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Neural Control and Coordination – Class 11 Biology Chapter 18 Notes & NCERT PDF

Class 11BiologyChapter 18NCERT book: Biology - Class 11

Notes and a simple summary of Chapter 18 of the NCERT Class 11 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 18: Neural Control and Coordination

Introduction

Organs must work together to maintain homeostasis. Coordination is the process by which two or more organs interact and complement each other — for example, during exercise, respiration rate, heart beat and blood flow all rise to meet the muscles' energy demand, and return to normal afterwards. The neural system provides organised point-to-point connections for quick coordination, while the endocrine system provides chemical integration through hormones. This chapter covers the human neural system, nerve impulse generation and conduction, and transmission across synapses.

Key Concepts

18.1 Neural System

Made of neurons, which detect, receive and transmit stimuli. It is simple in lower invertebrates (a network of neurons in Hydra), better organised in insects (brain + ganglia), and most developed in vertebrates.

18.2 Human Neural System

  • Central neural system (CNS) — brain and spinal cord; site of information processing and control.
  • Peripheral neural system (PNS) — all nerves associated with the CNS. Its fibres are:

    • - Afferent — carry impulses from tissues/organs to the CNS.

    - Efferent — carry regulatory impulses from the CNS to tissues/organs.

  • PNS divisions:

    • - Somatic neural system — CNS → skeletal muscles.

    - Autonomic neural system — CNS → involuntary organs and smooth muscles; subdivided into sympathetic and parasympathetic.

  • Visceral nervous system — the part of the PNS (nerves, fibres, ganglia, plexuses) through which impulses travel between the CNS and the viscera.

    • 18.3 Neuron — Structural and Functional Unit

    Three parts:

  • Cell body — cytoplasm, organelles and Nissl's granules.
  • Dendrites — short, repeatedly branched fibres with Nissl's granules; carry impulses towards the cell body.
  • Axon — long fibre whose branched end forms synaptic knobs containing synaptic vesicles with neurotransmitters; carries impulses away from the cell body to a synapse or neuromuscular junction.

    • Types by number of processes:

  • Multipolar — one axon, two or more dendrites; cerebral cortex.
  • Bipolar — one axon, one dendrite; retina.
  • Unipolar — cell body with one axon only; usually embryonic stage.

    • Axons:

  • Myelinated — enveloped by Schwann cells forming a myelin sheath; gaps are nodes of Ranvier; found in spinal and cranial nerves.
  • Unmyelinated — Schwann cell does not form a myelin sheath; common in autonomous and somatic neural systems.

    • #### 18.3.1 Generation and conduction of nerve impulse

    Resting (polarised) state

  • The axonal membrane is more permeable to K⁺, nearly impermeable to Na⁺, and impermeable to the negatively charged proteins of the axoplasm.
  • Inside: high K⁺ and negative proteins, low Na⁺. Outside: low K⁺, high Na⁺.
  • Gradients are maintained by the sodium-potassium pump, which transports 3 Na⁺ outwards for 2 K⁺ inwards.
  • Outer surface positive, inner surface negative → membrane polarised; the potential difference is the resting potential.

    • Action potential (nerve impulse)

  • A stimulus at site A makes the membrane freely permeable to Na⁺ → rapid influx of Na⁺.
  • Polarity reverses: outside negative, inside positive → depolarised. This potential difference at A is the action potential.
  • Current flows on the inner surface from A to B and on the outer surface from B to A, so site B depolarises too; the sequence repeats along the axon — conduction.
  • The rise in Na⁺ permeability is very short-lived; it is followed by a rise in K⁺ permeability. K⁺ diffuses out and restores the resting potential (repolarisation), and the fibre can respond again.

    • #### 18.3.2 Transmission of impulses — synapses

    A synapse is formed by the membranes of a pre-synaptic and a post-synaptic neuron, which may or may not be separated by a gap called the synaptic cleft.

