Major Bones of the Human Skeleton

Why This Matters

The skeletal system isn't just a collection of 206 bones to memorize—it's an integrated framework that reveals how form follows function throughout the human body. In Honors Anatomy and Physiology, you're being tested on your ability to connect bone structure to its purpose: protection, support, movement, and leverage. Every bone's shape, location, and articulation tells a story about the mechanical demands placed on it.

When you study these bones, focus on the underlying principles: Why is the femur the strongest bone? Why do some bones fuse while others remain separate? How do bones work together as functional units? Don't just memorize names and locations—know what structural category each bone belongs to, what it protects or supports, and how it articulates with neighboring bones. This conceptual approach will serve you well on both multiple-choice questions and FRQs that ask you to explain relationships.

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Axial Skeleton: The Central Axis of Protection

The axial skeleton forms your body's central column, and its primary job is protection of vital organs. These bones sacrifice mobility for security—the more critical the structure inside, the more rigid the bony housing around it.

Skull (Cranium)

• 8 cranial bones fuse along suture lines to create a rigid vault protecting the brain—this immobility is intentional
• Facial bones (14 total) provide structure for sensory organs and form cavities for the eyes, nasal passages, and ears
• Foramen magnum at the skull's base allows the spinal cord to connect with the brain—a key landmark for identification

Mandible

• Only movable skull bone—its mobility enables mastication (chewing) while all other skull bones remain fused
• Temporomandibular joint (TMJ) connects the mandible to the temporal bone, allowing hinge and gliding movements
• Alveolar processes house the lower teeth and transmit the forces of chewing to the skull

Vertebrae

• 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal) protect the spinal cord while allowing flexibility
• Regional differences reflect function—cervical vertebrae are small and mobile; lumbar vertebrae are massive for weight-bearing
• Intervertebral discs between vertebrae act as shock absorbers and allow flexion, extension, and rotation

Sternum

• Three parts (manubrium, body, xiphoid process) fuse gradually throughout life—the xiphoid remains cartilaginous into adulthood
• Costal notches provide attachment points for ribs via costal cartilage, forming the anterior thoracic cage
• Protects the heart and great vessels—CPR landmarks reference the sternum for this reason

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Thoracic Cage: Protection Meets Respiration

The ribs and sternum form a semi-rigid cage that must accomplish two competing goals: protect the heart and lungs while still allowing the chest to expand during breathing. This is why ribs articulate with cartilage rather than fusing directly.

Ribs

• 12 pairs classified by their sternal attachment—true ribs (1-7) attach directly, false ribs (8-10) attach indirectly, floating ribs (11-12) have no anterior attachment
• Costal cartilage provides flexibility for thoracic expansion during inspiration—without it, breathing would be impossible
• Intercostal spaces between ribs house muscles, nerves, and vessels critical for respiratory mechanics

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Appendicular Skeleton: The Pectoral Girdle and Upper Limb

The upper limb prioritizes range of motion over stability. Notice how the shoulder connects to the axial skeleton by only one small joint (sternoclavicular)—this minimal attachment maximizes mobility but increases injury risk.

Clavicle (Collarbone)

• Only bony connection between the upper limb and axial skeleton—articulates with the sternum medially and scapula laterally
• S-shaped structure acts as a strut, transmitting forces from the arm to the trunk while holding the shoulder laterally
• Most commonly fractured bone due to its subcutaneous position and role in absorbing impact forces

Scapula (Shoulder Blade)

• Flat, triangular bone that "floats" on the posterior thorax, held in place only by muscles—enabling exceptional mobility
• Glenoid cavity forms the shallow socket of the shoulder joint; its small size allows range of motion but reduces stability
• Acromion and coracoid processes serve as attachment points for muscles and ligaments stabilizing the shoulder

Humerus

• Long bone of the upper arm with a rounded head that articulates with the scapula's glenoid cavity
• Greater and lesser tubercles provide attachment for rotator cuff muscles—injury here affects shoulder stability
• Distal end forms the elbow joint with the radius and ulna via the capitulum and trochlea

Radius

• Lateral forearm bone (thumb side) that rotates around the ulna during pronation and supination
• Proximal head articulates with the capitulum of the humerus; distal end forms the major wrist joint surface
• Colles' fracture of the distal radius is common when falling on an outstretched hand—a classic clinical correlation

