THE SKELETON

CHAPTER 79/30/2007

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

– The skull has about 85 named openings (foramina, canals and fissures)

Cranium

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

The 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 Articulates with parietal & temporal

Occipital bone 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

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

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

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

PalatinePalatine

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

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

Ethmoidal air cells

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 in adult

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

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

Characteristics - Ligaments

The ligamentum flavum connects the lamina of adjacent vertebrae

The ligamentum flavum contains significant amount of elastic fibers and is especially strong

The ligament stretches forward, then recoils as we straighten to an erect position

Intervertebral Discs Intervertebral discs are cushion like pads interposed between vertebra

The discs provide compressibility of the spine and resist tension on the spine

Compression flattens discs Discs are thickest in the cervical and lumbar regions to which improves flexibility

Intervertebral Discs Discs are pads positioned between vertebral bodies

Two components– Anulus fibrosus

– Nucleus pulposus

Intervertebral Discs Nucleus pulposus is the gelatinous mass that enables the spine to absorb compressive stress

The Anulus fibrosus has an outer ring consisting of ligamentous tissue and an inner ring consisting of fibrocartilage– Functions to contain the nucleus pulposus during compression

– Collagen fibers are organized similar to fibers in osteons forming X’s that resist twisting

Characteristics - discs

Anulus fibrosus surrounds the outer margin

Nucleus pulposus can shift under pressure

Herniated or prolapsed disc typically occurs posteriolaterally compressing nerve roots

Herniation Herniation of diskof disk

Characteristics - discs

MRI of lumbar region showing normal and herniated discs

Note the posterior displacement

Normal Curvatures

Cervical and lumbar are concave

Thoracic and are sacral are convex

Curves increase spinal resiliency

Primary curvatures– Thoracic and sacral

Secondary curvatures– Cervical and lumbar

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

General structure of vertebrae

Common pattern– Body or centrum

– Vertebral arch• lamina• pedicle

– Vertebral foramen• Passage for spinal cord

General structure of vertebrae

Seven different processes project from each arch– Spinous process

– Transverse process

– Superior and inferior articular processes

– Facets

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 as 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

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

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

Disorders of the Axial Skeleton

Abnormal Curvatures Scoliosis

– An abnormal lateral curvature of the spinal column

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

Abnormal Curvatures Kyphosis

– An exaggerated dorsal curvature in the dorsal region

– Common is aged individuals because of osteoporosis

Abnormal Curvatures Lordosis

– Accentuated lumbar curvature

– Being overweight or pregnant causes an excessive load up front

The Axial Skeleton Throughout Life

Fontanels Cleft palate Adult Skeletal Changes

The Fetal Skull

The Axial Skeleton Throughout Life

Discs become thinner and more prone to herniation

Loss of a few centimeters of height

Osteoporosis Rigid thorax (costal cartilage ossification) restricts breathing

Loss of bone mass in facial bones

End of Chapter 7