Coordination and Control - Vocabulary Flashcards

COORDINATION AND CONTROL – COMPREHENSIVE STUDY NOTES

INTRODUCTION

  • All organisms respond to stimuli (internal or external) at molecular, sub-cellular, cellular or organismal levels.

  • Coordination of activities across body parts enables integration of functions for organismal behavior.

  • Coordination is essential for survival.

  • In unicellular organisms, coordination exists among cellular processes to respond to environmental changes (temperature, light, chemicals, electric current).

  • In multicellular organisms, cells can respond to local changes; even humans cannot detect or respond to all stimuli (e.g., surface bacteria on skin may be undetected by sensory cells, yet internal cells may respond to pathogens).

  • We may not perceive all radiations (beyond visible light), but body cells can respond to some of them.

COORDINATION IN PLANTS

CONTROL THROUGH HORMONES

  • Plants are dynamic, complex organisms that grow, change and respond to stimuli, unlike animals which rely on rapid muscle-based movement.

  • Plants are sessile; behavior largely occurs via growth changes and turgor movements rather than fast muscle action.

  • Plant control is primarily through plant hormones; animals use a wider variety of hormones plus nervous control for speed.

  • Hormonal control in plants is slower; a delay exists between hormone synthesis, release, arrival at target cells, and action.

  • Despite slow movement mechanisms, the hormonal control in plants governs growth, development, and ripening.

  • Plant responses to stimuli include:

    • Regulating growth and development appropriately

    • Controlling body functions through plant hormones (growth regulators)

PLANT MOVEMENTS

  • Plants exhibit movements of organs rather than whole-organism locomotion.

  • Movements are modified by external stimuli in terms of nature and intensity.

  • Two kinds of plant movements:

    • Autonomic movements

    • Paratonic movements

RESPONSES TO ENVIRONMENTAL STRESSES IN PLANTS

  • Plants require water, light, CO₂, and nutrients; shortages cause environmental stress affecting health and survival.

  • Etiolation: growth under darkness leads to elongated, pale plants with little chlorophyll.

  • Chlorosis: yellowing due to insufficient mineral nutrients hindering chlorophyll formation.

  • Defense against pathogens: infections by viruses, bacteria, fungi, or lichens cause diseases (studied in Class XI);

    • Wounding often leads to callus formation (undifferentiated tissue masses).

    • Plant tumors and cancers may arise via amorphous invasion of tissues.

    • Galls: growths induced by parasites with highly organized growth (e.g., bacterial tumors in galls).

BIOLOGICAL CLOCKS AND CIRCADIAN RHYTHMS

  • Organisms exhibit biorhythms (biological rhythms) at regular intervals; circadian rhythms are ~24 hours (diurnal).

  • circannual rhythms are about 365 days.

  • External cyclical changes (days, tides, seasons) influence internal clocks to prepare organisms for periodic changes.

  • Origins of rhythms may be:
    1) Direct responses to exogenous stimuli
    2) Endogenous rhythms aligned with external cycles
    3) A combination of 1 and 2

  • Internal genetic basis with environmental modulation; timing results from interactions between internal processes and environmental timing cues.

  • Plant growth regulatory substances (hormones) are part of the clock system; exposure to constant conditions may still preserve ~24 h rhythms in some species.

  • Basic period of the clock is innate; examples include Drosophila showing persistent ~24 h rhythm under constant conditions for multiple generations.

PLANT GROWTH REGULATORY SUBSTANCES

  • Plant hormones have various chemical natures:

    • Proteins (e.g., insulin, glucagon)

    • Amino acids and derivatives (e.g., thyroxine T4, adrenaline, noradrenaline)

    • Polypeptides (e.g., vasopressin/ADH, oxytocin)

    • Steroids (e.g., estrogens, testosterone, cortisone)

(a) Auxins (IAA and variants)

  • In stems: promote cell enlargement behind the apex; promote cambial cell division.

  • In roots: promote growth at low concentrations; inhibit growth at high concentrations (geotropism).

