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State Board · Class 12 · Biology

Lesson 9: Control and Coordination

7 concepts · 56 practice questions with answers · Free to read

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Neurons and neuroglia

Link to Std 9–10

The last lesson showed how blood reaches every part; here we see how the nervous and endocrine systems control and coordinate the body.

From daily life

Like a phone wire carrying a signal, a neuron carries messages in the body.

Simple definition

A neuron = structural and functional unit of the nervous system. Neuroglia = supporting cells of neurons.

NeuronNeuron and neurogliaCytonAxonMyelin; nodes of RanvierDendritesHydra: nerve netPlanaria: ladder + ganglionHuman: CNS + PNSNeuron: cyton + dendrons/dendrites + axon; Nissl granules, neurofibrilsMultipolar, bipolar, unipolar; axon ends in telodendriaNeuroglia (more than neurons): astrocytes, microglia, oligodendrocytes, ependymalPNS: Schwann cells (myelin), satellite cellsNerve = bundle of axons outside CNS; inside CNS = tractHydra: impulse non-polar; Planaria: cerebral ganglion + ventral nerve cordsMedullated (white) and non-medullated nerves

In the figure : Neuron and nervous systems in animals.

Rule 1 : Nervous systems in animals — Hydra: scattered neurons form a nerve net; impulse non-polar; no centre. Planaria: cerebral (cephalic) ganglion in the head; two ventral nerve cords joined by ladder-like commissures; light-sensing eyespots. Higher animals have brain, spinal cord and nerves. Humans: CNS (brain + spinal cord) and PNS (nerves).

  • Easy : Hydra: nerve net.
  • Medium : Planaria: ladder.
  • Exam-type (CET) : CNS = brain + spinal cord.

Rule 2 : Neuron and neuroglia — Neuron: cyton (nucleus, Nissl granules, neurofibrils), dendrons/dendrites (carry message to the cyton) and axon (away from cyton; axon hillock; ends in telodendria). Around the axon: myelin sheath (insulation) and nodes of Ranvier. Types: multipolar, bipolar, unipolar. Nerve = bundle of axons outside the CNS (neurilemma/epineurium); inside the CNS = tract. Neuroglia (outnumber neurons): astrocytes, microglia (phagocytic), oligodendrocytes (myelin in CNS), ependymal (CSF), Schwann cells (myelin in PNS), satellite cells.

  • Easy : Axon: away; dendron: towards.
  • Medium : Schwann = PNS myelin.
  • Exam-type (CET) : Microglia = phagocytes.
Remember

Dendron delivers to the cell body; axon carries away.

Common mistake and CET trap

‘Axon brings impulse to the cyton’ is wrong (carries away). Trap: ‘neurons outnumber neuroglia’ is wrong.

Shortcut

Memory clue : "Dendrites in; axon out".

Spot the difference

PartFunction
DendriteReceive
AxonSend
MyelinInsulation

Practice questions

Easy
  1. 1Nervous system of Hydra?
  2. 2Planaria's ganglion?
  3. 3Nissl granules are in?
Medium
  1. 4Role of myelin?
  2. 5Myelin in PNS from?
  3. 6Myelin in CNS from?
Challenging
  1. 7Ependymal cells do?
  2. 8Define nerve.
Show answers (try them yourself first)
  1. 1Nerve net.
  2. 2Cerebral ganglion.
  3. 3Cyton.
  4. 4Insulation, faster impulse.
  5. 5Schwann cells.
  6. 6Oligodendrocytes.
  7. 7Produce/circulate CSF.
  8. 8Bundle of axons outside CNS.

Nerve impulse and synapse

From daily life

Press a switch and light is instant; a nerve impulse is similar.

Simple definition

A nerve impulse = electrochemical wave along an axon membrane. A synapse = junction between two neurons with a tiny gap (synaptic cleft).

ImpulseNerve impulse and synapse+30 mV−70 mVAPPre-synapticPost-synapticNeurotransmitterResting potential −70 mV: Na⁺ outside, K⁺ inside; pump 3 Na⁺ out, 2 K⁺ inAction potential: Na⁺ in → +30 mV (depolarisation); then K⁺ out (repolarisation)All-or-none; threshold; refractory period; myelinated = saltatory (faster)Synapse: synaptic cleft; vesicles → exocytosis; synaptic delay 0.3–0.5 msCholinesterase destroys neurotransmitter; synaptic fatigueChemical (one-way) and electrical (gap junction, two-way, reflex)Velocity: thick, long, medullated = faster; autonomic 10–20 m/s

In the figure : Action potential and synapse.

