Skeletal & Muscular System

Why This Chapter Matters

Skeletal and muscular system questions show up in almost every SSC CGL, CHSL, MTS and RRB NTPC General Awareness paper, usually as one or two direct one-liners: "How many bones in an adult human body?" or "Which is the longest bone in the human body?" These are not analysis questions. They are pure recall, and recall questions are the easiest marks in the entire paper if you have the right facts sitting ready in your head. Skip this chapter and you are leaving free marks on the table for someone who spent ten minutes less than you preparing.

Here is the shape of what's coming: the bone count and the big bone landmarks first, then joints (this is where most students lose marks), then the three muscle types, and finally the disorders examiners love to ask about. The single biggest mistake aspirants make with this topic is mixing up joint types with bone types, or worse, confusing a disorder's cause with its symptom, like writing that osteoporosis is caused by "weak bones" (that's the definition, not the cause) instead of naming the actual trigger, calcium and Vitamin D deficiency with age. Examiners build wrong options around exactly this kind of confusion. Read this chapter once, properly, and you will stop falling for it.

1. The Skeletal System: The Body's Load-Bearing Frame

Think of your skeleton as the reinforced concrete frame of a building under construction. Before the walls, wiring and paint go in, there has to be a frame that holds everything up and gives it shape. Your skeleton does exactly that for the rest of your body: it supports weight, protects soft organs, and gives muscles something firm to pull against.

An adult human skeleton has 206 bones. This is the single most-repeated fact from this entire chapter across SSC and RRB papers, so lock it in. Exam trap: a newborn baby is NOT born with 206 bones. An infant's skeleton has roughly 270 bones at birth. As a child grows, many small bones (especially in the skull and pelvis) fuse together into single, larger bones, which is why the adult count is lower than the infant count, not higher. Students who assume "more growth means more bones" get this one backwards every single time.

Bones are grouped by shape, and each shape does a different job:

• Long bones — found in limbs (femur, humerus), built for leverage and movement, like a lever arm.
• Short bones — roughly cube-shaped (carpals of the wrist, tarsals of the ankle), built for shock absorption in tight spaces.
• Flat bones — thin and broad (skull bones, ribs, sternum), built for protection of organs underneath, like a shield.
• Irregular bones — complex shapes that don't fit the other categories (vertebrae, facial bones).
• Sesamoid bones — small bones embedded inside a tendon. The patella (kneecap) is the largest sesamoid bone in the body, and it is a favourite exam answer precisely because students forget it is a sesamoid bone and not a flat or irregular one.

Memory hook: to recall the five bone shapes in order, use "Lucky Sardar Farms Irregular Sheep" — Long, Short, Flat, Irregular, Sesamoid. Silly on purpose. Silly sentences survive exam-hall panic better than serious ones do.

The Skeleton's Two Divisions

The skeleton splits into two functional groups, and SSC papers occasionally test which bones belong to which group:

• Axial skeleton (80 bones): the central axis of the body — skull (22 bones), vertebral column (26 bones after fusion), ribs and sternum (25 bones), plus the hyoid bone in the throat.
• Appendicular skeleton (126 bones): the limbs and their girdles — shoulder girdle, arms, hands, pelvic girdle, legs, and feet.

Add 80 and 126 and you get 206, so if a question ever gives you one number and asks for the other, you can work it out on the spot instead of memorising two separate facts.

2. Major Bones and Landmarks You Must Know

You don't need to memorise all 206 bones by name. You need the handful that examiners actually ask about, again and again.

Bone / Region	Key Fact	Why It's Tested
Femur (thigh bone)	Longest and strongest bone in the human body	Repeated almost every year in some form
Stapes (middle ear)	Smallest bone in the human body, shaped like a stirrup	Paired opposite of femur, both asked together
Patella (kneecap)	Largest sesamoid bone	Confused with "flat bone" category
Skull	22 bones total: 8 cranial (protect the brain) + 14 facial	Total count is the trap; students forget the split
Vertebral column	33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into sacrum), 4 coccygeal (fused into coccyx)	"7 cervical" is asked on its own very often — even giraffes have exactly 7
Ribs	12 pairs (24 bones); first 7 pairs are "true ribs," next 3 pairs "false ribs," last 2 pairs "floating ribs"	True vs false vs floating classification is a classic MCQ
Hand	27 bones per hand (8 carpals, 5 metacarpals, 14 phalanges)	Compared against foot count
Foot	26 bones per foot (7 tarsals, 5 metatarsals, 14 phalanges)	Hand has one more bone than the foot — easy to mix up

