THE SKELETON

CHAPTER 7

Introduction A strong, yet light, internal support for

the human body The skeleton is adapted for the

protection, locomotor, and manipulative functions

The upright stance increases the ability of the skeletal muscle to resist gravity

Introduction The skeleton maintains its upright

position through a series of compensating curves

The skeleton accounts for approximately 20% of the body mass

The 206 bones of the body are grouped into the axial and appendicular skeleton

Introduction

Axial skeleton Forms the long axis

of the body 80 bones in three

major regions– skull

– vertebral column

– bony thorax• Ribs

• Sternum

Appendicular Bones of upper &

lower extremities and girdles

126 bones in three major regions– Girdles

• Shoulder girdle

• Pelvic girdle

– upper extremity

– lower extremity

THE SKULL

SECTION I

The Skull The skull is the body’s most complex

bony structure It is formed by two sets of bones, the 8

cranial bones and the 14 facial bones These 22 bones combine to form the

cranial cavity and the facial features In addition, there are 3 bones in each

inner ear to assist in sound transmission

The Skull: Introduction The bones of the skull provide . . .

– A case to house the brain, the cranium– A framework for the face– Cavities to house the organs of sight, taste,

and smell– Passages for air and food– Attachment sites for the teeth– Attachment sites for muscle

The Skull: Introduction Most bones of the skull are flat bones Except for the mandible, all bones are firmly

united by interlocking sutures The major sutures of the skull are . . .

– Coronal (Between Frontal & Parietal)– Sagittal (Between Parietal bones) – Squamosal (Between Parietal & Temporal)– Lambdoidal (Between Parietal & Occipital)

Other skull sutures connect facial bones and are named after these structures

________________________________________________SagittalSagittal

CoronalCoronal

LambdoidLambdoid

SquamousSquamous

Overview of Skull Geography

Facial bones form the anterior aspect The cranial bones enclose the brain

Vault The cranial vault

or calvaria forms the superior, lateral, and posterior aspects of skull

The cranial base forming the inferior aspect of skull

Cranial Base Cranial base forms

the skull’s inferior aspect

Three prominent ridges divide the base into fossae

The brain rests on these cranial fossae completely enclosed by the cranial vault

The brain occupies the cranial cavity

Cavities of the Skull In addition to the large cranial cavity

there are many smaller cavities– Middle and inner ear cavities– Nasal cavity– Orbits of the eyes– Several bones contain air filled sinuses

• Sinuses surrounding the nasal cavity are referred to as the paranasal sinuses

Study Note

As you read about the bones of the skull, locate each bone on the different skull views in Figures 7.2, 7.3, 7.4

The skull bones and their important markings and features are summarized in Table 7.1 on pages 213-214

Cranium

The 8 cranial bones include; 2 parietal, 2 temporal frontal, occipital, sphenoid, ethmoid

Cranium is self- bracing allowing the bones to be thin, yet strong

Frontal bone Forms the

anterior portion of the cranium, the forehead, roofs of the orbits, and most of the anterior cranial fossa

Frontal bone - landmarks Frontal

squama Supraorbital

margins Supraorbital

foramen Orbits Anterior

cranial fossa Glabella Frontal

sinuses

Parietal bones Forms most of

the superior & lateral aspects of the skull

Articulates with other cranial bones to form four major sutures

ParietalParietal

Parietal bones - landmarks

The four largest sutures cranial sutures, Coronal, Sagittal, Lambdodial, Squamosal

Occipital bone Forms most of

the posterior wall and base of skull

Articulates with parietal & temporal

Joins w/ sphenoid in the cranial floor

Forms internal walls of posterior cranial fossa

Occipital bone - Ext. landmarks Foramen magnum,

Occipital condyles, External occipital protuberance, Nuchal lines, External occipital crest

Occipital bone - Int. landmarks

Hypoglossal canal, Posterior cranial fossa

Temporal Bone Forms the infero-

lateral aspects of the skull

Parts of the cranial floor

Divided into four regions; squamous tympanic, mastoid, and petrous-(int)

Temporal Bone The internal

petrous region contributes to the cranial base

The petrous region and the sphenoid bone form the middle cranial fossa

Temporal Bone - landmarks Zygomatic

process– Meets the

zygomatic bone

– Forms the cheek

Mandibular fossa– Receives

condyle of mandible

Temporal Bone - landmarks External

Auditory Meatus– Middle and

inner ear Styloid

process– Muscle of

tongue Mastoid

process– Muscles of

neck

Temporal bones - landmarks Jugular

foramen– Entry point for

the Jugular artery

Internal acoustic meatus– Entry point for

the auditory nerve

Jugular ForamenJugular Foramen

Temporal bones - landmarks Stylomastoid

foramen– exit for facial

nerve Carotid canal

– entrance for the carotid artery which supplies blood to cerebral hemispheres

Sphenoid bone Bone spanning the

width of middle cranial fossa

Articulates as central wedge of all cranial bones

Consists of central body and three processes; greater and lesser wings and pterygoid process (pos. view)

