Chapter 6: Control and Coordination
1. Introduction
All living things need to respond to changes around them.
For example:
- We move our hand away when something is hot.
- Plants bend towards light.
These changes in surroundings are called stimuli, and the actions we take are called responses.
In animals, this work is done by two systems:
- Nervous System – for quick actions.
- Endocrine System – for slow but long-lasting actions (hormones).
Plants do not have nerves or a brain, but they still respond to light, gravity, touch, etc., using plant hormones.
2. Why Do We Need Control and Coordination?
Every living being needs control and coordination to:
- Respond to changes quickly.
- Make all body parts work together.
- Maintain internal balance (called homeostasis).
Help the body grow, move, and function smoothly
3. Control and Coordination in Animals
Animals, especially humans, have a nervous system that helps in controlling and coordinating activities.
It receives information, processes it, and then sends messages to the body to act.
4. The Nervous System
The human nervous system is made of neurons (nerve cells).
They carry messages in the form of electrical impulses.
4.1. Parts of the Human Nervous System
- Central Nervous System (CNS) – Brain and Spinal Cord
- Peripheral Nervous System (PNS) – Nerves from the brain and spinal cord to the rest of the body
4.2. Neuron – The Nerve Cell
It is the basic unit of the nervous system.
Parts of a Neuron:
- Dendrites: Receive messages from other cells.
- Cell Body (Cyton): Has the nucleus and controls the neuron.
- Axon: Carries messages away from the cell body.
- Axon Terminal: Sends messages to the next neuron or muscle.
Function:
Messages travel as tiny electrical signals from dendrites → cell body → axon → axon terminal → next neuron.
4.3. Synapse
A synapse is a small gap between two neurons.
The message crosses this gap with the help of chemicals called neurotransmitters.
4.4. Types of Neurons
Type | Function |
Sensory Neuron | Carries message from sense organs (eye, skin) to the brain/spinal cord |
Motor Neuron | Carries message from brain/spinal cord to muscles or glands |
Interneuron | Connects sensory and motor neurons |
5. Reflex Action
A reflex action is a quick and automatic response to a stimulus.
It protects the body from harm.
Examples:
- Pulling hand away from a hot object.
- Blinking eyes when something comes close.
The pathway of a reflex action is called a Reflex Arc.
Pathway:
Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector (muscle)
💡 Reflex actions happen through the spinal cord, not the brain, to save time.
6. Human Brain
The brain is the main control center of the body.
It receives messages, interprets them, and sends commands.
It is protected by the skull and three membranes (meninges).
It also has a liquid called cerebrospinal fluid (CSF) that protects it from shocks.
6.1. Main Parts of the Brain
- Forebrain
- Midbrain
- Hindbrain
6.1.1. Forebrain
- Largest part of the brain.
- Includes Cerebrum, Thalamus, and Hypothalamus.
Cerebrum:
- Controls thinking, memory, learning, and voluntary actions.
- It helps in understanding sensations like touch, taste, and sound.
Thalamus:
- Acts as a relay station for messages from sense organs.
Hypothalamus:
- Controls hunger, thirst, emotions, and body temperature.
- Also controls hormone release through the pituitary gland.
6.1.2. Midbrain
- Controls eye movements and hearing reflexes.
- Acts as a link between forebrain and hindbrain.
6.1.3. Hindbrain
Made up of Cerebellum, Pons, and Medulla Oblongata.
Part | Function |
Cerebellum | Controls balance and posture |
Pons | Helps in breathing |
Medulla Oblongata | Controls involuntary actions like heartbeat and digestion |
7. Coordination between Brain and Spinal Cord
- The brain controls voluntary actions.
- The spinal cord handles reflexes and connects brain to body parts.
Together, they keep all organs working properly.
8. Control and Coordination in Plants
Plants don’t have a brain or nerves, but they can still sense changes and respond to them.
They do this using plant hormones and movements.
8.1. Types of Movements in Plants
- Tropic Movements – Directional growth in response to a stimulus.