Exam trap: questions love to ask "how many cervical vertebrae does a human have?" expecting the answer 7, and then, in a different paper entirely, ask the same about a giraffe. Both answers are 7. The giraffe just has much longer individual vertebrae, not more of them. If you only remember one weird fact from this table, make it this one, because it gets asked as a "trick" question disguised as a general knowledge one.

3. Joints: Where Bones Meet, and How Much They Move

A joint is simply the point where two or more bones meet. Not all joints move. Think of your body like a train with different types of couplings between coaches: some couplings are rigid and never separate, some flex a little on curves, and some rotate freely so the train can turn a full corner. Your joints work on the same logic, graded by how much movement they allow.

There are three broad categories:

Fibrous joints (immovable)

Bones are held together directly by fibrous connective tissue with no gap between them. The classic example is the sutures of the skull, the zig-zag joints between your cranial bones. They allow essentially zero movement in an adult, which is exactly what you want protecting your brain.

Cartilaginous joints (slightly movable)

Bones are connected by cartilage, allowing limited flexibility. The joints between vertebrae (via intervertebral discs) are the standard example. This is why your spine can bend and twist a little but each individual joint in it barely moves on its own — the movement adds up across many small joints.

Synovial joints (freely movable)

These are the joints with a fluid-filled cavity (synovial fluid) that lets bones glide smoothly against each other, like oil between two gears. Most joints you actively think about, elbow, knee, shoulder, are synovial. This category has several important subtypes, and SSC papers test the subtype-to-example pairing directly:

Synovial Joint Type	Movement Allowed	Example
Ball-and-socket	Movement in almost every direction	Shoulder, hip
Hinge	Back-and-forth movement in one plane only, like a door	Elbow, knee
Pivot	Rotation around a single axis	Joint between the atlas and axis vertebrae (lets you shake your head "no")
Gliding	Bones slide past each other	Wrist (carpal bones), ankle
Saddle	Movement in two planes, like a rider in a saddle	Base of the thumb
Condyloid	Movement in two planes but no rotation	Wrist joint (between radius and carpal bones)

Memory hook: picture a cricket match to fix the three big synovial types. The shoulder bowling action is ball-and-socket (full rotation, like a fast bowler's arm). The elbow and knee bending to run is a hinge (one direction only, like an umpire raising one finger). Turning your head to check the field before a throw uses the pivot joint at your neck. Three joints, three real cricket moments, and you will not forget which is which under exam pressure.

Exam trap: students frequently swap "hinge" and "pivot." A hinge joint (elbow, knee) moves like a door on its frame, only one direction. A pivot joint (neck) rotates around an axis, like a key turning in a lock. If the question example is the neck, the answer is pivot, never hinge, even though both sound like "just moves in a simple way."

4. Bones Don't Move on Their Own: Ligaments and Tendons

Two connective tissues do the actual work of holding your skeleton together and letting it move, and exams frequently test which does which:

• Ligaments connect bone to bone. They stabilise joints and stop them from moving too far (this is what tears in a sprained ankle).
• Tendons connect muscle to bone. They transmit the pulling force of a contracting muscle to the bone it needs to move (this is what you feel as your Achilles tendon at the back of your ankle).

Memory hook: "Ligaments Link bones, Tendons Tug bones via muscle." L for Link (bone-bone), T for Tug (muscle-bone). Two letters, two jobs, impossible to mix up once it clicks.

5. The Muscular System: Three Types, Three Jobs

If the skeleton is the building's frame, muscles are the motors. The human body has around 600-plus muscles, but you do not need that number. You need the three types, because SSC and RRB ask about their differences constantly, often as a "which of the following is true" question with four close-sounding options.