  • Promote root formation from cuttings and calluses; promote bud initiation in shoots; can be antagonistic to cytokinins; promote apical dominance and fruit growth; can induce parthenocarpy.

  • Delay leaf senescence in some species; can inhibit abscission.

  • Commercially important: synthetic auxins (economical and often more active than IAA because plants lack enzymes to degrade them).

  • Examples:

    • NAA (Naphthaleneacetic acid)

    • Indole-propionic acid

    • 2,4-D (2,4-Dichlorophenoxyacetic acid) – weed killer; selective for broad-leaved species; used to eliminate weeds in cereals; can retard potato sprouting; retards premature fruit drop.

(b) Gibberellins

  • Naturally produced by fungi and plants; promote cell enlargement with auxins; promote cell division in apical meristem and cambium.

  • Promote bolting in some rosette plants; promote bud initiation in chrysanthemum callus; promote leaf and fruit growth; may induce parthenocarpy.

  • In apical dominance, enhance the action of auxins.

  • Break bud and seed dormancy; under some conditions substitute red light to promote flowering in long-day plants; inhibit in short-day plants.

  • Delays leaf senescence in some species; commercial applications include:

    • Promoting fruit setting (e.g., in citrus fruits) and seedless grapes (parthenocarpy)

    • In brewing to stimulate α-amylase in barley (malt production)

    • Delaying ripening and improving storage life of bananas and grapes

(c) Cytokinins

  • Promote stem growth via cell division in apical meristem and cambium; inhibit primary root growth but promote lateral root growth.

  • Promote bud initiation and leaf growth; promote fruit growth and can induce rare parthenocarpy.

  • Promote lateral bud growth and break bud dormancy; delay leaf senescence; promote stomatal opening.

  • Commercial use: delay senescence in leafy vegetables (e.g., cabbage, lettuce) and help keep flowers fresh; can break seed dormancy.

(d) Abscisic acid (ABA)

  • Inhibits stem and root growth under physiological stress (drought, waterlogging).

  • Promotes bud and seed dormancy; promotes flowering in short-day plants (antagonistic to gibberellins).

  • May promote leaf senescence and abscission; ABA can regulate stomatal closure under water stress.

  • Commercial use: ABA can be sprayed on trees to regulate fruit drop at season end.

(e) Ethene (ethylene)

  • Inhibits stem growth under stress; inhibits root growth; breaks bud dormancy; promotes flowering in some species (pineapple).

  • Promotes fruit ripening.

  • Commercial uses: ethephon (ethylene-releasing compound) to induce flowering in some crops; stimulates ripening of tomatoes and citrus; used to stimulate latex flow in rubber plants.

CO-ORDINATION IN ANIMALS

NERVOUS CO-ORDINATION

  • Involves specialized cells (neurons) linked via the central nervous system (CNS) to form networks connecting receptors to effectors.

  • Neuron capabilities: generate and conduct impulses that travel across synapses to connect receptors to effectors.

  • Key components of the nervous system:
    1) Receptors – detect changes in external/internal environments
    2) Neurons – transmit impulses
    3) Effectors – respond (muscles or glands)

1) Receptors

  • Types of receptors (modalities of sensation):

    • Chemoreceptors: smell, taste, blood CO₂, O₂, glucose, amino acids, fatty acids (e.g., hypothalamus receptors)

    • Mechanoreceptors: touch, pressure, hearing, equilibrium (e.g., free endings, expanded ends, hair endings)

    • Photoreceptors: light (retina, rods and cones)

    • Thermoreceptors: cold and warm free nerve endings

    • Nociceptors: pain (undifferentiated endings)

  • Modality explanation: different modalities arise because each nerve tract terminates in a specific CNS region; receptors are specialized to receive particular stimuli.

2) Neurons

  • Basic structural and functional units; neuroglia provide nutrition and protection via myelin sheath.

  • Three functional neuron types: sensory, associative (relay), and motor neurons.

