Chapter 7: The Axial Skeleton I. The Axial Division of the Skeletal System, p. 206 Objective 1. Identify the bones of the axial skeleton and their functions. • In studying individual bones, we are concerned with their functions, including which bones they connect or articulate with, and their structures and marks, including muscle and ligament attachments, and openings for nerves and blood vessels (foramina). Figure 7-1 • The axial skeleton: - forms the longitudinal axis of the body - has 80 bones • The axial skeleton includes: - the skull (8 cranial bones and 14 facial bones) - bones associated with the skull (6 auditory ossicles and the hyoid bone) - the vertebral column (24 vertebrae, the sacrum and the coccyx) - the thoracic cage (24 ribs and the sternum) • Functions of the axial skeleton include: - support and protect organs in the body cavities - attach to muscles that support head, neck and trunk - attach to breathing muscles - attach to muscles of the appendicular skeleton • Axial bones are strong, with many ligaments, but are restricted in motion. II. The Skull, p. 206 Objectives 1. Identify the bones of the cranium and face, and the significance of their markings. 2. Describe the structures and functions of the nasal complex. 3. Explain the functions of paranasal sinuses. 4. Describe the differences between the skulls of infants, children and adults. • The skull protects the brain and entrances to respiratory and digestive systems. Figure 7-2 • The skull has 22 bones: - 8 cranial bones form the braincase or cranium. The cranial bones enclose the cranial cavity, which contains the brain and associated fluids, blood vessels, nerves and membranes. - 14 facial bones protect and support the entrances to the digestive and respiratory tracts. Superficial facial bones are for muscle attachment (including the maxillary, lacrimal, nasal, zygomatic and maxillary bones, and the mandible). The deep facial bones separate the oral and nasal cavities, and form the nasal septum (including the palatine bones, inferior nasal conchae, and the vomer). • The bones of the skull also contain the sinuses, cavities which decrease the weight of the skull and are lined with mucus membranes that help protect the entrances of the respiratory system. Figure 7-3 • The immovable joints of the skull are called sutures. The 4 major sutures are: 1. The lambdoid suture separates the occipital bone from the parietal bones and may contain sutural bones. 2. The coronal suture attaches the frontal bone to the parietal bones. The calvaria is made up of the occipital, parietal and frontal bones. 3. The sagittal suture, between the parietal bones, extends from the lambdoid suture to the coronal suture. 4. The squamous sutures form the boundaries between temporal bones and parietal bones. Figure 7-4 Cranial Bones, p. 212 • The 8 cranial bones include the occipital bone, frontal bone, sphenoid, ethmoid, parietal bones and temporal bones. Figure 7-5 1. The Occipital Bone Functions: - forms the posterior and inferior surfaces of the cranium. Articulations: - parietal bones - temporal bones - sphenoid - first cervical vertebra (atlas) Marks: - external occipital protuberance - external occipital crest (attach ligaments) - occipital condyles (articulate with neck) - inferior and superior nuchal lines (attach ligaments) Foramina: - foramen magnum (connects cranial and spinal cavities) - jugular foramen (jugular vein) - hypoglossal canals (hypoglossal nerves) Figure 7-5b 2. The Parietal Bones Functions: - forms part of the superior and lateral surfaces of the cranium Articulations: - parietal bone - occipital bone - temporal bone - frontal bone - sphenoid bone Marks: - superior and inferior temporal lines (temporalis muscle) - grooves for cranial blood vessels Figure 7-6 3. The Frontal Bone Functions: - forms the anterior cranium and upper eyesockets - contains frontal sinuses Articulations: - parietal bone - sphenoid bone - ethmoid bone - nasal bone - lacrimal bone - maxillary bone - zygomatic bone - metopic suture (fusion of 2 frontal bones, disappears about age 8) Marks: - frontal squama (forehead) - supraorbital margin (protects eye) - lacrimal fossa (tear ducts) - frontal sinuses Foramina: - supraorbital foramen (blood vessels of eyebrows, eyelids and frontal sinuses) - supraorbital notch (an incomplete supraorbital foramen) Figure 7-7 4. The Temporal Bones Functions: - form part of the lateral walls of the cranium and zygomatic arches - articulate with the mandible - surround and protect the inner ear - attach muscles of jaws and head Articulations: - zygomatic bone - sphenoid bone - parietal bone - occipital bone - mandible Marks: - squamous part (borders the squamous suture) - zygomatic process (articulates with the temporal process of the