Live figure

Nerve impulse and synapse

In the app you can move this figure with your finger.

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Rule 1 : Resting and action potential — Resting potential: axon membrane is more permeable to K⁺ than Na⁺; Na⁺ outside, K⁺ and negative proteins inside ⇒ −70 mV; the Na⁺–K⁺ pump moves 3 Na⁺ out for 2 K⁺ in. Stimulus must reach threshold (subliminal: no effect). Action potential: Na⁺ channels open, Na⁺ rushes in ⇒ inside positive, +30 mV (depolarisation); then Na⁺ channels close, K⁺ leaves ⇒ repolarisation. All-or-none law; refractory period; in medullated nerves the impulse jumps (saltatory) — faster.

  • Easy : Resting = −70 mV.
  • Medium : AP peak = +30 mV.
  • Exam-type (CET) : Pump: 3 Na⁺ out, 2 K⁺ in.

Rule 2 : Synapse — Parts: pre-synaptic neuron, synaptic cleft, post-synaptic neuron/muscle/gland. Chemical synapse: when the impulse reaches the axon terminal Ca²⁺ enters ⇒ synaptic vesicles release neurotransmitter (acetylcholine) by exocytosis ⇒ binds post-synaptic receptors, impulse continues; cholinesterase then destroys it. One-way; synaptic delay 0.3–0.5 ms; synaptic fatigue. Electrical synapse (gap junctions): fast, two-way; in defence reflexes.

  • Easy : Cholinesterase destroys ACh.
  • Medium : Delay 0.3–0.5 ms.
  • Exam-type (CET) : Chemical = one-way.
Remember

Rest −70, peak +30.

Common mistake and CET trap

‘More Na⁺ inside at rest’ is wrong (K⁺). Trap: ‘electrical synapses are one-way’ is wrong.

Shortcut

Memory clue : "Na⁺ in = up; K⁺ out = back down".

Spot the difference

TypeChemicalElectrical
DirectionOneTwo
SpeedSlowerFaster

Practice questions

Easy
  1. 1Resting potential?
  2. 2Peak of AP?
  3. 3What does the pump do?
Medium
  1. 4Depolarisation due to?
  2. 5Saltatory conduction?
  3. 6All-or-none law?
Challenging
  1. 7Neurotransmitter stored in?
  2. 8Synaptic delay?
Show answers (try them yourself first)
  1. 1−70 mV.
  2. 2+30 mV.
  3. 33 Na⁺ out, 2 K⁺ in.
  4. 4Na⁺ entry.
  5. 5Jumping between nodes.
  6. 6Full or none.
  7. 7Synaptic vesicles.
  8. 80.3–0.5 ms.

The human brain

From daily life

A phone has a cover; the brain sits in the skull wrapped in three membranes.

Simple definition

Meninges = three membranes around the brain and spinal cord. CSF = fluid cushioning the brain and spinal cord.

BrainHuman brainForebrainMidbrainHindbrainCerebrum, thalamus, hypothalamusCorpora quadrigeminaCerebellum, pons, medullaMeninges: dura (outer), arachnoid, pia (inner); CSF is a shock absorberCerebrum: 4 lobes (frontal, parietal, temporal, occipital) + insulaCorpus callosum = largest commissure (joins hemispheres)Basal nuclei: movement; limbic system: emotion, memoryThalamus: sensory relay; hypothalamus: temperature, hunger, thirst, pituitaryEpithalamus: pineal → melatonin (sleep)Cerebellum: balance and coordination; pons: breathing; medulla: heart, breathing, vomitingMedulla joins spinal cord; CSF in ventricles; choroid plexus

In the figure : Three parts of the brain.

