Axial Skeleton

• Axial skeleton

  – Bones of head and trunk

  – Forms longitudinal axis of body
• Axial skeleton has 80 bones 

  – Skull

  • 8 cranial bones and 14 facial bones***

  – Bones associated with the skull

  • 6 auditory ossicles and hyoid bone

  – Thoracic cage

  • Sternum and 24 ribs 

  – Vertebral column

  • 24 vertebrae, sacrum, and coccyx
• Functions of the axial skeleton

  – Supports and protects organs in body cavities 

  – Provides points of attachment for muscles that

  • Adjust positions of head, neck, and trunk 

  • Perform breathing movements

  • Stabilize parts of appendicular skeleton
• The skull contains 22 bones

  – 8 cranial bones form the cranium

  • Including calvaria (skullcap)

  • Enclose cranial cavity, containing the brain

  • Frontal, Parietal, Occipital, Temporal, Sphenoid, Ethmoid

  – 14 facial bones

  • Protect and support entrances to digestive and respiratory tracts

  • Maxillae, Palatine bones, Nasal bones, Inferior nasal conchae

  Zygomatic bones, Lacrimal bones, Vomer, Mandible
• Sutures

  – Immovable joints of the skull 

  – 4 major sutures

  • Lambdoid suture: Separates occipital from parietal bones

  • may contain sutural bones

  • Coronal suture: Attaches frontal bone to parietal bones

  • Sagittal suture: Between parietal bones

  • Squamous sutures: Join temporal bones with parietal bones
• Facial bones

  • external acoustic meatus
  • mastoid process (parts of the ear)
  • zygomatic arch = cheek bone, easily fractured
  • mental = chin
• Foramen***

  - all foramen allow for arteries, veins, and cranial nerves to pass through skull

  - foramen magnum, bottom of occipital bone, opening for medulla oblongata, accessory nerve and vertebral arteries

  - jugular foramen, with temporal bone, vagus, accessory nerves, and internal jugular vein
• Sinuses

  – Air-filled chambers in the skull

  – Functions

  • Decrease weight of the skull

  • Lined with mucous membranes, which produce mucus to moisten and clean the air

  • Serve as resonating chambers in speech production
• Occipital bone

  – General functions

  • Forms much of posterior and inferior surfaces of cranium

  – Joints

  • Parietal bones, Temporal bones, Sphenoid, First cervical vertebra (atlas)
• Occipital bone

  – Regions/markings

  • Occipital condyles articulate with first vertebra 

  – Foramina

  • Foramen magnum connects cranial cavity with vertebral canal

  • Jugular foramen for internal jugular vein

  • Hypoglossal canals for hypoglossal nerves
• Parietal bones

  – General functions

  • Form part of superior and lateral surfaces of the cranium

  – Joints

  • With each other and with occipital, temporal, frontal, and sphenoid bone

  - Regions/markings

  • Superior and inferior temporal lines attach temporalis muscle

  • Grooves for cranial blood vessels
• Frontal bone

  – General functions

  • Forms the anterior part of cranium and roof of eye sockets (forehead and eyebrow ridges)

  • Contains frontal sinuses 

  – Joints

  • Parietal, sphenoid, ethmoid, nasal, lacrimal, maxillary, and zygomatic bones
• Frontal bone

  – Regions/markings

  • Forehead, Supra-orbital margin (protects eye), Glabella (between supra-orbital margins), Lacrimal fossa (for lacrimal gland), Frontal sinuses

  – Foramina

  • Supra-orbital foramen – For blood vessels of eyebrows, eyelids, and frontal sinuses

  • Supra-orbital notch – An incomplete supra-orbital foramen
• Temporal bones

  – General functions

  • Form parts of lateral walls of cranium and zygomatic arches

  • Articulate with mandible

  • Surround and protect internal ear

  • Attach muscles of jaws and head

  – Joints

  • Zygomatic, sphenoid, parietal, and occipital bones,and mandible
• Temporal bones

  – Regions/markings

  • Squamous part

  • Zygomatic process

  • Mandibular fossa

  • Mastoid process – filled with air pockets

  • Styloid process – many neck muscles attach

  • Petrous part

  • Auditory ossicles
• Temporal bones - Regions/markings

  • Squamous part – Borders the squamous suture

  • Zygomatic process – Inferior to the squamous part

  – Articulates with temporal process of zygomatic bone

  • Together, these processes form zygomatic arch

  • Mandibular fossa

  – Site of articulation with mandible
• Temporal bones - Regions/markings

  ▪ Mastoid process

  – For muscle attachment

  – Contains mastoid cells that connect to middle ear cavity

  ▪ Styloid process

  – Attaches tendons and ligaments of the hyoid, tongue, and pharynx

  ▪ Petrous part

  – Encloses structures of internal ear

  ▪ The auditory ossicles

  – 3 tiny bones in tympanic cavity (middle ear)

  – Transfer sound vibrations from tympanic membrane (eardrum) to internal ear
• Temporal bones 

  – Foramina

  • Carotid canal for internal carotid artery

  • External acoustic meatus ends at tympanic membrane

  • Stylomastoid foramen for facial nerve 

  • Internal acoustic meatus contains

  – Blood vessels and nerves of internal ear 

  – Facial nerve
• Sphenoid

  – General functions

  • Forms part of the floor of the cranium 

  • Strengthens sides of the skull

  • Unites cranial and facial bones

  – Contains sphenoidal sinuses 

  – Joints

  • Ethmoid and frontal, occipital, parietal, and temporal bones, palatine bones, zygomatic bones, maxillae, and vomer
• Sphenoid - Regions/markings

