The Axial Skeleton

1. The Axial Skeleton

2. The Axial Skeleton • Forms the longitudinal part of the body • Divided into three parts • Skull • Vertebral column • Bony thorax

3. The Axial Skeleton Figure 5.6

4. The Skull • Two sets of bones • Cranium – encloses & protects brain. • Facial bones – holds eyes in anterior position & allows the facial muscles to show emotions. • All but 1 of the bones are joined by sutures (interlocking, immovable joints) • Only the mandible is attached by a freely movable joint

5. The Cranium • Frontal – forms forehead, brow bone, superior eye orbit • Parietal (2) – form most of the superior & lateral walls of the cranium • Meet in midline = sagittal suture • Meet frontal = coronal suture

6. The Cranium • Temporal (2) – inferior to parietals & join to them at the squamous sutures • Important bone markings found here • Externalacoustic (auditory) meatus – canal leading to eardrum • Styloidprocess – sharp needle-like projection inferior to external auditory meatus (attachment point for many neck muscles and the hyoid bone) • Zygomaticprocess – thin bridge of bone that joins w/ the zygomatic (cheek) bone

7. The Cranium • Important bone markings found in temporal bone • Mastoidprocess – rough projection posterior & inferior to the external auditory meatus • Full of air cavities (sinuses) • Attachment for some neck muscles • Close to middle ear & leads to ear infections • Jugularforamen – junction of occipital & temporal • Allows for passage of jugular vein • Largest vein of the head – drains the brain

8. The Cranium • Important bone markings found in temporal bone • Internalauditorymeatus – anterior to jugular foramen • Transmits cranial nerves 7 & 8 (facial & vestibulocochlear) • Carotidcanal - anterior to jugular foramen • Carotid artery runs through it to brain

9. The Cranium • Occipital – most posterior bone of cranium forming back wall & floor of the skull • Joins parietals anteriorly at lambdoid suture • Foramen magnum = large opening in base of the occipitals (spinal cord connects with the brain) • Lateral to the foramen magnum are rockerlike occipital condyles which rest on the 1st vertebra

10. The Cranium • Sphenoid – butterfly-shaped – spans the width of the skull and forms part of cranial cavity floor • Sella turcica “Turk’s saddle” = small depression on the midline of the sphenoid, holds the pituitary gland • Foramen ovale = large oval opening in line w/ the posterior end of the sella turcica (allows cranial nerve 5 (trigeminal) to pass to chewing muscles of mandible • Parts of the sphenoid form part of the eye orbits • 2 important openings: • Optic canal (optic nerve) • Superior orbital fissure (cranial nerves 3, 4 & 6 – eye movements) • Central part of the sphenoid riddled w/ air cavities = sphenoid sinuses

11. The Cranium • Ethmoid – irregularly shaped, anterior to sphenoid – forms roof of nasal cavity and medial walls of the orbits. • Cristagalli “cock’s comb” = superior ethmoid surface projection – outermost brain covering attaches • Cribriformplates – holey areas on sides of crista galli= nerve fibers for smell pass through from nose • Superior&middle nasalconchae – extensions of the ethmoid – form part of lateral walls of nasal cavity & increase turbulence of air flowing

12. The Facial Bones • 14 bones • 12 paired, only the mandible and vomer are single

13. The Facial Bones • Maxillae (2) / maxillary bones – fused to form upper jaw • Upper teeth carried in the alveolar margin • Palatineprocesses- extensions that form the anterior part of the hard palate • ParanasalSinuses – drain the nasal passages, lighten the skull bones, amplify sounds as we speak

14. The Facial Bones • Paranasal Sinuses • Hollow portions of bones surrounding the nasal cavity • Sinusitis(infection of sinuses) – can result in headache or upper jaw pain

15. The Facial Bones • Palatine(2) – posterior to palatine processes of maxillae – form posterior part of hard palate • cleft palate= failure of these to fuse • Zygomatic (2) – cheek bones – form portion of lateral walls of orbits • Lacrimal (2) – fingernail sized bones forming part of medial walls of orbits • Groove serves as passageway for tears

16. The Facial Bones • Nasal (2)– small rectangular bones – form bridge of nose – lower part of nose made of cartilage • Vomer “plow”(1) – median line of nasal cavity – forms most of the nasal septum • Inferior nasal conchae (2) – thin, curve bones projecting from lateral walls of the nasal cavity

17. The Facial Bones • Mandible (lower jaw) – largest, strongest bone of the face – joins temporal bones on each side of face, forming the only freely movable joints in the skull (find them!) • Horizontal part (body) forms the chin • 2 upright bars of bone (rami) extend from the body to connect the mandible with the temporal bone. • Lower teeth lie in alveolarmargin

18. The Hyoid Bone • Not really part of the skull • Horseshoe shaped w/ a body and 2 pair of horns (cornua) • Closely related to mandible and temporal bones • Unique b/c it’s the only bone that does not articulate w/ any other bone

19. The Hyoid Bone • Suspended in mid–neck region 2 cm above the larynx, anchored by ligaments to the styloid processes of the temporal bones • Serves as a movable base for the tongue & attachment point for neck muscles (lower and raise larynx when we swallow & speak)

20. The Fetal Skull • Face small compared to size of cranium (skull is large compared to body length) • Adult skull is 1/8 total body length; newborn is 1/4

21. The Fetal Skull • Fontanels – fibrous membranes connecting the cranial bones • Baby’s pulse can be felt in these soft spots (explains their name “little fountain”) • Allow fetal skull to be compressed in birth process • Allow infants brain to grow • Largest fontanels are diamond shaped anterior shaped fontanel and smaller triangular shaped posterior • Convert to bone within 24 months after birth

