The human skeleton has 206 bones that give the body shape, support and protection. CBSE Class 11 covers axial and appendicular divisions. NEET asks about bone counts and specific joint types.
Core Concepts
Axial skeleton
80 bones — skull (22), hyoid (1), vertebrae (26), ribs (24), sternum (1), ear ossicles (6). Protects the brain, spinal cord and thoracic organs.
Let us break down the skull further because NEET sometimes asks specific bone counts:
- Cranial bones: 8 (frontal 1, parietal 2, temporal 2, occipital 1, sphenoid 1, ethmoid 1)
- Facial bones: 14 (maxilla 2, zygomatic 2, nasal 2, lacrimal 2, palatine 2, inferior nasal conchae 2, vomer 1, mandible 1)
- Ear ossicles: 6 (malleus, incus, stapes — 2 of each, one per ear)
The stapes is the smallest bone in the body. The mandible is the only movable skull bone — it forms the temporomandibular joint (TMJ).
Appendicular skeleton
126 bones — upper limbs and pectoral girdle (64), lower limbs and pelvic girdle (62). Involved in locomotion and manipulation.
Upper limb breakdown: humerus (2), radius (2), ulna (2), carpals (16), metacarpals (10), phalanges (28), clavicle (2), scapula (2) = 64.
Lower limb breakdown: femur (2), tibia (2), fibula (2), patella (2), tarsals (14), metatarsals (10), phalanges (28) = 60, plus pelvic girdle (hip bones) 2 = 62.
The hand has 27 bones per side (8 carpals + 5 metacarpals + 14 phalanges). The foot has 26 bones per side (7 tarsals + 5 metatarsals + 14 phalanges). These are high-yield numbers for NEET.
Vertebral column
26 vertebrae — cervical (7), thoracic (12), lumbar (5), sacrum (1, fused from 5), coccyx (1, fused from 4). Protects spinal cord and supports the head. Curvatures absorb shock.
The number 7 for cervical vertebrae is universal across almost all mammals. Whether it is a giraffe with a long neck or a mouse with a short one, both have exactly 7 cervical vertebrae. This is a favourite NEET trivia fact.
The four curvatures of the vertebral column — cervical (convex forward), thoracic (concave forward), lumbar (convex forward), sacral (concave forward) — are not present at birth. They develop as the child learns to hold its head up and walk, adapting the spine for bipedal posture.
Rib cage
12 pairs of ribs. True ribs (first 7 pairs) attached directly to sternum. False ribs (pairs 8 to 10) attached via cartilage to the 7th rib. Floating ribs (pairs 11 and 12) have no sternal attachment.
- True ribs (vertebrosternal): Pairs 1-7, directly joined to sternum by costal cartilage
- False ribs (vertebrochondral): Pairs 8-10, indirectly joined to sternum via 7th rib’s cartilage
- Floating ribs (vertebral): Pairs 11-12, no anterior attachment at all
Joints
Fibrous (immovable, skull sutures), cartilaginous (slightly movable, between vertebrae), synovial (freely movable, most limb joints). Synovial types — ball-and-socket, hinge, pivot, saddle, gliding, condyloid.
Here is a detailed breakdown of synovial joint types with examples:
| Joint Type | Movement | Example |
|---|---|---|
| Ball-and-socket | All directions (multiaxial) | Shoulder, hip |
| Hinge | One plane (uniaxial) | Elbow, knee |
| Pivot | Rotation around axis | Atlas-axis (neck rotation) |
| Saddle | Two planes (biaxial) | Base of thumb (carpometacarpal) |
| Gliding | Sliding surfaces | Between carpals, between tarsals |
| Condyloid (ellipsoid) | Two planes (biaxial) | Wrist, metacarpophalangeal |
Worked Examples
Multiple bones fused by immovable sutures, forming a rigid helmet. The sutures allow slight growth in childhood but lock solid in adulthood.
Curvature creates the thoracic cavity space for lungs and heart, and allows expansion during breathing by elevating the ribs.
A question says: “A joint allows movement in only one plane, like a door opening and closing.” This is a hinge joint. Examples: elbow (between humerus and ulna) and knee (between femur and tibia). The key clue is “one plane” — that eliminates ball-and-socket (all directions) and saddle (two planes).
The pelvic girdle bears the entire weight of the upper body during standing and walking. It is fused and rigid (the two hip bones are joined at the pubic symphysis and to the sacrum). The pectoral girdle is lighter and more mobile because it needs range of motion for arm movement, not weight bearing.
Each finger (index to little) has 3 phalanges (proximal, middle, distal). The thumb has 2 phalanges (proximal, distal). So phalanges per hand = . Add 5 metacarpals and 8 carpals = 27 bones per hand. Both hands = 54 bones.
Disorders of the Skeletal System
Understanding skeletal disorders helps answer application-based NEET questions:
- Arthritis — inflammation of joints. Osteoarthritis is wear-and-tear of cartilage in weight-bearing joints. Rheumatoid arthritis is autoimmune — the immune system attacks synovial membrane.
- Osteoporosis — decreased bone density, common in post-menopausal women due to reduced estrogen. Bones become brittle and fracture easily.
- Gout — uric acid crystals deposit in joints (especially the big toe), causing intense pain. Related to purine metabolism.
- Rickets — vitamin D deficiency in children causes soft, deformed bones because calcium is not properly absorbed.
- Slipped disc — intervertebral disc protrudes and presses on spinal nerves, causing pain.
Common Mistakes
Writing 207 or 208 bones. Adults have 206.
Calling the knee a ball-and-socket joint. It is a hinge.
Confusing atlas and axis. Atlas is the first vertebra (supports skull), axis is the second (provides rotation).