Sphenoid - landmarks

Sella turcica (enclosure for pituitary gland) Optic foramina (passage of optic nerves) Superior orbital fissure (Nerves III, IV, V enter orbit) Foramen rotundum & ovale (Cranial Nerve V to face) Foramen spinosum (Middle meningeal artery)

Ethmoid bone Forms most of

the area between the nasal cavity & orbits of eyes

Lies between nasal bones & sphenoid

Complex shape gives rise to nasal septum, sinuses and cribiform plate

Ethmoid bone - landmarks Cribiform plates

– Forms roof of nasal cavity

Olfactory formina– Olfactory nerves

enter brain Crista galli

– Attachment of the dura mater which secures brain in cavity

Ethmoid bone - landmarks Perpendicular

plate– Forms superior

part of nasal septum

Lateral mass– House ethmoid

sinuses Nasal concha

– Project into nasal cavity

Orbital plates– Medial walls of

orbits

Facial bones Consists of 14

bones w/ only mandible and vomer unpaired

Others include maxillae, lacrimals, nasals, zygomatics, inferior nasal conchae, and palatines (not pictured)

Mandible Forms the lower

jaw Largest,

strongest bone of the face

It has a body and two upwardly projecting sections called rami

Houses lower dentition

Mandible - landmarks Mandibular angle Mandibular notch Coronoid process Mandibular

condyle Alveolar margin Mandible formina Mental formina Ramus of

mandible

Maxillary bone Forms upper

jaw and central portion of facial skeleton

Fused medially Articulates with

all facial bones except mandible

Upper dentition Forms 2/3 of

hard palate of the mouth

MaxillaryMaxillarybonebone

Zygomatic Zygomatic processprocess

Maxillary bones - landmarks Alveolar margin

– Upper dentition Frontal process

– Forms lateral aspects of nose

Zygomatic process– Articulates with

zygomatic bone Maxillary

sinuses – (Fig. 7.11)

Maxillary bones - landmarks Palatine

processes– Forms roof of

mouth Incisive fossa

– Passage of nerves and blood vessels

Infraorbital foramen– Infraorbital

nerve and blood vessel to face

Palatine ProcessPalatine Process

Maxillary bones - landmarks Inferior

orbital fissure– Located deep

within the orbit

– Permits passage of the zygomatic nerve, maxillary nerve, and blood vessels to reach face

Zygomatic bones Commonly called

the cheekbones Form prominences

of cheeks and inferolateral margins of orbits

Articulate with the Zygomatic process of temporal bone and Zygomatic process of maxallae

Zygomatic Zygomatic bonebone

ZygomaticZygomaticProcess of Process of TemporalTemporal

Nasal bones Forms bridge of

the nose Thin,

rectangular shape

Fused medially Articulate with

the frontal bone and maxillary bones laterally

Nasal cartilages– (Fig. 6.1)

Lacrimal Bones Forms part of

the medial border of each orbit

Articulates with frontal, ethmoid & maxillae

Forms part of Lacrimal fossa– Permits tears to

drain from orbit to nasal cavity

Lacrimal Bones Lacrimal fossa

– Permits tears to drain from orbit to nasal cavity

Palatine bones The horizontal

plates forms the posterior portion of hard palate

Vertical plate forms part of the posterolateral wall of nasal cavity and a small portion of orbit

Palatine bones - landmarks Horizontal plate

– Posterior section of hard palate

Vertical plate– Part of the

posteriolateral walls of nasal cavity

Orbital surface– Part of inferior

medial aspect of orbit

Vomer Forms part of

the nasal septum

Discussed with the nasal cavity

Vomer - landmarks Plow shape

– Divides nasal septum into right and left parts

Inferior Nasal Conchae Form lateral

walls of nasal cavity

Project medially from the lateral walls of nasal cavity

Largest of nasal conchae

Inferior Nasal Conchae - Landmark

The Inferior nasal conchae is just one of three in the nasal cavity

Superior and middle concha are on the Ethmoid bone

The Orbits The orbits are bony cavities within which

the eyes are encased and cushioned by fatty tissue

The muscles that move the eyes and the tear producing lacrimal glands are housed within the orbit

Formed by frontal, sphenoid, maxilla, zygomatic, lacrimal palatine & ethmoid

Contain superior & inferior orbital fissures Optic foramina

The Orbits

Nasal cavity The nasal cavity is constructed of bone

and hyaline cartilage The cavity is divided into right and left

parts by the nasal septum Superior, middle and inferior nasal

concha project into the cavity The nasal septum and conchae are lined

with mucus-secreting mucosa

Nasal cavity Roof of the

cavity is the cribriform plates of ethmoid

Lateral walls are the superior, middle, and inferior conchae, and vertical plates of palatines

