ADH (antidiuretic hormone/vasopressin) and oxytocin are synthesised in the hypothalamus but transported along axons and stored in the posterior pituitary (neurohypophysis), from where they are released into the blood.

Learned behaviour is acquired and modified during an individual's lifetime through experience. Instinctive behaviour is genetically programmed and present from birth without prior experience.

Habituation is the simplest form of learning — a decrease in response to a repeated, meaningless stimulus. It requires no reward or punishment, just the repeated presentation of a non-harmful stimulus.

Insulin inhibits glycogenolysis (hydrolysis/breakdown of glycogen to glucose) in liver and muscles. It promotes glycogenesis (glycogen synthesis) and glucose uptake by cells, thereby lowering blood glucose.

High blood Ca²⁺ stimulates thyroid parafollicular (C) cells to release calcitonin. Calcitonin acts to decrease blood Ca²⁺ by inhibiting osteoclasts (preventing bone resorption) and increasing renal Ca²⁺ excretion.

The thyroid gland produces: T3 (triiodothyronine — more potent, 3 iodine atoms), T4 (thyroxine — less potent, 4 iodine atoms, converted to T3 in tissues), and calcitonin (from C-cells, lowers blood calcium).

Excess somatotrophin (STH/growth hormone) during childhood before epiphyseal plate closure causes gigantism — abnormally tall stature. In adults, excess GH causes acromegaly (enlargement of hands, feet, and facial features).

Insulin (51 amino acids) and glucagon (29 amino acids) are protein/polypeptide hormones. Oestrogens, testosterone, and cortisone are steroids (lipid-based, derived from cholesterol).

In Addison's disease (primary adrenal insufficiency), cortisol deficiency causes elevated ACTH secretion (negative feedback failure). ACTH has melanocyte-stimulating activity causing hyperpigmentation of skin.

The 12 pairs of cranial nerves in humans are numbered I-XII (olfactory to hypoglossal). They emerge from the brain and brainstem and supply the head, neck, and major visceral organs (via vagus nerve X).

Acetylcholine, adrenaline (norepinephrine), and dopamine are all neurotransmitters. Others include serotonin, GABA, glutamate, glycine, and substance P. Each has specific effects at postsynaptic receptors.

Axons are the processes of neurons that conduct impulses away (efferent) from the cell body toward other neurons or effectors. Dendrites conduct impulses toward (afferent) the cell body from receptors or other neurons.

During an action potential (active membrane potential), the neuron conducts a nerve impulse — a wave of electrochemical changes propagating along the axon membrane. This is the basis of neural communication.

Chemoreceptors are sensory receptors that detect chemical stimuli. Olfactory receptors (smell) in the nasal epithelium and gustatory receptors (taste) in taste buds are both chemoreceptors detecting dissolved chemicals.

Auxins (particularly indole-3-acetic acid, IAA) are the main natural plant auxins. They promote cell elongation, apical dominance, root initiation, phototropism, and fruit development. Synthetic auxins (2,4-D) are used as herbicides.

Latent learning is learning that occurs without apparent reward or reinforcement and without being expressed immediately. A rat exploring a maze latently learns the layout; this knowledge is later used when food reward is introduced.

Operant (instrumental) conditioning (B.F. Skinner) is trial-and-error learning where behaviour is shaped by consequences (rewards/punishments). Animals learn to repeat behaviours that are rewarded and avoid those that are punished.

Ivan Pavlov (1904 Nobel Prize) demonstrated classical conditioning — dogs were conditioned to salivate at the sound of a bell (conditioned stimulus) that had been paired repeatedly with food (unconditioned stimulus).

Habituation is the simplest form of learning — the reduction of response to a repeated, harmless stimulus. Rodents habituate to alarm calls that are never followed by danger, learning to ignore them to conserve energy.

Imprinting (studied by Konrad Lorenz) is irreversible learning during a critical sensitive period early in life. Young precocial birds (goslings, ducklings) follow and bond to the first large moving object they see after hatching.

Taxis is an innate, directed movement response — the organism moves directly toward (positive taxis) or away from (negative taxis) the source of a stimulus. Phototaxis (light), chemotaxis (chemicals), thermotaxis (temperature).

Learning is the process of adaptive modification of behaviour through experience. It includes habituation, classical conditioning, operant conditioning, latent learning, insight learning — all resulting in changed responses to stimuli.

