Class 11 Biology Chapter 17 Locomotion and Movement Notes
These Locomotion and Movement Class 11 Notes explain how muscles and the skeleton work together to produce movement. Revise the types of movement, structure and contraction of skeletal muscle, bones, joints, and important disorders in one place.
Table of Contents
Movement and locomotion
Movement is a change in the position of a body part. Locomotion is movement that takes an organism from one place to another. Every locomotion involves movement, but movement does not always cause locomotion. For example, moving your arm while sitting is movement; walking across a room is locomotion.
Types of movement
| Type | How it occurs | Example |
|---|---|---|
| Amoeboid | Cell forms temporary projections called pseudopodia | Movement of white blood cells |
| Ciliary | Coordinated beating of cilia | Movement of materials along ciliated passages |
| Flagellar | Movement of a flagellum | Swimming of a sperm cell |
| Muscular | Contraction and relaxation of muscles | Walking or moving an arm |
Types of muscles
| Muscle | Appearance and control | Location |
|---|---|---|
| Skeletal muscle | Striated and generally voluntary | Attached to bones |
| Smooth or visceral muscle | Non-striated and involuntary | Walls of internal organs |
| Cardiac muscle | Striated, branched and involuntary | Heart |
Skeletal muscles produce many movements of the body by pulling on bones. Muscles can contract and relax, but they do not push bones.
Structure of skeletal muscle
A skeletal muscle contains bundles called fascicles. Each fascicle contains muscle fibres, and each fibre contains many myofibrils. Myofibrils have repeating functional units called sarcomeres.
A sarcomere extends from one Z line to the next. Its main regions are:
- Thin filaments: Primarily contain actin and extend from the Z lines.
- Thick filaments: Primarily contain myosin and occupy the centre of the sarcomere.
- I band: Light region containing thin filaments without overlap with thick filaments.
- A band: Dark region spanning the full length of thick filaments.
- H zone: Central part of the A band containing thick filaments without overlap with thin filaments.
The thin filament also contains tropomyosin and troponin, which help regulate the interaction between actin and myosin. A myosin molecule has heads that can bind to actin and use energy from ATP.
Sliding filament theory of muscle contraction
According to the sliding filament theory, thin actin filaments slide past thick myosin filaments. The filaments themselves do not become shorter; the sarcomere shortens because their overlap increases.
Steps in muscle contraction
- A motor nerve impulse reaches the muscle fibre. The nerve ending releases acetylcholine, which triggers an electrical signal in the muscle.
- The signal causes the sarcoplasmic reticulum to release calcium ions.
- Calcium binds to troponin. This moves the regulating proteins so that myosin-binding sites on actin become accessible.
- Myosin heads attach to actin, forming cross-bridges.
- Using energy from ATP, myosin heads pull the thin filaments towards the centre of the sarcomere.
- Myosin detaches and can attach again while calcium and ATP are available. Repeated cycles produce contraction.
- When stimulation stops, calcium is pumped back into the sarcoplasmic reticulum. The binding sites become covered again, and the muscle relaxes.
Remember: During contraction, the I band and H zone become narrower, while the A band remains the same length.
Human skeletal system
The adult human skeleton has 206 bones. It gives the body support and shape, protects organs, provides attachment points for muscles, and helps produce movement.
| Division | Number of bones | Main parts |
|---|---|---|
| Axial skeleton | 80 | Skull, vertebral column, ribs and sternum |
| Appendicular skeleton | 126 | Limb bones and pectoral and pelvic girdles |
The vertebral column supports the trunk and protects the spinal cord. The rib cage helps protect the heart and lungs. The pectoral girdle connects the upper limbs to the axial skeleton, while the pelvic girdle connects the lower limbs.
Joints and their types
A joint is a point of contact between bones, or between bone and cartilage. Joints differ in how much movement they allow.
| Joint type | Movement | Example |
|---|---|---|
| Fibrous | No movement | Sutures between skull bones |
| Cartilaginous | Limited movement | Joints between adjacent vertebrae |
| Synovial | Considerable movement | Shoulder, knee and other freely moving joints |
Common synovial joints include the ball-and-socket joint at the shoulder or hip, hinge joint at the knee, pivot joint between the atlas and axis, gliding joints between wrist bones, and saddle joint at the base of the thumb.
Disorders of muscles and bones
- Myasthenia gravis: An autoimmune disorder affecting communication between nerves and skeletal muscles, causing muscle weakness.
- Muscular dystrophy: A group of largely genetic conditions involving progressive degeneration of skeletal muscle.
- Tetany: Rapid, involuntary muscle spasms associated with low calcium in body fluid.
- Arthritis: Inflammation of a joint.
- Osteoporosis: Reduced bone mass, which increases the chance of fractures.
- Gout: Joint inflammation associated with deposits of uric acid crystals.
Quick revision
- Locomotion moves an organism from place to place; movement may involve only a body part.
- Skeletal muscle is striated and voluntary; smooth and cardiac muscles are involuntary.
- A sarcomere is the functional unit of a myofibril.
- Actin forms the main part of thin filaments; myosin forms thick filaments.
- Calcium and ATP are essential for the sliding filament process.
- The skeleton has 206 bones: 80 axial and 126 appendicular.
- The three main structural types of joints are fibrous, cartilaginous and synovial.
Check your understanding
1. What is the difference between movement and locomotion?
Locomotion changes the place of the whole organism. Movement can occur without changing its place.
2. What happens to the A band during muscle contraction?
Its length remains the same.
3. Which ion exposes the myosin-binding sites on actin?
Calcium ions, through their action on troponin.
4. What type of joint is found between the atlas and axis?
A pivot joint.
5. Name the two main divisions of the human skeleton.
The axial skeleton and the appendicular skeleton.
Explore the other chapters in the CBSE Class 11 Biology Complete Study Guide.
Frequently Asked Questions
What is the difference between movement and locomotion?
Movement changes the position of a part or whole body; locomotion moves the organism from place to place.
What are the main types of cellular movement?
Amoeboid, ciliary and muscular movements occur in human cells; a sperm cell moves using a flagellum.
What are the three types of human muscle?
Skeletal, smooth (visceral) and cardiac muscle.
Which muscles are generally voluntary?
Skeletal muscles are generally under voluntary control.
What is a sarcomere?
It is the functional contractile unit of a myofibril, extending between two Z lines.
Which proteins form the thin and thick filaments?
Actin is the main thin-filament protein; myosin forms the thick filaments.
What is the sliding filament theory?
Muscle contracts when actin filaments slide past myosin filaments and shorten the sarcomere.
What role does calcium have in muscle contraction?
Calcium binds to troponin, helping expose myosin-binding sites on actin.
What role does ATP have in muscle contraction?
ATP supplies energy for the cross-bridge cycle and helps myosin detach from actin.
What happens to the A band during contraction?
Its length remains approximately constant while the I band and H zone become narrower.
How many bones are in the adult human skeleton?
The adult human skeleton is conventionally described as having 206 bones.
What makes up the axial skeleton?
The skull, vertebral column, ribs and sternum.
What makes up the appendicular skeleton?
The limb bones and the pectoral and pelvic girdles.
What are the three structural classes of joints?
Fibrous, cartilaginous and synovial joints.
What is osteoporosis?
It is a condition of reduced bone mass and greater fracture risk.