BiologyISC Class 11 · Locomotion and Movement

The Human Skeleton, Joints and Disorders of Muscles and Bones

Updated 17 October 2026 · Fact-checked

The human skeleton has 206 bones: the axial skeleton (80: skull, vertebral column, sternum and ribs) and the appendicular skeleton (126: limbs and girdles). Joints are fibrous, cartilaginous or synovial. Disorders include arthritis, osteoporosis, gout, myasthenia gravis, muscular dystrophy and tetany.

Notice the sums: 29 + 26 + 1 + 24 = 80 axial, and 6 + 120 = 126 appendicular, giving 206 bones in all.

Illustration drawn for QuestionBuddy.

Understand Skeletal System, Joints and Disorders

Axial skeleton (80 bones). *Skull* (29 bones): cranium of 8 bones (frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid), face of 14 bones, hyoid 1 and ear ossicles 6 (malleus, incus and stapes in each ear). The skull articulates with the vertebral column through two occipital condyles (dicondylic). *Vertebral column* (26 bones): 7 cervical (the first is the atlas), 12 thoracic, 5 lumbar, 1 sacral (fused 5) and 1 coccygeal (fused 4); it protects the spinal cord and supports the head. *Sternum*: 1 flat bone. *Ribs*: 12 pairs: true ribs (7 pairs, attached to the sternum), false ribs (3 pairs, joined to the 7th rib by cartilage) and floating ribs (2 pairs). The thoracic vertebrae, ribs and sternum form the rib cage. Total: 29 + 26 + 1 + 24 = 80.

Appendicular skeleton (126 bones). Pectoral girdle (clavicle and scapula, 4 bones) with the glenoid cavity; forelimb of 30 bones on each side (humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges); pelvic girdle of two coxal bones (each of ilium, ischium and pubis, meeting at the pubic symphysis) with the acetabulum; hindlimb of 30 bones on each side (femur, tibia, fibula, patella, 7 tarsals, 5 metatarsals, 14 phalanges). Total: 4 + 60 + 2 + 60 = 126.

Joints. *Fibrous* (immovable; sutures of the skull). *Cartilaginous* (slightly movable; between vertebrae). *Synovial* (freely movable, with a synovial fluid cavity): ball-and-socket (shoulder, hip), hinge (knee, elbow), pivot (atlas and axis), gliding (between carpals) and saddle (carpometacarpal joint of the thumb).

Disorders. Myasthenia gravis: an autoimmune disorder affecting the neuromuscular junction, causing weakness. Muscular dystrophy: progressive degeneration of skeletal muscle, mostly genetic. Tetany: rapid muscle spasms from low Ca²⁺ in body fluid. Arthritis: inflammation of joints. Osteoporosis: decreased bone mass and increased fracture risk, common in old age (often with a fall in oestrogen). Gout: inflammation of joints by accumulation of uric acid crystals.

Skeletal System, Joints and Disorders: key facts

Axial skeleton: $S k u l l 29 + v er t e b r a l co l u mn 26 + s t er n u m 1 + r ib s 24 = 80$; Appendicular: 126; total 206.
Vertebrae: $C er v i c a l 7∣ T h or a c i c 12∣ Lu mba r 5∣ S a cr a l 1∣ C occy g e a l 1$; Total 26 in an adult.
Ribs: $T r u e 7 p ai r s ∣ F a l se 3 p ai r s ∣ F l o a t in g 2 p ai r s$; 12 pairs.
Synovial joints: Ball and socket shoulder
Hinge knee
Pivot atlas-axis
Gliding carpals
Saddle thumb; Freely movable.

Ball and socket	shoulder
Hinge	knee
Pivot	atlas-axis
Gliding	carpals
Saddle	thumb

Skeletal System, Joints and Disorders in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Counting the bones of the leg

Suppose a student counts the bones of one lower limb and the pelvic girdle.

Name the bones of one hindlimb, count them, and find the number of bones in the pelvic girdle and both hindlimbs.

Try it first, then show the solutionSolution

One hindlimb: femur 1, tibia 1, fibula 1, patella 1, tarsals 7, metatarsals 5, phalanges 14 = 30.
Both hindlimbs = 60; pelvic girdle (two coxal bones) = 2.
Total = 62 bones.

Answer: 30 per hindlimb; 62 in total with the pelvic girdle.

Memory hook: The forelimb also has 30 bones.

Tricks to remember Skeletal System, Joints and Disorders

Short memory aids. Say each one aloud once, then use it on a question the same day.

7, 12, 5, 1, 1
Cervical, thoracic, lumbar, sacral, coccygeal vertebrae in order.
Use it when: Vertebral formula.
Hinge bends one way, ball rotates
Knee/elbow: back and forth; shoulder/hip: all directions.
Use it when: Types of synovial joints.

Skeletal System, Joints and Disorders: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Number of bones in the axial skeleton · 1 mark · MCQBoard level

The number of bones in the human axial skeleton is:
(a) 80
(b) 126
(c) 206
(d) 29

Try it first, then show the solutionSolution

Skull 29, vertebral column 26, sternum 1 and ribs 24 give 80.

Answer: (a) 80

Example 2: Vertebral column · 3 marks · Short answerBoard level

Name the regions of the vertebral column with the number of vertebrae in each and write one function of the column.

Try it first, then show the solutionSolution

Cervical 7, thoracic 12, lumbar 5. (1 mark)
Sacral 1 (fused 5) and coccygeal 1 (fused 4): total 26. (1 mark)
Function: protects the spinal cord, supports the head and gives attachment to ribs and muscles. (1 mark)

Answer: 7 + 12 + 5 + 1 + 1 = 26 vertebrae.