  • Structural features include dendrites, cell body, axon, axon terminals; myelin and nodes of Ranvier; Schwann cells; Nissl bodies; Golgi apparatus; mitochondria.

  • Dendrites vs dendrons: dendrites conduct impulses toward the cell body; axons conduct impulses away.

  • Mature neurons generally do not divide after maturation.

3) Effectors

  • Respond to impulses via glands (secretion) or muscles (contraction).

  • Reflex arcs illustrate flow: receptor -> sensory neuron -> associative neuron (in CNS) -> motor neuron -> effector.

REFLEX ARC AND NEURAL PATHWAYS

  • Reflex arc involves four elements: sensory receptor, sensory neuron, association (relay) neuron, motor neuron, and effector.

  • Example: pain withdrawal reflex (Fig. 17.3): pain receptor in skin -> sensory neuron -> spinal cord -> association neuron -> motor neuron -> muscle contraction to withdraw limb; sensory neuron may also relay signals to brain for awareness.

  • Reflex actions are involuntary and rapid; higher brain centers may receive information in parallel.

NERVE IMPULSE AND MEMBRANE POTENTIALS

  • Nerve impulse is an electrochemical wave along neurons, driven by ion movements across the membrane.

  • Resting membrane potential: ≈ V_{rest} \,\approx -70\ \mathrm{mV}

  • Major contributing factors to resting potential:

    • Na⁺ and K⁺ distribution and Na⁺/K⁺-ATPase pumps pump Na⁺ out and K⁺ in, using ATP (3 Na⁺ out and 2 K⁺ in per ATP hydrolyzed)

    • Large negatively charged organic ions inside the cell

    • Membrane permeability and leakage of K⁺ outward

  • Initiation of nerve impulse occurs when a threshold stimulus causes a rapid, localized change in membrane potential, generating an action potential.

  • Action potential (active membrane potential): inner surface becomes more positive than outside; peak around +50\ \mathrm{mV} temporary reversal happens for about a millisecond.

  • Propagation: impulse travels along the length of the neuron; in myelinated neurons, saltatory conduction leaps from node to node (Nodes of Ranvier).

  • Typical speed of nerve impulse in humans: ≈ 100\ \mathrm{m/s}; maximum observed ≈ 120\ \mathrm{m/s}.

  • Recovery: after impulse, ions return to resting distribution via Na⁺/K⁺-ATPase pumps and diffusion.

SYNAPSES AND NEUROTRANSMISSION

  • Consecutive neurons connect at synapses where axon endings are near dendrites of the next neuron; no cytoplasmic continuity (synaptic cleft).

  • Transmission across the synapse uses neurotransmitters (chemical messengers): acetylcholine, adrenaline (epinephrine), noradrenaline (norepinephrine), serotonin, dopamine.

  • Release mechanism: when an impulse reaches the synaptic knob, synaptic vesicles fuse with the presynaptic membrane releasing neurotransmitters into the synaptic cleft.

  • Neurotransmitters bind to receptors on the postsynaptic membrane, altering permeability to ions and triggering an action potential in the postsynaptic neuron.

  • Acetylcholine generally acts at neuromuscular junctions outside the CNS; other transmitters are more involved within brain and spinal cord.

EVOLUTION OF THE NERVOUS SYSTEM

  • Two primary designs:
    1) Diffuse nervous system (e.g., Hydra): network of neurons without a centralized brain; responses are widespread; simple behavior.
    2) Centralized nervous system (Planaria and humans): differentiated neurons into sensory, associative, and motor; presence of brain and nerves; specialized sense organs and organized nervous pathways.

  • Hydra: diffuse network, no centralized brain; rapid body-wide response to stimuli; tentacles show high responsiveness.

  • Planaria: beginning of CNS with bilobed brain-like ganglia; differentiation of neurons; sensory organs present (eyes, chemoreceptors); defined nerves in planaria (longitudinal nerves); more advanced than Hydra.

