Chapter 8 The Skeletal System

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Chapter 8 The Skeletal System Powered By Docstoc
					• Axial Skeleton – central supporting axis of the body – skull –
  facial bones – auditory ossicles – hyoid bone – vertebral
  column – thoracic cage

• Appendicular Skeleton – bones of the pectoral girdle and
  the upper limbs – bones of the pelvic girdle and the lower

• Bones of the Skeleton – 206 bones in the adult – there are
  270 bones at birth – bones fuse – by late adolescence to
  mid-20s an individual has the adult bone count – number
  varies even among adults – sesamoid bones
• The Skull – calvaria, base, anterior cranial
  fossa, middle cranial fossa, posterior cranial
• Cavities of the Skull

•   Cranial cavity
•   Orbits of the eyes
•   Middle and inner ear cavities
•   Nasal cavity
•   Buccal cavity
•   Paranasal sinuses – frontal – ethmoid –
    maxillary – sphenoid sinuses
• Frontal bone – supraorbital margin –
  supraorbital foramen – contains frontal
  sinuses – diploe
• Parietal bone – forms most of the cranial roof
  and part of its walls
• Each is bordered by four sutures – sagittal
  suture between the parietal bones – coronal
  suture at the anterior margin – lambdoid
  suture at the posterior margin – squamous
  suture laterally
• Superior and inferior temporal lines mark the
  insertion of the temporalis muscle that passes
  under the zygomatic arch and inserts on the
• Temporal bones

•   Squamous part
•   Zygomatic process and arch
•   Mandibular fossa
•   Tympanic part
•   External acoustic meatus
•   Mastoid part
•   Mastoid process
•   Mastoid notch
•   Petrous part
•   Internal acoustic meatus
•   Carotid canal
•   Jugular foramen
• Occipital bone
• Basilar part
• Occipital condyle – where the skull rests on
  the vertebral column
• Hypoglossal canal – nerve supplies muscles of
  the tongue
• External occipital protuberance – attachment
  for the nuchal ligament which binds the skull
  to the vertebral column
• Superior nuchal line and inferior nuchal line –
  attachments for several neck and back
• Sphenoid bone – medial body – greater and
  lesser wings
• Optic foramen
• Anterior clinoid processes
• Superior orbital fissure
• Sella Turcica
• Foramen Rotundum
• Foramen Ovale
• Foramen Spinosum
• Foramen Lacerum
• Nasal choanae or internal nares
• Medial and lateral pterygoid plates
• Pterygoid process
• Ethmoid bone
• Vertical perpendicular plate that forms the
  superior two-thirds of the nasal septum – divides
  the nasal cavity into right and left air spaces
  called nasal fossae
• Cribiform plate
• Crista galli – attachment point for meninges
• Cribiform foramina – olfactory bulbs of the brain
  rest here
• Labyrinth – ethmoidal cells
• Orbital plate
• Superior and middle nasal conchae
• Injury to the Ethmoid
• Sharp upward blow to the nose – common in
  dashboard injuries
• Can drive fragments through the cribiform
  plate into the brain
• Can sheer off the olfactory nerves that pass
  through the ethmoid bone and cause anosmia
• Can leak cereborospinal fluid through the
  nasal cavity
• Facial bones – 14 bones – 2 maxillae – 2
  palatine bones – 2 zygomatic bones – 2
  lacrimal bones – 2 nasal bones – 2 inferior
  nasal conchae – 1 vomer – 1 mandible
• Maxillae – alveolar processes – alveolus –
  infraorbital foramen – inferior orbital fissure
• Palate – hard palate anteriorly and soft palate
  posteriorly – most of the hard palate is formed
  from the palatine processes – failure of these
  to join at 12 weeks gestation results in a cleft
• Palatine bones – form the rest of the hard
  palate – part of the wall of the nasal cavity –
  part of the floor of the orbit
• Zygomatic bones – the zygomatic arch that
  flares from each side of the skull is formed by
  the union of the zygomatic process of the
  temporal bone and the temporal process of
  the zygomatic bone
• Lacrimal bones – form part of the medial wall
  of each orbit – lacrimal fossa houses the
  lacrimal sac
• Nasal bones – form the bridge of the nose
• Inferior nasal conchae – superior and middle
  nasal conchae are parts of the edthmoid bone
  – inferior is a separate bone
• Vomer – forms the inferior half of the nasal
• Mandible – strongest bone in the skull – only
  one that can move – body – ramus – angle –
  mental symphysis – mental spines – mental
  foramen – condyloid process – mandibular
  condyle – temperomandibular joint –
  coronoid process – mandibular notch –
  mandibular foramen
• Bones associated with the skull
• Auditory ossicles – malleus – incus – stapes
• Hyoid bone – does not articulate with any
  other bone – suspended from the styloid
  process of the skull – serves for attachment
  for several muscles that control the mandible,
  tongue and larynx
• The skull in infancy and childhood
• Fontanels – anterior and posterior – usually
  ossify by one year – anterior is the largest –
  formed by sagittal suture, lambdoid suture
  and coronal suture
• Skull grows faster than the rest of the body
• Reaches half its adult size by 9 months, three-
  quarters by age 2 and final adult size by age 9
• Diagnostic importance
• Vertebral Column – supports the skull and trunk –
  allows for their movement – protects the spinal
  cord – absorbs stresses from running, walking
  and lifting – provides attachments for limbs,
  thoracic cage, and postural muscles
• Consists of a chain of 33 vertebrae with 23
  fibrocartilage intervertebral discs
• Vertebrae are divided into 7 cervical, 12 thoracic,
  5 lumbar, 5 sacral and 4 coccygeal
• Beyond the age of 3 years there are curves called
  the cervical curvature, the thoracic curvature, the
  lumbar curvature and the pelvic curvature
• Abnormal spinal curvatures – multiple
  etiologies – disease, congenital
• Scoliosis – abnormal lateral deviation – most
  often in the thoracic region – frequently in
  adolescent girls – most common deformity
• Kyphosis – exaggerated thoracic curvature –
  seen in older population – usually caused by
• Lordosis – exaggerated lumbar curvature –
  seen in pregnancy and obesity
• General Structure of the Vertebra
• Body – mass of spongy bone and red bone
  marrow covered with a thin layer of compact
  bone – weight bearing portion of the vertebra
• Vertebral foramen – collectively the foramina
  comprise the vertebral canal – foramen is
  bordered by the vertebral arch made up of the
  lamina and the pedicle
• Spinous process and transverse process –
  provide points of attachment for ligaments
  and spinal muscles
• Intervertebral foramen – allows passage for
  spinal nerves that connect with the spinal
  cord – formed by inferior vertebral notch and
  by the superior vertebral notch
• Intervertebral discs – inner gelatinous nucleus
  pulposus surrounded by a ring of
  fibrocartilage called the anulus pulposus
• Herniated disc – crack in the anulus pulposus
  allowing the nucleus to ooze out – places
  pressure on the spinal cord and or spinal
• Treated by laminectomy with both lamina and
  the spinal process removed
• Cervical vertebrae C1-C7

