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Chapter 8
The Skeletal System
• Overview of the skeleton
• The skull
• The vertebral column and
thoracic cage
• The pectoral girdle and
upper limb
• The pelvic girdle and
lower limb
Overview of the Skeleton
• Regions of the skeleton
– axial skeleton forms the central axis
• skull, vertebral column, ribs, sternum and sacrum
– appendicular skeleton includes the limbs & girdles
• Number of bones
– 206 in typical adult skeleton
• varies with development of sesamoid bones (patella)
– start at 270 at birth, decreases with age as bones fuse
• Surface markings defined in Table 8.2
• 4 regions of the skeleton = skull, vertebral column & thorax, upper and
lower limbs and girdles
Surface Features of Bones
Axial & Appendicular Skeleton
• Axial skeleton in yellow
– skull, vertebrae, sternum, ribs, sacrum & hyoid
• Appendicular skeleton in blue
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pectoral girdle
upper extremity
pelvic girdle
lower extremity
Major Skull Cavities
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Cranial cavity holds brain
Orbit contains eyeball & extraocular muscles
Ethmoid sinus
Nasal cavity
• Maxillary sinus
• Oral cavity
The Skull
• 22 bones joined together by sutures
• Cranial bones surround cranial cavity
– 8 bones in contact with meninges
• frontal, parietal,
– calvaria (skullcap) forms roof & walls
• Facial bones support teeth & form nasal cavity & orbit
– 14 bones with no direct contact with brain or meninges
– attachment of facial & jaw muscles
Cranial Fossa
• 3 basins that comprise the cranial floor or base
– anterior fossa holds the frontal lobe of the brain
– middle fossa holds the temporal lobes of the brain
– posterior fossa contains the cerebellum
• Swelling of the brain may force tissue through foramen magnum resulting
in death
Frontal Bone
• Forms forehead and part of the roof of the cranium
• Forms roof of the orbit
• Contains frontal sinus
Parietal Bone
• Forms cranial roof and part of its lateral walls
• Bordered by 4 sutures
– coronal, sagittal, lambdoid and squamous
• Marked by temporal lines of temporalis muscle
Temporal Bone
• Forms lateral wall & part of floor of cranial cavity
– squamous part
• zygomatic process
• mandibular fossa & TMJ
– tympanic part
• external auditory meatus
• styloid process for muscle attachment
– mastoid part
• mastoid process
– mastoiditis from ear infection
• mastoid notch
– digastric muscle
Petrous Portion of Temporal Bone
• Forms part of cranial floor
– separates middle from posterior cranial fossa
• Houses middle and inner ear cavities
– receptors for hearing and sense of balance
– internal auditory meatus is opening for CN VII (vestibulocochlear nerve)
Openings in Temporal Bone
• Carotid canal
– passage for internal carotid artery supplying the brain
Occipital Bone
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Rear & much of base of skull
Foramen magnum holds spinal cord
Skull rests on atlas at occipital condyles
Hypoglossal canal transmits hypoglossal nerve (CN XII) supplying tongue
muscles
• External occipital protuberance for nuchal ligament
• Nuchal lines mark neck muscles
Sphenoid Bone
• Lesser wing
Sphenoid Bone
• Body of the sphenoid
– sella turcica contains deep pit (hypophyseal fossa)
– houses pituitary gland
• Lesser wing
– optic foramen contains optic nerve & ophthalmic a.
• Greater wing -- 3 foramen
– foramen rotundum & ovale for brs. trigeminal nerve
– foramen spinosum for meningeal artery
Sphenoid Bone
• Sphenoid sinus
Ethmoid Bone
• Found between the orbital cavities
• Forms lateral walls and roof of nasal cavity
• Cribriform plate & crista galli
• Ethmoid air cells form ethmoid sinus
• Perpendicular plate forms part of nasal septum
• Concha or turbinates on lateral wall
Ethmoid Bone
• Superior & middle concha
Maxillary Bones
• Forms upper jaw
– alveolar processes are bony points
between teeth
– alveolar sockets hold teeth
• Forms inferomedial wall of orbit
– infraorbital foramen
• Forms anterior 2/3’s
of hard palate
– incisive foramen
– cleft palate
Locations of Paranasal Sinuses
• Maxillary sinus fills maxillae bone
• Other bones containing sinuses are frontal, ethmoid & sphenoid.