CENTRAL NERVOUS SYSTEM (CNS) AND PERIPHERAL NERVOUS SYSTEM (PNS)

CNS

  • Brain and spinal cord protected by:

    • Cranium (brain case) and vertebral column vertebrae; meninges in three layers; cerebrospinal fluid (CSF) cushions brain and spinal cord.

  • Brain divisions: forebrain, midbrain, hindbrain.

    • Forebrain: thalamus, limbic system, cerebrum.

    • Limbic system: hypothalamus, amygdala, hippocampus; involved in basic emotions, drives, and memory formation; hypothalamus regulates body temperature, hunger, thirst, sleep-wake cycle, water balance, etc.

    • Thalamus: relay center for senses to cortex and limbic system.

    • Cerebrum: largest part; two hemispheres connected by corpus callosum; cortex handles sensory processing, memory, intelligence, reasoning, voluntary movement.

    • Midbrain: auditory relay, reflex movements of eyes; contains reticular formation for filtering inputs to higher centers; cerebral aqueduct and related pathways.

    • Hindbrain (Rhombencephalon): medulla (autonomic functions like breathing, heart rate, swallowing), pons, cerebellum (coordination and motor learning).

  • Spinal cord: center for reflexes and a conduit for impulses between brain and body; gray matter (cell bodies) inside, white matter (myelinated tracts) outside; central canal contains CSF.

  • Cerebrospinal fluid (CSF): bathes CNS, cushions, provides nutrients, removes wastes.

PNS

  • Connects CNS to the rest of the body via nerves and ganglia.

  • Comprised of sensory (afferent) and motor (efferent) neurons; nerves may be mixed.

  • Peripheral nervous system subdivides into:

    • Somatic nervous system: controls voluntary movements via skeletal muscles.

    • Autonomic nervous system: controls involuntary responses affecting organs, glands, and smooth muscles; subdivided into:

    • Sympathetic division: prepares body for stress (“fight or flight”); accelerates heart rate, dilates pupils, inhibits digestion, etc.

    • Parasympathetic division: promotes rest and digestion; constricts pupils, stimulates digestion, slows heart rate, etc.

SENSORY RECEPTION AND NEURAL SIGNALING IN DETAIL

SENSORY MODALITIES AND RECEPTORS

  • Receptor types detect specific stimuli; pathway discriminates modality by where the signal is processed in CNS.

  • Skin receptors for touch, pressure, heat, cold, and pain include:

    • Hair end organs: touch stimuli at hair base.

    • Meissner's corpuscles: touch; located in papillae near ridges of fingertips.

    • Pacinian (Lamellar) corpuscles: deep pressure; located deep in tissues; contribute to vibration sense.

  • Receptor abundance and distribution vary: pain receptors are abundant; cold receptors outnumber heat receptors; touch receptors are plentiful in fingertips.

  • Receptors transmit signals to CNS via sensory neurons; processed by associative neurons in brain and spinal cord; motor neurons carry impulses to effectors (muscles or glands).

NEURONS

  • Dendrites and dendrons collect impulses toward the cell body; axons transmit impulses away.

  • Neuroglia provide nutrition and protection; myelin sheath insulates axons; nodes of Ranvier enable saltatory conduction.

  • Neuron cell body (soma) contains nucleus, organelles; growth and maintenance occur here; neurons mature and typically do not divide.

  • Three functional neuron types in mammals: sensory (afferent), associative (relay), motor (efferent).

REFLEX ARC AND SENSORY PATHWAYS

  • Reflex arc comprises: receptor -> sensory neuron -> association neuron (in CNS) -> motor neuron -> effector.

  • A reflex is an involuntary, rapid response; brain may receive signals in parallel via divergent pathways.

  • Example: pain withdrawal reflex (Fig. 17.3) demonstrates a simple reflex circuit with three main neurons and an effector muscle.

NERVE IMPULSE, MEMBRANE POTENTIALS, AND SYNAPSES

NERVE IMPULSE AND RESTING POTENTIAL

  • Nerve impulses are waves of electrochemical changes traveling along neurons.