Learning is modification of behaviour based on individual experience. Unlike innate behaviour, learning requires a nervous system capable of forming and storing memory traces (engrams) through synaptic plasticity.

A sign stimulus (releaser) is a specific feature that triggers an innate releasing mechanism (IRM) and subsequent fixed action pattern (FAP). The red belly of male sticklebacks is a classic example studied by Tinbergen.

Darwin described instinct as inherited behaviour — complex, stereotyped patterns encoded in genes and shaped by natural selection. Instincts are performed without prior learning, such as bird migration, nest building, and courtship.

Kinesis is a non-directional movement response — the organism changes its speed or rate of turning (not direction) in response to stimulus intensity. A woodlouse moves faster in dry conditions and slower in moist conditions.

All plant behaviour is innate (genetically programmed) — plants cannot learn from experience as they lack a nervous system. Plant movements (tropisms, nasties) and responses are all pre-programmed responses to stimuli.

Both chemical (endocrine) and nervous coordination are homeostatic — they work together to maintain a stable internal environment. The nervous system makes rapid adjustments; the endocrine system provides sustained regulation.

Gastrin is a peptide hormone produced by G-cells in the stomach's pyloric region in response to food. It stimulates parietal cells to produce HCl, peptic cells to produce pepsinogen, and stomach motility.

Ripening Graafian follicles in the ovary secrete oestrogen (oestradiol). Oestrogen stimulates development of secondary sexual characteristics, endometrial thickening, and triggers the LH surge causing ovulation.

Aldosterone (mineralocorticoid from adrenal cortex) stimulates Na⁺ reabsorption and K⁺ secretion in distal tubules and collecting ducts of kidneys. This conserves Na⁺ (and water), regulating blood pressure and fluid balance.

Adrenaline (epinephrine) is the primary stress hormone from the adrenal medulla. It dilates blood vessels in muscles and heart, increases heart rate, bronchodilates, raises blood glucose — the complete fight-or-flight response.

Cushing's syndrome (disease) results from excess cortisol. High cortisol causes protein catabolism (muscle wasting, thinning of skin), osteoporosis (bone weakness), central obesity, hypertension, and hyperglycaemia.

Cortisol (hydrocortisone) is a glucocorticoid from the adrenal cortex that raises blood glucose (by stimulating gluconeogenesis), suppresses inflammation, and has some mineralocorticoid activity regulating Na⁺ balance.

Adrenaline (epinephrine) and noradrenaline (norepinephrine) are catecholamine hormones produced by the adrenal medulla. They are released in response to stress, activating the fight-or-flight response.

The adrenal (suprarenal) glands are a pair of triangular glands, one sitting on top of each kidney. Each consists of an outer cortex (secretes corticosteroids) and inner medulla (secretes adrenaline and noradrenaline).

Glucagon (from alpha cells of pancreatic islets) promotes glycogenolysis — breakdown of glycogen to glucose — in both liver and muscles, raising blood glucose levels during fasting or low blood sugar states.

Glucagon is the physiological antagonist of insulin. Insulin lowers blood glucose; glucagon raises it by stimulating glycogenolysis (glycogen breakdown) and gluconeogenesis in the liver when blood glucose falls.

Insulin promotes glycogen synthesis (glycogenesis) and inhibits glycogen breakdown (glycogenolysis) in both the liver and muscles. By inhibiting glycogenolysis, insulin prevents glucose release into blood, lowering blood sugar.

The Islets of Langerhans (pancreatic endocrine cells) respond to blood glucose levels and pituitary hormones. Beta cells secrete insulin when blood glucose rises; alpha cells secrete glucagon when blood glucose falls.

Graves' disease (hyperthyroidism) is caused by autoantibodies that mimic TSH, causing excessive thyroxine production. Symptoms include weight loss, rapid heart rate, exophthalmos (bulging eyes), heat intolerance, and tremors.

The parathyroid glands secrete parathormone (PTH/parathyroid hormone). PTH raises blood calcium levels and lowers phosphate levels by acting on bones (resorption), kidneys (Ca²⁺ reabsorption, phosphate excretion), and intestine (indirect).

Low blood Ca²⁺ (hypocalcaemia) stimulates the parathyroid glands to secrete PTH (parathormone). PTH raises blood calcium by stimulating osteoclasts (bone resorption), renal Ca²⁺ reabsorption, and vitamin D activation.

High blood Ca²⁺ stimulates the thyroid gland (parafollicular C-cells) to release calcitonin. Calcitonin lowers blood calcium by inhibiting bone resorption (osteoclast activity) and increasing renal Ca²⁺ excretion.