  • Electrical synapse — membranes in very close proximity; current flows directly; transmission similar to conduction along an axon and always faster than across a chemical synapse; rare in our system.
  • Chemical synapse — membranes separated by a fluid-filled synaptic cleft:

    • 1. Action potential arrives at the axon terminal.

    2. Synaptic vesicles move to the membrane, fuse with it and release neurotransmitters into the cleft.

    3. Neurotransmitters bind to specific receptors on the post-synaptic membrane.

    4. Ion channels open; ions enter and generate a new potential, which may be excitatory or inhibitory.

    18.4 Central Neural System

    The brain is the 'command and control system': it controls voluntary movements, balance, vital involuntary organs (lungs, heart, kidneys), thermoregulation, hunger and thirst, circadian (24-hour) rhythms, endocrine activity and behaviour, and processes vision, hearing, speech, memory, intelligence, emotions and thoughts. It is protected by the skull and cranial meninges: outer dura mater, thin middle arachnoid, inner pia mater (in contact with brain tissue). Three parts: forebrain, midbrain and hindbrain.

    #### 18.4.1 Forebrain — cerebrum, thalamus, hypothalamus

  • Cerebrum — major part of the brain; a deep cleft divides it into left and right cerebral hemispheres, connected by the corpus callosum.
  • Cerebral cortex — outer layer of cells, thrown into prominent folds; grey matter (neuron cell bodies). Contains motor areas, sensory areas and association areas (intersensory associations, memory, communication).
  • White matter — inner part; myelinated fibre tracts give an opaque white look.
  • Thalamus — major coordinating centre for sensory and motor signalling; the cerebrum wraps around it.
  • Hypothalamus — at the base of the thalamus; centres controlling body temperature, urge for eating and drinking; neurosecretory cells secrete hypothalamic hormones.
  • Limbic system (limbic lobe) — inner parts of the hemispheres plus deep structures like amygdala and hippocampus; with the hypothalamus, regulates sexual behaviour, emotional reactions (excitement, pleasure, rage, fear) and motivation.

    • #### 18.4.2 Midbrain

    Located between the thalamus/hypothalamus and the pons. The cerebral aqueduct passes through it. Its dorsal portion has four round swellings — corpora quadrigemina. (Summary: receives and integrates visual, tactile and auditory inputs.)

    #### 18.4.3 Hindbrain — pons, cerebellum, medulla oblongata

  • Pons — fibre tracts interconnecting different regions of the brain.
  • Cerebellum — very convoluted surface to provide space for many more neurons; integrates information from the semicircular canals of the ear and the auditory system.
  • Medulla — connected to the spinal cord; centres for respiration, cardiovascular reflexes and gastric secretions.
  • Brain stem = midbrain + pons + medulla oblongata; connects brain and spinal cord.

    • Diagrams to Know (in words)

  • Neuron: cell body with nucleus and Nissl's granules; dendrites; axon with Schwann cells, myelin sheath and nodes of Ranvier; branched terminal with synaptic knobs.
  • Impulse conduction: axon showing depolarised site A (inside +, outside −) and polarised site B, with local current arrows.
  • Chemical synapse: axon terminal, synaptic vesicles, neurotransmitter release into the cleft, receptors on the post-synaptic membrane.
  • Sagittal section of brain: cerebrum, corpus callosum, thalamus, hypothalamus, midbrain, pons, cerebellum, medulla, spinal cord.

    • Key-Facts Sheet

  • Na⁺-K⁺ pump: 3 Na⁺ out, 2 K⁺ in
  • Resting: outside +, inside −; action potential: outside −, inside +
  • Multipolar — cerebral cortex; bipolar — retina; unipolar — embryonic stage
  • Meninges (outside → inside): dura mater, arachnoid, pia mater
  • Brain stem: midbrain, pons, medulla

    • Exam Focus

  • Compare CNS vs PNS, resting vs action potential, myelinated vs non-myelinated axons, dendrites vs axons, thalamus vs hypothalamus, cerebrum vs cerebellum, afferent vs efferent neurons.
  • Explain polarisation, depolarisation and chemical synaptic transmission; role of Na⁺ in the action potential.
  • Most developed part of the human brain — cerebrum; the book's exercise also asks which part acts as a master clock (the brain controls circadian rhythms; the hypothalamus is the centre that regulates such body functions).
  • Draw a neuron and a brain.