  • Resting membrane potential is typically around V_{rest} \approx -70\ \mathrm{mV}.

  • Key contributors to resting potential:

    • Na⁺/K⁺-ATPase pumps move Na⁺ out and K⁺ in, powered by ATP; classic stoichiometry: for every ATP hydrolyzed, 3 Na⁺ are pumped out and 2 K⁺ are pumped in.

    • Large negative organic ions inside the cell.

    • Membrane leakage, especially of K⁺ out of the cell, contributing to inside negativity.

  • Initiation and propagation of an action potential involve rapid depolarization (Na⁺ influx) followed by repolarization (K⁺ efflux), lasting milliseconds.

  • Action potential peak: about +50\ \mathrm{mV} relative to outside.

  • Conduction in myelinated neurons is saltatory, jumping between nodes of Ranvier; speed around 100\ \mathrm{m/s}, can reach up to \sim 120\ \mathrm{m/s}.

SYNAPSES AND NEUROTRANSMISSION

  • Synapse: junction between neurons where impulses are transmitted chemically via neurotransmitters.

  • Mechanism: impulse reaches presynaptic terminal → neurotransmitter release into synaptic cleft → binding to postsynaptic receptors → initiation of postsynaptic potential, potentially triggering an action potential in the next neuron.

  • Major neurotransmitters include acetylcholine (ACh), adrenaline (epinephrine), noradrenaline (norepinephrine), serotonin, and dopamine.

  • Acetylcholine primarily mediates synapses outside CNS; other neurotransmitters predominate in brain/spinal cord signaling.

EVOLUTION OF THE NERVOUS SYSTEM AND CNS/PNS ORGANIZATION

DIFFUSED vs CENTRALIZED NERVOUS SYSTEM

  • Diffuse nervous system (Cnidarians like Hydra): network of neurons with no centralized brain; responses are broad and uniform; tentacles may be highly receptive to stimuli.

  • Centralized nervous system (Planaria and humans): concentration of neurons into brain and nerve cords; specialization into sensory, associative, and motor neurons; presence of defined sense organs in Planaria; human CNS features mature brain organization with higher processing capabilities.

CENTRAL NERVOUS SYSTEM (CNS) AND PERIPHERAL NERVOUS SYSTEM (PNS) STRUCTURES

  • CNS protected by bone and meninges; CSF cushions brain and spinal cord; ventricles and central canal present.

  • Brain subdivisions: forebrain (thalamus, limbic system, cerebrum), midbrain, hindbrain (pons, medulla, cerebellum).

  • Limbic system components: hypothalamus, amygdala, hippocampus; role in emotions, drives, memory, and homeostatic regulation.

  • Thalamus: relay station for sensory information to cortex and limbic system.

  • Hypothalamus: major coordinating center; regulates temperature, hunger, water balance, sleep-wake cycles, endocrine control via pituitary connections.

  • Cerebrum: consciousness, thought, intelligence, planning; left/right hemispheric functions; corpus callosum connects hemispheres.

  • Midbrain and reticular formation: relay and filtering of sensory information; control of reflexive movements of eyes and arousal.

  • Hindbrain: medulla (autonomic control), pons, cerebellum (coordination and motor learning).

  • Spinal cord: reflexes and transmission pathway for CNS-body communication.

  • PNS: somatic (voluntary control of skeletal muscles) and autonomic (involuntary control of organs, glands, and smooth muscles); autonomic further divided into sympathetic and parasympathetic branches.

THE NERVOUS AND ENDOCRINE SYSTEMS: A COMPARATIVE VIEW

NEUROTRANSMISSION VS HORMONAL COMMUNICATION

  • Similarities:

    • Both synthesize chemical messengers and release them into extracellular spaces.

    • Both coordinate body functions and respond to stimuli; both contribute to homeostasis.

  • Differences:

    • Nervous system uses neurons (electrical signals) and neurohormones; chemical coordinates are often released at synapses near target cells.

    • Hormones circulate in blood to reach distant targets; nervous signals are fast, short-lived, and often localized.