Thyroxine deficiency in adults causes goitre (thyroid enlargement) and myxoedema (decreased metabolism, weight gain, fatigue, cold intolerance). Cretinism results from congenital thyroxine deficiency in infants.

Both thyroxine (T4) and triiodothyronine (T3) act on basal metabolic rate — they increase cellular respiration, glucose oxidation, heat generation, and ATP production. T3 is more potent; T4 is converted to T3 in target tissues.

The thyroid gland increases its output of thyroxine (T3/T4) during rapid growth periods (childhood), sexual maturation (puberty), and metabolic stress (cold, hunger) when higher basal metabolic rate is needed.

The thyroid gland has two lobes connected by the isthmus, situated in front of and around the trachea just below the larynx (voice box) in the neck. It produces thyroxine (T4), triiodothyronine (T3), and calcitonin.

In Addison's disease (adrenal cortex insufficiency), low cortisol causes elevated ACTH from the pituitary. ACTH has MSH-like activity (they share sequences), causing excessive skin pigmentation — a classic sign of Addison's disease.

Diabetes insipidus is caused by ADH (antidiuretic hormone) deficiency. Without ADH, the kidneys cannot concentrate urine, producing large volumes of dilute urine (polyuria) and causing excessive thirst (polydipsia).

Prolactin (PRL) is sometimes called luteotrophic hormone (LTH) because in some mammals it maintains the corpus luteum. Its primary function is stimulating milk production (lactation) after childbirth.

Corticotrophin releasing factor (CRF) from the hypothalamus is controlled by blood cortisol levels (a steroid) via negative feedback. High cortisol suppresses CRF and ACTH; low cortisol stimulates the HPA axis.

MSH (Melanocyte Stimulating Hormone) is produced by the intermediate (median) lobe of the pituitary. Elevated MSH/ACTH during pregnancy causes hyperpigmentation (darkening of skin, melasma, linea nigra).

LH (luteinising hormone), also called ICSH (interstitial cell stimulating hormone) in males, stimulates the Leydig cells (interstitial cells) of the testes to produce and secrete testosterone, the male sex hormone.

Blood thyroxine (T3/T4) levels control TRF (thyrotrophin releasing factor) release from the hypothalamus via negative feedback. High thyroxine inhibits TRF; low thyroxine stimulates TRF → TSH → more thyroxine production.

The hypothalamus is both a neural and endocrine structure. It synthesises ADH (vasopressin) and oxytocin, which are stored in and released from the posterior pituitary. The hypothalamus also produces releasing/inhibiting hormones.

Insulin (51 amino acids, two chains) and glucagon (29 amino acids, single chain) are protein/polypeptide hormones secreted by the pancreatic islets of Langerhans. They regulate blood glucose levels.

Vasopressin (ADH/antidiuretic hormone) is a nonapeptide (9 amino acids) — a polypeptide hormone. Thyroxine is a tyrosine derivative, and epinephrine/norepinephrine are catecholamines (amino acid derivatives).

ACTH (adrenocorticotrophic hormone) is secreted by the anterior pituitary. It stimulates the adrenal cortex to produce cortisol. Oxytocin and ADH are secreted by the posterior pituitary; calcitonin by the thyroid.

Hormones are chemically diverse: proteins (FSH, LH, GH, insulin), polypeptides (ADH, oxytocin, glucagon), steroids (cortisol, testosterone, oestrogen), and amino acid derivatives (thyroxine, adrenaline). All regulate body functions.

Anticonvulsant (antiepileptic) drugs like phenytoin, valproate, carbamazepine, and lamotrigine reduce the frequency and severity of seizures by stabilising neuronal membranes and modulating neurotransmitter activity.

Nicotine stimulates the autonomic nervous system causing increased heart rate, blood pressure, and digestive motility. It can cause nausea, vomiting, and affects kidney function — all effects of nicotinic receptor activation.

Electroencephalography (EEG) records electrical activity of the brain using electrodes placed on the scalp. It is the most important diagnostic test for epilepsy, as seizures produce characteristic abnormal brain wave patterns.

Hormones are organic chemical messengers secreted directly into the bloodstream by endocrine glands. They travel to specific target organs/tissues where they regulate physiological processes by binding to specific receptors.

