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ICSE Class 8 Biology Question 1 of 16

Nervous System — Question 2

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Question

Question 2(b)

Assertion (A): Cerebellum enables us to remember, think and reason.

Reason (R): It is the largest portion of the brain and occupies the whole central area.

  1. Both A and R are true.
  2. Both A and R are false.
  3. A is true and R is false.
  4. A is false and R is true.
Answer

Both A and R are false.

Explanation — The main function of cerebellum are muscular coordination and body balance. Cerebrum, the largest portion of the brain, is the seat of intelligence, consciousness and will power. Hence, it enables us to remember, think and reason. Therefore both the Assertion and the Reason are incorrect.

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Biology | Chapter 9: Nervous SystemWeb Content

Nervous System – Interactive Study Guide

Quick Overview

The nervous system controls and coordinates all body activities through electrical impulses. It consists of the CNS (brain + spinal cord) and PNS (nerves connecting CNS to body).

Neuron – Quick Structure

Parts & Functions
  • Cell body: Nucleus, metabolic centre
  • Dendrites: Receive impulses (towards cell body)
  • Axon: Carries impulses away (from cell body)
  • Myelin sheath: Insulation, speeds up impulse
  • Synaptic knob: Transmits to next neuron

Brain Parts – Quick Reference

PartFunctionMemory Aid
CerebrumThinking, memory, senses, voluntary actionsBRainpower
CerebellumBalance, coordinationBaLLance
MedullaInvoluntary actions (breathing, heartbeat)Must Do

Reflex Action – Step by Step

Reflex Arc

Stimulus → Receptor (skin) → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector (muscle) → Response (hand pulls away)

Controlled by spinal cord (NOT brain) for faster response.

Voluntary vs Involuntary vs Reflex

VoluntaryInvoluntaryReflex
ControlConsciousUnconsciousUnconscious
CentreCerebrumMedullaSpinal cord
SpeedSlowModerateVery fast
ExampleWritingBreathingKnee-jerk

Self-Test Questions

Test Yourself
  1. Draw and label a neuron.
  2. Why are reflex actions controlled by the spinal cord and not the brain?
  3. Name the three parts of the brain and state one function of each.
  4. What is the difference between sensory and motor neurons?
  5. Draw a reflex arc and label all parts.

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