Rule 1 : Meninges, CSF and forebrain — Meninges: dura mater (outer, tough), arachnoid (middle), pia mater (inner, vascular). CSF is made by the choroid plexus and pia; in ventricles and central canal; shock absorber, nourishes. Forebrain: olfactory lobes; cerebrum (two hemispheres; 4 lobes frontal, parietal, temporal, occipital + insula; outer grey, inner white matter; thought, memory, speech, vision, hearing); corpus callosum = largest commissure; basal nuclei; diencephalon: thalamus (sensory relay), hypothalamus (temperature, hunger, thirst, controls pituitary), epithalamus (pineal → melatonin).

  • Easy : Dura = outer; pia = inner.
  • Medium : Corpus callosum = commissure.
  • Exam-type (CET) : Hypothalamus controls pituitary.

Rule 2 : Midbrain and hindbrain — Midbrain: cerebral peduncles and corpora quadrigemina (visual and auditory reflexes). Hindbrain: cerebellum (balance, muscle coordination; arbor vitae), pons (helps control breathing; bridge of fibres), medulla oblongata (heart rate, breathing, blood pressure, vomiting, coughing, swallowing) — continues into the spinal cord. Brainstem = midbrain + pons + medulla. Reticular activating system (RAS): wakefulness-sleep. Limbic system: emotion, memory.

  • Easy : Cerebellum = balance.
  • Medium : Medulla = heart, breathing.
  • Exam-type (CET) : Brainstem = 3 parts.
Remember

D-A-P: dura, arachnoid, pia — outside to inside.

Common mistake and CET trap

‘Cerebellum does thinking’ is wrong (cerebrum). Trap: ‘thalamus regulates temperature’ is wrong (hypothalamus).

Shortcut

Memory clue : "Cerebellum = balance".

Spot the difference

PartFunction
CerebrumThought, memory
CerebellumBalance
MedullaHeart, breathing

Practice questions

Easy
  1. 1Three meninges?
  2. 2Role of CSF?
  3. 3Lobes of cerebrum?
Medium
  1. 4Largest commissure?
  2. 5Temperature control?
  3. 6Melatonin from?
Challenging
  1. 7Balance centre?
  2. 8Corpora quadrigemina in?
Show answers (try them yourself first)
  1. 1Dura, arachnoid, pia.
  2. 2Shock absorber.
  3. 3Frontal, parietal, temporal, occipital.
  4. 4Corpus callosum.
  5. 5Hypothalamus.
  6. 6Pineal (epithalamus).
  7. 7Cerebellum.
  8. 8Midbrain.

Spinal cord, reflex arc and PNS

From daily life

A hand jerks away from a hot pan before we even think.

Simple definition

A reflex action = rapid, involuntary response to a stimulus. A reflex arc = its pathway. The ANS controls involuntary organs.

Reflex and PNSSpinal cord, reflex arc and PNSReceptorSensoryCNSMotorEffectorReflex arc: receptor → sensory neuron → spinal cord → motor neuron → effectore.g. knee-jerk (single synapse); withdrawing the handSpinal cord: inner grey (H-shaped), outer white; dorsal/ventral rootsCranial nerves 12 pairs; spinal nerves 31 pairs (mixed)PNS = somatic (voluntary) + autonomic (involuntary)Sympathetic: adrenaline; pupil dilates, heart ↑, digestion ↓ (fight/flight)Parasympathetic: acetylcholine; pupil constricts, heart ↓, digestion ↑The two are antagonistic

In the figure : Reflex arc and PNS.

Rule 1 : Spinal cord and reflex arc — Spinal cord: from the foramen magnum; inner grey matter (H/butterfly-shaped; cell bodies), outer white matter (tracts); central canal (CSF); dorsal root (sensory) and ventral root (motor). Reflex arc: receptor → sensory neuron → spinal cord (interneuron) → motor neuron → effector. E.g. knee-jerk (single synapse; monosynaptic), withdrawing the hand from a hot object. The brain is informed afterwards.

  • Easy : Dorsal = sensory.
  • Medium : Knee-jerk = monosynaptic.
  • Exam-type (CET) : Grey inside, white outside.

Rule 2 : PNS and ANS — PNS: 12 pairs of cranial nerves (sensory/motor/mixed; e.g. I olfactory, II optic, VIII vestibulocochlear, X vagus, XII hypoglossal) and 31 pairs of spinal nerves (all mixed). PNS = somatic (voluntary; skeletal muscle) + autonomic (ANS) (involuntary; smooth muscle, heart, glands). Sympathetic: adrenergic (adrenaline/noradrenaline) — pupil dilates, heart ↑, digestion ↓ (fight/flight). Parasympathetic: cholinergic (acetylcholine) — pupil constricts, heart ↓, digestion ↑ (rest/digest). The two are antagonistic.