- Nastic Movements – Non-directional movements due to changes in cell pressure.
8.2. Tropic Movements (Directional)
Type | Stimulus | Example |
Phototropism | Light | Stem bends toward light |
Geotropism | Gravity | Roots grow downward |
Hydrotropism | Water | Roots grow toward moisture |
Thigmotropism | Touch | Tendrils wrap around support |
Chemotropism | Chemicals | Pollen tube grows toward ovule |
8.3. Nastic Movements (Non-Directional)
- Not dependent on direction of stimulus
Examples: - Touch-me-not plant folds its leaves when touched.
- Flowers open and close with light and temperature.
9. Plant Hormones (Phytohormones)
Plants control their growth using natural chemical messengers called hormones.
Hormone | Function |
Auxin | Helps in cell elongation and bending of stem towards light |
Gibberellin | Helps in stem growth and seed germination |
Cytokinin | Helps in cell division and delays aging of leaves |
Abscisic Acid (ABA) | Stops growth, helps in stress (drought, injury) |
Ethylene | Helps in fruit ripening and leaf fall |
10. Chemical Coordination in Humans (Hormonal System)
Along with the nervous system, humans have endocrine glands that release hormones.
Hormones are chemical messengers that travel in the blood and control various functions like growth, metabolism, and mood.
10.1. Major Endocrine Glands and Their Functions
Gland | Hormone | Function |
Pituitary Gland | Growth hormone, TSH, etc. | Controls other glands; helps in growth |
Thyroid Gland | Thyroxine | Controls body metabolism |
Parathyroid Gland | Parathormone | Maintains calcium balance |
Adrenal Gland | Adrenaline | Prepares body for emergencies (“fight or flight”) |
Pancreas | Insulin, Glucagon | Controls blood sugar level |
Testes | Testosterone | Develops male features |
Ovaries | Estrogen, Progesterone | Controls female body changes and reproduction |
10.2. Common Hormonal Problems
- Less Thyroxine → Goitre (neck swelling)
- Less Insulin → Diabetes (high blood sugar)
- Less Growth Hormone → Dwarfism
- Too Much Growth Hormone → Gigantism
11. Difference Between Nervous and Hormonal Systems
Feature | Nervous System | Endocrine System |
Type of message | Electrical impulse | Chemical (hormone) |
Speed | Very fast | Slow |
Effect duration | Short | Long-lasting |
Pathway | Neurons | Bloodstream |
Example | Reflex action | Insulin controlling sugar |
12. Connection Between Brain and Hormones
- The hypothalamus in the brain controls the pituitary gland.
- The pituitary controls other glands (thyroid, adrenal, etc.).
Thus, the brain and endocrine glands work together for perfect coordination.
13. Importance of Control and Coordination
- Helps in adjusting to surroundings.
- Makes all organs work in proper rhythm.
- Controls growth, movement, and balance.
- Maintains internal stability.
- Keeps body safe and functional.
13. Summary
Concept | Key Point |
Stimulus | Any change in surroundings |
Reflex Action | Fast, automatic response |
Brain Parts | Forebrain, Midbrain, Hindbrain |
Plant Hormones | Auxin, Gibberellin, Cytokinin, ABA, Ethylene |
Animal Hormones | Thyroxine, Insulin, Adrenaline, Growth Hormone |
Coordination | Cooperation between all organs |
14. Key Terms
- Neuron: Nerve cell that carries message
- Synapse: Gap between two neurons
- Reflex Arc: Path of reflex action
- Cerebrum: Controls intelligence and thinking
- Cerebellum: Maintains body balance
- Medulla: Controls involuntary actions
- Phytohormones: Hormones in plants
- Endocrine glands: Glands that release hormones directly into blood
15. In Short
- Control and coordination help living things survive and function.
- In humans – done by nervous and hormonal systems.
- In plants – done by hormones and growth movements.
- Both ensure that the body stays balanced and active.