MCQs: Action Potential, Graded Potential & Synapses

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    ["Resting membrane potential", "-70 mV"],
    ["Threshold", "~-55 mV"],
    ["Depolarization ion", "Na⁺ influx (5000x conductance increase)"],
    ["Repolarization ion", "K⁺ efflux"],
    ["Hyperpolarization cause", "K⁺ channels stay open too long"],
    ["Absolute refractory period", "~1 ms → max 1000 impulses/sec"],
    ["Relative refractory period", "2-4 ms (hyperpolarization phase); needs stronger stimulus"],
    ["AP initiation site", "Axon initial segment (not soma)"],
    ["Terminals needed for EPSP → threshold", "40-80 simultaneous presynaptic terminals"],
    ["Presynaptic terminals on dendrites", "80-95%"],
    ["Chemical synapse direction", "One-way (presynaptic → postsynaptic) only"],
    ["Electrical synapse direction", "Often bidirectional"],
    ["Electrical synapse structure", "Gap junction channels"],
    ["Graded potential", "Summable, non-propagating, below threshold; amplitude varies with stimulus"],
    ["All-or-Nothing principle", "AP fires fully once threshold is reached; absent below threshold"],
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// ─── ALL MCQ DATA ─────────────────────────────────────────────────────────────
const sections = [
  {
    title: "SECTION 1: ACTION POTENTIAL",
    questions: [
      {
        num: 1,
        text: "The resting membrane potential of a typical large myelinated nerve fiber is approximately:",
        options: [{ l: "A", t: "-55 mV" }, { l: "B", t: "-90 mV" }, { l: "C", t: "-70 mV", correct: true }, { l: "D", t: "-45 mV" }],
        answer: "C) -70 mV",
        explanation: "Guyton states the resting membrane potential is -70 mV, at which point the membrane is described as 'polarized.' This is maintained by K⁺ leak channels and the Na⁺-K⁺ ATPase pump. Threshold is ~-55 mV."
      },
      {
        num: 2,
        text: "During the depolarization phase of an action potential, which ion channel opens first and most dramatically?",
        options: [{ l: "A", t: "Voltage-gated K⁺ channels" }, { l: "B", t: "Voltage-gated Na⁺ channels", correct: true }, { l: "C", t: "Cl⁻ channels" }, { l: "D", t: "Ca²⁺ channels" }],
        answer: "B) Voltage-gated Na⁺ channels",
        explanation: "Guyton describes that when the membrane is depolarized to threshold (~-55 mV), voltage-gated Na⁺ channels open almost instantaneously, allowing up to a 5000-fold increase in sodium conductance. K⁺ channels open more slowly and drive repolarization."
      },
      {
        num: 3,
        text: "The overshoot of the action potential (positive membrane potential) occurs because:",
        options: [{ l: "A", t: "K⁺ rushes into the cell" }, { l: "B", t: "Cl⁻ rushes out of the cell" }, { l: "C", t: "Na⁺ influx exceeds the zero level due to massive sodium conductance", correct: true }, { l: "D", t: "The Na⁺-K⁺ pump is activated" }],
        answer: "C) Na⁺ influx exceeds the zero level",
        explanation: "In large nerve fibers, the great excess of positive sodium ions moving inside causes the membrane potential to overshoot beyond zero to a somewhat positive value. In smaller fibers and some CNS neurons, the potential merely approaches zero without overshoot."
      },
      {
        num: 4,
        text: "Repolarization of the nerve membrane during an action potential is primarily achieved by:",
        options: [{ l: "A", t: "Inactivation of Na⁺ channels alone" }, { l: "B", t: "Activation of the Na⁺-K⁺ pump" }, { l: "C", t: "Opening of voltage-gated K⁺ channels with efflux of K⁺", correct: true }, { l: "D", t: "Influx of Cl⁻ ions" }],
        answer: "C) Opening of voltage-gated K⁺ channels with K⁺ efflux",
        explanation: "Guyton explains that in less than 1 ms after Na⁺ channels become maximally permeable, they begin to close while K⁺ channels open more than normal. Rapid K⁺ efflux reestablishes the normal negative resting potential - this is repolarization."