    • Neural signals are short-lived; hormonal signals can have prolonged effects.

    • Neurotransmitters act locally and often quickly; hormones may act over longer timescales.

BEHAVIOUR: INNATE AND LEARNED

INNATE BEHAVIOUR

  • Behaviors predetermined by inherited nervous/cytoplasmic pathways; exhibited by all members of a species under given conditions.

  • Types:

    • Orientation: kineses (nondirectional changes in speed) and taxes (directed movement toward/away from a stimulus).

    • Reflexes and instincts: rapid, predetermined responses; complex patterns including rhythms, territorial behavior, courtship, aggression, altruism, social hierarchies, and organization.

  • All plant behavior is innate.

INSTINCTS AND LEARNING

  • Instincts: inherited response sequences enabling adaptive behavior; sign stimuli influence instinctive responses via innate releasing mechanisms (IRM).

  • Learning: modification of behavior based on experience; higher animals show more learning; lower animals may have limited learning due to simpler nervous systems.

  • Examples:

    • Honey bees: inherited flight muscles and wing movement; innate tendency to fly toward flowers; may learn during life.

    • Digger wasp: instinctive nest-building while also learning spatial aspects of nests.

    • Conditioned reflex in dogs (Pavlov): meeting bell associated with food leads to salivation at bell alone.

    • Trial-and-error learning in rats and cats in mazes and lever pressing.

    • Snail habituation to repeated taps reduces response over time.

    • Sign stimuli and innate releasing mechanisms explain instinctive responses to certain cues.

LEARNING TYPES (THORPE, SIX TYPES)

  • Imprinting: rapid learning shortly after birth/hatching; species-specific following (e.g., birds following mother).

  • Habituation: diminished response to repeated non-harmful stimuli; conserves energy.

  • Conditioning or conditioned reflex type I (Pavlovian): association of a neutral stimulus with a primary stimulus to elicit a response.

  • Operant conditioning or conditioned reflex type II (trial-and-error): learning via rewards/punishments leading to goal-directed behavior.

  • Latent learning: learning without immediate reward; knowledge is demonstrated later when advantageous.

  • Insight learning: high-level problem solving via understanding relationships and applying reasoning to novel situations (chimpanzee box example).

ENDOCRINE SYSTEM AND CHEMICAL COORDINATION

CHEMICAL COORDINATION OVERVIEW

  • Hormones are organic compounds transported by the blood to target tissues, regulating existing enzymatic and cellular processes rather than initiating entirely new reactions.

  • Hormones have varying structure: proteins, amino acid derivatives, polypeptides, steroids.

  • Endocrine glands/tissues include hypothalamus, pituitary, thyroid, parathyroids, pancreas (Islets of Langerhans), adrenal glands, gonads, gut, and others.

HYPOTHALAMUS – PITUITARY AXIS

  • Hypothalamus integrates nervous system activity with endocrine responses; it produces releasing and inhibiting hormones.

  • Neurosecretory cells in the hypothalamus produce oxytocin and vasopressin (ADH), stored in the posterior pituitary, released upon stimulation.

  • Hypothalamus also secretes releasing/inhibiting hormones that regulate anterior pituitary secretion of tropic hormones (growth hormone, prolactin, thyroid-stimulating hormone, etc.).

  • The hypothalamus–pituitary connection is a central control point for endocrine regulation.

THE PITUITARY GLAND

  • An oval gland (~0.5 g in adults) with three lobes: anterior, intermediate (median), and posterior (neurohypophysis).

  • Anterior lobe (master gland) secretes tropic hormones that regulate other endocrine glands as well as direct hormones.

  • Posterior lobe stores and releases hypothalamic hormones (ADH and oxytocin).

