The Axial Skeleton

The SkullThis structure is composed of 27 bones and is formed from cranial and facial bones.

The cranial bones protect the brain and allow attachment for the neck and head muscles.

The SkullThe facial bone have several functions:• Form the frame work for the face• Contain cavities for the senses• Provided openings for air and food• Secure the teeth• Anchor the facial muscles

Sutures• With the exception of the mandible all bones of the adult skull are interlocked by joints called sutures.• The major sutures are the

– Coronal– Sagittal– Squamous– Lambdoid

Figure 7.2a The skull: Cranial and facial divisions and fossae.

Bones of cranium (cranial vault)

Lambdoidsuture

Facialbones

Squamoussuture

(a) Cranial and facial divisions of the skull

Coronalsuture

The FloorThe floor is divided into the

anterior , middle and posterior fossae

Figure 7.2b The skull: Cranial and facial divisons and fossae.

Anterior cranialfossa

Middle cranialfossa

Posterior cranialfossa

(b) Superior view of the cranial fossae

External Features

Anterior and Posterior Aspects of the Skull

• Supraorbital margin is a throw back to our simian cousins

• For us it supports our eye brows

• The Supraorbital foramen is the path for the supraorbital nerve and vessels

Anterior and Posterior Aspects

The superior nuchal and inferior nuchal lines serve as attachment points for muscles and ligaments.

Figure 7.5a Bones of the lateral aspect of the skull, external and internal views.

Coronal suture Frontal bone

Sphenoid bone(greater wing)

Ethmoid bone

Lacrimal bone

Lacrimal fossa

Nasal bone

Zygomaticbone Maxilla

Alveolarmargins

MandibleMental foramen

Parietal bone

Lambdoidsuture

SquamoussutureOccipitalbone

OccipitomastoidsutureExternal acousticmeatusMastoid processStyloid process

Mandibular condyleMandibular notch

Mandibular ramus

(a) External anatomy of the right side of the skull

Mandibular angle Coronoid process

Zygomaticprocess

Temporal bone

Figure 7.7b The floor of the cranial cavity.

Sphenoid

Anterior cranial fossa

Middle cranialfossa

Temporal bone(petrous part)

Posteriorcranial fossaParietal bone

Occipital bone

Foramenmagnum

(b) Superior view of the skull, calvaria removed

Ethmoidbone

Hypophyseal fossaof sella turcica

Lesserwing Greaterwing

Cribriformplate

Crista galli Frontal bone

Olfactoryforamina Optic canal

Foramenrotundum Foramen ovale

Foramenspinosum

Jugular foramen

Foramen lacerum

Figure 7.6b Inferior aspect of the skull, mandible removed.

Hard palate

Mandibularfossa

Mastoidprocess

ZygomaticarchForamen ovale

Foramen lacerumCarotid canal

Styloid process

Jugular foramenOccipital condyle

Foramen magnum

Superior nuchalline(b) Photo of inferior view of the skull

Foramen spinosum

Skull Fractures

Figure 7.11a Detailed anatomy of the mandible and the maxilla.

Coronoidprocess

Mandibular foramen

Mentalforamen

Mandibularangle

Ramusofmandible

Mandibularcondyle

Mandibular notch

Mandibular fossaof temporal bone

Body of mandible

Alveolarmargin

(a) Mandible, right lateral view

Temporomandibularjoint

Broken Jaw

The Hyoid Bone

This is a “U” shaped bone. It is not connected to the skull.

It forms the base for the tongue.

The Spinal Column

The vertebral column consists of 26 irregular bones.

It provides the main axial support for the skeleton.

Figure 7.16 The vertebral column.

Cervical curvature (concave)7 vertebrae, C1–C7

Thoracic curvature(convex)12 vertebrae,T1–T12

Lumbar curvature(concave)5 vertebrae, L1–L5

Sacral curvature(convex)5 fused vertebrae sacrum

Coccyx4 fused vertebrae

Anterior view Right lateral view

Spinousprocess

Transverseprocesses

Intervertebraldiscs

Intervertebralforamen

The Spinal Column

There are 7 cervical vertebrae

12 Thoracic vertebrae

5 Lumbar vertebrae

5 Sacral vertebrae

You have breakfast at

You have lunch at 12

You have dinner at 5

You have to go to the bathroom at 5 am

The Spinal Column

The major supporting ligaments are the anterior and posterior longitudinal ligaments.

Figure 7.17a Ligaments and fibrocartilage discs uniting the vertebrae.

