Chapter 8The 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– pectoral girdle

– upper extremity

– pelvic girdle

– lower extremity

Major Skull Cavities

• 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 muscleTemporal lines

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

• Jugular foramen– irregular opening between

temporal & occipital bones

– passageway for drainage of blood from brain to internal jugular vein

Occipital Bone

• 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

• Greater wing

• Body of sphenoid

• Medial and lateral pterygoid processes

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• Perpendicular plate of nasal

septum

Maxillary Bones• Forms upper jaw

– alveolar processes are bony pointsbetween teeth

– alveolar sockets hold teeth

• Forms inferomedial wall of orbit– infraorbital foramen

• Forms anterior 2/3’sof hard palate– incisive foramen– cleft palate

Locations of Paranasal Sinuses

• Maxillary sinus fills maxillae bone• Other bones containing sinuses are frontal, ethmoid &

sphenoid.

EthmoidMaxillarySphenoid

Frontal

Palatine Bones

• 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 fossaof 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

• Auditory ossicles– malleus– incus– stapes

• Hyoid bone– suspended from styloid

process of skull by stylohyoid muscle and ligament

– greater & lesser cornua

Bones Associated With the Skull

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– 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• 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

• Intervertebral discs– bind vertebrae together

– absorb shock

– inner gelatinous nucleus pulposus surrounded by annulus fibrosus (ring of fibrocartilage)

– herniated disc puts pressure on spinal nerve or spinal cord

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)

• 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

• 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

Tubercle Head

Numbered Rib Articulations

True and False Ribs

• True ribs (1 to 7) attach to sternum with hyaline cartilage

• False ribs (8-12)– 11-12 are floating and not

attached to sternum

• 12 pairs of ribs in both sexes

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

• 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• 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

• Metacarpals are bones of the palm– base, shaft & head

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 tothe vertebral column at thesacroiliac 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– 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

• 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