Nicotine binds to nicotinic acetylcholine receptors (nAChRs) at postsynaptic membranes throughout the CNS and PNS (autonomic ganglia, neuromuscular junctions). It mimics acetylcholine, causing widespread stimulation.

The sympathetic nervous system activates the fight-or-flight response in emergencies: increases heart rate and BP, dilates pupils and bronchioles, stimulates adrenaline release, redirects blood to muscles, and suppresses non-essential functions.

Sympathetic preganglionic fibres originate in the thoracolumbar region (T1-L2) of the spinal cord and synapse in ganglia close to the spinal cord (paravertebral/sympathetic chain ganglia) before reaching target organs.

Parkinson's disease results from progressive degeneration of dopaminergic neurons in the substantia nigra (midbrain). Loss of dopamine causes tremors, rigidity, slow movements (bradykinesia), and postural instability.

Cranial nerves can be purely sensory (I olfactory, II optic, VIII vestibulocochlear), purely motor (III, IV, VI eye movements; XII hypoglossal), or mixed containing both sensory and motor fibres (V trigeminal, VII facial, X vagus).

There are 31 pairs of spinal nerves arising from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair. Each spinal nerve has a dorsal root (sensory) and ventral root (motor).

Ganglia (singular: ganglion) are clusters of neuron cell bodies located outside the CNS in the PNS. Examples include dorsal root ganglia (sensory), autonomic ganglia, and cranial nerve ganglia.

The cerebellum is proportionally very large and highly developed in birds, reflecting their need for precise flight coordination. It is involved in motor learning, procedural memory, and fine-tuning movements.

The pons (bridge) contains the pneumotaxic and apneustic centres that regulate breathing rate and pattern. It also contains the locus coeruleus (sleep-wake transitions) and connects the cerebellum to the rest of the brain.

Humans have 12 pairs of cranial nerves (I-XII) that arise from the brain and brainstem. They include the optic (II), oculomotor (III), facial (VII), vestibulocochlear (VIII), vagus (X), and hypoglossal (XII) nerves.

Nerves are bundles of axons (and sometimes dendrites) bound together by connective tissue sheaths (endoneurium around each fibre, perineurium around fascicles, epineurium around the whole nerve). They form the PNS.

The hypothalamus is the master homeostatic regulator — it controls body temperature, hunger, thirst, sleep-wake cycles, circadian rhythms, water balance, and the menstrual cycle through neural and hormonal mechanisms.

The limbic system (emotional brain) includes: hypothalamus (homeostasis, hormones), amygdala (fear, aggression, emotional memory), hippocampus (spatial navigation, memory consolidation), and the cingulate gyrus.

The hindbrain (rhombencephalon) consists of three parts: the medulla oblongata (controls breathing, heart rate, blood pressure, reflexes), pons (connects medulla to cerebellum, breathing rhythm), and cerebellum (movement coordination, balance).

The midbrain (mesencephalon) is relatively small in humans. It contains the inferior colliculi (auditory relay) and superior colliculi (visual reflex coordination — controlling eye and head movements in response to visual/auditory stimuli).

The cerebral cortex is the folded outer layer of the cerebrum — grey matter containing billions of neuron cell bodies. Folding (convolutions/gyri separated by sulci) greatly increases surface area, enabling higher cognitive functions.

The brain is the master control centre — it receives and integrates all sensory information, initiates voluntary and involuntary responses, stores memories, generates emotions and consciousness, and coordinates all body functions.

The forebrain (prosencephalon) consists of three main parts: the thalamus (sensory relay), the limbic system (emotions, memory — including hypothalamus, hippocampus, amygdala), and the cerebrum (highest cognitive functions).

The sympathetic division of the ANS activates the fight-or-flight response — increases heart rate, blood pressure, dilates pupils and bronchioles, releases glucose, redirects blood to muscles, and suppresses digestion.

The thalamus is the main relay station of the brain — it receives sensory information (from all senses except smell) and relays it to appropriate areas of the cerebral cortex. It also regulates consciousness and alertness.

The CNS is protected by: bone (cranium surrounds brain, vertebral column surrounds spinal cord), meninges (three connective tissue membranes — dura, arachnoid, pia mater), and cerebrospinal fluid (CSF) filling the subarachnoid space.

In Hydra, the nerve net consists of neurons located in the mesoglea — the jelly-like layer between the ectoderm and endoderm. This is the simplest type of nervous system found in multicellular animals.

Planaria has two nerve networks: a superficial sub-epidermal nerve plexus and a deeper plexus embedded in the parenchyma. These connect to two ventral nerve cords and a primitive brain (cerebral ganglia).

