Animals coordinate via nervous system (fast, short-term) and endocrine system (slow, long-term). Plants use hormones and tropic movements. AMU asks 3–4 MCQs — focus on neuron, reflex arc, brain parts, endocrine glands & their hormones, plant hormones (especially auxin, ethylene, ABA), phototropism, and geotropism.
1) Neuron and nerve impulse
Neuron = structural & functional unit of nervous system.
• Parts: Dendrites (receive impulse) → Cell body (nucleus, Nissl granules) → Axon (conducts impulse) → Axon terminals (release neurotransmitters).
• Myelin sheath (Schwann cells in PNS, oligodendrocytes in CNS) — insulates, speeds up conduction.
• Nodes of Ranvier — gaps between myelin → saltatory conduction (impulse jumps).
• Resting potential: Inside = −70 mV (more K⁺ inside, more Na⁺ outside). Na⁺/K⁺ ATPase pump maintains this (3 Na⁺ out, 2 K⁺ in).
• Action potential: Stimulus → Na⁺ channels open → Na⁺ rushes in → depolarisation (+40 mV) → K⁺ channels open → K⁺ rushes out → repolarisation.
• Parts: Dendrites (receive impulse) → Cell body (nucleus, Nissl granules) → Axon (conducts impulse) → Axon terminals (release neurotransmitters).
• Myelin sheath (Schwann cells in PNS, oligodendrocytes in CNS) — insulates, speeds up conduction.
• Nodes of Ranvier — gaps between myelin → saltatory conduction (impulse jumps).
• Resting potential: Inside = −70 mV (more K⁺ inside, more Na⁺ outside). Na⁺/K⁺ ATPase pump maintains this (3 Na⁺ out, 2 K⁺ in).
• Action potential: Stimulus → Na⁺ channels open → Na⁺ rushes in → depolarisation (+40 mV) → K⁺ channels open → K⁺ rushes out → repolarisation.
Synapse: Junction between two neurons. Presynaptic neuron releases neurotransmitters (acetylcholine, dopamine, serotonin) → diffuse across synaptic cleft → bind to receptors on postsynaptic membrane → new impulse. After transmission, enzymes (acetylcholinesterase) break down neurotransmitters → signal stops. One-way transmission.
Types of neurons: Sensory (receptor → CNS), Motor (CNS → effector), Interneurons (relay within CNS).
2) Human nervous system
| Division | Components | Functions |
|---|---|---|
| CNS | Brain + Spinal cord | Control centre; processes information; reflex centre |
| PNS | 12 cranial + 31 spinal nerves | Connects CNS to body |
| → Somatic | Voluntary nerves | Skeletal muscle control |
| → Autonomic | Sympathetic (fight/flight) + Parasympathetic (rest/digest) | Involuntary control of internal organs |
2.1 Brain
| Part | Subparts | Key functions |
|---|---|---|
| Forebrain | Cerebrum (4 lobes — frontal, parietal, temporal, occipital), Thalamus, Hypothalamus | Thinking, memory, voluntary actions, sensory processing; Thalamus = relay station; Hypothalamus = temperature, hunger, thirst, sleep, links to pituitary |
| Midbrain | Corpora quadrigemina | Reflex responses to visual & auditory stimuli |
| Hindbrain | Cerebellum, Pons, Medulla oblongata | Cerebellum = balance & coordination; Pons = connects brain parts, breathing; Medulla = heartbeat, breathing, BP, vomiting, coughing, sneezing |
Fig: Major parts of the human brain
🔥 AMU PYQ: Which part of the brain controls balance?
(A) Cerebrum (B) Cerebellum (C) Medulla (D) Pons Ans: B
(A) Cerebrum (B) Cerebellum (C) Medulla (D) Pons Ans: B
🔥 AMU PYQ: Which part controls body temperature?
(A) Cerebrum (B) Medulla (C) Hypothalamus (D) Pons Ans: C
(A) Cerebrum (B) Medulla (C) Hypothalamus (D) Pons Ans: C
2.2 Reflex action
Reflex arc: Receptor → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector (muscle/gland).
• Quick, automatic, involuntary — protects body without involving brain.
• Quick, automatic, involuntary — protects body without involving brain.
2.3 Sense organs — Eye
Key parts: Sclera, Cornea (bends light), Iris (controls pupil size), Lens (focuses by accommodation), Ciliary muscles (change lens shape), Retina (rods → dim light/b&w; cones → colour/bright light), Optic nerve, Blind spot (no photoreceptors).
• Accommodation: Near objects → ciliary muscles contract → lens thickens (high power). Far objects → ciliary muscles relax → lens thins (low power).
• Defects: Myopia (concave lens), Hypermetropia (convex lens), Presbyopia (bifocal), Cataract (cloudy lens → surgery).
• Accommodation: Near objects → ciliary muscles contract → lens thickens (high power). Far objects → ciliary muscles relax → lens thins (low power).
• Defects: Myopia (concave lens), Hypermetropia (convex lens), Presbyopia (bifocal), Cataract (cloudy lens → surgery).
