Control and Coordination – Comprehensive Study Notes

Coordination: Fundamental Idea

  • Coordination = systematic, controlled, efficient working-together of all organs so that the body produces proper responses to diverse stimuli.

  • Multicellular organisms evolve specialised tissues to achieve this.

    • Animals: Nervous system + endocrine (hormonal) system.

    • Plants: No nerves; depend on electro-chemical signalling & hormones.

Nervous System: Organisation & Components

  • Control centre of animals (incl. humans); works with muscular tissue.

  • Key elements

    • Specialised cells: neurons

    • Bundles: nerves

    • Organs: brain, spinal cord, ganglia, sense organs

  • Receptors (in sense organs)

    • Gustatory → detect taste

    • Olfactory → detect smell

    • Others: photoreceptors (eye), phonoreceptors (ear), thermoreceptors (skin), etc.

Neuron – Structural & Functional Unit

  • Longest cell in human body (some reach 90\text{–}100\,\text{cm}).

  • Parts

    • Cell body / Cyton: nucleus, cytoplasm, organelles (no centrioles).

    • Dendrites: branched processes; receive stimuli & carry them to cyton.

    • Axon: single long fibre; carries impulse away; often wrapped in myelin sheath (insulation ↑ speed).

    • Nerve endings (axon terminals): fine branches forming synapses or neuromuscular junctions.

Nerve-Impulse Pathway (simplified)

Stimulus → Receptor → Sensory neuron dendrite → cyton → axon → synapse → relay neurons/CNS → motor neuron → effector (muscle/gland).

Synapse

  • Microscopic gap between two neurons.

  • Impulse arrives at pre-synaptic knob → vesicles release neurotransmitter (e.g. acetylcholine) → diffuses across gap → binds post-synaptic membrane → triggers new electrical impulse.

  • One-way transmission (chemicals only on one side).

Neuromuscular Junction

  • Synapse between motor-neuron axon terminal & muscle fibre membrane.

  • Same neurotransmitter principle; initiates muscle contraction.

Electrical Impulse – Merits & Limitations

  • Extremely fast (ms range); ideal for rapid responses.
    − Reaches only cells connected by nerves.
    − After firing, neuron needs refractory period to reset, limiting firing rate.

Reflex Action & Reflex Arc

  • Reflex action: automatic, rapid response lacking conscious thought (e.g., blinking, coughing, sneezing).

  • Reflex arc: specific neuronal route mediating the reflex.

    1. Receptor (sense organ)

    2. Sensory (afferent) neuron → spinal cord

    3. Relay neuron (interneuron) in spinal cord

    4. Motor (efferent) neuron

    5. Effector (muscle/gland)

  • Most reflexes handled by spinal cord → quicker than routing via brain; signals still ascend to brain for awareness/memory.

  • Functions

    • Immediate protection from harm

    • Prevents brain overload

    • Increases survival probability

Divisions of Human Nervous System

1. Central Nervous System (CNS)

  • Brain + spinal cord; integrates information & issues commands.

Brain (within cranium + cerebrospinal fluid for shock absorption)

  • Forebrain

    • Cerebrum (largest; thinking, voluntary actions, reasoning, memory, speech, interpretation of sensory data; has sensory, association, motor areas)

    • Olfactory lobes (smell)

    • Hypothalamus (homeostasis: body temperature, hunger, thirst, size regulation; also neuro-endocrine control)

  • Midbrain

    • Connects fore & hind brain; controls head/neck/trunk reflexes toward stimuli; important for visual & auditory reflex orientation.

  • Hindbrain

    • Cerebellum: coordination, precision of voluntary movements, posture & equilibrium

    • Pons: bridge; relays signals; assists in respiration control

    • Medulla oblongata: continuation into spinal cord; regulates involuntary actions (breathing rhythm, heartbeat, blood pressure, vomiting, salivation)

  • Brain stem = midbrain + hindbrain (pons & medulla)

  • Functions of brain (summary)

    • Coordinates organ activities; integrates neural & hormonal responses

    • Receives impulses from all receptors

    • Correlates multi-sensory input → appropriate output

    • Sends instructions to effectors

    • Stores information → learning & behaviour modification

Spinal Cord

  • Tubular bundle from medulla to lumbar region; protected by vertebral column.

  • Two-way conduction path between brain & body; mediates many reflexes.

2. Peripheral Nervous System (PNS)

  • Nerves outside CNS; links CNS to body.

    • Cranial nerves (12 pairs) ←→ head/neck organs.