• C1 is called the atlas – supports the head – has
  lateral mass with deeply concave superior
  articular facet that articulates with occipital
  condyle of the skull – makes nodding “yes”
  motion possible – inferior articular facets
  articulate with C2 – lateral masses connected
  by anterior and posterior arches which bear
  the anterior and posterior tubercles
• C2 called the axis – allows rotation of the head
  in gesturing “no” – has odontoid process or
  dens on its anterosuperior side – no other
  vertebra has a dens – it projects into the
  vertebral foramen of the atlas and is held in
  place by the transverse ligament
• Articulation between the atlas and the
  cranium is called the atlanto-occipital joint –
  articulation between the atlas and the axis is
  called the atlantoaxial joint
• Other features of cervical vertebrae
• Axis is the first vertebra to exhibit a spinous
• In C2-C6 the spinous process is forked or bifid
• In C7 the spinous process is not forked and it
  is long – forms a prominent bump on the back
  of the neck, the vertebra prominens
• All 7 cervical vertebra have a transverse
  foramen allowing passage of the vertebral
  arteries – no other vertebra have a transverse
• Thoracic Vertebrae – 12 in number
  corresponding to the 12 pairs of ribs attached
  to them – have no transverse foramina or
  transverse processes – have distinctive
  features of their own
• Spinous processes are relatively pointed and
  angle sharply downward
• Body is heart shaped, more massive than in
  the cervical vertebrae but less than in the
  lumbar vertebrae
• The body has costal facets for rib attachments
• T1-T10 transverse costal facets at the end of each
  transverse process – provides a second point of
  articulation for ribs 1-10 – no transverse costal
  facets on T11 or T12 because ribs 11 and 12
  attach only to the bodies of the vertebrae
• Only thoracic vertebra have ribs articulating with
• Usually the rib inserts between two vertebra so
  each vertebra contributes one-half of the
  articular surface – a rib articulates with the
  inferior costal facet of the upper vertebra and
  with the superior facet of the lower vertebra.
• T1-T12 all have complete costal facets on the
  bodies for ribs 1-12 – ribs 10-12 articulate on the
  body and not between the vertebrae
• Each thoracic vertebra has a pair of superior
  articular facets and a pair of inferior articular