  • Body

  – Forms central axis of the sphenoid

  • Sella turcica

  – Saddle-shaped enclosure

  – On superior surface of the body

  • Hypophyseal fossa

  – A depression within the sella turcica 

  – Holds the pituitary gland
• Sphenoid - Regions/markings

  • Sphenoidal sinuses

  – On either side of the body 

  – Inferior to the sella turcica

  • Lesser wings

  – Extend horizontally anterior to sella turcica

  • Greater wings

  – Extend laterally from the body

  – Form parts of cranial floor and posterior wall orbit

  – Sphenoidal spine lies at corner of each wing

  • Pterygoid processes

  – Form pterygoid plates

  – To attach muscles of the lower jaw and soft palate
• Sphenoid – Foramina*** (where)

  • Optic canals for optic nerves

  • Prechiasmatic sulcus (optic groove) 

  • Superior orbital fissure

  – For blood vessels and nerves of the orbit

  • Foramen rotundum and foramen ovale

  – For blood vessels and nerves of face and jaws

  • Foramen spinosum

  – For blood vessels and nerves of membranes
• Ethmoid

  – General functions

  • Forms

  – Anteromedial floor of the cranium

  – Roof of the nasal cavity

  – Part of the nasal septum and medial orbital wall

  • Contains ethmoidal cells (network of sinuses) 

  – Joints

  • Frontal bone, sphenoid, maxillae, nasal, lacrimal, palatine bones, inferior nasal conchae, and vomer
• Ethmoid

  • Cribriform plate

  – Forms roof of nasal cavity and floor of cranium (part)

  – Contains crista galli to attach falx cerebri

  • Ethmoidal labyrinths

  – Consist of ethmoidal cells (air-filled cavities) 

  – Superior nasal conchae

  – Middle nasal conchae

  • Perpendicular plate

  – Forms part of nasal septum
• Ethmoid

  – Foramina

  • Olfactory foramina

  – In the cribriform plate 

  – For olfactory nerves
• Maxillae

  – Regions/markings

  • Orbital rim protects eye and other structures
  • Anterior nasal spine attaches anterior nasal septum
  • Alveolar process supports upper teeth
  • Palatine processes form most of hard palate
  • Maxillary sinuses lighten the bone
  • Nasolacrimal canal protects lacrimal sac and nasolacrimal duct
• Maxillae

  – Foramina

  • Infra-orbital foramen

  – For sensory nerve to brain (via foramen rotundum of sphenoid)

  • Inferior orbital fissure

  – For cranial nerves and blood vessels
• Palatine bones

  – Regions/markings

  • Horizontal plate forms posterior part of hard palate

  • Perpendicular plate extends from horizontal plateto orbital process of orbit floor

  – Foramina

  • Many in the lateral portion of the horizontal plate

  • For small blood vessels and nerves of roof of the mouth
• Nasal bones

  – General functions

  • Support bridge of the nose

  • Connect to cartilages of distal parts of the nose that extend to external nares 

  – Joints

  • With each other, ethmoid, frontal bone, and maxillae
• Vomer

  – General functions

  • Forms inferior portion of the bony nasal septum

  – Joints

  • Maxillae, sphenoid, ethmoid, and palatine bones 

  • Cartilaginous part of the nasal septum
• Zygomatic bones

  – General functions

  • Contribute to rims and lateral walls of orbits

  • Form parts of zygomatic arches

  – Regions/markings

  • Temporal process

  – Meets the zygomatic process of temporal bone

  – Foramin

  • Zygomaticofacial foramen

  – For a sensory nerve of cheek
• Lacrimal bones

  – Smallest facial bones

  – General functions

  • Form parts of medial walls of orbits
• Mandible

  – General functions

  • Forms the lower jaw

  • body (horizontal) and alveolar part supports teeth

  • On each ramus

  – Condylar process articulates with temporal bone at temporomandibular joint

  – Coronoid process - insertion point for temporalis muscle (closes the jaws)

  – Mandibular notch separates condylar and coronoid processes
• Mandible

  – Foramina

  • Mental foramina

  – For sensory nerves of lips and chin

  • Mandibular foramen

  – Entrance to mandibular canal

  – For blood vessels and nerves of lower teeth
• Hyoid bone

  - supports larynx

  - body, lesser horns, greater horns: for muscles of tongue, larynx, pharaynx
• Orbit (eye socket)

  - 7 bones come together to form orbital complex for each orbit

  - Frontal, Zygomatic, Maxilla, Lacrimal, Ethmoid, Sphenoid, Palatine,
• Nasal complex

  - Made up of bones enclosing nasal cavities and

  paranasal sinuses
• Paranasal sinuses

  – Air-filled chambers connected to nasal cavities

  • Lighten skull bones

  • Contain mucous epithelium

  – Releases mucus into nasal cavities
• Infant skull

  – Grows rapidly

  – Is large compared to the body

  – Has many ossification centers

  – Fusion of bones is not complete at birth

  • Two frontal bones

  • Four occipital bones

  • Several sphenoid and temporal elements
• Fontanelles

  – Large areas of fibrous connective tissue 

  – Cover unfused sutures in the infant skull 

  – Allow the skull to flex during birth