CHAPTER 7

1. CHAPTER 7 The Axial Skeleton

2. DIVISIONS OF THE SKELETAL SYSTEM • Axial Skeleton • 80 bones • bones of longitudinal axis • skull, hyoid, vertebrae, ribs, sternum, ear ossicles • Appendicular Skeleton • 126 bones • upper & lower limbs and pelvic & pectoral girdles

3. 5 basic shapes of bones: long = compact short = spongy except surface flat = plates of compact enclosing spongy irregular = variable sesamoid = develop in tendons or ligaments (patella) Sutural bones = in joint between skull bones Types of Bones

4. BONE SURFACE MARKINGS • Structural features adapted for specific functions • Tension results in raised areas • Compressions results in depressed areas • Two major types of surface markings • Depressions/openings • form joints • allow the passage of soft tissue • Processes = projections/outgrowths • form joints • serve as attachment points for connective tissue • Table 7.2 describes various surface markings

5. SKULL • 22 bones, • 8 cranial bones form cranial cavity (cranium) • 14facialbones form face (most are paired) • Figures. 7.3 thru 7.8 • General Features • forms large cranial cavity & several smaller cavities • nasal cavity, orbits • paranasal sinuses • mucous membrane-lined cavities that open into nasal cavity • mandible (jawbone) = only movable bone of skull • skull bones held together by immovable joints called sutures

6. Sphenoid bone • Forms middle part of base of skull • Keystone bone: articulates w/ all other cranial bones • Pterygoid processes are attachment sites for jawmuscles • Sella turcica = site where pituitary gland rests

7. Unique Features of the Skull • Sutures • Immovable joints found only btwn adult skull bones • Named for bones they unite • 4 prominent sutures • Coronal: joins frontal & both parietal bones • Sagittal: joins parietal bones @ superficial midline • Lambdoid: joins parietal/occipital bones • Squamous: joins parietal/temporal bones @ lateral aspect

8. Unique Features of the Skull • Paranasal sinuses • Cavities in bones of skull that communicate with nasal cavity • Lined by mucous membranes • continuous w/ linings of nasal cavity • produce mucus • Serve as resonating chambers for speech • Cranial bones containing the sinuses are the frontal, sphenoid, ethmoid, and maxillae • Sinusitis occurs when membranes of the paranasal sinuses become inflamed due to infection or allergy.

9. Unique Features of the Skull • Fontanels • “soft spots” between the cranial bones in fetal skull • Unossified mesenchyme • remain unossified at birth but close early in life • replaced by intramembranous ossification • 6 major fontanels • Two major functions • enable fetal skull to modify its size and shape as it passes through birth canal • permit rapid growth of brain during infancy

10. VERTEBRAL COLUMN • Spine  built of 26 vertebrae • Five vertebral regions • cervical vertebrae(7) • thoracic vertebrae (12) • lumbar vertebrae (5) • sacrum (5, fused) • coccyx (4, fused)

11. Intervertebral Discs • Absorb vertical shock between adjacent vertebrae • Permit various movements of the vertebral column • Fibrocartilaginous ring with a pulpy center

12. Normal Curves of the Vertebral Column • Primary curves • thoracic and sacral are formed during fetal development • Secondary curves • cervical formed when infant raises head at 4 months • lumbar forms when infant sits up & begins to walk • Column curves either anteriorly or posteriorly • No naturally occurring LATERAL curves in column

13. UNIQUE CERVICAL VERTEBRAE • C1 & C2 are different from other cervical vertebrae • Atlas (C1) • Lacks spinous process & body • Articulates with occipital condyles of skull • Allows for nodding “yes” movement • Inferior surface articulates with C2 • Axis (C2) • Odontoid process: projects superiorly thru vertebral foramen of atlas • Forms pivot for atlas & head “no” nodding movement

