CHAPTER 7
The Axial Skeleton
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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
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Types of Bones
• 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
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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
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SKULL
• 22 bones,
– 8 cranial bones form cranial cavity (cranium)
– 14 facial bones 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
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Sphenoid bone
• Forms middle part of base of skull
• Keystone bone: articulates w/ all other cranial bones
• Pterygoid processes are attachment sites for jaw muscles
• Sella turcica = site where pituitary gland rests
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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
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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.
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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
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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)
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Intervertebral Discs
• Absorb vertical shock between adjacent vertebrae
• Permit various movements of the vertebral column
• Fibrocartilaginous ring with a pulpy center
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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
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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
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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
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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
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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
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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!!
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Chapter 8
The Skeletal System: Appendicular Skeleton
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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
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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
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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)
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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
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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
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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
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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 (heartshaped in males)
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