Chapter 7

Axial Skeleton
Chapter 7

Skull

Cranial Bones (8)
Facial Bones (14)
Cavities: Cranial, Nasal, Sinuses, Middle & Inner Ear Chambers, Orbits.

Chico state - skull module Great site for practicing bone identification!
Skull Anatomy Tutorial (Another great site!)
Axial Skeletal Overview
Nose & paranasal sinuses

Cranium:
Frontal Bone (1). Forms superior portion of orbit; Frontal sinus.
Since it forms from two embryonic bones, it can be two bones in the adult with the "metopic suture" between left and right frontals.

Parietal (2) . Top of skull. Simple bones

Temporal (2). Complex bone. Four regions.

Squamous: flattened region on side of skull. Also has zygomatic process, mandibular fossa.
Tympanic : External auditory meatus & styloid process (site of muscle attachment).
Mastoid: posterior to meatus, mastoid process is a site of muscle attachment, passage for facial nerve. Has a sinus.
Petrous: internal; passageways for carotid artery and jugular vein.

Occipital (1). Base of skull; foramen magnum; occipital condyles (paired on side of foramen magnum); Wormian bones often formed at suture; occipital protuberance--area is site of muscle attachment.

Sphenoid (1). "Winged" bone. Spans the ventral aspect of cranium.
Sella Turcica or "Turkish Saddle" is a support for pituitary gland; numerous foramina.
Called the "keystone bone" because it articulates with all other cranial bones.
Pop Quiz: which state is called the Keystone State and why?

Ethmoid (1). Forms perpendicular plate of nasal septum; concha; passageway for olfactory nerves.

Facial Bones

Bones of skull not in contact with brain.
Provides basic shape of face. Teeth and muscle attachment.

Maxilla
Paired. Supports upper teeth. Alveoli = sockets.
Each maxilla has: Incisors (2), canine (1), premolars (2), molars (3).
Forms part of hard palate. Function.
Maxillary sinus.

Palatine.
Small paired bones. Forms posterior portion of hard palate (horizontal plates).

Zygomatic: Forms part of zygomatic arch with temporal bone.

Nasals: Small, paired bones = bridge of nose.

Lacrimal: Lacrimal sulcus (nasolacrimal canal--tear drainage).

Inferior nasal concha
Lateral wall of nasal cavity. Other conchae are part of ethmoid bone.
Concha = "snail" - (curved or coiled structure)

Vomer
Thin, plate-like (vomer = "plow") bone which forms part of nasal septum.
Shape is similar to blade of horse-drawn plows (image from www.usda.gov)

Other Bones of Head Region

Mandible

Jaw bone. Supports 16 teeth which occlude with 16 teeth of 2 maxillas.
Articulates with mandibular fossa of temporal bone..
Body + Rami with condyloid process (jaw articulation) and coronoid process (attachment of temporalis muscle).

Hyoid

Suspended in neck via stylohyoid ligaments.
Body + greater and lesser cornu (horns).
Attachment for muscles of tongue and neck muscles. Elevates when swallowing.

Hyoid and pharynx image

Middle Ear Ossicles
Malleus, Incus and Stapes.
Transfer and amplify sound impulses.
Ossicles and surgical considerations
Computer model of ossicles

Vertebral Column

Functions

Support head & upper extremities while allowing movement.
Attachments for muscles, ribs, pectoral & pelvic girdles, and visceral structures.
Protect spinal cord and permit passage of spinal nerves along with some vessels.

Vertebral column - interactive tutorial site
Back - Surface Anatomy and Vertebral Column

26 movable vertebrae separated by intervertebral discs. The discs are made of fibrocartilage giving them flexibility and the ability to withstand stress.

(Intervertebral discs will be discussed in Chapter 9, Articulations)

33 vertebral units. 5 regions.

Cervical (7)

Thoracic (12)

Lumbar (5)

Sacral (5 fused)

Coccygeal (3-5 fused)

General Structure
Test Yourself on vertebral anatomy!