14. THORAX • The term thorax refers to the entire chest. • Formed by sternum, costal cartilages, ribs, and the bodies of the thoracic vertebrae (Figure 7.22) • Sternum = breastbone • Manubrium = superior part • Xiphoid process = inferior part • Attachment point for some abdominal muscles • Articulates with costal cartilages of ribs • Thoracic cage = skeletal part of thorax • encloses & protects organs in thoracic and superior abdominal cavities • provides support for the bones of the shoulder girdle and upper limbs

15. THORAX • Ribs • give structural support to the sides of the thoracic cavity • 12 pairs (men & women) • Each pair articulates w/ thoracic verterbra • True ribs = first 7 pair • Costal cartilages attach directly to sternum • Form sternocostal joints • False ribs = remaining 5 pair • Attach indirectly to sternum thru cartilage of 7th rib • 11th & 12th pair = floating ribs  no attachment • Intercostal space = spaces btwn ribs occupied by muscles, blood vessels & nerves

16. Herniated (Slipped) Disc • Protrusion of the nucleus pulposus • Most commonly in lumbar region • Pressure on spinal nerves causes pain • Surgical removal of disc after laminectomy

17. Clinical Problems • Abnormal curves of the spine • scoliosis (lateral bending of the column) • kyphosis (exaggerated thoracic curve) • lordosis (exaggerated lumbar curve) • Spina bifida is a congenital defect • failure of the vertebral laminae to unite during fetal devel. • nervous tissue is unprotected • paralysis • Why adequate folate intake during pregnancy is CRUCIAL!!

18. Chapter 8 The Skeletal System: Appendicular Skeleton

19. APPENDICULAR SKELETON • Includes bones of: • upper/lower extremities (limbs) • shoulder/hip girdles  connect limbs to axial skeleton • Primary function is to facilitate movement • Contains 126 of the 206 bones in body

20. UPPER LIMB (EXTREMITY) • Consists of 30 bones • Arm = humerus • Forearm (2) • ulna on “pinky” side • radius on thumb side • Hand/wrist (27) • carpals = bones of wrist • metacarpals = bones of palm • phalanges = bones of fingers

21. Pectoral (Shoulder) Girdle • Attaches bones of upper limbs to axial skeleton (Fig. 8.1) • Clavicle = collarbone • medial end articulates with manubrium of sternum  sternoclavicular joint • lateral (acromial) end articulates with scapula  acromioclavicular joint • acromion = high point of shoulder • lateral end of spine of scapula • coracoid process = attachment point for tendons/muscles of shoulder • Upper limb attaches at shoulder (glenohumeral joint)

22. Lower Limb (Extremity) • 30 bones • Thigh = femur • Kneecap = patella • Leg • tibia = shin • fibula = small, lateral bone • Ankle/foot • tarsals = bones of ankle • metatarsals = bones of forefoot • phalanges = toes

23. PELVIC (HIP) GIRDLE • Provides strong and stable support for lower extremities • Consists of two hipbones (os coxa) • unite anteriorly @ pubic symphysis • unite posteriorly with sacrum @ sacroiliac joints • Bony pelvis = 2 hipbones, sacrum & pubic symphysis • At birth each hip bone is 3 separate bones • ilium, pubis, ischium • eventually fuse at depression called the acetabulum forms socket for hip joint

24. True and False Pelves • Two hipbones, sacrum and coccyx form pelvis • Greater (false) and lesser (true) pelves = anatomical subdivisions of pelvis • False pelvis • Portion superior to pelvic brim • Bordered by lumbar vertebrae, upper portions of hips, abdominal walls • Does not contain pelvic organs • Bladder when full • Uterus when pregnant • True pelvis • Inferior to pelvic brim • Inlet & outlet = superior, inferior openings • Bordered by sacrum, coccyx, inferior portions of ilium/ischium, and pubis

25. COMPARISON OF FEMALE & MALE PELVES • Male bones generally larger & heavier than those of female • Male’s joint surfaces also tend to be larger • Muscle attachment points more well-defined in male due to larger muscle size • A number of anatomical differences exist between pelvic girdles of male/female • wider pelvic outlet in females  facilitates childbirth • angle of pubic arch in females is greater than 90° • false pelvis shallower, oval-shaped in females (heart-shaped in males)