Chapter 8 The Skeletal System

1. 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

2. 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

3. Surface Features of Bones

4. 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

5. Major Skull Cavities • Cranial cavity holds brain • Orbit contains eyeball & extraocular muscles • Ethmoid sinus • Nasal cavity • Maxillary sinus • Oral cavity

6. 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

7. 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

8. Frontal Bone • Forms forehead and part of the roof of the cranium • Forms roof of the orbit • Contains frontal sinus

9. 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 lines

10. 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

11. 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)

12. 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

13. 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

14. Sphenoid Bone • Lesser wing • Greater wing • Body of sphenoid • Medial and lateral pterygoid processes

15. 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

16. Sphenoid Bone • Sphenoid sinus

17. 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

18. Ethmoid Bone • Superior & middle concha • Perpendicular plate of nasal septum

19. 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

20. Maxillary sinus fills maxillae bone Other bones containing sinuses are frontal, ethmoid & sphenoid. Frontal Locations of Paranasal Sinuses Ethmoid Maxillary Sphenoid

21. Palatine Bones • L-shaped bone • Posterior 1/3 of the hard palate • Part of lateral nasal wall • Part of the orbital floor

22. 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

23. 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

24. Nasal Bones • Forms bridge of nose and supports cartilages of nose • Often fractured by blow to the nose

25. Inferior Nasal Conchae • A separate bone • Not part of ethmoid like the superior & middle concha or turbinates

26. Vomer • Inferior half of the nasal septum • Supports cartilage of nasal septum

27. 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

28. Ramus, Angle and Body of Mandible

29. 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

30. 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

31. 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

32. Newborn Spinal Curvature • Spine exhibits one continuous C-shaped curve • Known as primary curvature

33. 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

34. 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

35. 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)

36. 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

37. 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

38. 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”

39. Atlas & Axis Articulation

40. 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

41. Lumbar Vertebrae • Thick, stout body and blunt, squarish spinous process • Superior articular processes face medially • lumbar region resistant to twisting movements

42. 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

43. 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

44. 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

45. 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

46. Rib Structure Tubercle Head • 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

47. Numbered Rib Articulations

48. 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

49. 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

50. Clavicle • S-shaped bone, flattened dorsoventrally • Inferior surface marked by muscle & ligament attachments • Sternal end is rounded -- acromial end is flattened