Skeletal Anatomy Notes:

Skeletal Anatomy

The adult skeleton consists of 206 bones divided into the axial and appendicular skeletons.

Divisions of the Skeleton

  • Axial Skeleton (80 bones): Skull, middle ear bones, hyoid bone, vertebral column, thoracic cage.
  • Appendicular Skeleton (126 bones): Pectoral girdle, upper limbs, pelvic girdle, lower limbs.

Skeletal Structure Terms

  • Condyle: Rounded process for articulation.
  • Crest: Narrow, ridge-like projection.
  • Epicondyle: Projection above a condyle.
  • Facet: Small, flat surface.
  • Fissure: Cleft or groove.
  • Fontanel: Soft spot in skull.
  • Foramen: Opening for vessels/nerves.
  • Fossa: Shallow depression.
  • Fovea: Tiny pit.
  • Head: Enlarged end of bone.
  • Linea: Narrow ridge.
  • Meatus: Tube-like passageway.
  • Process: Prominent projection.
  • Ramus: Branch-like extension.
  • Sinus: Cavity within a bone.
  • Spine: Thorn-like projection.
  • Sulcus: Furrow or groove.
  • Suture: Interlocking line between bones.
  • Trochanter: Large process.
  • Tubercle: Knob-like process.
  • Tuberosity: Large tubercle.

The Skull

Composed of 22 bones (8 cranial, 14 facial), interlocked by sutures (except mandible).

  • Cranium: encloses and protects the brain
    • Frontal Bone (1): Forehead, eye orbit roofs, contains frontal sinuses and supraorbital foramen/notch.
    • Parietal Bones (2): Sides and roof of cranium, joined by sagittal suture; coronal suture joins to frontal bone.
    • Occipital Bone (1): back of skull, base of cranium; includes foramen magnum and occipital condyles.
    • Temporal Bones (2): Sides and base of cranium; includes external acoustic meatus and mandibular fossa.
    • Sphenoid Bone (1): Base of cranium, eye orbit sides; sella turcica holds pituitary gland, contains sphenoid sinuses.
    • Ethmoid Bone (1): Front of sphenoid; forms nasal cavity roof/walls, eye orbit walls; includes cribriform plates and crista galli.
  • Facial Skeleton: forms the shape of the face
    • Maxillae (2): Upper jaw, hard palate, eye orbit floors; contain maxillary sinuses.
    • Palatine Bones (2): Behind maxillae; hard palate posterior section, nasal cavity floor/walls.
    • Zygomatic Bones (2): Cheek prominences, eye orbit lateral walls.
    • Lacrimal Bones (2): Eye orbit medial walls.
    • Nasal Bones (2): Bridge of nose.
    • Vomer Bone (1): Nasal cavity midline, inferior nasal septum.
    • Inferior Nasal Conchae (2): Lateral nasal cavity walls.
    • Mandible (1): Lower jaw; includes mandibular condyle and mental foramen.

Vertebral Column

Supports head/trunk and protects the spinal cord. It consists of 26 bones in adults (33 in infants) separated by intervertebral discs.

  • Curvatures: cervical, thoracic, lumbar, and sacral.
  • Vertebrae Composition:
    • 7 cervical vertebrae (transverse foramina, bifid spinous processes)
    • 12 thoracic vertebrae (articulate with ribs)
    • 5 lumbar vertebrae (large bodies)
    • Sacrum (5 fused vertebrae)
    • Coccyx (4 fused vertebrae).

Typical Vertebra Structure

  • Body: Drum-shaped, anterior portion.
  • Pedicles: Stalks projecting from the body
  • Laminae: Plates arising from pedicles that fuse to form Spinous process.
  • Spinous process: Posterior projection.
  • Transverse processes: Lateral projections.
  • Vertebral foramen: Opening for the spinal cord.
  • Superior and inferior articular processes: Articulate with adjacent vertebrae.

Thoracic Cage

Includes ribs, thoracic vertebrae, sternum; protects thoracic and upper abdominal viscera.

  • Ribs (12 pairs):
    • True ribs (7 pairs): connect directly to the sternum.
    • False ribs (5 pairs):
      • Vertebrochondral ribs (3 pairs): costal cartilages connect to cartilage #7.
      • Floating ribs (2 pairs): no connection to the sternum
  • Sternum (breastbone): manubrium, body, xiphoid process.

Pectoral Girdle

Consists of 2 clavicles and 2 scapulae; supports upper limbs.

  • Clavicles (collarbones): brace the scapulae.
  • Scapulae (shoulder blades): acromion and coracoid processes, glenoid cavity.

Upper Limb

  • Humerus: Head, greater and lesser tubercles, deltoid tuberosity, capitulum, trochlea, epicondyles, coronoid fossa, olecranon fossa.
  • Radius: Lateral forearm bone; includes head, radial tuberosity, styloid process.
  • Ulna: Medial forearm bone; includes trochlear notch, olecranon and coronoid processes, styloid process.
  • Hand: 8 carpals, 5 metacarpals, 14 phalanges.

Pelvic Girdle

Consists of 2 hip bones; supports the trunk and provides attachment for the lower limbs.

  • Ilium: iliac crest, iliac spines, greater sciatic notch.
  • Ischium: ischial spines, ischial tuberosity.
  • Pubis: pubic symphysis, pubic arch.
  • Acetabulum: Depression for head of femur.
  • Obturator foramen: Opening between pubis and ischium.

Lower Limb

  • Femur: Head, fovea capitis, trochanters, linea aspera, condyles, epicondyles.
  • Patella: Kneecap, sesamoid bone located in the quadriceps tendon
  • Tibia: Medial bone; includes condyles, tibial tuberosity, medial malleolus.
  • Fibula: Lateral to tibia; includes head, lateral malleolus.
  • Foot: 7 tarsals, 5 metatarsals, 14 phalanges.

Life-Span Changes

  • Height decreases, calcium levels fall, bones become brittle.
  • Bone loss accelerates in menopausal women.
  • Fractures (hip, vertebral compression) are common.