The Axial Skeleton Eighty bones segregated into three regions

The Axial Skeleton Eighty bones segregated into three regions Skull Vertebral column Bony thorax

Bones of the Axial Skeleton Figure 7.1

The Skull The skull, the body s most complex bony structure, is formed by the cranium and facial bones (22 in all) Cranium Made up of cranial bones protects the brain and is the site of attachment for head and neck muscles

Facial bones Facial bones Form the framework of the face Contain cavities for special sense organs (smell, sight, taste, hearing) Provide openings for the passage of air and food Secure the teeth Anchor the facial muscles of expression

Bones of the Skull Most of the bone of the skull are flat bones All of the bones of the skull are tightly united by sutures (interlocking joints) except the mandible

Major Skull Sutures Sutures of the skull connect the cranial bones The major sutures of the skull are: Coronal Sagittal Squamous Lambdoid w/ other sutures connecting the facial bones

Overview of Skull Geography The cranium can be divided into a vault and a base The cranial vault (calvarin) forms the superior, lateral, and posterior aspects of the skull (and forehead) The cranial base (floor) forms the skull s inferior aspect

Overview of Skull Geography The internal bony ridges divide the base into 3 steps (or fossae): Anterior cranial fossae Middle cranial fossae Posterior cranial fossae The brain sits within these 3 cranial fossae

Overview of Skull Geography Other cavities include: Middle & internal ear cavities Nasal cavity Orbits sinuses

Anatomy of the Cranium Eight cranial bones Parietal (2) Temporal (2) Frontal Occipital Sphenoid Ethmoid The curvatures of the cranial bones makes them strong and allows them to be thin (e.g. an eggshell)

Frontal Bone Forms the anterior portion of the cranium Articulates posteriorly with the paired parietal bones via the coronal suture Most anterior part is the vertical frontal squama (otherwise known as the forehead ) The frontal squama ends inferiorly at the supraorbital margins The supraorbital margin is pierced by the supraorbital foramen allowing passage of the supraorbital artery and nerve to the forehead Extending posteriorly, the frontal bone forms the superior wall of the orbits and the anterior cranial fossa The glabella is the smooth part of the bone between the orbits The frontonasal suture joins the glabella and the nasal bones The frontal sinuses are found deep and lateral to the glabella

Frontal Bone Figure 7.2a

Parietal Bones and Major Associated Sutures The parietal bones form the superior and lateral aspects of the skull They make up the bulk of the cranial vault The 4 largest sutures are associated with the parietal bones: Coronal suture articulation between parietal bones and frontal bone anteriorly Sagittal suture where right and left parietal bones meet superiorly Lambdoid suture where parietal bones meet the occipital bone posteriorly Squamosal or squamous suture where parietal and temporal bones meet

Parietal Bones and Major Associated Sutures Form most of the superior and lateral aspects of the skull Figure 7.3a

Occipital Bone and Its Major Markings The occipital bone forms most of the skulls posterior wall and base It articulates anteriorly w/ the paired parietal and temporal bones via the lambdoid and occipitomastoid sutures, respectively It articulates w/ the sphenoid bone via the basioccipital plate Internally, the occipital bone forms the walls of the posterior cranial fossa The foramen magnum found at the base of the occipital bone if where the inferior part of the brain connects with the spinal cord The occipital condyles flank the foramen magnum laterally and articulate w/ the first vertebra permitting a nodding movement The external occipital proturbence (can you feel yours??) External occipital crest: secures the legamentum nuchae (an elastic ligament that connects the vertebrae to the skull) Superior & inferior nuchal lines: anchor many muscles of the neck & back

Occipital Bone and Its Major Markings Forms most of skull s posterior wall and base Major markings include the posterior cranial fossa, foramen magnum, occipital condyles, and the hypoglossal canal Figure 7.2b

Temporal Bones Figure 7.5

Temporal Bones Lie inferior to the parietal bones and join them at the squamous sutures Form the inferolateral aspects of the skull and parts of the cranial floor Divided into four major regions Squamous Tympanic Mastoid petrous

Temporal Bones: Squamous Region The squamous region has the bar-like zygomatic process that meets the zygomatic bone forming the zygomatic arch (the cheek bone) The mandibular fossa on the inferior surface of the zygomatic process receives the condyle of the mandible (lower jawbone) forming the temporomandibular joint

Temporal Bones: Tympanic Region The Tympanic region surrounds the external acoustic meatus (external ear canal) Inferior to the exteranl acoustic meatus lies the styloid process, an attachment point for several tongue and neck muscles

Temporal Bones: Mastoid Region The mastoid region contains the large mastoid process which anchors some neck muscles Feel it right behind your ear go ahead, feel it! The stylomastoid foramen allows cranial nerve VII (the facial nerve) to leave the skull

Temporal Bones: Petrous Region The petrous region contributes to the cranial base It lies between the occipital bone and the sphenoid bone Together w/ the sphenoid bone they form the middle cranial fossa which supports the temporal lobes of the brain This region also houses the middle & internal ear cavities