2.4 Sense organs — Ear
• Outer ear: Pinna (collects sound) → Ear canal → Eardrum (vibrates).
• Middle ear: Ossicles (malleus, incus, stapes — amplify vibrations) + Eustachian tube (equalises pressure).
• Inner ear: Cochlea (hearing — hair cells convert vibrations to impulses) + Semicircular canals (balance).
• Middle ear: Ossicles (malleus, incus, stapes — amplify vibrations) + Eustachian tube (equalises pressure).
• Inner ear: Cochlea (hearing — hair cells convert vibrations to impulses) + Semicircular canals (balance).
3) Endocrine system
Hormones = chemical messengers secreted by ductless endocrine glands directly into blood → act on target organs (specific receptors).
• Exocrine glands have ducts (sweat, salivary). Endocrine glands are ductless.
• Exocrine glands have ducts (sweat, salivary). Endocrine glands are ductless.
| Gland | Hormones | Functions | Disorders (if relevant) |
|---|---|---|---|
| Hypothalamus | Releasing hormones (TRH, GnRH, CRH), ADH, Oxytocin | Controls pituitary; thermoregulation, hunger, thirst | — |
| Pituitary (Master gland) | GH, TSH, ACTH, FSH, LH, Prolactin (anterior); ADH, Oxytocin (posterior) | Controls other glands; growth, metabolism, reproduction, water balance | Gigantism, Dwarfism, Acromegaly, Diabetes insipidus |
| Thyroid | T₃, T₄ (thyroxine), Calcitonin | Regulates BMR (metabolism), growth, development; lowers blood Ca²⁺ | Hypo: Goitre (I₂ deficiency), Cretinism, Myxoedema Hyper: Graves' disease |
| Parathyroid | PTH (Parathormone) | Increases blood Ca²⁺ (from bone, gut, kidney) | Hypo: Tetany (low Ca²⁺ → spasms) |
| Adrenal | Cortex: Cortisol, Aldosterone Medulla: Adrenaline, Noradrenaline | Cortisol = stress, anti-inflammatory; Aldosterone = Na⁺/K⁺ balance; Adrenaline = fight-or-flight (↑ HR, BP, blood sugar, dilates pupils/airways) | Hypo: Addison's disease Hyper: Cushing's syndrome |
| Pancreas | Insulin (β-cells), Glucagon (α-cells) | Insulin ↓ blood glucose (↑ uptake, glycogenesis); Glucagon ↑ blood glucose (glycogenolysis, gluconeogenesis) | Diabetes mellitus (insulin deficiency/resistance) |
| Testes | Testosterone | Spermatogenesis, male secondary sexual characteristics | Hypogonadism |
| Ovaries | Estrogen, Progesterone | Female secondary sexual characteristics, menstrual cycle, pregnancy maintenance | Menstrual irregularities |
| Pineal | Melatonin | Regulates sleep-wake cycle (circadian rhythm) | Jet lag, insomnia |
| Thymus | Thymosin | T-lymphocyte maturation (immunity); shrinks with age | Weakened immunity |
🔥 AMU PYQ: Master gland of the body is:
(A) Thyroid (B) Adrenal (C) Pituitary (D) Hypothalamus Ans: C
(A) Thyroid (B) Adrenal (C) Pituitary (D) Hypothalamus Ans: C
🔥 AMU PYQ: Iodine deficiency causes:
(A) Diabetes (B) Goitre (C) Anaemia (D) Rickets Ans: B
(A) Diabetes (B) Goitre (C) Anaemia (D) Rickets Ans: B
🔥 AMU PYQ: Fight-or-flight hormone is:
(A) Insulin (B) Thyroxine (C) Adrenaline (D) Estrogen Ans: C
(A) Insulin (B) Thyroxine (C) Adrenaline (D) Estrogen Ans: C
4) Coordination in plants — hormones
| Hormone | Produced in | Functions |
|---|---|---|
| Auxins (IAA, IBA) | Shoot apex, young leaves | Cell elongation, phototropism (shaded side more elongation → bends toward light), apical dominance, rooting of cuttings, fruit development |
| Gibberellins | Young shoots, seeds | Stem elongation (internode growth), seed germination, bolting |
| Cytokinins | Root tips, young fruits | Cell division (cytokinesis), delays senescence, opposes auxin apical dominance → promotes lateral bud growth |
| Abscisic acid (ABA) | Leaves, fruits, seeds (under stress) | Stress hormone — stomatal closure (water stress), seed dormancy, abscission, inhibits growth |
| Ethylene (C₂H₄) | Ripening fruits, senescent tissues | Fruit ripening (commercial — bananas, mangoes), abscission, senescence, promotes flowering in pineapple |
🔥 AMU PYQ: Fruit ripening hormone is:
(A) Auxin (B) Gibberellin (C) Cytokinin (D) Ethylene Ans: D
(A) Auxin (B) Gibberellin (C) Cytokinin (D) Ethylene Ans: D
🔥 AMU PYQ: Stress hormone in plants is:
(A) Auxin (B) Gibberellin (C) ABA (D) Ethylene Ans: C
(A) Auxin (B) Gibberellin (C) ABA (D) Ethylene Ans: C
4.1 Plant movements
| Type | Stimulus | Response | Mechanism |
|---|---|---|---|
| Phototropism | Light | Shoot → + (towards); Root → − | Auxin redistributes to shaded side → more elongation shoots; inhibits root elongation |
| Geotropism | Gravity | Root → + (downward); Shoot → − (upward) | Statoliths settle → auxin on lower side → inhibits root/shoot elongation differently |
| Hydrotropism | Water | Root → + (towards water) | Roots detect moisture gradient |
| Chemotropism | Chemicals | Pollen tube → + (towards ovule) | Chemical signals (Ca²⁺, sugars) from ovule guide growth |
| Thigmotropism | Touch | Tendrils coil around support | Contact side cells stop elongating → curling |
Nastic movements: Non-directional, reversible. Example: Mimosa pudica leaf folding on touch (thigmonasty) — loss of turgor at pulvini.