Curvatures: Vertebral column is S-Shaped.

Cervical, Thoracic, Lumbar and Pelvic curvatures.
Change during growth. Thoracic and Pelvic curvatures are "primary"
Cervical and lumbar curvatures are "secondary."

General Structure of Vertebrae:

Body (Centrum), Neural arch (supported by pedicle, arch formed by lamina). Vertebral foramen.
Processes: Spinous process, transverse processes, articular processes.

Regional Characteristics

Cervical: Transverse foramen on each side for vertebral vessels.
Atlas (C1) and axis (C2) (pivot for head).

Atlas
Superior View
Inferior View

Axis - has dens or odontoid process (for pivot joint) -- occupies area of body of axis.
Superior View
Inferior View
Lateral View

Cervical Vertebra ("generic" - C3-C6): bifid spinous process

Seventh cervical vertebra (C7) has blunt spinous process (vertebral prominens)

Thoracic: Facets for rib articulations. Spinous processes point down.
Superior View
Inferior View
Lateral View

Lumbar: Heavy and thick bodies. Short, blunt spinous processes.
Superior View
Inferior View
Lateral View

Sacrum: Wedge shaped, 5 fused vertebrae (transverse lines are sites of fusion).
Sacroiliac articulation.Sacral promontory. Base. Apex. Sacroiliac articulation (auricular surface)
Sacrum: superior view

Coccyx: 3-5 small triangular often fused vertebrae. First coccygeal vertebra has cornua (horns).

Rib Cage

12 Thoracic vertebrae and 12 Paired ribs
Costal Cartilage
Sternum

General Anatomy
Bony Parts of Thoracic Wall
Surface Anatomy of Thorax

Functions:

Supports pectoral girdle (sternum--clavicle--scapula)
Protects thoracic viscera (heart & lungs)
Involved in breathing
Sternum is a site of red bone marrow.

Sternum (breastbone): 3 "separate" bones. Manubrium ("shield'), body and xiphoid process.

Manubrium has clavicular notch (sternoclavicular joint)--articulation with clavicle. Jugular notch at top.

Sternum (manubrium and body) is site for rib connection via costal cartilage.

Xiphoid process is site for abdominal muscle attachment. Last cartilage in body to ossify.

Ribs

12 pair. Each pair attached to 1 or 2 thoracic vertebra.
First 7 pair are "true ribs" : They have their own costal cartilages.
Ribs 8, 9 & 10 are "false ribs" : They share costal cartilage of rib 7.
Ribs 11 & 12 are floating ribs: no attachment to sternum.

Note: Both men and women have 12 pairs of ribs!
(But what about the creation story in Genesis? What about Tracy and Hepburn in Adam's Rib?)

Rib structure:

Elongate and flattened. Head, neck, angle and shaft (common to all ribs).
Tubercle: first 10 pair have this for articulating with transverse process of thoracic vertebrae.
Space between ribs is called the intercostal spaces; occupied by intercostal muscles.

Clinical Considerations of Axial Skeleton

Cleft Palate: incomplete fusion of palatine process of maxillary and palatine bones forming the hard palate.

Spina bifida: Laminae of vertebra(e) do not fuse resulting in exposed spinal cord.

Abnormal Curvatures:

Kyphosis: hunchback condition. Abnormal thoracic curvature.
Scoliosis: Abnormal thoracolumbar curvature--lateral deviation.
Lordosis: "swayback" or exaggerated lumbar curvature.

Normal & Abnormal spinal anatomy (abnormal has scoliosis, kyphosis, etc)
Scoliosis
Scoliosis - Univ. of Utah
Scoliosis overview - good diagrams and radiograms.
Scoliosis - gross anatomy with X-ray link

Cervical Ribs: Small ribs can develop from lower (typically 7th) cervical vertebrae.
Sometimes related to thoracic outlet syndrome.

LUMEN's Bone Box

From the "History is Weird Files"Galileo's Fifth Lumbar Vertebra