Temporal Bones: Petrous Region Several foramen penetrate the petrous region: -the jugular foramen: internal jugular & 3 cranial nerves -the carotid canal: internal carotid artery -the foramen lacerum -the internal acoustic meatus: cranial nerves VII & VIII -the foramenia rotundum, ovale, and spinosum

Sphenoid Bone Butterfly-shaped bone that spans the width of the middle cranial fossa The Keystone Bone: Forms the central wedge that articulates with all other cranial bones Consists of a central body, greater wings, lesser wings, and pterygoid processes Contains the sphenoid sinuses

Sphenoid Bone The superior surface bears the sella tucica which bears the hypophyseal fossa that forms the enclosure for the pituitary gland The hypophyseal fossa is abutted anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae, which terminates in the posterior clinical processes

Sphenoid Bone Figure 7.6a

Sphenoid Bone Figure 7.6b

Sphenoid Bone The greater wings project laterally from the body and form: Middle cranial fossa Dorsal walls of the orbits External wall of the skull (medial to the zygomatic arch) The lesser wings form: Part of the floor of the anterior cranial fossa Part of the medial walls of the orbits Terminate medially at the anterior clinoid process (an anchoring site for the brain)

Sphenoid Bone The pterygoid processes project inferior from the body. Function to anchor the pterygoid muscles that we use when we chew Openings in the sphenoid bone: Optic canals: connected by the optic chiasmatic groove. Allow the optic nerves to pass Superior orbital fissure: Allow the passage of cranial nerves III, IV, and VI which control eye movement

Sphenoid Bone More openings in the sphenoid bone: Foramen rotundum: Branch of cranial nerve V for the maxillary nerve Foramen ovale: Branch of cranial nerve V for the mandibullar nerve Foramen spinosum: Transmits the middle meningreal artery that serves internal faces of some cranial bones

Ethmoid Bone Figure 7.7

Ethmoid Bone Deepest of the skull bones; lies between the sphenoid and nasal bones Forms most of the bony area between the nasal cavity and the orbits The cribiform plates (seen from above) form the roof of the nasal cavities and the floor of the anterior cranial fossa The olfactory foramina: allow the olfactory nerves to pass

Ethmoid Bone Crista galli: (triangular process) Attachment site for the dura mater (the outermost covering of the brain) Perpendicular plate Projects inferiorly in the median plane Forms the superior part of the nasal septum (which divides the nasal cavity right and left)

Ethmoid Bone Right & left lateral masses: Riddled w/ ethmoid sinuses (acts as sieve) Superior/middle nasal conchae (turbinates) Protrude into the nasal cavity Orbital plate: Located on the lateral surfaces of the lateral masses Contribute to the medial walls of the orbits

Wormian Bones Tiny irregularly shaped bones that appear within sutures

Facial Bones 14 bones (6 paired sets) of which only the mandible and vomer are unpaired The paired bones are: Maxillae Zygomatics Nasals Lacrimals Palatines inferior conchae

Mandible and Its Markings The mandible (lower jawbone) is the largest, strongest bone of the face Its major markings include the coronoid process, mandibular condyle, the alveolar margin, and the mandibular and mental foramina

Mandible and Its Markings Figure 7.8a

Mandible and Its Markings The mandible (lower jaw) is the largest, strongest bone of the face The body forms the chin The rami meet the body posteriorly at a mandibular angle The mandibular notch separates the coronoid and condyle processes or the rami The coronoid process (anterior) is the insertion point for the large temporalis muscle that elevates the lower jaw during chewing

Mandible and Its Markings The mandibular condyle (posterior) articulates with the mandibular fossa of the temporal bone forming the temporomandibular joint Mandibular body anchors the teeth Alveolar margin: the superior border of the body contains the sockets win which the teeth are embedded

Mandible and Its Markings Mandibular symphysis: Site of fusion of the two mandibular bones ( in infancy) Mandibular foramina Found on the medial surface of each ramus Nerve passage for tooth sensation (injection site for Lidocaine) Mental foramina: Lateral aspects of body Allow blood vessels and nerves to pass to skin of the chin

Maxillary Bone Figure 7.8b

Maxillary Bones (maxillae) Medially fused bones that make up the upper jaw and the central portion of the facial skeleton Facial keystone bones that articulate with all other facial bones except the mandible

Maxillary Bones: Major Markings Alveolar margins: Carry the upper teeth Anterior nasal spine: Site of fusion of maxillae (inferior to nose) Palatine processes: Project posteriorly from the alveolar margins Fuse medially forming the anterior 2/3 of the hard palate or bony roof of the mouth

Maxillary Bones: Major Markings Incisive fossa (midline foramen) Posterior to teeth Passage for blood vessels/nerves Maxillary sinuses Largest of the paranasal sinuses Extend from the orbits to the roots of the upper teeth

Maxillary Bones: Major Markings Zygomatic processes: Lateral articulation between the maxillae and zygomatic bones Inferior orbital fissure: Located deep within the orbit at the junction of the maxilla and the greater wings of the sphenoid Permits zygomatic nerve, maxillary nerve (cranial nerve V branch) and blood vessels to pass to the face