• The superior facets of one vertebra articulates
  with the inferior facets of the vertebra above
• Lumbar Vertebra – L1-L5

• Thick stout body and blunt square spinous
• Articular processes are oriented differently –
  superior processes face medially and inferior
  processes face laterally
• Resistant to twisting
• Sacrum – S1-S5 – posterior wall of the pelvic
  cavity – Five separate vertebrae in children –
  begin to fuse at age 16 and fully fused at age
• Four pairs of anterior sacral foramina
• Spinous processes of the sacral vertebrae fuse
  to form the median sacral crest
• Transverse processes fuse to form the lateral
  sacral crests
• Four pairs of posterior sacral foramina
• Sacral canal – runs through the sacrum and
  ends in the sacral hiatus
• Auricular surface on each side – articulates
  with os coxae and forms the sacroiliac joint
• At the superior end of the sacrum lateral to
  the median crest a pair of superior articular
  processes articulate with L5

• Coccyx Co1-Co4
• Thoracic Cage – consists of the thoracic
  vertebrae, sternum and ribs
• Sternum – boney plate anterior to the heart
• Manubrium – has a median suprasternal
  notch – right and left clavicular notches where
  it articulates with the clavicles
• Body of the sternum – joins the manubrium at
  the sternal angle – second rib attaches here
• Xiphoid – at the inferior end of the sternum
• Ribs – 12 pair of ribs – each attached at its
  posterior (proximal) end to the vertebral
  column – costal cartilage (hyaline cartilage)
  extends from anterior ends (proximal) of ribs
  1-7 to the sternum
• Ribs 1-7 are true ribs – ribs 8, 9 and 10 attach
  to the costal cartilage of rib 7 – ribs 11 and 12
  do not attach to anything – ribs 8-12 are false
  ribs – ribs 11 and 12 are floating ribs
• Ribs 1-10 each have a proximal head and
  tubercle connected by a neck – ribs 11-12
  have a head only
• Ribs 2-9 have beveled heads that come to a
  point between superior and inferior articular
  facets for vertebral bodies – angle in ribs 2-10
  – shaft – costal groove
• Pectoral Girdle – supports the arm – two
  bones on each side of the body
• Clavicle – median end articulates with the
  sternum at the sternoclavicular joint – lateral
  end articulates with the scapula at the
  acromioclavicular joint – S-shaped bone with a
  sternal end, acromial end and conoid tubercle
• Scapula – triangular shape and overlies ribs 2
  to 7 – articulates with the humerus at the
  humeroscapular joint
• Triangle consists of superior, medial
  (vertebral) and lateral (axillary) borders
• Scapula angles – superior, inferior and lateral
• Posterior surface of the scapula – spine,
  supraspinous fossa, infraspinous fossa
• Lateral angle – the most complex region of the
  scapula – three main features
• Acromion – forms apex of the shoulder –
  articulates with the clavicle – sole point of
  attachment of the arm and scapula to the rest
  of the skeleton
• Coracoid – provides attachment for the biceps
• Glenoid – socket that articulates with the
  head of the humerus
• Upper Limb – four regions containing thirty
  bones per limb
• Brachium – shoulder to elbow – contains one
  bone, the humerus
• Antebrachium – elbow to wrist and contains
  two bones, the radius and the ulna
• Carpus – wrist – contains eight small bones in
  two layers
• Manus – the hand – contains nineteen bones
  in two groups – five metacarpals in the palm –
  fourteen phalanges in the fingers
• Humerus
• Head articulates with glenoid cavity of the
• Anatomical neck and surgical neck
• Greater and lesser tubercles and
  intertubercular space
• Deltoid tuberosity – insertion of the deltoid
• Capitulum is a lateral condyle that articulates
  with the radius
• Trochlea is a medial condyle that articulates
  with the ulna
• Lateral and medial epicondyles just proximal
  to the condyles – medial epicondyle protects
  the ulnar nerve
• Lateral and medial supracondyles
• Three pits at distal end of humerus –
  olecranon fossa accommodates the olecranon
  of the ulna when the arm is extended –
  coronoid fossa accommodates the the
  coronoid process of the ulna when the arm is
  flexed – radial fossa near the head of the
• Radius