Planaria has the most advanced sensory system among the flatworms — it has primitive eyes (ocelli that detect light direction) and chemoreceptors in the auricles (ear-like projections) that detect chemicals in the environment.

The tentacles of Hydra are the most responsive part — they contain the highest density of nematocysts and sensory cells. They respond instantly to touch or chemical stimuli to capture prey or retract from danger.

Hydra has a diffuse nerve net — neurons are scattered throughout the body without any centralised brain or ganglia. Any stimulus can spread throughout the network. Planaria has a more centralised ladder-type nervous system.

Saltatory conduction is the jumping of action potentials from one node of Ranvier to the next in myelinated axons. This is much faster (up to 120 m/s) than continuous conduction in unmyelinated fibres and requires less energy.

The resting membrane potential (RMP) of a neuron is approximately -0.07 volts (-70 mV) — the inside of the membrane is 70 millivolts more negative than the outside when the neuron is not conducting impulses.

A synapse is the microscopic junction between two neurons (or a neuron and effector) where nerve signals are transmitted. Chemical synapses use neurotransmitters released from presynaptic vesicles to activate postsynaptic receptors.

The threshold for action potential initiation is about -55 to -50 mV. Once threshold is reached, an all-or-none action potential is generated, reaching a peak of about +30 to +40 mV (about 0.07 volts from resting -70 mV).

During the rising phase of an action potential, voltage-gated Na⁺ channels open, causing a sudden increase in Na⁺ permeability. Na⁺ rushes in, depolarising the membrane from -70 mV to +30 mV.

The Na⁺/K⁺ pump transports 3 Na⁺ out for every 2 K⁺ in — this unequal exchange creates a net movement of one positive charge outward per cycle, making the pump electrogenic (contributes to membrane potential).

K⁺ concentration is about 20-35 times higher inside the neuron than outside (140 mM vs 4-5 mM). K⁺ tends to leak out of the cell, making the inside more negative — contributing to the resting membrane potential.

Na⁺ concentration is about 10 times higher outside the neuron than inside (145 mM vs 15 mM). The Na⁺/K⁺-ATPase pump (sodium-potassium pump) actively maintains this gradient by pumping 3 Na⁺ out and 2 K⁺ in per cycle.

Membrane potential is the voltage difference across a cell membrane due to unequal ion distribution. The resting membrane potential (RMP) is the membrane potential of a non-conducting neuron (about -70 mV).

Effectors are organs that respond to nerve impulses to produce effects. The principal effectors are muscles (skeletal, smooth, cardiac — produce movement) and glands (endocrine, exocrine — produce secretions).

Mammals have all three functional types of neurons: sensory neurons (carry signals from receptors to CNS), association neurons/interneurons (within CNS for processing), and motor neurons (carry signals from CNS to effectors).

Pacinian corpuscles (lamellar corpuscles) are large encapsulated mechanoreceptors found deep in the skin, detecting heavy pressure and high-frequency vibration. Meissner's corpuscles detect light touch and low-frequency vibration.

The cell body (soma/cyton/perikaryon) is the metabolic centre of the neuron — it contains the nucleus and all major organelles (mitochondria, ER with Nissl granules) responsible for protein synthesis and energy production for the whole cell.

Neuroglia (glial cells) make up about 50% of the cells in the CNS. They include astrocytes, oligodendrocytes, Schwann cells, and microglia. They support, insulate, protect, and nourish neurons.

Vibration sensing in terrestrial vertebrates is primarily through mechanoreceptors in joints (detecting bone vibration) and skin (Pacinian corpuscles detect deep pressure and high-frequency vibrations).

Chemoreceptors detect chemical stimuli. The hypothalamus has chemoreceptors monitoring blood CO₂/pH levels. Peripheral chemoreceptors in the olfactory epithelium detect smell; taste buds detect taste chemicals.

The nervous system coordinates via three elements working together: receptors (detect stimuli), neurons (transmit and process information), and effectors (muscles/glands that produce the response to stimuli).

Thermoreceptors are sensory receptors that detect temperature changes. Warm receptors respond to temperatures above skin temperature and cold receptors respond to temperatures below. They are found in skin and hypothalamus.

Receptors are structures that detect stimuli. They may be individual cells (taste cells, photoreceptors), free or encapsulated nerve endings (skin receptors), or complex receptor organs (eye, ear, nose).