      },
      {
        num: 5,
        text: "Hyperpolarization (undershoot) after an action potential occurs because:",
        options: [{ l: "A", t: "Na⁺ channels remain open too long" }, { l: "B", t: "The Na⁺-K⁺ pump overshoots" }, { l: "C", t: "Potassium channels remain open longer than needed, allowing excess K⁺ efflux", correct: true }, { l: "D", t: "Cl⁻ rushes into the cell" }],
        answer: "C) K⁺ channels remain open longer than needed",
        explanation: "Guyton states K⁺ channels 'may remain open longer than needed to return the membrane to its resting potential, resulting in hyperpolarization (undershoot).' Once they close, the membrane returns to normal resting value."
      },
      {
        num: 6,
        text: "The voltage-gated sodium channel has how many gates?",
        options: [{ l: "A", t: "One (activation gate only)" }, { l: "B", t: "Three gates" }, { l: "C", t: "Two gates - an activation gate (outside) and an inactivation gate (inside)", correct: true }, { l: "D", t: "No gates; it is always open" }],
        answer: "C) Two gates",
        explanation: "Guyton describes the voltage-gated Na⁺ channel has two gates: an activation gate (near outside) and an inactivation gate (near inside). At rest: activation gate closed, inactivation gate open. During AP: activation gate opens rapidly, then inactivation gate closes."
      },
      {
        num: 7,
        text: "During the absolute refractory period:",
        options: [{ l: "A", t: "An action potential can be elicited with a stronger-than-normal stimulus" }, { l: "B", t: "An action potential can be elicited only with a subthreshold stimulus" }, { l: "C", t: "A new action potential cannot be elicited regardless of stimulus strength", correct: true }, { l: "D", t: "Hyperpolarization prevents re-excitation, but depolarization is possible" }],
        answer: "C) No AP regardless of stimulus strength",
        explanation: "During the absolute refractory period, Na⁺ channels are inactivated and 'no amount of excitatory signal will open the inactivation gates.' The membrane must return to near resting potential first. For large myelinated fibers this is ~1 ms, limiting transmission to ~1000 impulses/second."
      },
      {
        num: 8,
        text: "During the relative refractory period, which of the following is TRUE?",
        options: [{ l: "A", t: "No action potential can be generated under any condition" }, { l: "B", t: "An action potential can be generated, but requires a greater-than-normal stimulus", correct: true }, { l: "C", t: "The membrane potential is more positive than resting" }, { l: "D", t: "Na⁺ channels are maximally open" }],
        answer: "B) AP possible but needs a stronger stimulus",
        explanation: "During the relative refractory period (2-4 ms, hyperpolarization phase), the neuron can fire another AP 'but a greater stimulus is required' because the membrane is hyperpolarized (more negative than resting)."
      },
      {
        num: 9,
        text: "The 'All-or-Nothing' principle of the action potential means:",
        options: [{ l: "A", t: "The action potential amplitude varies with stimulus strength" }, { l: "B", t: "Once threshold is reached, the full AP propagates; below threshold it does not propagate at all", correct: true }, { l: "C", t: "Action potentials can be graded in size" }, { l: "D", t: "The action potential travels only in one direction" }],
        answer: "B) Full AP propagates above threshold; none below",
        explanation: "Guyton: 'Once an action potential has been elicited at any point on the membrane of a normal fiber, the depolarization process travels over the entire membrane if conditions are right, but it does not travel at all if conditions are not right.' The safety factor must be >1 for continued propagation."
      },
      {
        num: 10,
        text: "The maximum frequency of impulse transmission in large myelinated nerve fibers is approximately:",
        options: [{ l: "A", t: "100 impulses/second" }, { l: "B", t: "500 impulses/second" }, { l: "C", t: "1000 impulses/second", correct: true }, { l: "D", t: "5000 impulses/second" }],
        answer: "C) 1000 impulses/second",
        explanation: "Guyton calculates this from the absolute refractory period: since it is ~1 ms, the fiber can transmit a maximum of ~1000 impulses per second (1000 ms ÷ 1 ms = 1000)."
      },
    ]
  },
  {
    title: "SECTION 2: GRADED (LOCAL/SUBTHRESHOLD) POTENTIALS",
    questions: [
      {
        num: 11,
        text: "Acute local potentials (subthreshold potentials) differ from action potentials in that they:",
        options: [{ l: "A", t: "Always propagate along the full length of the nerve fiber" }, { l: "B", t: "Follow the all-or-nothing principle" }, { l: "C", t: "Are generated only by chemical stimuli" }, { l: "D", t: "Are graded in amplitude and do not propagate; they fade out near the stimulus site", correct: true }],
        answer: "D) Graded, non-propagating, fade near stimulus",
        explanation: "Guyton describes acute local potentials as subthreshold responses that vary with stimulus strength (graded), do not follow all-or-nothing principle, and do not propagate. Only when the local potential rises to threshold does a full action potential fire."