Saying all vertebrae are separate. The sacrum is 5 fused vertebrae and the coccyx is 4 fused vertebrae. We count them as 1 each in the adult skeleton.
Writing that the patella (kneecap) is part of the axial skeleton. It is appendicular — it is a sesamoid bone in the tendon of the quadriceps muscle.
Exam Weightage and Revision
Locomotion and Movement (which includes the skeleton) carries 2-3 NEET questions per year. The questions are predominantly factual — bone counts, joint types, and disorder identification. CBSE boards typically ask a 5-mark long answer on either the skeletal system or muscular system.
Most-asked question types in the last five years:
| Question Type | Frequency | Example |
|---|---|---|
| Bone count in a region | Every year | How many bones in the human skull? |
| Joint type identification | Most years | What type of joint is the shoulder? |
| Disorder identification | Every 2 years | What causes osteoporosis? |
| Rib classification | Occasional | How many pairs of floating ribs? |
The single most useful thing to memorise is the bone count breakdown: axial 80 + appendicular 126 = 206. Within axial, know skull (22), vertebral column (26), ribs + sternum (25), ear ossicles + hyoid (7). Within appendicular, know per-limb breakdown.
Practice Questions
Q1. How many bones are in the adult vertebral column? Name the five regions with their counts.
26 bones. Cervical (7), thoracic (12), lumbar (5), sacrum (1, fused from 5), coccyx (1, fused from 4). Note: before fusion, a child has 33 separate vertebrae.
Q2. Name the smallest bone in the human body. Where is it located?
The stapes (stirrup bone). It is located in the middle ear and is one of the three ear ossicles (malleus, incus, stapes). It transmits sound vibrations from the incus to the oval window of the inner ear.
Q3. A patient can rotate their head left and right but cannot nod. Which joint is affected?
This is a trick question. Rotation (shaking head “no”) happens at the pivot joint between atlas and axis (C1-C2). Nodding (saying “yes”) happens at the joint between the atlas and the occipital bone of the skull. If the patient can rotate but cannot nod, the atlanto-occipital joint is affected, not the atlanto-axial pivot joint.
Q4. Why do astronauts lose bone density in space?
Bones respond to mechanical stress — this is Wolff’s law. Weight-bearing activity stimulates osteoblasts to deposit new bone. In microgravity, there is no weight-bearing, so osteoclast activity (bone resorption) exceeds osteoblast activity (bone formation), leading to bone density loss of about 1-2% per month in space.
FAQs
Why do babies have more bones than adults?
Babies have about 270-300 bones. Many bones in the skull, sacrum, and coccyx are separate at birth and fuse during growth. By adulthood, the count stabilises at 206.
What is the difference between cartilage and bone?
Cartilage is flexible, avascular (no blood vessels), and made of chondrocytes in a matrix of collagen and proteoglycans. Bone is rigid, vascular, and made of osteocytes in a mineralised matrix (calcium phosphate). Cartilage acts as a shock absorber; bone provides structural support.
Which is the longest bone in the human body?
The femur (thigh bone). It is roughly one-quarter of a person’s height.
Why does a fracture heal but damaged cartilage does not heal easily?
Bone has a rich blood supply that delivers the cells and nutrients needed for repair. Cartilage is avascular — it gets nutrients only by diffusion from surrounding tissue, which is very slow. This is why cartilage injuries (like torn knee meniscus) often need surgical intervention.
Memorise bone counts in the axial and appendicular divisions. Both sum to 206.
Bone Structure and Composition
Understanding bone at the microscopic level helps answer NEET application questions.
Bone composition:
- Organic matrix (35%): collagen fibres — provide flexibility and tensile strength
- Inorganic salts (65%): mainly calcium phosphate (hydroxyapatite) — provide hardness and compressive strength
- The combination gives bone its unique property: strong yet slightly flexible (like reinforced concrete)
Bone cells:
- Osteoblasts: build new bone by depositing calcium salts on the collagen matrix
- Osteocytes: mature bone cells trapped in lacunae, connected by canaliculi (tiny channels)
- Osteoclasts: break down bone (resorption) — important for remodelling and calcium homeostasis
Bone is constantly being remodelled — osteoclasts remove old bone while osteoblasts deposit new bone. This is why bones heal after fractures, and why exercise strengthens bones (mechanical stress stimulates osteoblast activity — Wolff’s law).
Types of bone tissue:
- Compact bone: Dense, forms the outer layer of bones. Organised into Haversian systems (osteons) — concentric layers around a central canal containing blood vessels.
- Spongy (cancellous) bone: Porous, found inside bones. Contains red bone marrow where blood cells are produced. Lighter than compact bone but still strong.
The Pectoral vs Pelvic Girdle
| Feature | Pectoral Girdle | Pelvic Girdle |
|---|---|---|
| Bones | Clavicle + scapula (each side) | Two hip bones (each formed from ilium, ischium, pubis) |
| Attachment to axial | Clavicle connects to sternum | Sacrum connects to hip bone |
| Mobility | High (allows arm rotation) | Low (stability for weight-bearing) |
| Joint type | Ball-and-socket (shoulder) | Ball-and-socket (hip) |
| Stability | Less stable, more mobile | More stable, less mobile |
| Function | Supports arm movement | Supports body weight, protects pelvic organs |
The trade-off between mobility and stability is a key biological principle: the shoulder is the most mobile joint in the body but also the most commonly dislocated. The hip is very stable but less mobile.
Memorise bone counts in the axial and appendicular divisions. Both sum to 206.
The skeleton is your internal scaffold. Once you know the two divisions and the six synovial joint types, the chapter is nearly done.