Higher animals use both nervous coordination (rapid, electrical, specific responses through neurons) and chemical coordination (slow, widespread, sustained responses through hormones). Together they regulate all body functions.

Ethylene (ethene, C₂H₄) is a gaseous plant hormone responsible for fruit ripening. It triggers the ripening process — converting starch to sugar, softening cell walls (by activating cellulase and pectinase), and changing colour.

ABA (abscisic acid) causes stomatal closure during drought/water stress by triggering K⁺ efflux from guard cells, reducing turgor pressure. It is produced in leaves when they are water-stressed and detected by guard cell receptors.

Abscisic acid (ABA) is called the 'stress hormone' and promotes dormancy in buds and seeds, inhibits germination, closes stomata during water stress, and promotes leaf abscission (falling of leaves in autumn).

Gibberellins break bud and seed dormancy by stimulating cell division and elongation. They promote germination by activating alpha-amylase in seeds (breaks down starch for the embryo) and overcome stratification requirements.

Auxins (IAA) promote apical dominance (the growing tip suppresses lateral buds) and parthenocarpic fruit development. Auxins are produced in apical meristems and control phototropism, gravitropism, and root growth.

Plant activities — from seed germination, stem elongation, root growth, flowering, and fruit ripening — are regulated by plant hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

Biological rhythms (circadian, circannual) are encoded in genes. The molecular clock involves feedback loops of clock genes (CLOCK, BMAL1, PER, CRY) whose cyclical expression controls daily rhythms in physiology and behaviour.

Cyclic environmental changes include: daily (circadian) cycles of light/dark, tidal cycles (12.4 hours), lunar cycles (29.5 days), and seasonal (annual/circannual) cycles. All influence biological rhythms and behaviour.

Galls are abnormal growths (plant tissue tumours) induced by parasites — bacteria (Agrobacterium tumefaciens causes crown gall), fungi, insects (like gall wasps), nematodes, or viruses manipulate plant hormones to create galls.

Etiolation is the abnormal elongation of stems and yellowing (lack of chlorophyll) in plants grown in darkness. It is caused by high auxin levels stimulating rapid cell elongation — an adaptation to grow toward light.

An axon is a long process of a neuron (nerve cell) that conducts nerve impulses away from the cell body. Axons can be very long (up to 1 metre) and may be myelinated for faster conduction.

The ear (cochlea) contains sensory receptors (hair cells) for hearing that convert sound vibrations into nerve impulses. All the others listed are types of stimuli, not receptors. Mechanoreceptors in the cochlea detect sound.

Ethylene (ethene) is the plant hormone responsible for fruit ripening. It triggers the conversion of starch to sugar, softening of fruit, colour change, and production of flavour compounds. It is used commercially to ripen bananas and tomatoes.

The optic nerve (cranial nerve II) carries visual information from the retina to the brain. It passes through the optic chiasma (where fibres from nasal half of each retina cross) to the visual cortex in the occipital lobe.

Parathormone (PTH) from the parathyroid glands is the primary regulator of calcium homeostasis. PTH increases blood Ca²⁺ by stimulating bone resorption, renal Ca²⁺ reabsorption, and intestinal Ca²⁺ absorption (via vitamin D activation).

The pancreas functions as both a secretory (endocrine) gland — producing insulin, glucagon, somatostatin — and a digestive (exocrine) gland — producing pancreatic juice with digestive enzymes.

The labyrinth (from Greek: labyrinth) is the complex of cavities in the inner ear — including the cochlea (hearing) and vestibular apparatus (balance). It has an outer bony labyrinth and inner membranous labyrinth.

Acetylcholine (ACh) is a key neurotransmitter released at neuromuscular junctions and many CNS synapses. It is synthesised in axon terminals and stored in synaptic vesicles, released by exocytosis when an action potential arrives.

Gibberellins promote stem elongation, seed germination, and flowering. They stimulate cell division and elongation in stems. They also promote fruit development and break seed/bud dormancy.

W.H. Thorpe classified learned behaviour into four types: habituation, conditioning (classical and operant), latent learning, and insight learning/reasoning. Each represents a different mechanism for behaviour modification.

Endocrinology is the branch of physiology/medicine that studies the endocrine system — the glands, hormones they produce, the effects of those hormones, and diseases related to hormonal imbalances.

The placenta is a temporary endocrine gland that functions only during pregnancy. It secretes HCG (human chorionic gonadotropin), oestrogen, progesterone, and human placental lactogen to maintain pregnancy.

