves as a pivot for the atlas when moving up and down, is termed the axis. The C1, which has neither body nor spinous process, consists of two lateral masses connected by a short anterior and a longer posterior arch. Fig: An atlas The C2, (axis) is characterized by the dens (or odontoid process), which projects upward from the body and articulates with the anterior arch of the atlas. The lower cervical vertebrae, C2 to 6 are typical and present short, bifid spinous processes. Each transverse process, pierced by a foramen transversarium, The anterior tubercles of C6 vertebra are large and are termed the carotid tubercles, because the common carotid arteries can be compressed against them. C7 vertebra has a long, non-bifid spinous process and is known as the vertebra prominens. The anterior tubercles (costal processes) of C7 vertebra may develop separately as cervical ribs. (Lumbar ribs are less frequent.) Questions and answers Which curvatures first appear in the vertebral column? ◦ The thoracic and sacral curvatures are primary appearing during embryonic period, while the cervical and lumbar curvatures are secondary and appear during foetal period and accentuated in infancy period Where are the intervertebral foramina and what do they contain? ◦ In between the adjacent pedicles and typically each contains a spinal ganglion and a ventral root (rootlets) of a spinal nerve What are the key features of the cervical, thoracic, lumbar, and sacral vertebrae? ◦ Are respective foramina tranversaria, articulation with the ribs, absence of the mentioned features and fussion