• Proximal head of the radius is a disc that rotates
  on the humerus articulating with the capitulum
  of the humerus and the radial notch of the ulna
• Tuberosity of the radius is the attachment of the
• Styloid process at the distal end of the radius
• At the distal end of the radius there are two
  articular facets that articulate with the scaphoid
  and lunate bones of the wrist
• Ulna notch articulates with the end of the ulna
• Ulna

• Trochlear notch – C-shaped structure that
  wraps around the trochlea of the humerus –
  posterior side of the notch is formed by the
  olecranon – anterior side formed by the
  coronoid – laterally there is the radial notch
  which accommodates the head of the radius
• Styloid process at the distal end
• Interosseous membrane
• Interosseous margin
• Carpal Bones – form the wrist – two rows of
  four bones

• Proximal row – starting from the lateral side –
  scaphoid (navicular), lunate, triquetrum,
  pisiform (a sesamoid bone)
• Distal row – starting from the lateral side –
  trapezium, trapezoid, capitate and the hamate
• Metacarpal Bones – bones of the palm

• Metacarpal I is located at the base of the
  thumb and metacarpal V is located at the base
  of the little finger
• Proximal end is the base, shaft is the body
  and the distal end is the head – knuckles
• Phalanges – fingers
• Two phalanges in the thumb and three in each
  of the other digits
• Phalanges identified by Roman numerals
  preceded by proximal, middle or distal
• The thumb is I and the little finger is V
• Pelvic Girdle – adult hip bone called the os
  coxae – right and left os coxae called the
  pelvic girdle – pelvic girdle and the sacrum
  called the pelvis
• Os coxae formed by the fusion of the ilium,
  the ischium, and the pubis – joined to the
  vertebral column at the sacroiliac joint
• Pubic symphysis – where the right and left os
  coxae are joined anteriorly by a pad of
• Features of the os coxae – iliac crest,
  acetabulum, and obturator foramen
• Pelvis – pelvic inlet – pelvic outlet
• Lower Limb – divided into four regions with thirty
  bones per limb

• Femoral region – hip to knee and contains the
  femur – the patella is a sesamoid bone at the
  junction of the femoral and crural regions
• Crural region – knee to ankle and contains the
  tibia and the fibula
• Tarsal region – ankle
• Pedal region – foot – seven tarsal bones – five
  metatarsal bones – fourteen phalanges in the
• Femur – longest and strongest bone in the
  body – head articulates with the acetabulum
  of the pelvis – ball and socket joint
• Landmarks include – fovea capitis, neck,
  greater and lesser trochanters,
  intertrochanteric crest, intertrochanteric line,
  linea aspera, spiral line, medial and lateral
  supracondylar lines, gluteal tuberosity, medial
  and lateral epicondyles, medial and lateral
  condyles, intercondylar fossa, patellar surface,
  popliteal surface
• Patella – kneecap – sesamoid bone –
  embedded in the tendon of the knee –
  cartilaginous at birth and ossifies at three to
  six years of age
• Landmarks – superior base and an inferior
  apex – two facets on its posterior surface
  where it articulates with the femur
• Quadriceps femoris tendon extends from the
  quadriceps muscle to the patella and
  continues from the patella to the tibia
• Tibia – on medial side of the leg – weight
• Head with medial and lateral condyles –
  articulate with those of the femur
• Landmarks – tibial tuberosity –anterior crest –
  medial malleolus
• Fibula – on lateral side of leg – head – apex –
  lateral malleolus
• Ankle – Tarsal bones – arranged in proximal
  and distal groups
• Proximal group – contains the calcaneus which
  is the largest, forms the heel and is the point
  of attachment of the achilles tendon – talus is
  second largest and has an inferoposterior
  surface that articulates with the calcneus, a
  superior trochlear surface that articulates with
  the tibia, and an anterior surface which
  articualtes with the third proximal bone called
  the navicular
• Distal group of tarsal bones from medial to
  lateral – medial, intermediate and lateral
  cuneiforms, and the cuboid

• Foot – proximal metatarsals are I to V medial
  to lateral, metatarsal I being proximal to the
  great toe – metatarsals I through III articulate
  with the three cuneiforms and metatarsals IV
  and V articulate with the cuboid
• Phalanges of the foot
• Great toe contains only two bones – proximal
  and distal phalanx I
• The other toes each contain a proximal,
  middle and distal phalanx and are numbered II
  through V from medial to lateral

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