Muscle Type	Structure	Control	Location	Key Feature
Skeletal muscle	Striated (striped under a microscope)	Voluntary	Attached to bones via tendons	You consciously control it — biceps, quadriceps
Smooth muscle	Unstriated (smooth, no visible stripes)	Involuntary	Walls of internal organs — stomach, intestines, blood vessels, bladder	Works automatically, even while you sleep
Cardiac muscle	Striated, but branched	Involuntary	Only in the heart wall	Never gets tired, works non-stop your whole life

Notice cardiac muscle sits in an odd middle spot: it looks striated like skeletal muscle under a microscope, but it behaves involuntarily like smooth muscle. This overlap is exactly why examiners like asking about it. If a question describes a muscle as "striated but involuntary," the answer is always cardiac muscle, no other type fits that combination.

Exam trap: "striated" does not automatically mean "voluntary." Skeletal muscle is striated and voluntary, but cardiac muscle is striated and involuntary. Match the description carefully instead of assuming striated always equals under your control.

How Muscles Actually Move Bones

Muscles can only pull, they cannot push. That's why they work in pairs called antagonistic pairs, one muscle contracts while its partner relaxes, and then they swap roles for the opposite movement. Think of it like two people playing tug-of-war with the same rope: one side pulling means the other side has to give way, not push back.

The classic exam example is your upper arm: when you bend your elbow, the biceps contracts and the triceps relaxes. When you straighten your elbow again, the triceps contracts and the biceps relaxes. Neither muscle can push the arm back into place on its own; each can only pull.

Muscle contraction also produces energy waste in the form of lactic acid, which is why your muscles feel sore and tired after intense exercise like a long run or a heavy gym session. This is normal muscle biochemistry, not an injury, though prolonged buildup without rest can lead to cramps.

6. Common Bone and Joint Disorders

Disorders are a favourite because the disease name, the affected body part, and the cause can all be tested as three separate questions from one fact.

Arthritis is inflammation of a joint, causing pain, swelling and stiffness. There are two forms exams distinguish between:

• Osteoarthritis — the cartilage cushioning a joint wears down over time, mostly from age or overuse. Most common in weight-bearing joints like the knee and hip.
• Rheumatoid arthritis — an autoimmune condition where the body's own immune system attacks the joint lining. It can strike younger people too, unlike osteoarthritis, which is strongly linked to ageing.

Osteoporosis means bones become porous, brittle and prone to fracture, mainly from calcium and Vitamin D deficiency, and it becomes far more common after middle age, especially in women after menopause because of falling oestrogen levels. Exam trap: never write "weak bones" as the cause of osteoporosis in your own head. Weak, porous bones are the disease itself. The cause examiners want is the nutrient deficiency and the hormonal/age factor behind it.

Rickets affects children and is caused by Vitamin D deficiency, leading to soft, weak bones that can bow under the child's own body weight, producing the classic bent-leg appearance. In adults, the same underlying deficiency causes a related condition called osteomalacia.

Gout is a form of arthritis caused by a buildup of uric acid crystals in a joint, classically the big toe, causing sudden, sharp pain. It is linked to diet and metabolism rather than age or wear.

Tetany is uncontrolled muscle spasm and twitching caused by low calcium levels in the blood. It's a useful contrast fact against osteoporosis: both involve calcium, but osteoporosis is a slow bone disease over years, while tetany is a sudden muscular symptom.

Fractures are simply broken bones, and exams occasionally test types: a simple (closed) fracture doesn't pierce the skin, a compound (open) fracture does, and a greenstick fracture is a partial break common in children, whose bones are more flexible than an adult's, like a young green branch that bends and cracks instead of snapping clean through.

Memory hook: to remember four common bone/joint disorders in one go, use "A Rickety Old Goat" — Arthritis, Rickets, Osteoporosis, Gout. Four disorders, one small barnyard image that sticks.

7. Putting It All Together: Why the Frame and the Motor Need Each Other

Here's a real-world way to hold the whole chapter in your head at once. Picture a bullock cart. The wooden frame and wheels are your skeleton: rigid, load-bearing, giving the whole structure its shape and letting weight sit on it without collapsing. The bullocks pulling the cart are your muscles: they generate the pulling force but have nothing to push against without the frame. And the yoke and ropes connecting bullock to cart are your tendons and ligaments, transferring that pulling force into actual movement. Take away any one part, the rigid frame, the pulling force, or the connectors, and the cart goes nowhere. That is exactly how your skeletal and muscular systems depend on each other, and it is why exams almost always group these two systems into a single chapter rather than testing them separately.

