Skeleton Notes

Introduction

  • The skeleton consists of bones, cartilages, and ligaments, making up 20% of body mass.
  • Adults have around 206 bones, reduced from approximately 270 at birth due to fusion.
  • The number of bones may vary between individuals due to differences in rib count or sesamoid bones.

Cranial and Facial Bones

  • Cranial bones (8) enclose the brain and provide muscle attachment sites.
  • Facial bones provide the framework for facial features, sensory spaces, secure teeth, and anchor facial muscles.
  • Mandible is connected by a moveable joint; hyoid bone doesn't articulate directly with other bones.
  • Key bones to remember:
    • Parietal (2)
    • Frontal (1)
    • Temporal (2)
    • Occipital (1)
    • Sphenoid (1)
    • Nasal (2)
    • Zygomatic (2)
    • Maxilla (2)
    • Mandible (1)
  • Main sutures: Lambdoid, Sagittal, Coronal, and Squamous.

Vertebral Column

  • Consists of 26 irregular bones (vertebrae) that protect the spinal cord and support the head.
  • Transfers weight from the trunk to the legs.
  • Five major divisions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused), and 4 coccygeal (fused).
  • Spinal curvatures increase resilience and flexibility; cervical and lumbar are concave posteriorly, thoracic and sacral are convex posteriorly.
  • Major ligaments: anterior and posterior longitudinal ligaments.
  • Intervertebral discs act as shock absorbers.

Cervical Vertebrae

  • C1 (atlas): no body or spinous process; allows nodding.
  • C2 (axis): dens acts as a pivot for atlas rotation; allows head rotation.
  • C3-C6: bifid spinous processes, wide vertebral body, large triangular foramen, and transverse foramen.
  • C7: larger spinous process, not bifid.
  • C3-C7 have the greatest range of movement.

Thoracic Vertebrae

  • Long, downward-facing spinous processes and facets for rib articulation (except T11 and T12).
  • Increase in size moving down the spine; circular foramen and large heart-shaped body.
  • Primarily allow rotation; flexion and extension are limited.

Lumbar Vertebrae

  • Large, kidney-shaped body; short, blunt spinous processes; triangular foramen; thin, tapered transverse processes.
  • Provide stability and prevent rotation.
  • Spinal cord ends at L1-L2, becoming the cauda equina.

Sacrum and Coccyx

  • Sacrum: 5 fused vertebrae (S1-S5); center of gravity at S2.
  • Coccyx: 3-5 fused vertebrae; supports body weight when sitting.

Thoracic Cage

  • Consists of thoracic vertebrae, ribs, sternum, and costal cartilages.
  • Protects heart and lungs and supports shoulder girdles.
  • Sternum: Manubrium, body, and xiphoid process.
  • Ribs: 12 pairs; true ribs (1-7) attach directly to the sternum, false ribs (8-12) attach indirectly or not at all, floating ribs (11-12) have no anterior attachments.

Pectoral Girdle

  • Consists of 2 clavicles and 2 scapulae, attaching upper limbs to the axial skeleton.
  • Clavicles hold scapulae laterally.

Clavicles

  • S-shaped; attach to the sternum via the sternoclavicular joint.

Scapulae

  • Thin, triangular, flat bones on the dorsal rib cage between ribs 2 and 7.
  • Spine ends in the acromion process (attaches to clavicles).
  • Coracoid process is an attachment for the biceps.
  • Glenoid cavity articulates with the head of the humerus.

Upper Limb

Humerus

  • Articulates with scapula, radius, and ulna.
  • Features: head, greater and lesser tubercles (rotator cuff attachment), condyles (ulna and radius articulation).

Ulna and Radius

  • Forearm bones; radius (thumb side), ulna (pinkie side).
  • Ulna: longer, articulates with humerus and carpals; olecranon and coronoid processes form the elbow joint.
  • Radius: thinner proximally; radial head, radial tuberosity (biceps anchor), radial styloid process (hand muscle attachment).

Hand

  • Carpals (wrist): 8 short bones.
  • Metacarpals (palm): 5 long bones, numbered I-V.
  • Phalanges (fingers): 3 in each finger (distal, middle, proximal), 2 in the thumb (distal, proximal).

Hip Bone

  • Pelvic girdle: 2 hip bones and the sacrum.
  • Each hip bone consists of ilium, ischium, and pubis.

Ilium

  • Large, top part with iliac crests.

Ischium

  • Lower part; contains ischial tuberosity (sit bones).

Pubis

  • Upper part, joins at the symphysis pubis.
  • Acetabulum: socket for the head of the femur.
  • Female pelvis: wider, shallower, lighter, and rounder.

Lower Limbs

Femur

  • Largest, longest, strongest bone; allows standing and movement.
  • Femoral head fits into the acetabulum.
  • Greater and lesser trochanters: anchoring points for thigh and buttock muscles.
  • Condyles articulate with the tibia; patella (kneecap) protects the knee.

Tibia and Fibula

  • Lower leg bones; connected by an interosseous membrane.
  • Tibia (shin bone): medial, articulates with femur and talus; medial malleolus (inner ankle bump).
  • Fibula: lateral, stabilizes ankle joint; lateral malleolus (outer ankle bump).
  • Supports body weight and acts as a lever.
  • Tarsus: 7 tarsal bones (talus, calcaneus, cuboid, navicular, cuneiforms).
  • Metatarsus: 5 long bones, numbered I-V.
  • Phalanges (toes): 3 in each toe (distal, middle, proximal), 2 in the big toe (proximal, distal).