CribriformCribriformplateplate

Nasal cavity Floor of cavity is

formed by palatine processes of the maxillae and the palatine bones

Septum is formed by vomer and the perpendicular plate of ethmoid

Paranasal sinuses Five skull bones; frontal, sphenoid,

ethmoid, and the paired maxillary contain mucus-lined, air-filled sinuses

Cluster around nasal cavity Connected to nasal cavity to allow air to

enter and mucus to drain Lighten skull, warm and humidify air,

enhance voice resonance

Paranasal sinuses Note positioning

around nasal cavity

Paranasal sinuses Sphenoid sinus Frontal sinus Ethmoid sinus Maxillary

sinuses

Hyoid bone Not really a part of the skull, it is unique

in that it is the only bone that does not articulate with any other bone

Positioned just inferior to the mandible Anchored by stylohyoid ligaments to the

styloid processes of temporal bone Acts as a movable base for the tongue

Hyoid bone

Body– Neck muscle

attachment Greater horn

– Neck muscle attachment

Lesser horn

THE VERTEBRAL COLUMN

SECTION II

Vertebral Column:General Characteristics

Formed from 26 irregular bones It contains four distinct curvatures It provide axial support for the trunk Transmits weight of trunk to lower limbs Protects spinal cord Attachment site for ribs and muscles Separated by intervertebral discs There are 24 vertebrae, a sacrum (5 fused)

and a coccyx (4 fused)

General Characteristics Alignment

– Anterior/ posterior

– Lateral Curvatures

– Compensatory curves

Features– Weight bearing

– Muscle attachment

– Protection

RegionalCharacteristics Cervical C1-C7

– Neck / movable Thorasic T1-T12

– Rib cage / limited movement

Lumbar L1-L5– Low back / movable

Sacral 5 fused– Joins the pelvis

Coccyx 4 fused– Terminus

Clinicaldeviations Scoliosis

– An abnormal lateral curvature of the spinal column

– Curvature can occur in an “S” or “C” deviation

Clinical deviations Kyphosis

– An exaggerated dorsal curvature in the dorsal region

– Common is aged individuals because of osteoporosis

Clinical deviations Lordosis

– Accentuated lumbar curvature

– Being overweight or pregnant causes an excessive load up front

Curves develop in response to:Curves develop in response to:Upright postureUpright postureWeight bearingWeight bearing

MusculatureMusculature

Characteristics - Ligaments Ligaments hold the

vertebral column in an upright position– The broad Anterior

Longitudinal Ligament prevents hyperextension and is quite strong

– The cord like Posterior Longitudinal Ligament prevents hyperflexion and is relatively weak

Characteristics - Ligaments Ligaments

also connect specific vertebra and support disc position– Supraspinos

ligament

– Ligamentum flavum

– Interspinous ligament

Intervertebral Discs Intervertebral discs are cushion like pads

interposed between vertebra The discs provide elasticity and

compressibility Compression flattens discs Discs are thickest in the cervical and

lumbar to provide flexibility

Characteristics - discs Annulus fibrosus

surrounds the outer margin– Collagen fibers

Nucleus pulposus is the semi fluid substance which shifts under body weight & pressure

Herniation of disc Herniation Herniation of diskof disk

General structure of vertebrae Common pattern

– Body or centrum

– Vertebral arch• lamina

• pedicle

– Vertebral foramen

– Spinous process• Muscles attach

– Transverse process

• Muscles attach

General structure of vertebrae Interlocking

pattern– Superior and

inferior processes interlock

– The inferior from above and the superior from the vertebrae below form a movable joint

– The movement contributes to spinal rotation

Superior ArticularSuperior ArticularProcessProcess

General structure Pedicles have

notches on their superior and inferior borders

Lateral openings are called intervertebral foramen– Spinal nerves

from spinal cord exit through these foramina

Regional Characteristic: Cervical Body is oval, but wide

side to side C3 - C7 Spinous process is

short and bifid (split) except in C7

Vertebral foramen is triangular

Transverse processes contain foramina for blood vessels leading to brain

Cervical Vertebrae C1 and C2 The first two cervical vertebrae are named

the atlas and axis respectively There is no intervertebral disc between

them They are highly modified for carrying the

skull on top of the vertebral column The atlas (C1) functions are a cradle to

support the head The axis (C2) functions as a pivot point for

the rotation of the atlas

Cervical Vertebrae C1

Lateral masses articulates with the occipital condyles of the skull

Cervical Vertebrae C1

Inferior articular surface articulates with C2 below

Body of the Body of the Vertebrae is Vertebrae is

missing missing

Cervical Vertebrae C2 The axis has the

odontoid process or dens is its unique feature

The dens is the missing body of the atlas which fuses with the atlas during embryonic development