8. A Note on Bone Composition

You don't need biochemistry depth here, but one fact is worth knowing because it explains half the disorders above: bone is a living tissue, not a static rock. It is built mainly from a protein framework called collagen, hardened by deposits of calcium and phosphate minerals. The protein gives bone its flexibility, so it can absorb shocks without shattering, while the mineral gives it hardness, so it can bear weight. Lose too much mineral and bone becomes brittle, which is exactly what happens in osteoporosis. Lose the protein framework and bone becomes fragile in a different way, which is why nutrition, calcium and Vitamin D together, matters throughout life and not only in old age. Think of it like a reinforced water tank: the steel rods (collagen) stop it from cracking under stress, and the concrete (minerals) stops it from bending out of shape. You need both, in the right balance, for the whole structure to survive years of daily load.

Quick Revision — One-Line Facts

1. An adult human skeleton has 206 bones.
2. A newborn infant has roughly 270 bones, more than an adult, before fusion.
3. The femur (thigh bone) is the longest and strongest bone in the body.
4. The stapes, in the middle ear, is the smallest bone in the body.
5. The patella (kneecap) is the largest sesamoid bone.
6. The skull has 22 bones: 8 cranial and 14 facial.
7. There are 33 vertebrae in the spinal column before some fuse.
8. Humans have 7 cervical vertebrae, the same number as a giraffe.
9. There are 12 pairs of ribs (24 bones total).
10. The first 7 rib pairs are "true ribs"; the last 2 pairs are "floating ribs."
11. Each hand has 27 bones; each foot has 26 bones.
12. The axial skeleton has 80 bones; the appendicular skeleton has 126 bones.
13. Fibrous joints, like skull sutures, allow no movement.
14. Cartilaginous joints, like those between vertebrae, allow slight movement.
15. Synovial joints are freely movable and contain synovial fluid.
16. The shoulder and hip are ball-and-socket joints.
17. The elbow and knee are hinge joints.
18. The joint between the atlas and axis vertebrae is a pivot joint.
19. The base of the thumb is a saddle joint.
20. Ligaments connect bone to bone.
21. Tendons connect muscle to bone.
22. Skeletal muscle is striated and voluntary.
23. Smooth muscle is unstriated and involuntary, found in organ walls.
24. Cardiac muscle is striated but involuntary, found only in the heart.
25. Muscles work in antagonistic pairs because they can only pull, never push.
26. The biceps and triceps are the classic antagonistic pair in the upper arm.
27. Osteoarthritis is wear-and-tear joint damage, common with age.
28. Rheumatoid arthritis is an autoimmune attack on joint tissue.
29. Osteoporosis is caused by calcium/Vitamin D deficiency and ageing.
30. Rickets in children and osteomalacia in adults both come from Vitamin D deficiency.
31. Gout is caused by uric acid crystal buildup, classically in the big toe.
32. A greenstick fracture is a partial break, common in children.

Memory Tables

Table 1: Bone Count Quick Reference

Region	Bone Count
Whole adult skeleton	206
Newborn infant skeleton	~270
Skull	22 (8 cranial + 14 facial)
Vertebral column	33 (26 after fusion of sacrum and coccyx)
Ribs	24 (12 pairs)
One hand	27
One foot	26
Axial skeleton	80
Appendicular skeleton	126

Table 2: Three Muscle Types at a Glance

Feature	Skeletal	Smooth	Cardiac
Appearance	Striated	Unstriated	Striated, branched
Control	Voluntary	Involuntary	Involuntary
Found in	Attached to bones	Internal organ walls	Heart only
Fatigue	Tires with use	Rarely tires	Never tires

Table 3: Bone/Joint Disorders and Their Cause

Disorder	Affects	Main Cause
Osteoarthritis	Joints (cartilage)	Age, wear and tear
Rheumatoid arthritis	Joints (lining)	Autoimmune attack
Osteoporosis	Bones (density)	Calcium/Vitamin D deficiency, ageing
Rickets	Children's bones	Vitamin D deficiency
Gout	Joints (usually big toe)	Uric acid crystal buildup
Tetany	Muscles (spasms)	Low blood calcium