Simple (non-toxic) goitre is caused by iodine deficiency — the thyroid cannot make thyroxine, so TSH rises (negative feedback fails), stimulating thyroid cell growth and enlargement without hyperthyroidism.

Parathormone (PTH/parathyroid hormone) is also called Collip's hormone (after J.B. Collip who isolated it). PTH is secreted by the parathyroid glands and raises blood calcium by mobilising Ca²⁺ from bones and increasing reabsorption.

Thyroxine (T4) is a hormone secreted by the thyroid gland. It regulates basal metabolic rate, growth, development, and body temperature. It is an iodine-containing amino acid derivative.

Oxytocin is produced by the hypothalamus and stored in and released from the posterior pituitary gland. It stimulates uterine contractions during labour and milk ejection during breastfeeding.

Intermedin is another name for MSH (Melanocyte Stimulating Hormone), secreted by the intermediate lobe of the pituitary. It stimulates melanocytes to produce melanin, increasing skin pigmentation.

Hypophysis cerebri (or hypophysis) is the formal anatomical name for the pituitary gland. It is located at the base of the brain in the sella turcica of the sphenoid bone, connected to the hypothalamus by the infundibulum.

Gonadotropins are hormones that stimulate the gonads (testes and ovaries). FSH (follicle stimulating hormone) and LH/ICSH (luteinising hormone/interstitial cell stimulating hormone) are the two gonadotropins secreted by the anterior pituitary.

The pituitary gland (hypophysis) is called the master gland because it secretes multiple tropic hormones that regulate other endocrine glands. It is itself regulated by hypothalamic releasing and inhibiting hormones.

The pancreas is a mixed gland: its acini cells (exocrine) secrete digestive enzymes through the pancreatic duct, while the Islets of Langerhans (endocrine) secrete insulin and glucagon directly into blood.

Endocrine glands lack ducts — they secrete hormones directly into the surrounding interstitial fluid and bloodstream. The blood carries hormones to distant target organs where they exert their effects.

Hormones are chemically diverse — they can be proteins/polypeptides (insulin, FSH, LH), steroids (derived from cholesterol — cortisol, sex hormones), or amino acid derivatives (thyroxine, adrenaline).

Bipolar neurons have two processes — one dendrite and one axon. They are found in special sense organs: cochlea (hearing), retina (vision), and olfactory epithelium (smell). Most CNS neurons are multipolar.

Axons are efferent processes (carry impulses away from the cell body toward other neurons or effectors). Dendrites (afferent processes) carry impulses toward the cell body from receptors or other neurons.

Latent learning occurs without obvious reinforcement or reward — an animal learns about its environment without immediately showing the learned behaviour. It is revealed later when the information becomes useful.

Perikaryon (also called soma or cyton) is the cell body of a neuron. It contains the nucleus, organelles (mitochondria, ER, Nissl granules), and is the metabolic centre of the neuron maintaining the axon and dendrites.

Neurons (and glial cells) develop from the ectoderm — the outermost embryonic germ layer. The neural tube (precursor of brain and spinal cord) forms by invagination of the dorsal ectoderm during neurulation.

Learning behaviour is an adaptive change in an animal's behaviour resulting from experience with stimuli. It includes habituation, conditioning, imprinting, and insight learning — all modifying future responses.

Animals exhibit diverse behavioural patterns — innate (instinctive, genetic) and learned (acquired through experience). These include feeding, mating, migration, territorial, and social behaviours.

Each adrenal gland has two distinct parts: the outer adrenal cortex (secretes corticosteroids — cortisol, aldosterone, sex steroids) and the inner adrenal medulla (secretes adrenaline and noradrenaline).

Behaviour is any detectable activity of an organism in response to stimuli (environmental or internal). It includes movement, feeding, reproduction, communication, and social interactions.

The pancreas is a mixed gland with both exocrine function (secreting digestive enzymes via pancreatic duct into duodenum) and endocrine function (Islets of Langerhans secrete insulin and glucagon directly into blood).

Goitre is the swelling (enlargement) of the thyroid gland, visible as a swelling in the neck. It is caused by iodine deficiency (the gland enlarges trying to capture more iodine) or autoimmune thyroid disease.

The pituitary gland is called the 'master gland' because it secretes tropic hormones that control other endocrine glands (thyroid, adrenal cortex, gonads). However, it is itself controlled by the hypothalamus.