22. The Skull Figure 5.7

23. Bones of the Skull Figure 5.11

24. Human Skull, Superior View Figure 5.8

25. Human Skull, Inferior View Figure 5.9

26. The Vertebral Column • Serves as axial support of the body • Extends from the skull, which it supports, to the pelvis, where it transmits the weight of the body to the legs. • 26 irregular bones connected & reinforced by ligaments creating a flexible, curved structure. Figure 5.14

27. The Vertebral Column • Spinal cord runs through central cavity, protected by vertebrae • Before birth = 33 separate vertebrae but 9 later fuse to form 2 composite bones – the sacrum (5 fused) & the coccyx (4 fused). Figure 5.14

28. The Vertebral Column • Each vertebrae is given a name according to its location • 24 single vertebrae • 7 cervical vertebrae • 12 thoracic vertebrae • 5 lumbar vertebrae Figure 5.14

29. The Vertebral Column • Vertebrae separated by pads of flexible fibrocartilage – intervertebral discs –cushion & absorb shocks while allowing flexibility. • Young person – discs = 90% water content – spongy & compressible. • As you age – water content decreases – harder & less compressible. • Can lead to herniated (“slipped”) discs. • Can also occur from exceptional twisting forces. • If disc presses on spinal cord or nerves = numbness & excruciating pain.

30. The Vertebral Column • Disks & S-shaped curvature of spine prevent shock to head when we walk or run. • Primary curvatures • Thoracic & sacral regions • Present at birth • Secondary curvatures • Cervical curvature appears when baby begins to raise its head. • Lumbar curvature when baby begins to walk.

31. The Vertebral Column • Abnormal spinal curvatures • Scoliosis - abnormal lateral curvature of the spine. • Kyphosis - Abnormal rearward curvature of the spine, resulting in hunchback. • Lordosis - Abnormal forward curvature of the spine in the lumbar region.

32. Vertebrae • All vertebrae have a similar structural pattern. • Body: disclike, weight bearing part facing anteriorly. • Vertebral arch: formed from the joining of all posterior extensions, the laminae & pedicles. • Vertebral foramen: canal through which the spinal cord passes.

33. Vertebrae • Transverse processes: 2 lateral projections from the vertebral arch. • Spinous process: single projection arising from the posterior aspect of the vertebral arch (fused laminae). • Superior & inferior articular processes: paired projections lateral to the vertebral foramen allowing a vertebra to form joints w/ adjacent vertebrae.

34. Structure of a Typical Vertebrae Figure 5.16

35. Vertebrae

36. Cervical Vertebrae • 7 (C1 to C7) – form the neck region. • First 2 – atlas & axis – are different because they perform functions not shared by any other cervical vertebrae.

37. Cervical Vertebrae • Atlas (C1) has no body; the superior surfaces of its transverse processes contain large depressions that receive the occipital condyles of the skull; allows you to nod “yes.” • Axis (C2) has a large upright process (dens or odontoid process), which acts as a pivot point; allows you to indicate “no.”

38. Cervical Vertebrae • C3 through C7 are the smallest, lightest vertebrae • All transverse processes of cervical vertebrae only contain foramina through which vertebral arteries pass to the brain.

39. Thoracic Vertebrae • 12 with body somewhat heart shaped w/ 2 costal facets on each side, which receive the heads of the ribs. • Spinous process is long & hooks sharply downward (from the side looks like a giraffe’s head).

40. Lumbar Vertebrae • 5 w/ massive blocklike bodies & short hatchet-shaped spinous processes (looks like moose head from side). • Sturdiest vertebrae – most stress here.

41. Sacrum • Formed by the fusion of 5 vertebrae. • Winglike alae articulate laterally w/ the hipbones forming the sacroiliac joints. • Forms the posterior wall of the pelvis. • Median sacral crest roughens the posterior midline & are flanked by sacral foramina. • Vertebral canal continues inside the sacrum as the sacral canal – terminates in large inferior opening called the sacral hiatus.

42. Coccyx • Formed by fusion of 3 to 5 tiny, irregularly shaped vertebrae • This is the human “tailbone” – a remnant of the tail other vertebrate animals have.

43. Regional Characteristics of Vertebrae Figure 5.17a–b

44. Regional Characteristics of Vertebrae Figure 5.17c–d

45. The Bony Thorax • Made-up of three parts • Sternum • Ribs • Thoracic vertebrae Figure 5.19a

46. Bony Thorax • Often called the “thoracic cage” b/c it forms a cone-shaped cage of slender bones around the organs of the thoracic cavity. • Sternum – “breastbone” • Flat bone that is a result of the fusion of 3 bones – the manubrium, body and xiphoid process • Attached to the first 7 pairs of ribs

47. Sternum • Three important bony landmarks: • jugular notch (concave upper border of the manubrium) – can be felt easily – generally at level of T3 • sternal angle - where manubrium & body meet - formed at level of 2nd ribs (reference to locate 2nd intercostal space for listening to heart valves) • xiphisternal joint – body and xiphoid process fuse (level of T9) • Sternal puncture used to get bone marrow tissue to diagnose certain blood diseases

48. Bony Thorax • Ribs – 12 pair – form walls of bony thorax • Articulate w/ vertebral column posteriorly & curve downward toward anterior body surface. • True ribs = first 7 pair – attach directly to sternum by costal cartilage • False ribs = next 5 pair – attach indirectly to sternum or not at all (last 2 pair are called “floating ribs” b/c they are the ones not attached at all)

49. Bony Thorax • Contrary to popular myth – men & women have the same number of ribs!! 