  • Easy : 12 + 31 pairs.
  • Medium : Sympathetic: fight/flight.
  • Exam-type (CET) : Vagus = cranial X.
Remember

Sympathetic = stress; parasympathetic = peace and digestion.

Common mistake and CET trap

‘Reflexes need a brain decision’ is wrong. Trap: ‘dorsal root is motor’ is wrong (sensory).

Shortcut

Memory clue : "Dorsal brings in; ventral sends out".

Spot the difference

SystemHeartPupil
Sympathetic↑Dilates
Parasympathetic↓Constricts

Practice questions

Easy
  1. 1Order of reflex arc?
  2. 2Synapses in knee-jerk?
  3. 3Pairs of cranial nerves?
Medium
  1. 4Pairs of spinal nerves?
  2. 5Grey matter location?
  3. 6Sympathetic transmitter?
Challenging
  1. 7Parasympathetic transmitter?
  2. 8ANS controls?
Show answers (try them yourself first)
  1. 1Receptor → sensory → CNS → motor → effector.
  2. 2One.
  3. 312.
  4. 431.
  5. 5Inside the cord.
  6. 6Adrenaline / noradrenaline.
  7. 7Acetylcholine.
  8. 8Involuntary organs.

The human eye

From daily life

The pupil widens in a dark room and narrows in sun.

Simple definition

The retina = inner light-sensitive layer. Accommodation = changing lens shape to see near and far objects clearly.

EyeHuman eyeOptic nerveCornea · Lens · RetinaRods: dim light; rhodopsin (vit A)Cones: colour; 3 typesFovea: sharpest; blind spot: no visionThree layers: sclera (+cornea), choroid (+iris), retinaAqueous humour (front), vitreous humour (back)Rods ~120 million, cones ~6 million (approx.)Fovea in macula lutea; blind spot = where optic nerve leavesAccommodation: ciliary muscles thicken/thin the lensLight → photopigment breakdown → impulse → optic nerve → occipital lobeRhodopsin = opsin + retinal (from vit A); lack of vit A = night blindness

In the figure : Parts of the eye; rods and cones.

Rule 1 : Structure of the eye — Three layers: sclera (white; transparent cornea in front), choroid (pigmented; iris and pupil in front; ciliary body), retina (inner). Lens, with vitreous humour behind and aqueous humour in front. Rods (~120 million; dim light; rhodopsin = opsin + retinal (vit A)), cones (~6 million; colour; three types — red, green, blue). Macula lutea has the fovea (sharpest vision). Blind spot = where the optic nerve leaves, no receptors.

  • Easy : Rods = dim; cones = colour.
  • Medium : Fovea = sharpest.
  • Exam-type (CET) : Blind spot = optic nerve exit.

Rule 2 : Vision and accommodation — Light passes cornea → aqueous → lens → vitreous → retina; photopigment breakdown ⇒ impulse ⇒ bipolar → ganglion cells ⇒ optic nerve ⇒ occipital lobe. Accommodation: for distant objects ciliary muscles relax, lens thin; for near objects muscles contract, lens thick. In bright light pupil constricts (iris muscles). Vitamin A deficiency ⇒ night blindness (less rhodopsin). Defects: myopia, hypermetropia (corrected by glasses).

  • Easy : Far: lens thin.
  • Medium : Near: lens thick.
  • Exam-type (CET) : Vit A lack: night blindness.
Remember

Rods = night; cones = colour/day.

Common mistake and CET trap

‘Blind spot gives sharpest vision’ is wrong (fovea). Trap: ‘lens is thin for near vision’ is wrong.

Shortcut

Memory clue : "Near = fat lens; far = flat lens".