5) AMU PYQs — quick revision
Q1. The structural and functional unit of the nervous system is:
(A) Nephron (B) Neuron (C) Axon (D) Dendrite Ans: B
(A) Nephron (B) Neuron (C) Axon (D) Dendrite Ans: B
Q2. Myelin sheath is produced by:
(A) Schwann cells (B) Astrocytes (C) Microglia (D) Ependymal Ans: A
(A) Schwann cells (B) Astrocytes (C) Microglia (D) Ependymal Ans: A
Q3. Which is NOT part of the hindbrain?
(A) Cerebellum (B) Pons (C) Medulla (D) Thalamus Ans: D
(A) Cerebellum (B) Pons (C) Medulla (D) Thalamus Ans: D
Q4. The correct path of a reflex arc is:
(A) Receptor → Motor → Spinal → Sensory → Effector
(B) Receptor → Sensory → Spinal → Motor → Effector Ans: B
(A) Receptor → Motor → Spinal → Sensory → Effector
(B) Receptor → Sensory → Spinal → Motor → Effector Ans: B
Q5. Which hormone regulates blood sugar?
(A) Insulin (B) Glucagon (C) Both (D) Thyroxine Ans: C
(A) Insulin (B) Glucagon (C) Both (D) Thyroxine Ans: C
Q6. Growth hormone is secreted by:
(A) Thyroid (B) Pituitary (C) Adrenal (D) Pancreas Ans: B
(A) Thyroid (B) Pituitary (C) Adrenal (D) Pancreas Ans: B
Q7. The bending of a stem towards light is due to:
(A) Geotropism (B) Phototropism (C) Hydrotropism (D) Thigmotropism Ans: B
(A) Geotropism (B) Phototropism (C) Hydrotropism (D) Thigmotropism Ans: B
Q8. Conversion of electrical to chemical signal occurs at:
(A) Dendrite (B) Axon (C) Cell body (D) Synapse Ans: D
(A) Dendrite (B) Axon (C) Cell body (D) Synapse Ans: D
Q9. Which is both endocrine and exocrine?
(A) Liver (B) Pancreas (C) Salivary gland (D) Sweat gland Ans: B
(A) Liver (B) Pancreas (C) Salivary gland (D) Sweat gland Ans: B
Q10. Which hormone promotes seed dormancy?
(A) Auxin (B) Gibberellin (C) Cytokinin (D) ABA Ans: D
(A) Auxin (B) Gibberellin (C) Cytokinin (D) ABA Ans: D
Q11. Diaphragm and lens are controlled by which system?
(A) Somatic (B) Autonomic (C) Both (D) Neither Ans: A
(A) Somatic (B) Autonomic (C) Both (D) Neither Ans: A
Q12. Rods in the retina are responsible for:
(A) Colour vision (B) Dim light vision (C) Bright light (D) Peripheral vision only Ans: B
(A) Colour vision (B) Dim light vision (C) Bright light (D) Peripheral vision only Ans: B
Q13. Which plant hormone promotes cell division?
(A) Auxin (B) Gibberellin (C) Cytokinin (D) Ethylene Ans: C
(A) Auxin (B) Gibberellin (C) Cytokinin (D) Ethylene Ans: C
Q14. The movement of Mimosa pudica is an example of:
(A) Phototropism (B) Geotropism (C) Thigmonasty (D) Chemotropism Ans: C
(A) Phototropism (B) Geotropism (C) Thigmonasty (D) Chemotropism Ans: C
📝 Pro Tip for AMU: Brain parts (cerebellum = balance, medulla = involuntary, hypothalamus = thermostat). Reflex arc order. Endocrine glands: pituitary (master), pancreas (insulin), adrenal (adrenaline). Plant hormones: auxin (phototropism), ethylene (ripening), ABA (stress), cytokinin (division). Rods (dim light) vs Cones (colour). Myopia (concave) vs Hypermetropia (convex).