Chapter Summary

This chapter explains how the nervous system controls and coordinates body functions. It describes the structure of neurons, generation and transmission of nerve impulses, organization of the brain and spinal cord, reflex actions, and sensory reception through the eye and ear.

1. Neuron – Structural and Functional Unit

A neuron is the basic unit of the nervous system responsible for receiving and transmitting information.

Structure of a Neuron:

  • Dendrites: Receive signals from other neurons.
  • Cell Body (Cyton): Contains nucleus and metabolic machinery.
  • Axon: Conducts nerve impulses away from the cell body.

Types of Nerve Fibres:

  • Myelinated fibres: Covered by myelin sheath; conduction is fast due to saltatory conduction.
  • Non-myelinated fibres: Lack myelin sheath; impulse conduction is slow and continuous.

Memory Trick:

  • "DCA" → Dendrite → Cell body → Axon (Direction of impulse inside neuron).

2. Nerve Impulse and Action Potential

The nerve impulse is an electrical signal generated by changes in membrane potential.

Resting Membrane Potential:

  • Membrane is polarized.
  • Outside: Positive
  • Inside: Negative
  • Maintained by Na⁺–K⁺ pump (3 Na⁺ out / 2 K⁺ in).

Action Potential Steps:

  1. Depolarization: Rapid Na⁺ influx.
  2. Repolarization: K⁺ efflux restores original polarity.
  3. Restoration: Na⁺–K⁺ pump re-establishes ionic balance.

Memory Trick:

  • "Na IN → K OUT" for impulse generation.

3. Synapse – Transmission Between Neurons

A synapse is the junction between two neurons.

Types of Synapse:

  • Chemical Synapse: Uses neurotransmitters; most common in humans.
  • Electrical Synapse: Direct ion flow through gap junctions; rare but very fast.

Sequence: Impulse → Axon terminal → Neurotransmitter release → Receptor binding → New impulse generation.

4. Central Nervous System (CNS)

The CNS consists of brain and spinal cord.

Major Brain Regions:

Forebrain:

  • Cerebrum: Intelligence, memory, voluntary movement.
  • Thalamus: Sensory relay centre.
  • Hypothalamus: Controls temperature, hunger, thirst, hormones.

Midbrain:

  • Controls visual and auditory reflexes.

Hindbrain:

  • Cerebellum: Balance, posture, coordination.
  • Pons: Connects different parts of brain.
  • Medulla Oblongata: Controls heartbeat, respiration, blood pressure.

Memory Trick:

  • "CHM" → Cerebellum, Hindbrain, Medulla = Balance & Vital functions.

5. Reflex Action and Reflex Arc

A reflex action is a rapid, automatic, involuntary response to a stimulus.

Components of Reflex Arc: Stimulus → Receptor → Sensory neuron → Interneuron → Motor neuron → Effector → Response

Reflexes help the body respond quickly to dangerous stimuli.

Example: Withdrawal of hand from a hot object.

6. Sensory Reception – Eye

The eye is the organ of vision.

Three Layers of Eye Wall:

  1. Sclera: Outer protective layer.
  2. Choroid: Vascular layer with iris and ciliary body.
  3. Retina: Photoreceptor layer.

Photoreceptor Cells:

  • Rods: Dim light vision; contain Rhodopsin.
  • Cones: Colour and bright light vision.

Important Regions:

  • Fovea: Only cones; maximum visual acuity.
  • Blind Spot: No photoreceptors; optic nerve exits.

7. Sensory Reception – Ear

The ear performs two functions:

  • Hearing
  • Maintenance of balance

Parts of Ear:

Outer Ear: Pinna, external auditory canal, tympanic membrane.

Middle Ear: Three ossicles

  • Malleus
  • Incus
  • Stapes

Inner Ear:

  • Cochlea: Hearing (Organ of Corti).
  • Vestibular apparatus: Balance (semicircular canals, utricle, saccule).

Memory Trick:

  • MIS → Malleus → Incus → Stapes.

NEET Exam Tips

1. Ion Movement Questions (Very Frequently Asked)

Students often confuse ion movement during nerve impulse.

Remember:

  • Depolarization → Na⁺ enters neuron
  • Repolarization → K⁺ leaves neuron
  • Resting pump → 3 Na⁺ out / 2 K⁺ in

These concepts are repeatedly asked in NEET and AIIMS questions.

2. Brain Function Matching (High Probability Area)

Questions often ask to match brain parts with functions.

Important matches:

  • Hypothalamus → Thermoregulation, hunger, thirst
  • Medulla → Heartbeat, breathing
  • Cerebellum → Balance and posture
  • Corpus callosum → Connects hemispheres

Students should revise brain function tables carefully.

3. Sensory Organs – Frequently Asked Topics

NEET commonly asks questions from:

  • Photoreceptors (Rods vs Cones)
  • Blind spot vs Fovea
  • Ossicles sequence
  • Organ of Corti function

Important facts:

  • Rods → Dim light vision
  • Cones → Colour vision
  • Fovea → Highest visual acuity

4. Reflex Arc – Conceptual Questions

Students should clearly remember the order of reflex pathway.

Memory Trick:

  • "R S I M E"
  • Receptor → Sensory neuron → Interneuron → Motor neuron → Effector

5. High-Yield Diagrams for NEET

Students should revise diagrams of:

  • Neuron structure
  • Human brain regions
  • Eye anatomy
  • Ear anatomy (cochlea cross-section)

Diagram-based questions appear frequently in NEET.

Final Memory Capsule

For quick revision before the exam:

  • Neuron = Dendrite → Cell body → Axon
  • Na IN → K OUT (Impulse rule)
  • Brainstem = Midbrain + Pons + Medulla
  • Eye = Rods (night) / Cones (colour)
  • Ear bones = MIS (Malleus → Incus → Stapes)
  • Reflex arc = Receptor → Sensory → Interneuron → Motor → Effector

These points cover most of the repeatedly asked NEET questions from this chapter.