Spot the difference

ReceptorLightRole
RodsDimNight vision
ConesBrightColour vision

Practice questions

Easy
  1. 1Fovea is in?
  2. 2What is rhodopsin?
  3. 3Types of cones?
Medium
  1. 4Blind spot?
  2. 5Where is aqueous humour?
  3. 6Lens when seeing far?
Challenging
  1. 7Cause of night blindness?
  2. 8Role of iris?
Show answers (try them yourself first)
  1. 1Macula lutea.
  2. 2Rod photopigment.
  3. 33.
  4. 4Optic nerve exit.
  5. 5Between cornea and lens.
  6. 6Thin.
  7. 7Vitamin A deficiency.
  8. 8Controls pupil size.

The ear and other receptors

From daily life

In dizziness the world spins — the ear's balance organ is disturbed.

Simple definition

A receptor = structure that detects a stimulus and generates an impulse. The organ of Corti = hearing receptor in the cochlea.

EarEar and other receptorsOuter earMiddle earInner earPinna, tympanumMalleus-Incus-StapesCochlea + VestibuleSound → tympanic membrane → 3 ossicles (amplify) → cochleaEustachian tube: equalises pressure; cochlea: organ of Corti = hearing receptorVestibular apparatus: semicircular canals = balance and motionEndolymph (inside), perilymph (outside)Tongue: taste buds — sweet, sour, salty, bitter, umamiNose: olfactory epithelium; ~10,000 odours (approx.)Receptors: photo-, chemo-, mechano-, thermo-, osmo-, nociceptorsSkin: touch, pressure, pain, temperature

In the figure : Parts of the ear; other receptors.

Rule 1 : Structure of the ear and hearing — Ear = stato-acoustic organ. Outer: pinna + canal + tympanic membrane. Middle: three ossicles — malleus, incus, stapes (amplify vibrations); Eustachian tube to pharynx (equalises pressure). Inner: cochlea (coiled; scala vestibuli, scala tympani, endolymph/perilymph; organ of Corti) and vestibular apparatus (semicircular canals + utricle, saccule — balance). Sequence: sound → tympanum → ossicles → oval window → cochlear fluid → organ of Corti → auditory nerve → temporal lobe.

  • Easy : 3 ossicles: malleus, incus, stapes.
  • Medium : Cochlea = hearing.
  • Exam-type (CET) : Semicircular canals = balance.

Rule 2 : Other sensory receptors — Tongue: taste buds (papillae); sweet, sour, salty, bitter, umami. Nose: olfactory epithelium (upper nasal chamber) detects ~10,000 odours (approx.). Skin: touch, pressure, pain, temperature. Receptor types: photoreceptors (light), chemoreceptors (chemicals; taste/smell), mechanoreceptors (touch, pressure, sound), thermoreceptors (temperature), nociceptors (pain), osmoreceptors. Stimulus → receptor → action potential → sensory nerve → CNS.

  • Easy : 5 tastes including umami.
  • Medium : Nociceptor = pain.
  • Exam-type (CET) : Olfactory = smell.
Remember

Malleus → incus → stapes: ‘My Is Safe’.

Common mistake and CET trap

‘Cochlea keeps balance’ is wrong (vestibular). Trap: ‘Eustachian tube joins the nose’ is wrong (pharynx).

Shortcut

Memory clue : "Cochlea hears; canals balance".

Spot the difference

PartFunction
CochleaHearing
Semicircular canalsBalance
OssiclesAmplify vibration

Practice questions

Easy
  1. 1How many ossicles?
  2. 2Stapes is in?
  3. 3Role of Eustachian tube?
Medium
  1. 4Hearing receptor?
  2. 5Balance organ?
  3. 6Fifth taste?
Challenging
  1. 7Pain receptors?
  2. 8Smell receptors in?
Show answers (try them yourself first)
  1. 13.
  2. 2Middle ear.
  3. 3Equalises pressure.
  4. 4Organ of Corti.
  5. 5Vestibular apparatus.
  6. 6Umami.
  7. 7Nociceptors.
  8. 8Olfactory epithelium.

Endocrine system and hormones

From daily life

Fear before an exam makes the heart race — thanks to adrenaline.

Simple definition

A hormone = chemical messenger released into blood by a ductless (endocrine) gland; acts on distant target cells; destroyed after use.