    • Key Terms

  • Neuron (तंत्रिका कोशिका)
  • Dendrite (द्रुमिका)
  • Axon (तंत्रिकाक्ष)
  • Myelin sheath (माइलिन आच्छद)
  • Node of Ranvier (रैनवियर पर्व)
  • Resting potential (विश्राम विभव)
  • Action potential (क्रिया विभव)
  • Depolarisation (विध्रुवण)
  • Synapse (अंतर्ग्रथन)
  • Neurotransmitter (तंत्रिका संचारी)
  • Cerebrum (प्रमस्तिष्क)
  • Cerebellum (अनुमस्तिष्क)
  • Hypothalamus (अधश्चेतक)
  • Medulla oblongata (मेडुला ऑब्लांगेटा)
  • Corpus callosum (कार्पस कैलोसम)

    • Common Mistakes

  • Reversing the pump: it moves 3 Na⁺ out and 2 K⁺ in, not the other way.
  • Saying depolarisation is caused by K⁺ influx — it is Na⁺ influx; K⁺ efflux restores the resting potential.
  • Calling the chemical synapse faster — electrical synapses are faster.
  • Mixing up where neuron types occur: bipolar in the retina, multipolar in the cerebral cortex.

    • 💡 Key Learning Points

    • ✓The neural system gives fast point-to-point coordination; with the endocrine system it maintains homeostasis.
    • ✓The human neural system has CNS (brain, spinal cord) and PNS (somatic and autonomic divisions).
    • ✓The resting potential is maintained by ion gradients and the Na⁺-K⁺ pump (3 Na⁺ out, 2 K⁺ in); Na⁺ influx produces the action potential.
    • ✓Impulses cross synapses electrically (fast, rare) or chemically via neurotransmitters binding post-synaptic receptors.
    • ✓The brain has forebrain (cerebrum, thalamus, hypothalamus), midbrain and hindbrain (pons, cerebellum, medulla).

    👨‍🏫 Teaching Tips

    • →Act out impulse conduction: students in a line flip cards from +/− to −/+ as the 'impulse' passes.
    • →Use a flowchart for the PNS: afferent/efferent, somatic vs autonomic, sympathetic vs parasympathetic.
    • →Draw a neuron together on the board and label parts in the order impulses travel.
    • →Compare electrical and chemical synapses side by side using a quick T-chart.
    • →Use a brain model or sagittal diagram and assign each group one region's functions to present.
    • →Connect the hypothalamus here to hypothalamic hormones in Chapter 19.
    • →Use the book's 'Differentiate between' exercises for short-answer practice.

    📋 Assessment Questions

    1. Explain polarisation and depolarisation of an axon membrane.
    2. Describe transmission of an impulse across a chemical synapse.
    3. Differentiate myelinated and non-myelinated axons; thalamus and hypothalamus.
    4. Name the parts of the forebrain, midbrain and hindbrain and give one function of each.
    5. Draw a labelled diagram of a neuron.

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    Keep learning

    All chapters in Biology - Class 11

    1. 1. The Living World
    2. 2. Biological Classification
    3. 3. Plant Kingdom
    4. 4. Animal Kingdom
    5. 5. Morphology of Flowering Plants
    6. 6. Anatomy of Flowering Plants
    7. 7. Structural Organisation in Animals
    8. 8. Cell: The Unit of Life
    9. 9. Biomolecules
    10. 10. Cell Cycle and Cell Division
    11. 11. Photosynthesis in Higher Plants
    12. 12. Respiration in Plants
    13. 13. Plant Growth and Development
    14. 14. Breathing and Exchange of Gases
    15. 15. Body Fluids and Circulation
    16. 16. Excretory Products and their Elimination
    17. 17. Locomotion and Movement
    18. 18. Neural Control and Coordination
    19. 19. Chemical Coordination and Integration