Nervous System in Animals (CBSE Class 10 Science)

The nervous system helps animals sense the environment, process information, and respond quickly. It does this by sending signals to different parts of the body. Understanding this system is important because it helps us know how living things react and survive.

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1. Structure and Function of the Nervous System

Key Points

A. Main Divisions

1. Central Nervous System (CNS):

   • Made up of the brain and spinal cord.
   • The brain acts as the command centre. It controls thinking, memory, senses, and most body functions.
   • The spinal cord is like a highway. It sends messages between the brain and the rest of the body.

2. Peripheral Nervous System (PNS):

   • Made of nerves that branch out from the spinal cord and reach every part of the body.
   • Two parts:
     • Somatic nervous system: Controls voluntary actions like moving your arm.
     • Autonomic nervous system: Controls automatic actions like heartbeat and digestion.

Examples:

• If you accidentally touch a hot object, your CNS and PNS work together so you can quickly pull your hand back.
• When a cat hears a sound (PNS detects it), its brain (CNS) processes the sound, and the body reacts.

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B. Functions

1. Sensory Input:
   • Nerves sense changes around you, like light, touch, or temperature.
2. Integration:
   • The brain and spinal cord "think" about the information and decide how to respond.
3. Motor Output:
   • Nerves send signals to muscles or glands, causing you to act.

Examples:

• Hearing your name (sensory input), turning your head (motor output), and recognizing who called (integration).
• When a rabbit spots a predator, its senses (sensory input) notice danger, the brain (integration) processes that, and its legs run (motor output).

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2. Neurons: Structure and Function

Key Points

A. Structure of Neuron

A neuron is the smallest working part of the nervous system. It is like a messenger. It carries signals quickly around the body.

Parts of a Neuron:

1. Cell Body (Soma):
   • Contains the nucleus and tiny structures for cell function.
2. Dendrites:
   • Short branches that receive signals from other cells.
   • Carry messages to the cell body.
3. Axon:
   • A long fibre that carries messages away from the cell body.
   • Often covered with a myelin sheath (fatty layer) for faster signal movement.
   • Ends divide into axon terminals that pass messages to the next cell.

Diagram of a Neuron:
(Draw: Big circle for cell body in the middle, branching dendrites, a long line as axon, covering as myelin sheath, and axon endings)

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B. Types of Neurons

• Sensory Neurons: Carry information from sense organs (eyes, skin) to the CNS.
  • Example: Feeling a prick on your finger.
• Motor Neurons: Carry instructions from the CNS to muscles/glands.
  • Example: Your arm muscle moves to write.
• Interneurons: Connect neurons inside the CNS, helping them communicate.
  • Example: In the brain to process thinking.

Examples:

• In a snail, sensory neurons detect touch, and motor neurons help it withdraw into its shell.
• A dog’s sensory neurons sense food smell; motor neurons move its tongue and legs.

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3. Transmission of Nerve Impulse

Key Points

A. How Signals Travel in a Neuron (Electrical Transmission)

• At rest, the neuron is negatively charged inside and positively charged outside (resting potential).
• When a signal comes (stimulus), sodium ions rush in. The neuron’s charge changes (action potential).
• This change moves like a wave (nerve impulse) along the axon toward the terminals.

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B. How Signals Cross Between Neurons (Chemical Transmission)

• At the end of an axon, the signal reaches the synapse (a small gap between cells).
• Electrical signal triggers the release of chemicals called neurotransmitters.
• These neurotransmitters move across the synapse and attach to the next neuron’s membrane.
• The next neuron responds, passing along the message.

Diagram:
(Draw two neurons with a gap between them. Show tiny dots (neurotransmitters) crossing the gap and attaching to the next neuron.)

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Summary of Steps:

1. A stimulus triggers a signal (action potential) in neuron A.
2. The signal travels along the axon.
3. At the end, neurotransmitters are released into the synapse.
4. The next neuron receives the signal and sends its own impulse forward.

