ICSE 7 Biology Nervous Short

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Table of Contents

    Short Notes: Unit 4

    The Nervous System

    1.0 Core Terminology

    • Stimulus: A change in the environment that evokes a response.
    • Response: The reaction of an organism to a stimulus.
    • Impulse: An electrical signal that travels along a nerve fiber.
    • Synapse: The microscopic gap between two neurons.

    2.0 The Neuron (Nerve Cell)

    Structure & Direction:

    Dendrites → Cyton → Axon → Axon Terminals
    • Cyton: The cell body containing the nucleus.
    • Dendrites: Receive impulses toward the cyton.
    • Axon: Carries impulses away from the cyton.
    • Myelin Sheath: Insulating layer for faster conduction.

    3.0 Types of Neurons

    Type Function (Carries impulse...)
    Sensory From Sense Organs → Brain/Spinal Cord
    Motor From Brain/Spinal Cord → Muscles/Glands
    Association Links Sensory and Motor neurons within CNS
    💡 Revision Tip: Remember S.A.M. — Sensory (Afferent), Association (Interneuron), Motor (Efferent).

    4.0 The Human Brain

    The Brain is protected by the Cranium (skull) and three membranes called Meninges.

    Part Main Function
    Cerebrum Intelligence, Memory, Reasoning, Voluntary actions.
    Cerebellum Balance, Posture, Muscular coordination.
    Medulla Involuntary actions (Heartbeat, Breathing).

    5.0 The Spinal Cord

    • Location: Extends from Medulla through the Vertebral Column.
    • Function 1: Links the Brain to the rest of the body.
    • Function 2: Main center for Reflex Actions below the neck.

    6.0 Nerve Counts (Crucial for MCQs)

    The PNS consists of nerves connecting the CNS to the body:

    • 🧠 Cranial Nerves: 12 Pairs (Arise from Brain)
    • 🦴 Spinal Nerves: 31 Pairs (Arise from Spinal Cord)

    💡 Exam Note: The Medulla Oblongata continues as the Spinal Cord. If the Medulla is damaged, involuntary functions stop, often leading to death.

    7.0 Types of Actions

    Voluntary

    Conscious will. Controlled by Cerebrum.

    e.g., Writing, Jumping.

    Involuntary

    Without conscious will. Controlled by Medulla.

    e.g., Heartbeat, Sneeze.

    8.0 Reflex Action

    Reflex Action: Sudden, automatic, involuntary response to a stimulus. Controlled by the Spinal Cord.

    The Reflex Arc Pathway:

    Receptor → Sensory Neuron → Spinal Cord → Motor Neuron → Effector
    • Examples: Knee-jerk, Blinking of eyes, Withdrawal of hand from a hot plate.
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    9.0 Control Summary

    Center Controls...
    Cerebrum Thinking, Memory, Voluntary will.
    Cerebellum Balance and walking.
    Medulla Breathing and Pulse.
    Spinal Cord Reflex Actions.

    REVISION COMPLETE

    The Nervous System: Full Short Notes finished.

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