Head and Neck 1: Bones and Joints

• The skeleton of the head is formed by the skull, cervical spine (consisting of 7 cervical vertebrae), the hyoid bone, and cartilages of the larynx and trachea
• Inside the temporal bone is the ear, consisting of the three smallest bones of the body (stapes, incus, malleus) called the ossicles; they transmit vibrations to the tympanic membranes and then to small organs in the ear for balance and hearing
• C1 is called the atlas and is a ring-shaped structure with no body
• C1 lies on top of C2 (axis), and rotates around the Dens/odontoid process
• Generally the cervical vertebrae has a body anteriorly and posteriorly are the processes of the vertebral arches
• Intervertebral foramen (out the sides) transmits spinal nerves while the transverse foramina transmits the vertebral artery (up/down)
• Intervertebral discs are anterior and facet joints are posterior
• The skull is not a single bone and is in fact a collection of almost 30 different bones
• The skull can be divided into the neurocranium (bones that enclose the cranial cavity and contain the brain) and viscerocranium (bones that form the face)
• The skull can also be divided into the calvaria (skullcap) and basicranium (cranial base)
• Major bones of the skull forming the viscerocranium: zygomatic, palatine, lacrimal, nasal, maxilla, mandible, inferior nasal concha, vomer
• Major bones of the skull forming the neurocranium: frontal, parietal, temporal, occipital, sphenoid, ethmoid
• Some bones of the skull are hollow, e.g. the frontal, maxilla, ethmoid and sphenoid bones form the paranasal sinuses, the temporal bone also has some spaces connected to the ear (mastoid antrum and air cells)
• Majority of joints in the skull are solid joints except for the temporalmandibular joint, which is a hinge-type synovial joint
• Flat bones of the skull (skullcap, mandible) develop from intramembranous ossification, while most bones of the face develop from endochondral ossification
• The last parts of the skullcap to ossify are known as fontanelles (soft membranes of the skull that exist in newborns)
• Fontanelles: posterior fontanelle, anterior fontanelle, metopic suture, and mandibular symphysis
• Fontanelles serve as growth regions in early infancy and help the head pass through the vaginal canal during birth, also reduces risk of skull fractures
• Growth of the brain leads to growth of the cranial vault
• As we grow older, especially as the teeth are lost, alveolar bone tissue is reabsorbed and decreases the size of the skull
• Growth of the paranasal sinuses and eruption of primary and secondary dentition increases the size of the facial skeleton
• Orbit/orbital cavity: contains the eye, lacrimal glands, and ocular muscles
• The anterior nasal aperture forms the opening of the two nasal cavities, which are divided by the nasal septum
• Supraorbital foramen: leads to the scalp, carrying the supraorbital branch of opthalmic nerve and other supraorbital vessels
• • Optic canal: transmits the optic nerve annd opthalmic artery to supply the eye
• Superior orbital fissue: transfers various nerves and opthalmic veins into the orbit
• Inferior orbital fissure: transfers infraorbital and zygomatic branches of maxillary nerve and infraorbital vessels to the orbit
• Lacrimal groove: connects the orbit to the nasal cavity on the same side (e.g. nasolacrimal duct)
• Infraorbital groove: leads to the infraorbital canal and then foramen, carries the infraorbital branch of maxillary nerve and infraorbital vessels to the midface
• Pterion: H-shaped collection of sutures that connects the parietal, frontal, sphenoid and temporal bone (weak point, can lead to a hematoma if fractured)
• Above the zygomatic arch is the temporal fossa and below it is the infratemporal fossa, there is also a pterygopalatine fossa (small space behind the orbit and maxilla)
• Temporal fossa contains the temporalis muscle
• The frontal and parietal bones are connected by the coronal suture; two parietal bones are connected by the sagittal suture, the parietal and occipital bones are connected by the lambdoid suture
• Three major landmarks of the skull: crista galli, which is right in the center above the ethmoid bone; Turkish saddle, where the pituitary glands usually rest; and the foramen magnum, which connects the brain to the spinal chord
• Cribriform plate leads to the nasal cavity and allows the passage of olfactory nerves
• The optic canal leads to the orbit and carries branches of the optic nerve
• Superior orbital fissue leads to the orbit and carries various nerves and opthalmic veins
• Foramen rotundum carries the maxillary nerve to the pterygopalatine fossa
• Foramen lacerum is normally plugged with cartilage
• Foramen ovale leads ot the infratemporal fossa and carries mandibular nerve