Frontal
Palatine Bones
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L-shaped bone
Posterior 1/3 of the hard palate
Part of lateral nasal wall
Part of the orbital floor
Zygomatic Bones
• Forms angles of the cheekbones and part of lateral orbital wall
• Zygomatic arch is formed from temporal process of zygomatic bone and
zygomatic process of temporal bone
Lacrimal Bones
• Form part of medial wall of each orbit
• Lacrimal fossa houses lacrimal sac in life
– tears collect in lacrimal sac and drain into nasal cavity
Nasal Bones
• Forms bridge of nose and supports cartilages of nose
• Often fractured by blow to the nose
Inferior Nasal Conchae
• A separate bone
• Not part of ethmoid like the superior & middle concha or turbinates
Vomer
• Inferior half of the nasal septum
• Supports cartilage of nasal septum
Mandible
• Only bone of the skull that can move
– jaw joint formed between mandibular fossa
of temporal bone & condyloid process
• Holds the lower teeth
• Attachment of muscles of mastication
– temporalis muscle onto coronoid process
– masseter muscle onto angle of mandible
• Mandibular foramen
• Mental foramen
Ramus, Angle and Body of Mandible
Bones Associated With the Skull
• Auditory ossicles
– malleus
– incus
– stapes
• Hyoid bone
– suspended from styloid process of skull by stylohyoid muscle and
ligament
– greater & lesser cornua
The Skull in Infancy & Childhood
• Spaces between unfused skull bones called fontanels
– filled with fibrous membrane
– allow shifting of bones during birth & growth of brain in infancy
– fuse by 2 years of age
• 2 frontal bones fuse by age six
– metopic suture
• Skull reaches adult size by 8 or 9 causing heads of children to be larger in
proportion to trunk
General Features of the Vertebral Column
• 33 vertebrae & discs of fibrocartilage between them
• Five vertebral groups
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7 cervical in the neck
12 thoracic in the chest
5 lumbar in lower back
5 sacral fused into the sacrum
4 coccygeal fused into coccyx
• Variations in number of lumbar and sacral vertebrae
Newborn Spinal Curvature
• Spine exhibits one continuous C-shaped curve
• Known as primary curvature
Adult Spinal Curvatures
• S-shaped vertebral column with 4 curvatures
• Secondary curvatures develop after birth
– lifting head as it begins to crawl develops cervical curvature
– walking upright develops lumbar curvature
Abnormal Spinal Curvatures
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Result from disease, posture, paralysis or congenital defect
Scoliosis from lack of proper development of one vertebrae
Kyphosis is from osteoporosis
Lordosis is from weak abdominal muscles
General Structure of a Vertebra
• Body
• Series of vertebral foramen form the vertebral canal
• Neural arch
– 2 lamina
– 2 pedicles
• Processes
– spinous
– transverse
– articular (superior & inferior)
Intervertebral Foramen & Discs
• Intervertebral foramen
– formed from vertebral notches of adjacent vertebrae
– passageway for spinal nerves
Typical Cervical Vertebrae
• Small body and larger vertebral foramen
• Transverse process short with transverse foramen for protection of
vertebral arteries
• Bifid or forked spinous process in C2 to C6
• C7 vertebra prominens
The Unique Atlas and Axis
• Atlas (C1) supports the skull
– concave superior articular facet
• nod your head in “yes” movement
– ring surrounding large vertebral foramen
• anterior & posterior arch
• Axis (C2)
– dens or odontoid process is held in place inside the vertebral foramen of the atlas
by ligaments
– allows rotation of head -- “no”
Atlas & Axis Articulation
Typical Thoracic Vertebrae
• More massive body than cervical but smaller than lumbar
• Spinous processes pointed and angled downward
• Superior articular facets face posteriorly permitting some rotation between adjacent
vertebrae
• Rib attachment
– superior and inferior costal facets on vertebral body and transverse costal facets at ends of
transverse processes for articulation of ribs
Lumbar Vertebrae
• Thick, stout body and blunt, squarish spinous process
• Superior articular processes face medially
– lumbar region resistant to twisting movements
Sacrum (Anterior View)
• 5 separate sacral vertebrae fuse by age 26
• Anterior surface
– smooth & concave
– sacral foramina were intervertebral foramen
• nerves & blood vessels
– 4 transverse lines indicate line of fusion of vertebrae
Sacrum (Posterior View)
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Rough surface of sacrum
Spinous processes have fused into median sacral crest
Transverse processes fuse into lateral sacral crest
Posterior sacral foramina
Sacral canal ends as sacral hiatus
Auricular surface is part of sacroiliac joint
Coccyx
• Single, small, triangular bone
– 4 small vertebrae fused by age of 30
– Co1 to Co4
• Provides attachment site for muscles of pelvic floor
• Cornua
– hornlike projections on Co1 for ligaments attach coccyx to sacrum
• Fractured by fall or during childbirth
Thoracic Cage
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Consists of thoracic vertebrae, sternum & ribs
Attachment site for pectoral girdle and many limb muscles
Protects many organs
Rhythmically expanded by respiratory muscles to draw air into the lungs
Rib Structure
• Flat blade called a shaft
– inferior margin has costal groove for nerves & vessels
• Proximal head & tubercle are connected by neck
• Articulation
– head with body of vertebrae
– tubercle with transverse process
Numbered Rib Articulations