Maxillary Bones: Major Markings Infraorbital foramen: Allows the infraorbital nerve (a continuation of the maxillary nerve) and artery to reach the face

Zygomatic Bones Irregularly shaped bones (cheekbones) Articulate with the zygomatic processes of the temporal bones posteriorly, the zygomatic process of the frontal bone superiorly, and the zygomatic process of the maxillae anteriorly For part of the inferolateral Margins of the orbits

Other Facial Bones Nasal bones Thin medially fused bones that form the bridge of the nose Articulate with the frontal bone superiorly, the maxillary bones laterally, and the perpendicular plate of the ethmoid bone posteriorly Cartilages form the skeleton of the external nose inferiorly

Other Facial Bones Lacrimal bones: Contribute to the medial walls of the orbit Smallest and most fragile of the facial bones Articulate with the frontal bone superiorly, ethmoid bone posteriorly, and the maxillae anteriorly Contains a deep groove (lacrimal fossa) that houses the lacrimal sac that is part of the passage that allows tears to drain from the eye to the nasal cavity

Other Facial Bones Palatine bones: Fashioned from 2 bony plates Horizontal: complete posterior portion of the hard palate Perpendicular: forms the posterior walls of the nasal cavity and the small parts of the orbits 3 articulating processes: Pyramidal Sphenoidal orbital

Other Facial Bones Vomer plow-shaped bone that forms part of the nasal septum Inferior nasal conchae paired, curved bones in the nasal cavity that form part of the lateral walls of the nasal cavity

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Anterior Aspects of the Skull Frontal bone Parietal bone Frontal squama of frontal bone Nasal bone Sphenoid bone (greater wing) Temporal bone Ethmoid bone Lacrimal bone Zygomatic bone Infraorbital foramen Maxilla Mandible Glabella Frontonasal suture Supraorbital foramen (notch) Supraorbital margin Superior orbital fissure Optic canal Inferior orbital fissure Middle nasal concha Perpendicular plate Inferior nasal concha Vomer bone Ethmoid bone Mental foramen (a) Mandibular symphysis Figure 7.2a

Posterior Aspects of the Skull Sagittal suture Parietal bone Sutural bone Lambdoid suture Occipital bone Superior nuchal line External occipital protuberance Mastoid process Occipitomastoid suture (b) External occipital crest Occipital condyle Inferior nuchal line Figure 7.2b

External Lateral Aspects of the Skull Coronal suture Parietal bone Temporal bone Lambdoid suture Frontal bone Sphenoid bone (greater wing) Ethmoid bone Lacrimal bone Lacrimal fossa Squamous suture Occipital bone Zygomatic process Occipitomastoid suture Nasal bone Zygomatic bone Maxilla External acoustic meatus Mastoid process Styloid process Alveolar margins (a) Mandibular condyle Mandibular notch Mandibular ramus Mandibular angle Mandible Mental foramen Coronoid process Figure 7.3a

Midsagittal Lateral Aspects of the Skull Parietal bone Squamous suture Temporal bone Lambdoid suture Occipital bone Occipitomastoid suture External occipital protuberance (b) Internal acoustic meatus Sella turcica of sphenoid bone Pterygoid process of sphenoid Mandibular bone foramen Palatine bone Palatine process of maxilla Coronal suture Frontal bone Sphenoid bone (greater wing) Frontal sinus Crista galli Nasal bone Sphenoid sinus Ethmoid bone (perpendicular plate) Vomer bone Incisive fossa Maxilla Alveolar margins Mandible Figure 7.3b

Inferior Portion of the Skull Hard palate Maxilla (palatine process) Palatine bone (horizontal plate) Incisive fossa Medial palatine suture Infraorbital foramen Maxilla Zygomatic bone Temporal bone (zygomatic process) Vomer Mandibular fossa Styloid process Mastoid process Temporal bone (petrous part) Pharyngeal tubercle of basioccipital Parietal bone External occipital crest Sphenoid bone (greater wing) Foramen ovale Foramen lacerum Carotid canal External acoustic meatus Stylomastoid foramen Jugular foramen Occipital condyle Inferior nuchal line Superior nuchal line (a) External occipital protuberance Foramen magnum Figure 7.4a

Inferior Portion of the Skull Olfactory foramina Anterior cranial fossa Lesser wing Sphenoid Greater wing Tuberculum sellae Hypophyseal fossa Sella Dorsum sellae turcica Posterior clinoid process Frontal bone Cribriform plate Crista galli Ethmoid bone Optic canal Anterior clinoid process Foramen rotundum Foramen ovale Foramen spinosum Middle cranial fossa Temporal bone (petrous part) Internal acoustic meatus Posterior cranial fossa Parietal bone Foramen lacerum Jugular foramen Hypoglossal canal Anterior cranial fossa Occipital bone (b) Foramen magnum Middle cranial fossa (c) Posterior cranial fossa Figure 7.4b