Endocrine glands produce hormones — chemical messengers secreted into the blood that travel to target organs and regulate their activity. Hormones control growth, metabolism, reproduction, and homeostasis.

Endocrine glands are ductless — they secrete hormones directly into the bloodstream (not through ducts). Exocrine glands secrete through ducts (e.g., salivary glands, sweat glands, digestive glands).

Taste receptors (gustatory cells) are located in taste buds found primarily on the tongue, particularly on papillae. They detect the five basic tastes: sweet, sour, salty, bitter, and umami (savoury).

The middle ear contains three tiny bones (ossicles): the malleus (hammer), incus (anvil), and stapes (stirrup). They transmit and amplify sound vibrations from the eardrum to the oval window of the inner ear.

The retina is the innermost layer of the eyeball. It contains photoreceptor cells (rods for dim light vision and cones for colour vision) that convert light energy into neural signals sent to the brain via the optic nerve.

The human eye works like a camera — it has a lens system (cornea + lens) that focuses light, an iris (diaphragm) controlling light entry, and a retina (photographic film) that converts light to neural signals.

Reflexes are rapid, automatic, stereotyped responses to stimuli that bypass conscious control. They are mediated by reflex arcs and protect the body from harm (withdrawal reflex, knee-jerk reflex).

The cerebellum coordinates voluntary muscle movements, maintains body posture and balance (equilibrium), and fine-tunes motor activity. Damage to the cerebellum causes ataxia (loss of coordination).

The white matter of the brain and spinal cord consists of myelinated nerve fibres (axons). The myelin sheath gives the white appearance. White matter conducts impulses between different brain regions and the spinal cord.

The grey matter of the spinal cord contains aggregations of neuron cell bodies forming neuronal chains (interneuronal networks) along its entire length, enabling complex reflex arcs and ascending/descending pathways.

In humans, the spinal cord has considerably reduced independence from the brain compared to lower vertebrates. Most reflexes in humans are modifiable by higher brain centres, reflecting the dominance of the cerebral cortex.

The spinal cord's independence from the brain varies among vertebrates. In lower vertebrates (fish, frogs), the spinal cord is quite independent; in mammals, especially humans, the brain exerts greater control over spinal reflexes.

The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) includes all nerves outside the CNS. The CNS integrates information and coordinates responses.

In annelids and molluscs, cerebral ganglia above the pharynx are connected to ventral ganglia below by circumpharyngeal connectives — nerve cords encircling the pharynx, forming the primitive brain.

In simple animals like Hydra and jellyfish, neurons are arranged in a diffuse nerve net — an interconnecting mesh of neurons without any centralised brain. Stimulation of any part can spread throughout the net.

A nerve impulse is essentially a message encoded in electrical form — the pattern of action potentials (frequency and timing) carries information from receptors to the brain and from the brain to effectors.

The resting membrane potential of most neurons is between -40 to -90 mV (outside positive relative to inside), typically around -70 mV for most mammalian neurons. This is maintained by the sodium-potassium pump.

A nerve impulse (action potential) is initiated when a sufficient stimulus causes the resting membrane potential (RMP, around -70mV) to shift toward threshold, triggering a rapid depolarisation that propagates along the neuron.

Neurons generate and conduct electrical signals (nerve impulses/action potentials) along their length as changes in membrane potential. This is caused by movement of Na⁺ and K⁺ ions across the membrane.

There are three functional types of neurons: sensory neurons (carry impulses from receptors to CNS), motor neurons (carry impulses from CNS to effectors), and association/interneurons (connect sensory and motor neurons in CNS).

The nervous system provides the fastest means of communication in the body — nerve impulses travel at speeds of up to 120 m/s. The endocrine system is slower, using hormones transported in blood.

The environment has a profound effect on all living organisms — it provides stimuli that organisms must respond to for survival. Coordination systems allow organisms to detect and respond appropriately to environmental changes.

Axon terminals (synaptic knobs/boutons) are the fine branches at the end of an axon. They contain synaptic vesicles filled with neurotransmitters, released into the synapse to communicate with the next neuron or effector.

Nissl granules (Nissl bodies) are a characteristic feature of neurons — they are clusters of rough endoplasmic reticulum (ribosomes + rER) found in the cell body (cyton). They are involved in protein synthesis.

Coordination in animals is controlled by two mechanisms: the nervous system (rapid electrical signals) and the endocrine system (slower chemical signals via hormones). Both work together to maintain homeostasis.