Chapter 7 Part A The Skeleton Why This Matters Understanding the anatomy of the skeleton enables you to anticipate problems such as pelvic dimensions that may affect labor and delivery The Skeleton The skeletal system, or skeleton, is composed of bones, cartilages, joints, ligaments Mostly bone Cartilage occurs in isolated areas Ligaments connect bones and reinforce joints The skeleton accounts for 20% of body mass Two major divisions Axial skeleton Appendicular skeleton Part 1: The Axial Skeleton Axial skeleton consists of 80 bones divided into three major regions: Skull Vertebral column Thoracic cage Axial skeleton has three functions: 1. Form longitudinal axis of body 2. Support head, neck, and trunk 3. Protect brain, spinal cord, and thoracic organs 7.1 The Skull Skull is most complex bony structure in body Formed by two sets of bones: 1. Cranial bones (cranium) Enclose the brain in the cranial cavity Provide sites of attachment for head and neck muscles The Skull (cont.) 2. Facial bones Form framework of face Contain cavities for special sense organs for sight, taste, and smell Provide openings for air and food passage 2016 Pearson Education, Inc. 1
Secure teeth Anchor facial muscles used for facial expression Most skull bones are flat and firmly locked together (except for mandible) Joints are called sutures Have a serrated, saw-tooth appearance Overview of Skull Geography Facial bones form anterior aspect, with cranium forming the rest of skull Cranium is divided into a vault and a base Cranial vault (calvaria) forms superior, lateral, and posterior portion of skull, as well as forehead Cranial base forms inferior aspect of skull Internally base is divided into three steps, or fossae: anterior, middle, posterior fossae Brain sits within these fossae, enclosed by cranium vault Area referred to as cranial cavity Overview of Skull Geography (cont.) Cranium also contains other cavities: Middle and internal ear cavities Nasal cavity Orbits that house eyeballs Skull has 85 named openings Foramina, canals, fissures Provide passageways for spinal cord, major blood vessels, and the 12 cranial nerves Cranium Cranium is comprised of eight cranial bones: Frontal bone Parietal bones (two left and right) Occipital bone Temporal bones (two left and right) Sphenoid bone Ethmoid bone Frontal bone: shell-shaped bone forms anterior portion of cranium Vertical part, called squamous region, is also known as the forehead Inferior portion ends at supraorbital margins Area underneath eyebrows Forms superior wall of the orbits and most of anterior cranial fossa 2016 Pearson Education, Inc. 2
Supraorbital foramen (notch) allows supraorbital artery and nerve to pass to forehead Glabella is area of frontal bone between orbits Frontal sinuses located just lateral to glabella Parietal bones and the major sutures Two large parietal bones form most of superior and lateral aspects of cranial vault Four sutures mark articulations of parietal bones with frontal, occipital, and temporal bones: 1. Coronal suture: between parietal bones and frontal bone 2. Sagittal suture: between right and left parietal bones 3. Lambdoid suture: between parietal bones and occipital bone 4. Squamous (squamosal) sutures: between parietal and temporal bones on each side of skull Occipital bone Forms most of skull s posterior wall and posterior cranial fossa Articulates with parietal, temporal, and sphenoid bones Foramen magnum: large hole through which brain connects with spinal cord Flanked by pair of occipital condyles that articulate with 1st vertebra Hypoglossal canal allows cranial nerve XII to pass through External occipital protuberance: protrusion just superior to foramen magnum External occipital crest: ridges that are site of attachment for ligamentum nuchae Superior and inferior nuchal lines: site of attachment for many neck and back muscles Temporal bones: paired bones that make up inferolateral aspects of skull and parts of cranial base Three major regions: 1. Squamous: zygomatic processes articulate with zygomatic bone to form zygomatic arch and mandibular fossa makes up part of temporomandibular joint 2. Tympanic: surround external acoustic meatus (external ear canal) 2016 Pearson Education, Inc. 3