Regional Characteristic: Cervical Spinous processes

project directly posteriorly

Superior facets directed superoposteriorly

Inferior facets directed inferoanteriorly

Flexion/extension, lateral flexion and rotation

Regional Characteristic: Thoracic

Body is larger than cervical; heart shaped

Spinous process is long and sharp

Vertebral foramen is circular

Transverse processes project posteriorly and bear facets for ribs

Regional Characteristic: Thoracic Body bears two

costal demifacets Spinous processes

projects inferiorly Superior facets

directed posteriorly Inferior facets

directed anteriorly Rotation, limited

lateral flexion, flexion/extension prevented

Regional Characteristic: Lumbar

Body is massive and kidney shaped

Spinous processes are short and blunt

Vertebral foramen is triangular

Transverse processes are perpendicular to spinous process but has no special features

Regional Characteristic: Lumbar Spinous process

projects posteriorly Superior facets

directed medially Inferior facets

directed laterally Flexion/extension,

some lateral flexion, rotation prevented

Sacrum The triangular shaped structure formed

by five fused vertebrae Forms the posterior wall of the pelvis Articulates with L5 of the vertebral

column Articulates with the iliac bone of the

pelvic girdle Transfers the weight of the upper torso

and limbs to the lower extremities

Sacral Ala are fused remnants

of transverse processes that articulate with hip bones to form the sacro iliac joints of the pelvis

Sacral promontory – Center of gravity is 1 cm

posterior of this point Transverse line are sites

of vertebral fusion Sacral foramina

transmit blood vessels and nerves

SacralSacralpromontorypromontory

AlaAla

Sacral On the posterior aspect

median sacral crest are fused spinous processes

The vertebral canal continues inside the sacrum as the sacral canal

Sacral hiatus is at the inferior end of the sacral canal

Superior articular surface form a joint with the spinal column

Coccyx

Coccyx articulates with sacrum

The Bony Thorax The thorax is the chest which includes

– Thoracic vertebrae posteriorly– The ribs laterally– The sternum and costal cartilages anteriorly

It is cone shaped with its broad opening inferiorly

The thorax forms a bony cage around the heart, lungs and major blood vessels

Functions of The Bony Thorax Protection Attachment point for muscles of the

back, chest, and shoulders The intercostal muscles attach to the

thorax to lift and depress the thorax during respiration

The Sternum The sternum lies in the

anterior midline of the thorax

It is three fused bones – Manubrium

• Jugular notch

• Clavicular notch

– Sternal body• Sternal angle

– Xiphoid process• Xiphisternal joint

Bony Thorax Thorax is the chest and its bony

underpinnings is called the thoracic cage Elements consist of the thoracic vertebrae,

ribs, sternum, and costal cartilages which secure ribs to the sternum

A cone opening inferiorly, the thorax provides a protective cage around the vital organs of the thoracic cavity (heart, lungs, great blood vessels)

Bony Thorax - continued

Provides support for the shoulder girdles Bony attachment points for muscles of the

back, chest and shoulders Intercostal spaces between ribs are occupied

by the intercostal muscles which lift and depress the thorax during breathing

Sternum Located on the anterior

midline of the thorax Consists of three fused

bones; manubrium, body, and xiphoid process

Manibrium articulates with clavicle & 2 ribs

Body with ribs 2 - 7 Xiphoid attachment site

for abdominal muscle

Thorax to Vertebral Column

Ribs

Ribs Twelve pairs forming thoracic cage All attach posteriorly to thoracic vertebrae Curve inferiorly toward anterior body surface Ribs 1-7 attach directly to sternum by

separate costal cartilages and are referred to as true ribs

Ribs 8-10 attach indirectly to sternum by attaching to costal cartilages immediately above

Ribs 11-12 have no anterior attachments and are referred to as floating ribs

Ribs Ribs are bowed

flat bones Long shaft Tear drop shaped

with a costal groove on inner surface

Head of rib has 2 facets to articulate with its vertebrae as well as the one above

Ribs Neck is just

beyond the head Angle of rib Costal cartilages

attach rib to sternum

Attachments are secure but flexible

Ribs Tubercle of rib

articulates with transverse process

Ligaments secure rib to transverse process

Note how the transverse processes of thoracic vertebrae are angled posteriorly

The Appendicular Skeleton Appended to the axial skeleton Pectoral girdle is for manipulation and is

a lighter, less heavily reinforced structure Pelvic girdle is for weight bearing and

locomotion and is a heavier, more robust structure

Differences appear in bone structure, joint structure, ligaments, and muscle