Practice MCQs

Q1. How many bones are there in an adult human skeleton? (a) 196 (b) 206 (c) 216 (d) 226

Q2. Which is the longest bone in the human body? (a) Humerus (b) Tibia (c) Femur (d) Fibula

Q3. Which is the smallest bone in the human body? (a) Stapes (b) Patella (c) Femur (d) Radius

Q4. How many cervical vertebrae are present in a human being? (a) 5 (b) 7 (c) 9 (d) 12

Q5. Ligaments connect which of the following? (a) Muscle to bone (b) Bone to bone (c) Muscle to muscle (d) Skin to bone

Q6. Which type of muscle is found only in the heart? (a) Skeletal muscle (b) Smooth muscle (c) Cardiac muscle (d) Voluntary muscle

Q7. The shoulder joint is an example of which type of joint? (a) Hinge joint (b) Pivot joint (c) Ball-and-socket joint (d) Gliding joint

Q8. Which vitamin deficiency causes rickets in children? (a) Vitamin A (b) Vitamin B12 (c) Vitamin C (d) Vitamin D

Q9. The elbow joint is an example of which type of joint? (a) Ball-and-socket joint (b) Hinge joint (c) Saddle joint (d) Pivot joint

Q10. Which of the following bones is classified as a sesamoid bone? (a) Femur (b) Sternum (c) Patella (d) Humerus

Q11. Gout is caused by the accumulation of which substance in the joints? (a) Calcium (b) Uric acid (c) Lactic acid (d) Sodium

Q12. Which muscle type is unstriated and involuntary, found mainly in the walls of internal organs? (a) Skeletal muscle (b) Smooth muscle (c) Cardiac muscle (d) Striped muscle

Q13. The pivot joint that allows rotation of the head is located between which two vertebrae? (a) Atlas and axis (b) Sacrum and coccyx (c) Thoracic and lumbar (d) Cervical and thoracic

Q14. Osteoporosis mainly results from a deficiency of which two factors combined? (a) Iron and Vitamin C (b) Calcium and Vitamin D (c) Protein and Vitamin A (d) Sodium and Vitamin B12

Q15. In the human arm, which pair of muscles works as an antagonistic pair? (a) Biceps and deltoid (b) Triceps and forearm flexor (c) Biceps and triceps (d) Deltoid and triceps

Answer Key

Q	Answer	Reason
Q1	(b) 206	The standard adult bone count; infants have more (~270) before fusion.
Q2	(c) Femur	The femur is both the longest and the strongest bone, unlike the humerus or tibia.
Q3	(a) Stapes	Located in the middle ear, shaped like a stirrup, the smallest bone overall.
Q4	(b) 7	All mammals, including giraffes, have exactly 7 cervical vertebrae.
Q5	(b) Bone to bone	Ligaments link bone to bone; tendons are the ones linking muscle to bone.
Q6	(c) Cardiac muscle	Cardiac muscle is unique to the heart wall and never found elsewhere in the body.
Q7	(c) Ball-and-socket joint	This joint type allows movement in almost every direction, unlike a hinge which moves one way.
Q8	(d) Vitamin D	Vitamin D deficiency in children causes rickets; the same deficiency in adults causes osteomalacia.
Q9	(b) Hinge joint	The elbow moves in one plane only, like a door, which is the definition of a hinge joint.
Q10	(c) Patella	The patella (kneecap) is the largest sesamoid bone, embedded within a tendon.
Q11	(b) Uric acid	Gout results from uric acid crystal deposits, classically in the big toe joint.
Q12	(b) Smooth muscle	Smooth muscle lacks stripes and works involuntarily in organs like the stomach and intestines.
Q13	(a) Atlas and axis	This pivot joint at the top of the spine lets the head rotate side to side.
Q14	(b) Calcium and Vitamin D	Both nutrients are needed to maintain bone density; their deficiency, plus ageing, drives osteoporosis.
Q15	(c) Biceps and triceps	This is the textbook antagonistic pair: one contracts while the other relaxes to bend or straighten the elbow.