      },
      {
        num: 12,
        text: "At which point on a stimulated neuron is the threshold for action potential generation LOWEST (most easily excited)?",
        options: [{ l: "A", t: "The soma (cell body)" }, { l: "B", t: "The dendrites" }, { l: "C", t: "The initial segment of the axon (axon hillock)", correct: true }, { l: "D", t: "The presynaptic terminal" }],
        answer: "C) Axon initial segment (axon hillock)",
        explanation: "Guyton explains: 'The action potential does not begin adjacent to the excitatory synapses. Instead, it begins in the initial segment of the axon where the axon leaves the neuronal soma.' The soma has relatively few voltage-gated Na⁺ channels; the initial segment has the highest density."
      },
      {
        num: 13,
        text: "When a single presynaptic terminal fires, the resulting EPSP in a typical anterior motor neuron is:",
        options: [{ l: "A", t: "Always sufficient to trigger an action potential" }, { l: "B", t: "About -65 mV change (resting potential)" }, { l: "C", t: "Too small to trigger an AP alone; approximately 40-80 terminals must discharge simultaneously", correct: true }, { l: "D", t: "Exactly at threshold level" }],
        answer: "C) Too small alone; 40-80 terminals needed simultaneously",
        explanation: "Guyton: 'Discharge of a single presynaptic terminal does not increase the neuronal potential from -65 mV all the way up to -45 mV. An increase of this magnitude requires simultaneous discharge of many terminals - about 40 to 80 for the usual anterior motor neuron.'"
      },
      {
        num: 14,
        text: "Temporal summation of postsynaptic potentials occurs because:",
        options: [{ l: "A", t: "Multiple synaptic terminals fire simultaneously" }, { l: "B", t: "Successive discharges of the same terminal produce overlapping potentials lasting up to 15 ms", correct: true }, { l: "C", t: "The axon hillock amplifies each signal" }, { l: "D", t: "Na⁺-K⁺ pump activity is suppressed" }],
        answer: "B) Overlapping potentials from successive discharges (up to 15 ms duration)",
        explanation: "Guyton: 'The changed postsynaptic potential lasts up to 15 milliseconds after the synaptic membrane channels have already closed. Therefore, a second opening of the same channels can increase the postsynaptic potential further.' Spatial summation = multiple terminals firing simultaneously."
      },
      {
        num: 15,
        text: "A 'facilitated' neuron is one in which:",
        options: [{ l: "A", t: "An action potential has already been generated" }, { l: "B", t: "Inhibitory postsynaptic potentials (IPSPs) dominate" }, { l: "C", t: "The summated postsynaptic potential is excitatory but has not yet reached threshold for firing", correct: true }, { l: "D", t: "The neuron is in its absolute refractory period" }],
        answer: "C) Excitatory summated PSP, but below threshold",
        explanation: "Guyton defines facilitation directly: 'When the summated postsynaptic potential is excitatory but has not risen high enough to reach the threshold for firing by the postsynaptic neuron, the neuron is said to be facilitated.' Such a neuron is primed to fire with minimal additional input."
      },
    ]
  },
  {
    title: "SECTION 3: CHEMICAL vs. ELECTRICAL SYNAPSES",
    questions: [
      {
        num: 16,
        text: "Which is the KEY structural difference between chemical and electrical synapses?",
        options: [{ l: "A", t: "Chemical synapses have a larger synaptic cleft" }, { l: "B", t: "Electrical synapses use gap junction channels directly connecting cells; chemical synapses use neurotransmitters across a cleft", correct: true }, { l: "C", t: "Chemical synapses are faster than electrical synapses" }, { l: "D", t: "Electrical synapses require Ca²⁺ for signal transmission" }],
        answer: "B) Gap junctions (electrical) vs. neurotransmitter across cleft (chemical)",
        explanation: "Guyton's Fig. 46.5 shows: Chemical synapses (A) have a presynaptic terminal with synaptic vesicles and a cleft using neurotransmitters. Electrical synapses (B) have gap junction channels directly connecting pre- and postsynaptic cells, allowing ionic current to flow directly between them."
