ICSE 8 Biology Nervous System Short

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Table of Contents

    ⚡ Quick Revision: The Nervous System

    The Structural Unit: The Neuron
    • ✔ Neuron: The fundamental unit of the nervous system.
    • ✔ Cyton (Cell Body): Contains the nucleus and cytoplasm.
    • ✔ Dendrites: Short branched fibers that receive impulses.
    • ✔ Axon: A long fiber that carries impulses away from the cyton.
    Term Card

    Synapse: The microscopic gap between the axon terminal of one neuron and the dendrite of the next through which chemical signals pass.

    Type of Neuron Function
    Sensory Neuron Carries impulses from sense organs to the Brain/Spinal Cord.
    Motor Neuron Carries impulses from the Brain/Spinal Cord to muscles/glands.
    Association Neuron Connects sensory and motor neurons within the CNS.
    ❌ Don't Confuse:

    Stimulus with Impulse. A stimulus is an external change (heat, light), while an impulse is the electrical signal traveling along the neuron.

    ⚡ Quick Revision: The Central Nervous System (CNS)

    The Brain: Major Regions
    • ✔ Cerebrum: Largest part; seat of intelligence, memory, and voluntary actions.
    • ✔ Cerebellum: Located at the back; maintains posture, balance, and muscle coordination.
    • ✔ Medulla Oblongata: Controls involuntary actions like heartbeat and breathing.
    Term Card

    Meninges: The three protective membranes (Dura mater, Arachnoid, and Pia mater) that surround the brain and spinal cord.

    The Spinal Cord:
    • ✔ Extends from the Medulla down through the vertebral column.
    • ✔ Acts as a center for Reflex Actions and conducts impulses to/from the brain.
    ❌ Don't Confuse:

    Grey Matter vs White Matter. In the brain, Grey matter is outer and White is inner. In the spinal cord, it is the exact opposite!

    ⚡ Quick Revision: Reflex Action & the Reflex Arc

    Term Card

    Reflex Action: An automatic, quick, and involuntary response to a stimulus that does not involve the conscious brain.

    The Reflex Arc

    This is the pathway followed by a nerve impulse during a reflex action. The sequence is vital for exams:

    1. Receptor: Sense organ that receives the stimulus (e.g., skin).
    2. Sensory Neuron: Carries the message to the spinal cord.
    3. Association Neuron: Processes the message in the spinal cord.
    4. Motor Neuron: Carries the command to the muscle.
    5. Effector: The muscle or gland that reacts (e.g., pulling hand away).
    Type of Reflex Description Example
    Inborn Reflex Inherited, present since birth. Blinking, Knee jerk
    Conditioned Reflex Acquired through experience or learning. Cycling, Salivating at a bell
    ❌ Don't Confuse:

    Voluntary vs Involuntary actions. Voluntary actions are controlled by the Cerebrum (conscious), whereas Involuntary/Reflex actions are often handled by the Spinal Cord or Medulla.

    ⚡ Quick Revision: PNS, ANS & Final Summary

    The Peripheral & Autonomic Systems:
    • ✔ PNS: Consists of nerves arising from the brain (12 pairs of Cranial Nerves) and spinal cord (31 pairs of Spinal Nerves).
    • ✔ ANS (Autonomic): Controls internal organs automatically. It has two parts: Sympathetic (prepares for action) and Parasympathetic (restores calm).
    Chapter Master-List
    • ✔ Unit: Neuron (Cyton, Dendrites, Axon).
    • ✔ CNS: Brain (Cerebrum, Cerebellum, Medulla) and Spinal Cord.
    • ✔ Reflexes: Automatic responses; follow the Receptor → Sensory → Spinal Cord → Motor → Effector path.
    Exam Strategy

    Location & Function: Be ready for table-based questions. If the question asks for the function of the Cerebellum, always include "balance" and "muscular coordination."

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