CHAPTER 7“The Axial Skeleton #2”

Course objectives:

Define and identify the bones of Define and identify the bones of the axial skeletonthe axial skeleton

Vertebral columnVertebral column

composed of composed of 2626 irregularirregular bones. bones.

These bones provide a solid support These bones provide a solid support

structure, but are also remarkably structure, but are also remarkably flexible. flexible.

Regions of the Vertebral Regions of the Vertebral ColumnColumn

– CervicalCervical − neck region 7 vertebrae − neck region 7 vertebrae – ThoracicThoracic – thorax region 12 – thorax region 12

vertebrae vertebrae – LumbarLumbar – lower back 5 vertebrae – lower back 5 vertebrae – SacralSacral – low, low back 1 vertebrae – low, low back 1 vertebrae

(5 fused) (5 fused) – CoccygealCoccygeal – – tail bone 1 vertebrae tail bone 1 vertebrae

(4 fused)(4 fused)

Spinal CurvatureSpinal Curvature

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

Primary curves since they developed first.Primary curves since they developed first.

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

Vertebral columnVertebral column

VertebraeVertebrae

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

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

Cervical vertebrae – C1- C7Cervical vertebrae – C1- C7 Body is oval; spinous process is short (except C-Body is oval; spinous process is short (except C-

7) and sometimes split; 7) and sometimes split; Large vertebral foramen Large vertebral foramen Transverse foramen for vertebral artery to Transverse foramen for vertebral artery to

brainstem.brainstem. C1 is AtlasC1 is Atlas articulates (atlanto-occipital joint) articulates (atlanto-occipital joint)

with occipital bone of skull with occipital bone of skull

-allows “yes” motion of head-allows “yes” motion of head C2 is AxisC2 is Axis characterized by peg-like process characterized by peg-like process

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

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

Cervical VertebraeCervical Vertebrae

AtlasAtlas

Axis Axis

Atlanto/axial jointAtlanto/axial joint

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Atlas

(C1vertebra)

Transverse ligament

Axis C2 vertebrae)

Articular facet of densDens

(c) Axis and atlas, posterosuperior view

Cervical VertebraeCervical Vertebrae

Thoracic vertebrae T1- T12Thoracic vertebrae T1- T12

Body is roughly heart shapedBody is roughly heart shaped Demifacets for rib articulation Demifacets for rib articulation Vertebral foramen are circularVertebral foramen are circular Spinous process long and points Spinous process long and points

inferiorly inferiorly

The thoracic vertebra look like a The thoracic vertebra look like a giraffe’s head when viewed from the giraffe’s head when viewed from the lateral view!lateral view!

Thoracic vertebrae T1- T12

Lumbar Vertebrae L1-L5Lumbar Vertebrae L1-L5 Pedicles and laminae are short and thickerPedicles and laminae are short and thicker Spinous processes are short, flat and Spinous processes are short, flat and

hatchet shapedhatchet shaped Vertebral foramen is triangularVertebral foramen is triangular Inferior and superior processes lock the Inferior and superior processes lock the

adlacent vertebrae together for strength adlacent vertebrae together for strength and stability.and stability.

The lumbar vertebra look like a Moose’s The lumbar vertebra look like a Moose’s head!head!

Lumbar Vertebrae L1-L5

Sacral Vertebrae S1-S5Sacral Vertebrae S1-S5

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

Women sacrum is shorter, wider and more Women sacrum is shorter, wider and more curvedcurved

Connects the spine to the pelvic girdle at Connects the spine to the pelvic girdle at the sacroiliac joint.the sacroiliac joint.

Sacral canal is continuation of vertebral Sacral canal is continuation of vertebral canal. canal.