Ulna

• Medial forearm bone that forms the primary hinge joint at the elbow with the humerus
• Olecranon process is the bony point of your elbow—it fits into the olecranon fossa of the humerus during extension
• Trochlear notch creates a stable hinge articulation, while the ulna provides stability as the radius provides mobility

Carpals

• 8 small bones arranged in two rows (proximal and distal) that allow multiaxial wrist movement
• Scaphoid and lunate articulate with the radius; the scaphoid is the most commonly fractured carpal
• Carpal tunnel is formed by carpal bones and the flexor retinaculum—median nerve compression here causes carpal tunnel syndrome

Metacarpals

• 5 long bones numbered I-V (thumb to pinky) forming the palm of the hand
• Heads form the knuckles and articulate with the proximal phalanges at metacarpophalangeal (MCP) joints
• First metacarpal (thumb) has a saddle joint allowing opposition—critical for human grip and tool use

Phalanges (Hand)

• 14 bones total—each finger has 3 (proximal, middle, distal) while the thumb has only 2 (proximal, distal)
• Hinge joints between phalanges allow flexion and extension for precision grip and fine motor control
• Distal phalanges support the fingernails and contain dense sensory receptors for touch

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Appendicular Skeleton: The Pelvic Girdle and Lower Limb

The lower limb prioritizes stability and weight-bearing over mobility. Compare this to the upper limb: the pelvis is firmly attached to the axial skeleton, the hip socket is deep, and the bones are massive. Every structural difference reflects the demand of supporting body weight.

Pelvis (Hip Bones)

• Three fused bones (ilium, ischium, pubis) unite at the acetabulum—the deep socket for the femoral head
• Pelvic girdle attaches firmly to the sacrum via the sacroiliac joint, transferring upper body weight to the lower limbs
• Sexual dimorphism is pronounced—female pelves are wider and shallower to accommodate childbirth

Femur

• Longest, strongest bone in the body—its strength reflects the enormous forces transmitted during walking and running
• Femoral head fits into the acetabulum; the neck is a common fracture site, especially in osteoporosis
• Distal condyles articulate with the tibia to form the knee joint; the patellar surface accommodates the kneecap

Patella (Kneecap)

• Largest sesamoid bone—it develops within the quadriceps tendon and is not present at birth
• Increases mechanical advantage of the quadriceps by increasing the angle of pull during knee extension
• Articulates with the femur only (not the tibia)—its posterior surface is covered with the thickest cartilage in the body

Tibia

• Weight-bearing bone of the lower leg—its medial malleolus forms the inner ankle bump
• Tibial plateau receives the femoral condyles at the knee; anterior crest (shin) is subcutaneous and easily palpated
• Articulates with the talus to form the ankle joint, transmitting body weight to the foot

Fibula

• Non-weight-bearing bone that provides muscle attachment and lateral ankle stability
• Lateral malleolus forms the outer ankle bump—it extends further distally than the medial malleolus
• Articulates with the tibia proximally and distally but does not contact the femur—it's excluded from the knee joint

Tarsals

• 7 bones including the talus (articulates with tibia) and calcaneus (heel bone, largest tarsal)
• Calcaneus receives the Achilles tendon attachment and bears weight during standing
• Tarsal arrangement creates the arches of the foot—critical for shock absorption and propulsion

Metatarsals

• 5 long bones numbered I-V (big toe to little toe) forming the midfoot
• First metatarsal is the shortest and thickest, bearing significant weight during push-off in gait
• Metatarsal heads form the "ball of the foot" and are common sites for stress fractures in runners

Phalanges (Foot)

• 14 bones following the same pattern as the hand—3 per toe except the big toe (hallux), which has 2
• Shorter and less mobile than hand phalanges, reflecting their role in balance and propulsion rather than manipulation
• Distal phalanges bear weight during the final phase of the gait cycle

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Quick Reference Table

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Self-Check Questions

1. Compare and contrast the pectoral girdle and pelvic girdle. How do their structural differences reflect their functional priorities (mobility vs. stability)?

2. Which two forearm bones divide the labor of elbow stability and wrist mobility? Explain which bone dominates at each joint and why.

3. A patient fractures the bone that forms the only direct skeletal connection between the upper limb and axial skeleton. Which bone is injured, and why is this bone particularly vulnerable?

4. Identify three bones that protect central nervous system structures. What structural feature do they share that maximizes protection?

5. If an FRQ asks you to explain why the femur is the strongest bone in the body while the humerus is not, what functional differences between the upper and lower limbs would you discuss?