CHAPTER 7“The Axial Skeleton”

Course objectives:

Define and identify the bones of the axial skeleton

Axial Skelton

– 80 total bones

– consists of the bones that form the long axis of the body including the:

• Skull (total 28 with ear bones)

• Vertebral column [(total 26) C7;T12; L5; S1; Co1]

• Bony thorax [ribs and sternum (total 25)]

• Hyoid bone (1)

Skull Bones – the skull has two major divisions:

Cranium and Facial bonesCranium – the 8 bones that enclose the brain.

-1 occipital, 1 frontal, 2 parietal, 2 temporal, 1 sphenoid and 1 ethmoid.

• These typical flat bones of the cranium are connected by a special kind of joint called a suture (Synarthroses).

Cranial bones

Cranial Bones

Cranium

• Made up of 2 major divisions:1. Calvarium (skull cap)

2. Base

• Base contains three large depressions (fossa):– Anterior cranial fossa where the frontal lobes sit– Middle cranial fossa where the temporal lobes sit– Posterior cranial fossa where the cerebellum sits

Cranial Bones

Sutures/Sutural Bones• Sutures (synarthrotic) are immovable fibrous

joints; except for the jaw.

-all bones in the skull are united by sutures.

-Coronal -Sagittal

-Squamous -Lamboid

Sutural bones- small bones that occur within the sutures, especially the lamboid suture. They are not present in all people.

Facial bones• There are 14 bones that can be thought of as

creating the face. • As part of this function they provide:

- protection for many sense organs, -provide anchors for many muscles -create the openings for air and food to

pass.Facial Bones

2-maxilla; 2-palatine; 2-nasal; 2- zygomatic; 2-lacrimal; 2-inf nasal concha; 1- vomer; and 1-mandible

Sphenoid bone

Looks like a Bat in flight. Greater and lesser wings; optic foramen; sella turcica, superior orbital fissure.

Ethmoid bone

• Anterior to

sphenoid bone

forms anterior

base of skull

and nasal cavity.• Cribriform plate.• Crista gali• Perpendicular

plate

Foramen/ Orbits• Foramen: Special openings in bones where

nerves, blood vessels enter into the bone cavity.

- Ex.: Foramen magnum, Supraorbital Infraorbital, Mental, Jugular, Olfactory, Mandibular

• Orbits: Cone shaped bony cavities that hold the eyes, fat, occular muscles and tear glands.

Meatus/ Sinuses

• Meatus: a canal or opening into bone

- Ex.: external auditory, internal acoustic

• Sinus: cavities within bones filled with air.

-Ex.: frontal, ethmoid, sphenoid and maxillary sinuses

Cranial sinuses

• Frontal

• Ethmoid

• Sphenoid

• Maxillary

The Fetal Skull

• Sutures are called fontanels in fetus.

• Fontanels

-Frontal (anterior)

-Occipital (posterior)

-Sphenoidal (anterior lateral)

-Mastoid (posterior lateral)

Vertebral column

• composed of 26 irregular bones.

• These bones provide a solid support structure, but are also remarkably flexible.

Regions of the Vertebral Column

– Cervical − neck region 7 vertebrae

– Thoracic – thorax region 12 vertebrae

– Lumbar – lower back 5 vertebrae

– Sacral – low, low back 1 vertebrae (5 fused)

– COccygeal – tail bone 1 vertebrae (4 fused)

Spinal Curvature

• Thoracic and sacral are concave (i.e. backward)

• Primary curves since they developed first.

• Cervical and lumbar curves are convex (i.e. forward) and secondary curves.

Vertebrae

• Individual vertebrae are found in the cervical, thoracic and lumbar regions of the vertebral column.

• There are significant differences between the vertebrae in each of these regions that you should know.

Cervical vertebrae – C1- C7 • Body is oval; spinous process is short (except C-7)

and sometimes split; • Large vertebral foramen • Transverse foramen for vertebral artery to brainstem.• C1 is Atlas articulates (atlanto-occipital joint) with

occipital bone of skull

-allows “yes” motion of head• C2 is Axis characterized by peg-like process called

“dens” or odontoid process which interlocks with atlas (atlanto-axial joint)

-allows sideward rotation or “no” motion of head.

Cervical Vertebrae

Cervical Vertebrae

Atlanto/axial joint

Thoracic vertebrae T1- T12

• Body is roughly heart shaped

• Demifacets for rib articulation

• Vertebral foramen are circular

• Spinous process long and points inferiorly

• These vertebra look like a giraffe’s head!

Lumbar Vertebrae L1-L5• Pedicles and laminae are short and thicker

• Spinous processes are short, flat and hatchet shaped

• Vertebral foramen is triangular

• Inferior and superior processes lock the adlacent vertebrae together for strength and stability.

• These vertebra look like a Moose’s head!

Sacral Vertebrae S1-S5

• Sacral vertebrae consists of 5 fused vertebrae fully fused by 30 years of age

• Women sacrum is shorter, wider and more curved

• Joins the spine to the pelvic girdle via sacroiliac joint.

• Sacral canal is continuation of vertebral canal.

Sacrum and Coccyx

Coccyx Vertebrae Co1-Co4

• Coccyx is Greek for “cuckoo”

• Consists of 4 fused vertebrae

• Fuse between 20 and 30 years

• Tailbone is vestige of tail

- Men it points anteriorly

- Women it points inferiorly

Additional structures of the vertebral column Intervertebral discs

• Present between all vertebrae C2- L5/S1;

• Composed of fibro cartilage

• Two regions of disc:

- nucleus pulposis – central core of disc

- annulus fibrosis - outer covering of fibro cartilage

• Function: -discs permit various movements

-provide shock absorbing functions for vertebral column

Vertebra and vertebral disc

Slipped Intervertebral discs

Vertebral Ligaments

(1). Anterior and posterior longitudinal ligaments hold vertebral column together along with trunk skeletal muscles

-prevent hyper-extension and hyper-flexion of the vertebral column.

(2). Shorter ligaments connect adjoining vertebrae together.

-There are 3 of these ligaments the ligamentum flavum, the supraspinous ligaments and the interspinous ligaments.

Vertebral Ligaments

Bony Thorax• Consists of ribs attached to the vertebral

column and sternum

• True ribs R1-R7 attach directly to sternum

• False ribs R8-R10 attach indirectly

• Two floating ribs R11 & R12

• The Sternum consisting of:

- manubrium

- body

- Xiphoid process

Bony Thorax

Ribs1. true ribs – the first (superior) seven pairs of ribs R1-

R7 are directly connected to the sternum via costal cartilage.

- are called vertebrosternal ribs.

2. false ribs – the remaining five pairs of ribs.

There are two types of false ribs.» vertebrochondral ribs -- rib pairs #8, #9, and #10

are connected by a single band of costal cartilage to the inferior portion of the sternum. Unlike the first seven pairs of ribs they do not have their own individual attachments.

» floating or vertebral ribs – rib pairs #11 and #12 are connected only to the vertebral column, they have no anterior connection to the skeleton.

Sternum “breast plate”

• Anterior central portion of thorax

• Only bony attachment of axial skeleton to appendicular skeleton via clavicle.

• Consists of Manubrium, Body and Xiphoid process

• Key landmarks: calvicular notches, jugular notch “suprasternal notch”, sternal angle.

Sternum

Hyoid bone• Lies inferior to the mandible

• Is not attached to skeleton by bony means

• Helps movement of base of tongue

Hyoid bone