• consists of bones, cartilage, joints and ligaments
• composed of 206 bones grouped into 2 divisions:  Axial (80) & Appendicular (126) 

• consists of the skull, vertebral column and bony thorax

• encloses brain
• provides attachment sites for some head and neck muscles
• divided into 2 parts: the cranial vault and the base
• internally, bony ridges divide skull into distinct fossae

• form framework of face
• form cavities for the sense organs
• provide openings for the passage of food and air
• hold teeth in place
• anchor muscles of face

• middle and inner ear cavities
• nasal cavity
• orbits (eyes)
• air-filled sinuses

• foramen, canals, fissures
• provides openings for spinal cords, blood vessels, cranial nerves

The 8 Cranial Bones

• 2 temporal bones
• 2 parietal bones
• 1 frontal bone
• 1 occipital bone
• 1 sphenoid bone
• 1 ethmoid bone

• forms the forehead and roofs of the orbits
• forms superciliary arches
• contains frontal sinuses

• at the top, left and right hemispheres
• coronal suture: where they meet the frontal bone
• squamous suture: where each one meets a temporal bone
• sagittal suture: where the 2 meet each other at the top
• lambdoid suture: where they meet the occipital bone

• forms the posterior (back) side of the cranium
• foramen magnum located at base
• occipital condyles
• hypoglossal foramen
• external occipital protuberance
• superior and inferior nuchal lines

• lies inferior to the parietal bones (by the ears)
• 4 regions: squamous, temporal, petrous and mastoid regions

• spans width of cranial floor
• contains 5 important openings: superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, optic canal

Ethmoid Bone

• lies between the nasal and sphenoid bones
• forms most of the bony region between the nasal cavity and orbits

• lower jawbone; largest and strongest facial bone
• composed of 2 main parts: horizontal body and 2 upright rami

• cheeks 
• articulate with all other facial bones except the mandible
• contains maxillary sinuses - largest paranasal sinuses

1. zygomatic bones
2. lacrimal bones
3. palatine bones

1. lateral wall of orbits
2. medial wall of orbits
3. hard palate

1. nasal bones
2. vomer
3. inferior nasal conchae

1. bridge of nose
2. nasal septum
3. lateral walls of nasal cavity

• located within: frontal bone, ethmoid bone, sphenoid bone, maxillary bone
• lined with mucous membrane

• lies inferior to the mandible
• only bone with no direct articulation with any other bone
• acts as a movable base for the tongue

The Vertebral Column

(from head to tail)

1. Cervical curvature: concave, 7 vertebrae
2. Thoracic curvature: convex, 12 vertebrae
3. Lumbar curvature: concave, 5 vertebrae
4. Sacral curvature: convex, 5 fused vertebrae
5. Coccyx: 4 fused vertebrae

• cushion-like pads between vertebrae
• act as shock absorbers
• compose about 25% of height of vertebral column
• composed of nucleus pulposus and annulus fibrosis

1. nucleus pulposus
2. annulus fibrosis

1. gelatinous inner sphere of disc, enables spine to absorb stresses
2. outer sphere containing the nucleus pulposus, binds vertebrae together and also absorbs stresses

• may be caused by trauma to the spine and/or aging
• nucleus pulposus loses cushioning properties
• annulus fibrosis weakens

• smallest and lightest vertebrae
• C1 - C7
• C1 = the atlas; unlike the others in structure, allows flexion and extension of neck (nodding head 'yes')
• C2 = the axis; has same structure as others, allows rotation (shaking head 'no')

• T1 - T12 
• all articulate with the ribs
• allows rotation and prevents flexion and extension

Lumbar Vertebrae

• L1 - L5
• thick and robust
• allows flexion and extension, prevents rotation

1. Sacral Vertebrae 
2. Coccyx

1. S1 - S5; attached to pelvis
2. tailbone; offers some support to pelvic organs

• forms the framwork of the chest
• components: thoracic vertebrae, ribs, sternum and costal cartilage
• protects thoracic organs
• supports girdle and upper limbs
• provides attachment site for muscles

1. Manubrium - top part
2. Body - bulk of the middle
3. Xiphoid process - bottom end

1. Jugular notch - indentation at the top of the manubrium
2. Sternal angle - ridge where the manubrium meets the body of the sternum

• 12 of them
• the superior 7 are true ribs (attached to sternum)
• the inferior 5 are false ribs
• ribs 11 and 12 are floating ribs

Disorders of the Axial Skeleton

1. Scoliosis
2. Kyphosis
3. Lordosis

1. abnormal lateral curvature
2. exaggerated thoracic curvature
3. exaggerated lumbar curvature

1. primary curvatures - thoracic and sacral curvatures  (infant is c-shaped at birth
2. secondary curvatures - cervical and lumbar curvatures (develop when a baby begins to walk)

• water content of the intervertebral discs decreases
• by age 55, loss of a few cm in height is common
• thorax becomes more rigid
• bones lose mass