ANTERIOR LOBE HORMONES

1) Somatotrophin hormone (STH) / Growth Hormone (GH):

  • Regulated by hypothalamic releasing factor (SRF). Promotes protein synthesis and growth; excess in early life causes gigantism; excess in adulthood causes acromegaly; deficiency causes dwarfism.
    2) Thyroid-stimulating hormone (TSH):

  • Release controlled by hypothalamic thyrotropin-releasing factor and circulating thyroid hormones; stimulates thyroid gland to increase its size and secretory activity.
    3) Adrenocorticotrophic hormone (ACTH):

  • Release controlled by corticotropin-releasing factor; responds to stress (cold, heat, pain, fear, infections); stimulates adrenal cortex.
    4) Gonadotrophic hormones (FSH, LH/ICSH) and Prolactin:

  • FSH: stimulates follicle development and estrogen production in females; sperm production in males.

  • LH/ICSH: stimulates ovulation and corpus luteum formation; stimulates testosterone production in males.

  • Prolactin: stimulates milk production; inhibited by PIH (prolactin-inhibiting hormone).

  • Common hypothalamic releasing factors regulate FSH/LH release.
    5) Melanocyte-stimulating hormone (MSH) – intermediate lobe:

  • Stimulated by light exposure; increases melanin production; excessive MSH linked to Addison’s disease (skin darkening).

POSTERIOR LOBE HORMONES

1) Antidiuretic hormone (ADH) / Vasopressin:

  • Stimulated by decreased blood pressure/volume or increased plasma osmolality detected by hypothalamic osmoreceptors; increases water reabsorption in kidneys; deficits cause diabetes insipidus.
    2) Oxytocin:

  • Stimulated by cervical dilation, decreased progesterone, neural stimuli during parturition and suckling; promotes uterine contractions and milk ejection.

THYROID GLAND

  • Thyroxine (T4) and Tri-iodothyronine (T3): regulate basal metabolic rate, glucose metabolism, heat production, and ATP generation; influence brain development.

  • Calcitonin: modulates calcium metabolism in coordination with parathyroid hormone.

  • Disorders related to thyroid function include Graves’ disease (hyperthyroidism) and cretinism (congenital hypothyroidism); myxedema (hypothyroidism in adults).

  • Iodine intake is essential to prevent goiter and to support thyroid hormone synthesis.

PARATHYROID GLANDS

  • Parathormone (PTH) produced by parathyroids; increases blood calcium when low, inhibits when high.

  • Hypocalcemia can cause muscular tetany; hyperactivity leads to bone demineralization and kidney stones.

PANCREAS – ISLETS OF LANGERHANS

  • Insulin (β-cells) lowers blood glucose by promoting glycogen synthesis and cellular uptake; stimulates conversion of glucose to lipid and protein; suppresses glycogenolysis.

  • Glucagon (α-cells) raises blood glucose by promoting glycogenolysis and gluconeogenesis; also促进 fat breakdown.

  • Diabetes mellitus results from insulin deficiency or resistance; hypoglycemia may occur with excess insulin.

ADRENAL GLANDS

  • Adrenal cortex (corticosteroids): cortisol (glucocorticoid), corticosterone (glucocorticoid and mineralocorticoid), aldosterone (mineralocorticoid).

  • Adrenal medulla (neurosecretory cells): adrenaline (epinephrine) and noradrenaline (norepinephrine).

  • Adrenal hormones regulate stress responses, metabolism, and electrolyte balance; dysregulation can cause Addison’s disease or Cushing’s disease.

  • Adrenaline and noradrenaline increase blood glucose and promote sympathetic responses; cortisol raises blood glucose and supports metabolism during stress.

GONADS

  • Ovaries: estrogens and progesterone regulate female secondary sexual characteristics, menstrual cycle, uterine changes, and pregnancy maintenance.

  • Testes: testosterone regulates male secondary sexual characteristics, sperm production, libido.

GUT HORMONES

  • Gastrin: stimulates gastric juice secretion in response to protein digestion in the stomach.

  • Secretin: stimulates pancreatic juice production and bile secretion when acidic chyme enters the duodenum.

FEEDBACK MECHANISMS

  • Negative feedback controls hormone secretion by sensing the end products and adjusting hypothalamic and pituitary outputs accordingly.