True and False Ribs
• True ribs (1 to 7) attach to sternum with hyaline cartilage
Pectoral Girdle
• Attaches upper extremity to the body
• Scapula and clavicle
• Clavicle attaches medially to the sternum and laterally to the
scapula
– sternoclavicular joint
– acromioclavicular joint
• Scapula articulates with the humerus
– humeroscapular or shoulder joint
– easily dislocated because of its loose attachment
Clavicle
• S-shaped bone, flattened dorsoventrally
• Inferior surface marked by muscle & ligament attachments
• Sternal end is rounded -- acromial end is flattened
Scapula
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Triangular plate that dorsally overlies ribs 2 to 7
Spine ends as acromion process
Coracoid process for muscle attachment
Subscapular, infraspinous and supraspinous fossa
Glenoid fossa is shallow socket for head of humerus
Scapular Features
Upper Limb
• 30 bones per limb
• Brachium or arm contains the humerus
• Antebrachium or forearm contains the radius & ulna (radius on
thumb side)
• Carpus or wrist contains 8 small bones arranged in two rows
• Manus or hand contains 19 bones in 2 groups
– 5 metacarpals in the palm
– 14 phalanges in the fingers
Humerus
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Hemispherical head forms shoulder joint above anatomical neck
Muscles attach to greater & lesser tubercles and deltoid tuberosity
Intertubercular groove holds biceps tendon
Rounded capitulum articulates with radius
Pulleylike trochlea articulates with ulna
Olecranon fossa holds olecranon process of ulna in straightened arm
Forearm muscles attach to medial & lateral epicondyles
Ulna and Radius
• Radius
– head is disc that rotates freely during pronation & supination
• articulates with the capitulum
– radial tuberosity for biceps muscle
• Ulna
– olecranon and trochlear notch form proximal end
– radial notch holds head of ulna
• Interosseous membrane
– ligament attaches radius to ulna along interosseous margin of each bone
Carpal Bones
• Form the wrist
– allows flexion, extension, abduction & adduction
• 2 rows of 4 bones each
– proximal row is scaphoid, lunate, triquetrum & pisiform
– distal row is trapezium, trapezoid, capitate & hamate
Metacarpals and Phalanges
• Phalanges are bones of the fingers
– thumb or pollex has proximal & distal phalanx
– fingers have proximal, middle & distal phalanx
Pelvic Girdle
• Composed of 4 bones:
right & left os coxae,
sacrum and coccyx
• Supports trunk on the legs
& protects viscera
• Each os coxae is joined to
the vertebral column at the
sacroiliac joint
• Anteriorly, pubic bones are joined by pad of fibrocartilage to form pubic
symphysis
• False and true pelvis are separated at pelvic brim
• Infant’s head passes through pelvic inlet & outlet
Os Coxae (Hip Bone)
• Acetabulum is hip joint socket
• Ilium is superior portion
– iliac crest and iliac fossa
– greater sciatic notch contains sciatic nerve
• Pubis is anterior portion
– body, superior and inferior ramus
• Ischium is posterolateral portion
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ischial tuberosity bears body weight if sit
ischial spine
lesser sciatic notch lies between ischial spine & tuberosity
ischial ramus joins inferior pubic ramus
Comparison of Male & Female
• Female less massive, shallower pubic arch greater than 100 degrees, and
pubic inlet round or oval
• Male heavier, upper pelvis nearly vertical, coccyx more vertical, and
pelvic inlet heart-shaped, outlet smaller
Femur
• Nearly spherical head & constricted neck
– ligament to fovea capitis
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Greater & lesser trochanters for muscle attachment
Posterior ridge called linea aspera
Medial & lateral condyles and epicondyles found distally
Smooth patellar surface on anterior femur
Patella and Tibia
• Patella is triangular sesamoid bone
• Tibia is thick, strong weight-bearing bone on medial side of leg
– broad superior head with 2 flat articular surfaces
• medial & lateral condyles
– roughened anterior surface can be palpated below the patella
(tibial tuberosity)
– distal expansion is medial malleolus
Fibula
• Slender lateral strut that helps stabilize the ankle
• Does not bear any of the body’s weight
– use as spare bone tissue to replace bone elsewhere
• Head is proximal end
• Lateral malleolus is distal expansion
• Joined to tibia by interosseous membrane
The Ankle and Foot
• Tarsal bones are shaped & arranged differently from carpal bones due to
load-bearing role of the ankle
• Talus is most superior tarsal bone
– forms ankle joint with tibia & fibula
– sits upon calcaneus & articulates with navicular
• Calcaneus forms heel (achilles tendon)
• Distal row of tarsal bones
– cuboid, medial, intermediate and lateral cuneiforms
The Foot
• Remaining bones of foot are similar in name & arrangement to the hand
• Metatarsal I is proximal to the great toe (hallux)
– base, shaft and head
• Phalanges
– 2 in great toe
• proximal and distal
– 3 in all other toes
• proximal, middle & distal
Foot Arches
• Sole of foot does not normally rest flat on the ground
• 3 springy arches absorb stress of walking
– medial longitudinal arch extends from heel to hallux
– lateral longitudinal arch extends from heel to little toe
– transverse arch extends across the middle of the foot
• Arches held together by short, strong ligaments
– pes planis (flat feet)
X ray of the Right Foot
Bipedalism and Upright Stance
Bipedalism and Limb Adaptations
Bipedalism and Head Position