zygomatic bone to form the zygomatic arch or cheekbone) - zygomatic process (inferior to the squamous portion) - mandibular fossa (articulates with the mandible) - mastoid process (muscle attachment) contains mastoid air cells connected to the middle ear cavity - styloid process (attach tendons and ligaments of the hyoid, tongue and pharynx) - petrous part (encloses structures of the inner ear) - auditory ossicles (3 tiny bones in the tympanic cavity, or middle ear, transfer sound from the tympanic membrane or eardrum, to the inner ear) Foramina: - carotid canal (internal carotid artery) - foramen lacerum (carotid and small arteries, hyaline cartilage, auditory tube) - external acoustic canal (ends at the tympanic membrane) - stylomastoid foramen (facial nerve) - internal acoustic canal (blood vessels and nerves of the inner ear, facial nerve) Figure 7-8 5. The Sphenoid Functions: - forms part of the floor of the cranium - unites cranial and facial bones - strengthens the sides of the skull - contains the sphenoidal sinuses Articulations: - ethmoid - frontal bone - occipital bone - parietal bone - temporal bone - palatine bones - zygomatic bones - maxillary bones - vomer Marks: - sphenoid body (central axis of the sphenoid) - sella turcica (saddle-shaped enclosure on the superior surface of the body) - hypophyseal fossa (depression within the sella turcica, holds the pituitary gland) - sphenoidal sinuses (either side of the body, inferior to the sella turcica) - lesser wings (anterior to the sella turcica) - greater wings (form part of the cranial floor, sphenoidal spine and posterior wall of the orbit) - pterygoid processes (form pterygoid plates which attach muscles of the lower jaw and soft palate) Foramina: - optic canals (optic nerves) - superior orbital fissure (blood vessels and nerves of the orbit) - foramen rotundum (blood vessels and nerves of the face) - foramen ovale (blood vessels and nerves of the face) - foramen spinosum (blood vessels and nerves of the jaws) Figure 7-9 6. The Ethmoid Functions: - forms the anteromedial floor of the cranium - forms the roof of the nasal cavity - forms part of the nasal septum and medial orbital wall - contains ethmoidal air cells (sinuses) Articulations: - frontal bone - sphenoid - nasal bone - lacrimal bone - palatine bone - maxillary bones - inferior nasal conchae - vomer Marks: 1. The cribriform plate (floor of the cranium and roof of the nasal cavity): - contains the crista galli (bony ridge attached to the falx cerebri, a membrane that stabilizes the brain) 2. The 2 lateral masses: - contain the ethmoidal labyrinth (interconnected ethmoidal air cells open to nasal cavities) - superior nasal conchae (projections) - middle nasal conchae (projections) 3. The perpendicular plate (part of the nasal septum) Foramina: - olfactory foramina in the cribriform plate (olfactory nerves) Facial Bones, p. 217 Figure 7-10 1. The Maxillary Bones, the largest facial bones Functions: - support the upper teeth - form the inferior orbital rim - form the lateral margins of the external nares - form the upper jaw and hard palate - contain maxillary sinuses (the largest sinuses) Articulations: - frontal bones - ethmoid - with other maxillary bone - with all other facial bones except the mandible Marks: - orbital rim (protects the eye and orbit) - anterior nasal spine (attaches the cartilaginous anterior nasal septum) - alveolar processes (border the mouth, support upper teeth) - palatine processes (form the hard palate or roof of mouth) - contain maxillary sinuses (to lighten bone) - nasolacrimal canal (protects the lacrimal sac and nasolacrimal duct) Foramina: - infraorbital foramen (a major sensory nerve reaches the brain via the foramen rotundum of the sphenoid) - inferior orbital fissure (cranial nerves and blood vessels) 2. The Palatine Bones Functions: - form the posterior portion of the hard palate - contribute to the floors of the orbits Articulations: - with one another - maxillary bones - sphenoid - ethmoid - inferior nasal conchae - vomer Marks: The palatine bones have 2 parts in an L shape: - the horizontal plate (posterior part of the hard palate) - the perpendicular plate (from the horizontal plate to the orbital process of the orbit floor, which contains a small sinus open to the sphenoidal sinus) Foramina: - many in the lateral portion of the horizontal plate (small blood vessels and nerves of the roof of the mouth) Figure 7-11 3. The Nasal Bones Functions: - support the bridge of the nose (superior) - connect to cartilages that support the distal part of the nose (cartilages extend to the external nares or entrances to the nasal cavity) Articulations: - with one another - the ethmoid - frontal bones - maxillary bones 4. The Vomer Functions: - forms the inferior portion