Examples:

• When you step on something sharp, sensory neurons send a message to your brain. The brain quickly returns a signal to your foot muscles to step away.
• A frog jumps when its skin feels a sudden touch; the signal travels from skin to brain and then to leg muscles.

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4. Activities (Fun Learning!)

Activity: Testing Reflex Actions

Purpose: To understand how nervous system responds quickly to danger.

Steps:

1. Pair up. One student holds a ruler vertically.
2. The other student holds their hand ready at the bottom, not touching the ruler.
3. The first student releases the ruler without warning.
4. The second student tries to catch it as soon as possible.
5. Record the distance the ruler fell before being caught.

Observations:

• Shorter distances mean faster reflexes.
• This activity shows how some responses are very quick and do not always need the brain (spinal cord handles it).

Explanation:

• Reflex actions help us react fast to danger. The impulse travels from the sensory neuron (touch), to the spinal cord, and immediately via a motor neuron to the muscles—without waiting for the brain.

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Activity: Modeling Synaptic Transmission

Purpose: To visualize how signals jump between neurons at the synapse.

Steps:

1. Arrange two chairs (neurons) close, but not touching—leave a small gap (synapse).
2. Use a ball to represent the nerve impulse.
3. Student 1 (first neuron) rolls the ball to the other chair but cannot reach it due to the gap.
4. Use small blocks as "neurotransmitter molecules" to fill the gap.
5. Now, roll the ball using the blocks!

Observations:

• The ball stops at the gap until neurotransmitters help it across.
• This models the way signals need chemicals (neurotransmitters) to cross synapses.

Explanation:

• Neurons do not touch. Signals need help to jump the gap between neurons.

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5. Real Life Examples

• Insects: Cockroaches run quickly when touched because their neurons react speedily.
• Birds: Use fast nerve impulses to coordinate wings during flight.
• Humans: Blink when an object suddenly comes close, protecting the eyes.

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6. Scenario-Based Questions and Answers

1. Scenario: A student trips and puts out their hand to break the fall.

   • Question: Which part of the nervous system helped in this quick action?
   • Answer: The reflex action, managed by the spinal cord (part of CNS), helped move the hand quickly before thinking about it.

2. Scenario: You feel a mosquito bite and immediately swat it.

   • Question: How did your nervous system sense and respond so fast?
   • Answer: Sensory neurons in your skin detected the bite; the message traveled to the brain, then motor neurons sent a command to your arm muscles to swat the mosquito.

3. Scenario: A dog sits when its owner says "sit".

   • Question: Which neurons are involved in this learned behavior?
   • Answer: Sensory neurons (hearing), interneurons (brain processing), and motor neurons (limb movement) are involved.

4. Scenario: While running, you feel tired and stop.

   • Question: How does your nervous system bring about this change?
   • Answer: Sensory neurons send fatigue signals from muscles to the brain, which then sends commands via motor neurons to slow down or stop.

5. Scenario: A cat quickly closes its eyes when a flashlight is shone at it.

   • Question: What is occurring in the nerve cells?
   • Answer: Sensory neurons detect the bright light, interneurons in the brain process it, and motor neurons signal the eyelid muscles to blink.

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7. Important Diagrams to Practice

• Neuron structure (label: cell body, dendrites, axon, myelin, axon terminals)
• Synapse showing neurotransmitters crossing the gap

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8. In Summary

Part/Process	Details
CNS	Brain and spinal cord: control and coordinate all actions.
PNS	Nerves from CNS to all parts of the body, control voluntary/involuntary.
Neuron Structure	Cell body, dendrites (input), axon (output), myelin sheath (faster signals).
Impulse Travel	Electrical within neuron, chemical across synapse.
Real Examples	Reflexes, quick animal movements, learned and automatic behaviors.

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Remember: The nervous system lets animals sense, decide, and react. It is lightning-fast, which helps animals and humans survive and thrive!

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