CHAPTER 2: HUMAN NERVOUS SYSTEM
(Explained so every single word makes sense)
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1. WHAT DOES "NERVOUS SYSTEM" EVEN MEAN?
Let's not jump into scary biology words yet.
Your body is not just random parts.
It is organized.
When many organs work together to do one main job, we call that a system.
For example:
Digestive system → digests food
Respiratory system → helps in breathing
Circulatory system → transports blood
Now the nervous system is the most important system because it controls all other systems.
👉 The nervous system is the control and coordination system of the body.
This means:
It controls what happens in your body
It coordinates (connects) different parts of the body so they work together
Without the nervous system, the body cannot function properly.
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2. WHY DO WE NEED A NERVOUS SYSTEM?
Imagine this situation:
You touch something hot 🔥
If your body does not react fast, your skin will burn badly.
So your body must:
1. Feel the heat
2. Understand it is dangerous
3. React immediately
This is exactly what the nervous system does.
The nervous system helps you to:
Think
Feel pain
Feel touch, heat, cold
Move muscles
Remember things
Learn
React quickly to danger
Control breathing and heartbeat
So we can say:
👉 The nervous system helps the body receive information, process it, and give a response.
This sentence is VERY IMPORTANT for exams.
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3. BASIC WORKING OF THE NERVOUS SYSTEM (SIMPLE)
The nervous system works in three simple steps:
1. Receive information
Example: skin feels heat
2. Process information
Brain or spinal cord understands the message
3. Send response
Muscles move, glands act, body reacts
This happens in seconds or even milliseconds.
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4. MAIN PARTS OF THE NERVOUS SYSTEM
The human nervous system is divided into two main parts:
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
This division is EXTREMELY IMPORTANT.
Most exam questions come from here.
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5. CENTRAL NERVOUS SYSTEM (CNS)
What is the CNS?
The Central Nervous System is the main control center of the body.
It controls:
Thinking
Memory
Actions
Reflexes
Body coordination
What does the CNS include?
The CNS includes two organs:
1. Brain
2. Spinal cord
👉 CNS = Brain + Spinal cord
Never forget this line.
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6. THE BRAIN
The brain is the most complex organ in the human body.
It:
Controls all body activities
Receives messages from sense organs
Sends instructions to muscles and glands
The brain is protected by the skull because it is very delicate.
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7. PARTS OF THE BRAIN
The brain is divided into three main parts:
1. Cerebrum
2. Cerebellum
3. Medulla oblongata
Each part has a different function.
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7.1 CEREBRUM
The cerebrum is the largest part of the brain.
It is responsible for:
Thinking
Intelligence
Memory
Learning
Reasoning
Voluntary actions (actions we control)
Examples of voluntary actions:
Writing
Walking
Talking
Studying (yes, this pain right now 😭)
Whenever you think, decide, or remember something, your cerebrum is working.
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7.2 CEREBELLUM
The cerebellum is smaller than the cerebrum but very important.
It controls:
Balance
Posture
Coordination of muscles
Smooth body movements
Without the cerebellum:
You would fall while walking
Movements would be shaky
Example: When you ride a bicycle 🚲 or walk straight, your cerebellum helps you stay balanced.
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7.3 MEDULLA OBLONGATA
The medulla oblongata controls involuntary actions.
Involuntary actions are actions you do without thinking.
It controls:
Breathing
Heartbeat
Swallowing
Blood pressure
These actions are essential for life.
That is why damage to the medulla can be life-threatening.
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8. SPINAL CORD
The spinal cord is a long, thick bundle of nerves.
It extends from the brain down the backbone.
Functions of the spinal cord:
Connects the brain to the rest of the body
Carries messages to and from the brain
Controls reflex actions
The spinal cord is protected by the vertebral column (backbone).
Think of the spinal cord as a message highway between the brain and body.
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9. PERIPHERAL NERVOUS SYSTEM (PNS)
The Peripheral Nervous System includes all the nerves outside the brain and spinal cord.
This includes:
Nerves in arms
Nerves in legs
Nerves in skin
Nerves in organs
Function of PNS:
Carries messages from sense organs to CNS
Carries commands from CNS to muscles and glands
So the PNS acts as a connection system.
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10. NERVES AND NEURONS
What is a neuron?
A neuron is a nerve cell.
Neurons are the basic unit of the nervous system.
Their main function is to carry messages.
The message carried by a neuron is called a nerve impulse.
A nerve impulse is an electrical signal.
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11. STRUCTURE OF A NEURON
A neuron has three main parts:
11.1 DENDRITES
Short branched structures
Receive messages
Carry impulses toward the cell body
Think: D = Detect
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11.2 CELL BODY
Contains the nucleus
Processes the message
Decides what to do next
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11.3 AXON
Long fiber
Carries impulses away from the cell body
Sends message to another neuron or muscle
Mnemonic: 👉 D → C → A
Dendrites → Cell body → Axon
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12. HOW DOES A NERVE IMPULSE TRAVEL?
Let's use a real example.
You touch a hot object.
1. Skin receptors detect heat
2. Sensory neuron carries impulse to CNS
3. CNS processes the message
4. Motor neuron carries impulse to muscle
5. Muscle contracts
6. Hand pulls away
This entire process happens very quickly.
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13. TYPES OF NEURONS
There are three types of neurons:
1. Sensory neurons
2. Relay neurons
3. Motor neurons
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13.1 SENSORY NEURONS
Carry messages from sense organs to CNS
Example: skin to brain
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13.2 RELAY NEURONS
Found in CNS
Connect sensory and motor neurons
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13.3 MOTOR NEURONS
Carry messages from CNS to muscles or glands
Cause action
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14. REFLEX ACTION
A reflex action is a quick, automatic response to a stimulus.
It does not involve thinking.
Examples:
Pulling hand away from fire
Blinking
Sneezing
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15. WHY ARE REFLEX ACTIONS FAST?
Because reflex actions are controlled by the spinal cord, not the brain.
The spinal cord responds immediately to protect the body.
The brain is informed later.
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16. REFLEX ARC
The reflex arc is the pathway taken by nerve impulses during a reflex action.
Order of reflex arc:
1. Stimulus
2. Receptor
3. Sensory neuron
4. Relay neuron
5. Motor neuron
6. Effector
7. Response
This order is VERY IMPORTANT for exams.
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17. EFFECTORS
Effectors are:
Muscles
Glands
They respond to nerve impulses.
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18. DIFFERENCE BETWEEN VOLUNTARY AND INVOLUNTARY ACTIONS
Voluntary actions:
Under our control
Controlled by cerebrum
Example: writing
Involuntary actions:
Not under our control
Controlled by medulla
Example: heartbeat
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19. IMPORTANCE OF THE NERVOUS SYSTEM
The nervous system:
Protects the body
Helps in learning
Maintains balance
Controls body systems
Helps in survival
Without it, life is impossible.
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20. EXAM-READY DEFINITIONS (MEMORIZE)
Nervous system:
A system that controls and coordinates the activities of the body.
Neuron:
A nerve cell that carries nerve impulses.
Reflex action:
A quick and automatic response to a stimulus without conscious thinking.
CNS:
Consists of the brain and spinal cord.
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GORYA FINAL TALK 😭🎀
Listen.
If you understood even 70% of this, you are SAFE.
Understanding beats memorizing every single line.
Tonight:
Read slowly
Focus on headings
Memorize definitions + reflex arc
Sleep
You are doing your BEST. And that is enough 🫶
If you want next:
💯 Guess questions
🧠 Memory tricks
🎧 Another voice-style revision