Movement and Skeleton
Introduction
The skeletal system provides structural support, protects vital organs, and enables movement. ICSE Class 9 covers the human skeleton, joints, and muscle function.
Functions of the Skeleton
- Support: Provides framework for the body
- Protection: Protects vital organs (brain, heart, lungs)
- Movement: Provides attachment points for muscles
- Blood cell production: Red bone marrow produces RBCs
- Mineral storage: Stores calcium and phosphorus
The Human Skeleton
The human skeleton consists of 206 bones divided into two main parts.
Axial Skeleton (80 bones)
The central axis of the body.
Skull (22 bones)
- Cranium (8 bones): Protects the brain
- Facial bones (14 bones): Form the face structure
- Lower jaw (mandible): Only movable bone of the skull
Vertebral Column (26 bones)
33 vertebrae in children; 26 in adults (5 sacral + 4 coccygeal fuse)
| Region | Number | Characteristics |
|---|---|---|
| Cervical | 7 | Neck region; Atlas (C1) and Axis (C2) allow head movement |
| Thoracic | 12 | Attached to ribs |
| Lumbar | 5 | Lower back; largest and strongest |
| Sacrum | 5 fused | Connects to pelvic girdle |
| Coccyx | 4 fused | Tailbone |
Ribs and Sternum (25 bones)
| Type | Description | Number (pairs) |
|---|---|---|
| True ribs | Attached directly to sternum | 7 |
| False ribs | Attached indirectly to sternum | 3 |
| Floating ribs | Not attached to sternum | 2 |
Sternum: Flat bone in the centre of the chest.
Appendicular Skeleton (126 bones)
Bones of the limbs and their attachments (girdles).
Upper Limbs (each arm)
- Humerus: Upper arm
- Radius and Ulna: Forearm
- Carpals: 8 wrist bones
- Metacarpals: 5 palm bones
- Phalanges: 14 finger bones (thumb has 2, others have 3 each)
Lower Limbs (each leg)
- Femur: Thigh bone (longest bone in the body)
- Tibia and Fibula: Shin and calf bones
- Patella: Kneecap
- Tarsals: 7 ankle bones
- Metatarsals: 5 foot bones
- Phalanges: 14 toe bones
Girdles
- Pectoral girdle (shoulder): Clavicle + Scapula
- Pelvic girdle (hip): Two hip bones fused with sacrum
Joints
A joint is where two or more bones meet.
Types of Joints
| Joint Type | Movement | Examples |
|---|---|---|
| Ball and socket | Movement in all directions | Shoulder, hip |
| Hinge joint | Movement in one plane (like a door hinge) | Elbow, knee, finger |
| Pivot joint | Rotation (one bone rotates around another) | Neck (atlas-axis), wrist |
| Gliding joint | Sliding movement | Wrist, ankle, vertebrae |
| Fixed (fibrous) joint | No movement | Skull bones (sutures) |
Muscles and Movement
Antagonistic Muscle Pairs
Muscles work in pairs to produce movement. When one contracts, the other relaxes.
Example: Biceps and Triceps:
- Bending the arm: Biceps contracts, triceps relaxes
- Straightening the arm: Triceps contracts, biceps relaxes
Muscle Contraction
Sliding Filament Theory: Actin filaments slide over myosin filaments, shortening the sarcomere.
Energy source: ATP (from cellular respiration)
Types of Muscles (Review)
| Type | Location | Control | Characteristics |
|---|---|---|---|
| Striated (skeletal) | Attached to skeleton | Voluntary | Fast contraction, gets fatigued |
| Smooth | Internal organs | Involuntary | Slow contraction, no fatigue |
| Cardiac | Heart | Involuntary | Rhythmic, never fatigues |
Common Mistakes With Fixes
| Mistake | Correction |
|---|---|
| Ribs are attached to the sternum directly | Only true ribs (first 7 pairs) are directly attached |
| The femur is in the arm | Femur is in the THIGH; humerus is in the upper arm |
| All joints allow free movement | Fixed joints (skull) allow NO movement |
| Muscles push bones | Muscles only PULL bones (by contracting) |
ICSE Exam Focus
| Topic | Marks (approx.) | Frequency |
|---|---|---|
| Axial vs appendicular skeleton | 4-5 marks | Very common |
| Types of joints | 3-4 marks | Very common |
| Muscles and movement | 3-4 marks | Common |
| Bones of the skull and vertebral column | 3-4 marks | Frequently asked |
Self-Test
Q1: Differentiate between axial and appendicular skeleton.
Q2: List three types of movable joints with examples.
Q3: Explain how biceps and triceps work as an antagonistic pair.
Q4: Name the longest bone in the human body. Where is it located?
Q5: How many bones are present in the adult human skeleton?