Supraspinous ligamentIntervertebraldisc

Anteriorlongitudinalligament

Intervertebral foramen

Posterior longitudinalligament

Anulus fibrosus

Nucleus pulposus

Sectioned bodyof vertebra

Transverse process

Sectionedspinous process

Ligamentum flavum

Interspinousligament

Inferior articular process

(a) Median section of three vertebrae, illustrating the composition of the discs and the ligaments

The Spinal Column

The anterior ligament attaches to the vertebrae and discs.

It prevents hyperextension (bending backward)

The posterior ligament is weak and resists hyperflexation.

The Spinal Column

The Intervertebral discs accounts for 25% of your height and acts as a shock absorber.

A herniated or slip discs is a common cause of back injuries.

Figure 7.17c Ligaments and fibrocartilage discs uniting the vertebrae.

Vertebral spinous process(posterior aspect of vertebra)

Spinal nerve root

Anulus fibrosusof disc

Herniated portionof disc

Nucleuspulposusof disc

Spinal cord

(c) Superior view of a herniated intervertebral disc

Transverseprocess

Figure 7.17d Ligaments and fibrocartilage discs uniting the vertebrae.

Nucleuspulposus ofintact disc

(d) MRI of lumbar region of vertebral columnin sagittal section showing herniated disc

Herniatednucleuspulposus

Scoliosis

Scoliosis is an abnormal curvature of the spine which can occur during adolescence, old age or during pregnancy.

Scoliosis

• Lordosis. Also called swayback, the spine of a person with lordosis curves significantly inward at the lower back.

• Kyphosis. Kyphosis is characterized by an abnormally rounded upper back (more than 50 degrees of curvature).

• Scoliosis. A person with scoliosis has a sideways curve to their spine. The curve is often S-shaped or C-shaped

The Cervical Vertebrae

These are the smallest with C1 and C2 modified for the skull.

In general cervical vertebrae have– An oval body– A short spinous process which is split except

for C7– A transverse foramen for the vertebral

arteries.

The Thoracic Vertebrae

There are12 (T1-T12)

These have :

1) Circular vertebral foramen

2)A long spinous process that points downward.

3) Transverse processes have facets for the ribs

Figure 7.20b Posterolateral views of articulated vertebrae.

Transverseprocess

Spinousprocess

Superior articularprocess

Transversecostal facet (fortubercle of rib)

Intervertebraldisc

Inferior costalfacet (for headof rib)Inferior articularprocess

(b) Thoracic vertebrae

The Lumbar Vertebrae

There are 5(L1-L5)

These have :

1) Spinous process is short & flat

2) Vertebral foramen is triangular

3) articular processes face medially or laterally

Superiorarticularprocess

Transverseprocess

Spinousprocess

Intervertebraldisc

Inferiorarticularprocess

(c) Lumbar vertebrae

Figure 7.20c Posterolateral views of articulated vertebrae.

The Sacral Vertebrae

There are 5 (S1-S5)

These are fused and articulates with L5 and the ileum

Figure 7.21 The sacrum and coccyx.

Coccyx

CoccyxAnteriorsacralforamina

Posteriorsacralforamina

Mediansacralcrest

Sacralpromontory

Sacralcanal

Sacralhiatus

BodyFacet of superiorarticular process

Lateralsacralcrest

Auricularsurface

(b) Posterior view

Bodyof firstsacralvertebra

Transverseridges (sites of vertebralfusion)

(a) Anterior view

The Thoracic Cage

This is composed of the ribs, thoracic vertebrae dorsally and sternum ventrally.

Ribs 1-7 are true ribs because they attach directly to the sternum.

The Thoracic Cage

Ribs 8-10 are false ribs because they attach indirectly

The Thoracic Cage

Ribs 8-10 are false ribs because they attach indirectly

Ribs 11 & 12 are floating and are NOT attached to the sternum

Figure 7.22 The thoracic cage.

Intercostal spaces

Xiphisternaljoint

Sternalangle

Jugularnotch

Trueribs(1–7)

Falseribs(8–12)

Jugular notch

Clavicular notch

ManubriumSternal angleBodyXiphisternal jointXiphoid process

VertebraFloatingribs (11, 12) (b) Midsagittal section through the

thorax, showing the relationship of surface anatomical landmarks of the thorax to the vertebral column

(a) Skeleton of the thoracic cage, anterior view

Sternum

Costalcartilage

Costalmargin

Figure 7.23c Ribs.

Junction withcostal cartilage

Shaft Head Neck

Articularfaceton tubercle

Costal angleCostal groove

Facets forarticulationwith vertebrae

(c) A typical rib (rib 6, right), posterior view

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