    • Spinal nerves (31 pairs) ←→ trunk & limbs.

    • Visceral nerves (autonomic) ←→ internal organs.

  • Autonomic Nervous System (ANS) (a PNS part)

    • Sympathetic & parasympathetic pathways; regulate involuntary internal activities (heart rate, BP, gut motility).

Muscle Response Mechanism

  • Nervous impulse reaches muscle fibre → special contractile proteins slide/change configuration → fibre shortens & exerts force.

Coordination in Plants

Immediate (Nastic) Movements

  • Do NOT involve growth; often independent of stimulus direction.

  • Example: Mimosa pudica leaves fold on touch.

    • Electrical/chemical signal spreads cell-to-cell; cells lose/gain water → shrink/swell.

Growth-Dependent (Tropic) Movements

  • Directional growth due to external stimulus.

  • Types

    • Phototropism (light)
      • Shoots = positively phototropic; roots = negatively phototropic.

    • Geotropism (gravity)
      • Roots grow toward gravity (+ve); shoots grow opposite (−ve).

    • Hydrotropism (water)
      • Roots grow toward moisture gradient.

    • Chemotropism (chemicals)
      • Pollen tube growth toward ovule during fertilisation.

  • Tendril coiling (pea, pumpkin, cucumber)

    • Touch stimulus; auxin accumulates on side away from contact → faster growth there → curl around support.

Plant Hormones (Phytohormones)

  • Auxins: produced in shoot tips; promote cell elongation, apical dominance, phototropism.

  • Gibberellins: elongation of stem, bolting, flowering.

  • Cytokinins: promote cell division; highest in meristematic tissues, fruits, seeds.

  • Abscisic Acid (ABA): growth inhibitor; induces dormancy, wilting, stomatal closure.

Chemical Communication in Animals

Why Needed?

  • Electrical impulses too limited (only along nerves & require refractory periods). Hormones can reach every cell via bloodstream and act longer but slower.

Endocrine Glands (ductless)

  • Hypothalamus, pituitary (master), pineal, thyroid, parathyroids, thymus, pancreas (Islets), adrenals, gonads (testes/ovaries).

Major Hormones & Actions

  • Adrenaline (adrenal medulla)

    • "Fight-or-flight"; targets heart, lungs, vessels; ↑ heart rate, ↑ breathing, redirects blood to skeletal muscles.

  • Thyroxine (thyroid)

    • Regulates metabolism of carbs, proteins, fats; requires iodine.

  • Growth Hormone (GH) (anterior pituitary)

    • Stimulates overall growth and development.

  • Testosterone (testes) & Oestrogen (ovaries)

    • Initiate & maintain secondary sexual characters at puberty.

  • Insulin (β-cells, pancreas)

    • Lowers blood glucose; promotes uptake/storage.

Hormonal Disorders

  • Dwarfism: GH deficiency in childhood.

  • Gigantism: GH hyper-secretion in childhood.

  • Goitre: inadequate iodine → low thyroxine → thyroid enlargement.

  • Diabetes Mellitus: inadequate insulin secretion → hyperglycaemia; managed via insulin injections/diet.

Feedback Mechanism (Example: Blood Glucose)

  1. Carbohydrate-rich meal → \uparrow blood glucose.

  2. Pancreatic β-cells release insulin.

  3. Insulin → body cells store/use glucose → \downarrow blood glucose.

  4. Falling glucose inhibits further insulin release (negative feedback).

Key Comparative Points & Examples

  • Reflex vs Walking

    • Reflex: innate, involuntary, spinal cord, constant intensity.

    • Walking: learned, voluntary, coordinated by hindbrain/cerebellum, variable intensity.

  • Sensitive plant leaf folding vs shoot phototropism

    • Leaf movement: rapid, growth-independent, stimulus = touch, non-directional.

    • Shoot bending: slow, growth-dependent, stimulus = light, directional.

  • Synapse = chemical continuity break; ensures one-way impulse flow.

  • Cerebellum = posture/equilibrium centre.

Quick Facts & Fill-in-the-Blanks

  • Structural & functional unit of nervous system: Neuron.

  • Cranial + spinal nerves constitute the Peripheral Nervous System.

  • Brain protected by cranium; spinal cord by vertebral column.

  • Centre for smell, memory, sight, hearing, reasoning: Forebrain (cerebrum).

  • Hormone inhibiting growth & causing leaf wilting: Abscisic acid.

  • Growth of pollen tube toward ovule is example of positive chemotropism.