3. Petrous: houses middle and internal ear cavities Makes up part of the middle cranial fossa Several foramina penetrate petrous region:» Jugular foramen allows passage of three cranial nerves» Carotid canal: passageway for internal carotid artery» Foramen lacerum: jagged opening covered by cartilage in living human» Internal acoustic meatus and styloidmastoid foramen: cranial nerve passageways Mastoid and styloid processes: areas for attachment of several neck and tongue muscles Clinical Homeostatic Imbalance 7.1 Mastoid process contains cavities (sinuses) called mastoid air cells Mastoiditis can develop if a middle ear infection spreads into mastoid process area Mastoid air cells are separated from brain by a very thin bony plate, increasing chances that the infection could spread to brain Sphenoid bone: complex, bat-shaped bone Keystone bone that articulates with all other cranial bones Sphenoidal sinuses found within body of sphenoid Body also includes sella turcica prominence that includes hypophyseal fossa area enclosing the pituitary gland Sphenoid contains three pairs of processes: Greater wings Lesser wings Pterygoid processes Sphenoid contains several foramina: Optic canals: allow passage of optic nerves Superior orbital fissure: cranial nerve passage Foramen rotundum and foramen ovale: also passageways for cranial nerves Foramen spinosum: opening for arteries 2016 Pearson Education, Inc. 4
Ethmoid bone: deepest skull bone Superior part formed by paired cribriform plates that also form roof of nasal cavity and floor of anterior cranial fossa Crista galli: triangular process that is point of attachment for brain s dura mater covering Perpendicular plate: forms superior part of nasal septum and is flanked by lateral masses that contain sinuses called ethmoidal air cells Lateral masses extend medially to form superior and middle nasal conchae Orbital plates contribute to medial wall of orbits Sutural bones Tiny, irregularly shaped bones that appear within sutures Significance is unknown, as not everyone has these Facial Bones Facial skeleton is made up of 14 bones, 12 of which are paired (mandible and vomer are single) Mandible Maxillary bones (2) Zygomatic bones (2) Nasal bones (2) Lacrimal bones (2) Palatine bones (2) Vomer Inferior nasal conchae (2) Mandible: largest, strongest bone of face U-shaped lower jawbone made up of body (chin) and two upright rami Mandibular angle: point where rami and chin meet Coronoid process: superior end of rami serves as insertion point for large temporalis muscle Condylar process: posterior to coronoid forms part of temporomandibular joint Mandibular notch: separates processes Body consists of alveolar process that contains sockets for teeth and mandibular symphysis ridge Foramina include mandibular (for nerves) and mental foramina (for nerves and blood vessels) 2016 Pearson Education, Inc. 5
Maxillary bones (maxillae): medially fused to form upper jaw and central facial skeleton Upper teeth held in alveolar processes Anterior nasal spine forms just below nose Palatine process forms two-thirds of hard palate Frontal process: forms lateral bridge of nose Zygomatic processes articulate with zygomatic bones Maxillary sinuses: flank nasal cavity laterally Openings for nerves and blood vessels include: Inferior orbital fissure Infraorbital foramen Incisive fossa and canal Zygomatic bones Form cheekbones and inferolateral margins of orbits Articulate with zygomatic processes of temporal, frontal, and maxillary bones Nasal bones Form bridge of nose Articulate with frontal, maxillary, and ethmoid bones Attach to cartilage that forms tip of nose Lacrimal bones Form medial walls of orbits Articulate with frontal, maxillary, and ethmoid bones Lacrimal fossa that houses lacrimal sac allows passageway for tears to drain Palatine bones L-shaped bones made from two bony plates Horizontal plate: completes posterior one-third of hard palate Perpendicular plate: forms part of posterolateral walls of the nasal cavity and a small part of the orbits Vomer Plow-shaped bone; forms part of nasal septum 2016 Pearson Education, Inc. 6
Inferior nasal conchae Paired bones that form part of lateral walls of nasal cavity Largest of three pairs of conchae Ethmoid bone forms other two pairs The Hyoid Bone Not a bone of skull Lies in anterior neck inferior to mandible Only bone in body that does not articulate directly with another bone Anchored by ligaments Acts as a movable base for tongue and site of attachment for muscles of swallowing and speech Special Characteristics of the Orbits and Nasal Cavity Orbits Cavities that encase eyes and lacrimal glands Sites of attachment for eye muscles Formed by parts of seven bones Frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid Special Characteristics of the Orbits and Nasal Cavity (cont.) Nasal cavity: formed by parts of several bones Roof: cribriform plates of ethmoid Lateral walls: superior and middle conchae of ethmoid, perpendicular plates of palatine and Inferior nasal conchae Spaces between conchae called meatuses Conchae increase turbulence of air flow Floor: processes of palatine and maxillary bones Nasal septum Bony posterior formed by vomer and perpendicular plate of ethmoid Anterior formed by septal cartilage Special Characteristics of the Orbits and Nasal Cavity (cont.) Paranasal sinuses: formed from five skull bones: frontal, sphenoid, ethmoid, and paired maxillary bones All contain mucosa-lined, air-filled spaces Functions: Warm and humidify air Help to lighten skull 2016 Pearson Education, Inc. 7
Enhance resonance of voice 2016 Pearson Education, Inc. 8