      },
      {
        num: 17,
        text: "One-way (unidirectional) conduction is a property of which type of synapse?",
        options: [{ l: "A", t: "Electrical synapses only" }, { l: "B", t: "Both chemical and electrical synapses equally" }, { l: "C", t: "Neither - all synapses are bidirectional" }, { l: "D", t: "Chemical synapses only", correct: true }],
        answer: "D) Chemical synapses only",
        explanation: "Guyton explicitly: 'Chemical synapses always transmit signals in one direction - from the presynaptic neuron to the postsynaptic neuron. This one-way conduction at chemical synapses is different from conduction through electrical synapses, which often transmit signals in either direction.'"
      },
      {
        num: 18,
        text: "Electrical synapses are particularly useful for which function?",
        options: [{ l: "A", t: "Precise, targeted inhibitory signaling" }, { l: "B", t: "Slow neuromodulatory effects" }, { l: "C", t: "Coordinating simultaneous firing of large groups of neurons and detecting coincident subthreshold depolarizations", correct: true }, { l: "D", t: "One-way signal transmission to effector organs" }],
        answer: "C) Coordinating/synchronizing large groups of neurons",
        explanation: "Guyton states electrical synapses are 'useful in detecting the coincidence of simultaneous subthreshold depolarizations within a group of interconnected neurons; this enables increased neuronal sensitivity and promotes synchronous firing.' Hypothalamic hormone-secreting neurons also use them for synchronized burst secretion."
      },
      {
        num: 19,
        text: "When an action potential reaches a chemical synapse presynaptic terminal, what directly triggers neurotransmitter vesicle release?",
        options: [{ l: "A", t: "Change in K⁺ permeability" }, { l: "B", t: "Opening of voltage-gated Na⁺ channels" }, { l: "C", t: "Binding of neurotransmitter to autoreceptors" }, { l: "D", t: "Depolarization of the presynaptic terminal membrane causes vesicles to empty into the cleft", correct: true }],
        answer: "D) Presynaptic terminal depolarization triggers vesicle release",
        explanation: "Guyton: 'When an action potential spreads over a presynaptic terminal, depolarization of its membrane causes a small number of vesicles to empty into the cleft. The released transmitter in turn binds to receptors on the postsynaptic membrane.' (Mechanistically, depolarization opens voltage-gated Ca²⁺ channels driving vesicle fusion.)"
      },
      {
        num: 20,
        text: "The excitatory postsynaptic potential (EPSP) is primarily produced by:",
        options: [{ l: "A", t: "Opening of K⁺ channels causing K⁺ efflux" }, { l: "B", t: "Opening of Cl⁻ channels causing Cl⁻ influx" }, { l: "C", t: "Activation of the Na⁺-K⁺ pump" }, { l: "D", t: "Opening of Na⁺ channels causing Na⁺ influx, making the membrane potential less negative", correct: true }],
        answer: "D) Na⁺ influx → membrane becomes less negative",
        explanation: "Guyton: excitatory transmitters act on receptors to 'increase the membrane's permeability to Na⁺.' Na⁺ rapidly diffuses inside, increasing membrane potential from -65 mV toward -45 mV. This less-negative shift is the EPSP. If it reaches threshold, an AP fires at the axon initial segment."
      },
      {
        num: 21,
        text: "The inhibitory postsynaptic potential (IPSP) is primarily caused by:",
        options: [{ l: "A", t: "Na⁺ influx into the postsynaptic cell" }, { l: "B", t: "Depolarization of the postsynaptic membrane" }, { l: "C", t: "Opening of Cl⁻ channels (Cl⁻ influx) or K⁺ channels (K⁺ efflux), making the interior more negative", correct: true }, { l: "D", t: "Activation of excitatory receptors" }],
        answer: "C) Cl⁻ influx (via Cl⁻ channels) and/or K⁺ efflux (via K⁺ channels)",
        explanation: "Guyton states inhibitory synapses 'mainly open chloride channels, allowing for easier passage of chloride ions' inward, carrying negative charges inside and increasing negativity. Increased K⁺ conductance also contributes. The inhibited neuron shows a more negative potential (-70 mV vs. resting -65 mV) in Guyton's Fig. 46.11C."
      },
      {
        num: 22,
        text: "Approximately what percentage of presynaptic terminals on a typical anterior motor neuron are located on the dendrites?",
        options: [{ l: "A", t: "5-20%" }, { l: "B", t: "50%" }, { l: "C", t: "80-95%", correct: true }, { l: "D", t: "100%" }],
        answer: "C) 80-95%",
        explanation: "Guyton: a motor neuron may have 10,000-200,000 presynaptic terminals, 'about 80% to 95% of them on the dendrites and only 5% to 20% on the soma.' This large dendritic surface area allows massive integration of incoming signals."
