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
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