EndocrineEndocrine systemPituitaryThyroidAdrenalGH, TSH, ACTH, FSH, LHThyroxine, calcitoninCortisol, adrenalineHypothalamus → pituitary (master gland); posterior: oxytocin, ADHGH: low = dwarfism; high = gigantism / acromegalyThyroid: thyroxine (iodine); low: cretinism, myxoedema, goitre; high: GravesParathyroid: PTH (raises Ca); low = tetany; thymus: thymosinPancreas: insulin (β) lowers sugar, glucagon (α) raises; low insulin = diabetesAdrenal: cortisol, aldosterone, adrenaline/noradrenalineGonads: testosterone, estrogen, progesterone; pineal: melatoninHormones = ductless glands; via blood; destroyed after use

In the figure : Major glands and hormones.

Rule 1 : Hypothalamus, pituitary, thyroid, parathyroid — Hypothalamus controls the pituitary. Pituitary (‘master gland’): anterior — GH (low: dwarfism; high: gigantism, adult acromegaly), TSH, ACTH, FSH, LH, prolactin; posterior — oxytocin, ADH/vasopressin (low: diabetes insipidus). Thyroid: thyroxine (iodine; BMR); calcitonin (lowers Ca). Disorders: cretinism (infants), myxoedema, simple goitre (iodine deficiency), Graves’ disease (exophthalmic goitre; excess). Parathyroid: PTH (raises Ca); low ⇒ tetany. Thymus: thymosin (immunity).

  • Easy : Low GH: dwarfism.
  • Medium : Thyroxine needs iodine.
  • Exam-type (CET) : PTH raises Ca.

Rule 2 : Pancreas, adrenal, gonads, pineal — Pancreas (islets): β cells — insulin (lowers blood sugar); α cells — glucagon (raises); low insulin ⇒ diabetes mellitus. Adrenal (on the kidney): cortex — cortisol, aldosterone; medulla — adrenaline/noradrenaline (‘emergency’ hormones). Gonads: testis — testosterone; ovary — estrogen, progesterone. Pineal: melatonin (sleep). Kinds of hormones: amino-acid derivatives (thyroxine, adrenaline), peptide/protein (insulin, glucagon), steroids (cortisol, testosterone). Steroid hormones enter cells; others bind surface receptors. Nervous = fast, short-lived; endocrine = slow, long-lasting.

  • Easy : Insulin lowers sugar.
  • Medium : Glucagon raises sugar.
  • Exam-type (CET) : Adrenaline = emergency.
Remember

Insulin sends sugar in; glucagon sends sugar out.

Common mistake and CET trap

‘Insulin raises sugar’ is wrong. Trap: ‘excess GH = cretinism’ is wrong (gigantism).

Shortcut

Memory clue : "Pituitary = boss; thyroid = tempo (BMR)".

Spot the difference

GlandHormoneRole
ThyroidThyroxineBMR
PancreasInsulinLowers sugar
AdrenalAdrenalineEmergency

Practice questions

Easy
  1. 1Master gland?
  2. 2Low GH causes?
  3. 3Iodine deficiency causes?
Medium
  1. 4Which hormone lowers Ca?
  2. 5Low PTH causes?
  3. 6Insulin made by?
Challenging
  1. 7Adrenaline from?
  2. 8Melatonin from?
Show answers (try them yourself first)
  1. 1Pituitary.
  2. 2Dwarfism.
  3. 3Simple goitre.
  4. 4Calcitonin.
  5. 5Tetany.
  6. 6β cells of pancreas.
  7. 7Adrenal medulla.
  8. 8Pineal gland.

Quick revision of the whole lesson

ConceptKey fact
NeuronDendron towards, axon away; Schwann = PNS myelin
Impulse−70 → +30 mV; 3 Na⁺ / 2 K⁺
BrainDura–arachnoid–pia; cerebellum = balance
Reflex / ANS12 + 31 pairs; sympathetic = fight/flight
EyeRods dim; cones colour; fovea
EarM-I-S; cochlea hears; canals balance
HormonesPituitary master; insulin lowers sugar

🎯 Most important points for the exam

  • Neuron and neuroglia.
  • Action potential and synapse.
  • Parts of the brain.
  • Reflex arc, PNS, ANS.
  • Eye: rods, cones, accommodation.
  • Ear and sensory receptors.
  • Glands, hormones, disorders.
Study mantra

Understand the concept → draw the figure → memorise the key points → solve questions yourself.