Example 3: Counting bones · 4 marks · Short answerHarder board level

Calculate the number of bones in the human axial and appendicular skeleton from their parts, and the total.

Try it first, then show the solutionSolution

Axial: skull 29 (cranium 8, face 14, hyoid 1, ear ossicles 6) + vertebral column 26 + sternum 1 + ribs 24 = 80. (2 marks)
Appendicular: pectoral girdle 4 + forelimbs 60 + pelvic girdle 2 + hindlimbs 60 = 126. (1.5 marks)
Total = 206. (0.5 mark)

Answer: 80 + 126 = 206.

Example 4: Joints · 4 marks · Short answerHarder board level

Classify joints and give an example of each type of synovial joint with the movement allowed.

Try it first, then show the solutionSolution

Fibrous (immovable), cartilaginous (slightly movable), synovial (freely movable). (1 mark)
Ball and socket: shoulder and hip, movement in all directions. (1 mark)
Hinge: knee and elbow, movement in one plane. Pivot: atlas on axis, rotation. (1 mark)
Gliding: between carpals; saddle: thumb joint. (1 mark)

Answer: Fibrous, cartilaginous and synovial; five synovial types.

Example 5: Skeletal disorders · 5 marks · Long answerHOTS / competency

Distinguish between arthritis, osteoporosis and gout. A person has weakness of muscles due to antibodies against acetylcholine receptors; name the disorder. Why does low calcium cause tetany?

Try it first, then show the solutionSolution

Arthritis: inflammation of joints. (0.75 mark)
Osteoporosis: reduced bone mass and increased risk of fracture, common after menopause and in old age. (1 mark)
Gout: inflammation of joints caused by uric acid crystal deposits. (1 mark)
Myasthenia gravis, an autoimmune neuromuscular disease. (1 mark)
Low Ca²⁺ in body fluid increases the excitability of nerves and muscles, causing rapid spasms (tetany). (1.25 marks)

Answer: Arthritis, osteoporosis, gout; myasthenia gravis; low Ca²⁺ causes tetany.

Where students lose marks in Skeletal System, Joints and Disorders

The slips examiners see most often, and what to write instead.

Mistake: Wrong number of vertebrae
Writing 33 for an adult.
Do this: In the adult the sacral (5) and coccygeal (4) vertebrae fuse: 26 vertebrae.
Usually costs: 1 mark.
Mistake: Counting the hyoid separately
Forgetting the hyoid and the ear ossicles in the skull count.
Do this: Skull 29: 8 + 14 + 1 + 6.
Usually costs: 1 mark.
Mistake: Mixing arthritis and osteoporosis
Calling reduced bone mass arthritis.
Do this: Arthritis is joint inflammation; osteoporosis is reduced bone mass.
Usually costs: 1 mark.

Exam tips

Draw the human skeleton in outline with labels.
Learn the totals: 80 + 126 = 206.
Match each joint with a body example.
Give a cause for each disorder.

Practice questions on Skeletal System, Joints and Disorders

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The elbow and the knee are examples of:
(a) ball-and-socket joints
(b) hinge joints
(c) pivot joints
(d) fibrous joints
Hint
They bend in one plane.
Answer
(b) hinge joints
Q2 · 2 marks · Short answerBoard level
Name the three types of ribs.
Hint
True, false and floating.
Answer
True ribs (7 pairs), false ribs (3 pairs) and floating ribs (2 pairs).
Q3 · 3 marks · Short answerHarder board level
How many bones are in the human skull? Give the parts.
Hint
Cranial and facial.
Answer
29 bones: 8 cranial, 14 facial, 1 hyoid and 6 ear ossicles.
Q4 · 3 marks · Short answerHarder board level
Name the bones of the pectoral girdle and pelvic girdle and the cavities for the limbs.
Hint
Glenoid and acetabulum.
Answer
Pectoral: clavicle and scapula, with the glenoid cavity for the humerus. Pelvic: two coxal bones (ilium, ischium, pubis), with the acetabulum for the femur.
Q5 · 3 marks · Assertion-reasonHarder board level
Assertion (A): Elderly women are more prone to osteoporosis. Reason (R): Bone density falls and the level of oestrogen decreases after menopause. Choose: (a) both true and R explains A (b) both true, R does not explain A (c) A true, R false (d) A false, R true.
Hint
Think about hormones.
Answer
(a) Both true and R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
Case study: Suppose a doctor reports that a patient has severe pain in the big toe due to uric acid crystals.
(i) Name the disorder. (1 mark)
(ii) Name the type of joint affected, a synovial joint of the foot. (1 mark)
(iii) Name a bone disorder with reduced bone mass. (1 mark)
(iv) Give one preventive measure. (1 mark)
Hint
Recall the disorders.
Answer
(i) Gout. (ii) A synovial joint (metatarsophalangeal). (iii) Osteoporosis. (iv) A diet low in purines, adequate fluid and regular exercise (or enough calcium and vitamin D for osteoporosis).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Bones in the human skeleton?Show answer
206.
2.Cervical vertebrae?Show answer
7.
3.Floating ribs?Show answer
2 pairs.
4.Joint of the hip?Show answer
Ball and socket.

Skeletal System, Joints and Disorders: frequently asked questions

What are ear ossicles?

The three tiny bones of the middle ear (malleus, incus, stapes) that transmit sound.

Why is the fusion of sacral vertebrae important?

It makes a strong support for the pelvis and body weight.

What is the difference between a tendon and a ligament?

A tendon joins muscle to bone; a ligament joins bone to bone.