  • An example: thyroid axis – low body temperature or stress stimulates hypothalamic releasing hormones → TSH release from anterior pituitary → thyroid releases thyroxine; thyroxine increases metabolism and heat production, which feeds back to inhibit releasing hormones and TSH production.

  • The pituitary-thyroid axis illustrates negative feedback control of endocrine function.

COMPARISON: NERVOUS COORDINATION VS CHEMICAL COORDINATION

  • Similarities:

    • Both use chemical messengers and target specific cells.

    • Both respond to stimuli and contribute to homeostasis.

  • Differences:

    • Nervous: neurons/neurotransmitters act locally with fast, short-lived effects; electrical signaling is integral; electricity enables rapid responses.

    • Chemical: hormones travel via blood to distant targets; slower onset but longer-lasting effects; broad impact on many tissues.

SUMMARY OF KEY TERMS AND CONCEPTS

  • Stimulus, response, coordination

  • Hormones, growth regulators, plant vs animal control

  • Autonomic vs somatic nervous system; sympathetic vs parasympathetic

  • Receptors and modalities of sensation: chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptors, nociceptors

  • Neuron structure and function: dendrites, soma, axon, myelin, nodes of Ranvier, synapse

  • Reflex arc and reflex actions

  • Membrane potentials: resting potential, action potential, depolarization, repolarization, saltatory conduction

  • Neurotransmitters: acetylcholine, adrenaline, noradrenaline, serotonin, dopamine

  • CNS and PNS organization, limbic system, thalamus, hypothalamus, cortex, cerebellum

  • Endocrine glands and hormones: hypothalamus, pituitary (anterior and posterior), thyroid, parathyroid, pancreas, adrenals, gonads, gut hormones; negative feedback loops

  • Innate vs learned behavior; imprinting, habituation, conditioning (Types I and II), latent learning, insight learning

  • Hormonal control in plants: auxins, gibberellins, cytokinins, ABA, ethene; commercial uses

  • Plant responses to stress: etiolation, chlorosis, defense against pathogens

  • Evolution of nervous systems: Hydra vs Planaria vs humans

  • Nervous system disorders and basic pharmacology (nicotine effects, Parkinson’s, epilepsy, Alzheimer’s)

PRACTICAL APPLICATIONS AND EXAMPLES

  • Auxins used to promote root formation from cuttings and to delay organ senescence; synthetic auxins used as weed killers and fruit-set promoters.

  • Gibberellins used to promote flowering, fruit development, seedless fruit production, malting in barley, and delaying ripening to extend shelf life.

  • Ethene/ethephon used to induce flowering and ripen fruits and stimulate latex flow.

  • ABA used to control fruit drop in trees; stomatal closure under drought stress helps water conservation.

  • Negative feedback in thyroid function demonstrates how homeostasis is maintained via endocrine control.

  • Conditioned reflexes (Pavlov) show how environmental cues can modify behavior via associative learning.

  • Planaria illustrate early CNS development and specialization; Hydra demonstrates rudimentary nervous organization.

  • Nicotine acts on acetylcholine receptors, enhancing nerve activity and affecting heart rate, digestion, and other autonomic processes.

KEY NUMBERS AND FORMULAE

  • Resting membrane potential: V_{rest} \approx -70\ \mathrm{mV}

  • Action potential peak: V_{max} \approx +50\ \mathrm{mV}

  • Na⁺/K⁺-ATPase pump stoichiometry: for every ATP hydrolyzed, pumps move 3\ Na^+ out and 2\ K^+ in (toward maintaining the resting potential).

  • Typical nerve impulse speed: v \approx 100\ \mathrm{m/s} (max observed \approx 120\ \mathrm{m/s})

  • Membrane potential changes across a typical action potential: brief reversal from negative to positive inside with time course on the order of milliseconds.

If you want, I can convert this into a printable PDF-ready outline or tailor the notes to a specific chapter/page range from your course materials. I can also add a quick quiz with 10–15 practice questions to test key concepts from these notes.