Sacrum and CoccyxSacrum and Coccyx

Ant. ViewAnt. View

Post view Post view

Coccyx Vertebrae Co1-Co4Coccyx Vertebrae Co1-Co4

Coccyx is Greek for “cuckoo”Coccyx is Greek for “cuckoo” Consists of 4 fused vertebraeConsists of 4 fused vertebrae Fuse between 20 and 30 yearsFuse between 20 and 30 years Tailbone is vestige of tailTailbone is vestige of tail

- Men it points anteriorly- Men it points anteriorly

- Women it points inferiorly - Women it points inferiorly

Cervical and Thoracic Cervical and Thoracic vertebraevertebrae

Lumbar vertebraeLumbar vertebrae

Additional structures of the vertebral Additional structures of the vertebral

columncolumn Intervertebral discsIntervertebral discs

Present between all vertebrae C2- L5/S1;Present between all vertebrae C2- L5/S1; Composed of fibro cartilageComposed of fibro cartilage Two regions of disc:Two regions of disc:

- nucleus pulposis- nucleus pulposis – central core of – central core of discdisc

- annulus fibrosis- annulus fibrosis - outer covering of - outer covering of fibro cartilagefibro cartilage

Function: Function: -discs permit various movements -discs permit various movements

-provide shock absorbing functions for -provide shock absorbing functions for vertebral columnvertebral column

Vertebra and vertebral discVertebra and vertebral disc

Herniated Intervertebral Herniated Intervertebral discsdiscs

Dorsal root ganglion

Spinal cord

Vertebral LigamentsVertebral Ligaments

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

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

(2). Shorter ligaments connect adjoining (2). Shorter ligaments connect adjoining vertebrae together. vertebrae together.

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

Vertebral LigamentsVertebral Ligaments

Bony ThoraxBony Thorax Consists of ribs attached to the vertebral Consists of ribs attached to the vertebral

column and sternumcolumn and sternum True ribs R1-R7 attach directly to True ribs R1-R7 attach directly to

sternumsternum False ribs R8-R10 attach indirectlyFalse ribs R8-R10 attach indirectly Two floating ribs R11 & R12Two floating ribs R11 & R12 The Sternum consisting of:The Sternum consisting of:

- manubrium- manubrium

- body- body

- Xiphoid process- Xiphoid process

Bony ThoraxBony Thorax

RibsRibs1.1. true ribstrue ribs – – the first (superiormost) seven pairs of the first (superiormost) seven pairs of

ribs R1-R7 are directly connected to the sternum ribs R1-R7 are directly connected to the sternum via costal cartilage.via costal cartilage.

- are called - are called vertebrosternal ribsvertebrosternal ribs..

2.2. false ribsfalse ribs – – the remaining five pairs of ribs.the remaining five pairs of ribs.

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

#10 are connected by a single band of costal #10 are connected by a single band of costal cartilage to the inferior portion of the sternum. cartilage to the inferior portion of the sternum. Unlike the first seven pairs of ribs they do Unlike the first seven pairs of ribs they do notnot have their own individual attachments.have their own individual attachments.

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

All ribs articulate with vertebral column. The head All ribs articulate with vertebral column. The head of the rib articulates at a demifacet on the body of the rib articulates at a demifacet on the body of the vertebrae, while the tubercle of the rib of the vertebrae, while the tubercle of the rib articulates at a facet on the transverse process. articulates at a facet on the transverse process.

Sternum “breast plate”Sternum “breast plate”

Anterior central portion of thoraxAnterior central portion of thorax Only bony attachment of axial Only bony attachment of axial

skeleton to appendicular skeleton via skeleton to appendicular skeleton via clavicle.clavicle.

Consists of Manubrium, Body and Consists of Manubrium, Body and Xiphoid processXiphoid process

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

SternumSternum

The sternal foramen is an anomaly and occurs in ~ 4-10% of the population. It can The sternal foramen is an anomaly and occurs in ~ 4-10% of the population. It can be mistaken for a bullet puncture in cases of traumatic death. be mistaken for a bullet puncture in cases of traumatic death.

Hyoid boneHyoid bone Lies inferior to the mandibleLies inferior to the mandible Is not attached to skeleton by bony meansIs not attached to skeleton by bony means Helps movement of base of tongueHelps movement of base of tongue

Hyoid boneHyoid bone