      },
      {
        num: 23,
        text: "Which neurotransmitter is listed alone in Class I of Guyton's classification of small-molecule, rapidly acting transmitters?",
        options: [{ l: "A", t: "Dopamine" }, { l: "B", t: "Serotonin" }, { l: "C", t: "Glutamate" }, { l: "D", t: "Acetylcholine", correct: true }],
        answer: "D) Acetylcholine",
        explanation: "Guyton's Table 46.1: Class I = Acetylcholine (alone); Class II (Amines) = norepinephrine, epinephrine, dopamine, serotonin, melatonin, histamine; Class III (Amino Acids) = GABA, glycine, glutamate, aspartate; Class IV = ATP, arachidonic acid, nitric oxide, carbon monoxide."
      },
      {
        num: 24,
        text: "Regarding propagation of an action potential along a nerve fiber, which statement is CORRECT?",
        options: [{ l: "A", t: "The AP travels only in one direction (toward the axon terminal)" }, { l: "B", t: "Myelin sheaths speed up conduction by allowing continuous conduction" }, { l: "C", t: "The safety factor for propagation must be less than 1 for the impulse to continue" }, { l: "D", t: "The action potential travels in all directions away from the stimulus (both directions along the fiber)", correct: true }],
        answer: "D) AP travels in all directions from the stimulus point",
        explanation: "Guyton: 'An excitable membrane has no single direction of propagation, but the action potential travels in all directions away from the stimulus - even along all branches of a nerve fiber - until the entire membrane has become depolarized.' The safety factor must be >1 (not <1) for continued propagation."
      },
      {
        num: 25,
        text: "After many action potentials, the Na⁺-K⁺ pump restores ionic gradients. Which statement is TRUE?",
        options: [{ l: "A", t: "It is a passive process requiring no energy" }, { l: "B", t: "A single action potential causes a measurable drop in ionic gradients" }, { l: "C", t: "Pump activity is stimulated when extracellular Na⁺ accumulates" }, { l: "D", t: "Pump activity is stimulated when excess intracellular Na⁺ accumulates, and the process requires ATP", correct: true }],
        answer: "D) Stimulated by intracellular Na⁺ accumulation; requires ATP",
        explanation: "Guyton: pump activity increases 'approximately in proportion to the third power' of intracellular Na⁺ accumulation. The process is active (requires ATP), evidenced by increased heat production at higher impulse frequencies. A single AP is so trivial that '100,000 to 50 million impulses can be transmitted before concentration differences become critical.'"
      },
    ]
  }
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    indent: { left: 240 },
    children: [
      new TextRun({ text: "3. Read the explanation carefully - all facts trace directly to Guyton.", size: 20, font: "Calibri" })
    ]
  }),
  new Paragraph({
    spacing: { before: 40, after: 200 },
    shading: { type: ShadingType.SOLID, color: "FFF8E1" },
    indent: { left: 240 },
    children: [
      new TextRun({ text: "4. Review the Quick Reference Table at the end for rapid revision.", size: 20, font: "Calibri" })
    ]
  }),
  rule()
);

// QUESTIONS BY SECTION
for (const sec of sections) {
  children.push(sectionHeading(sec.title));
  for (const q of sec.questions) {
    children.push(questionPara(q.num, q.text));
    for (const opt of q.options) {
      children.push(optionPara(opt.l, opt.t, !!opt.correct));
    }
    children.push(explanationBlock(q.answer, q.explanation));
    children.push(rule());
  }
}

// QUICK REFERENCE TABLE
children.push(sectionHeading("QUICK REFERENCE TABLE - Key Guyton Facts"));
children.push(quickRefTable());

children.push(
  new Paragraph({
    alignment: AlignmentType.CENTER,
    spacing: { before: 360, after: 120 },
    children: [
      new TextRun({ text: "All content sourced from Guyton & Hall Textbook of Medical Physiology (ISBN: 9780443111013)", italics: true, size: 18, color: "777777", font: "Calibri" })
    ]
  })
);

// ─── EXPORT ──────────────────────────────────────────────────────────────────
const doc = new Document({
  sections: [{
    properties: {},
    children
  }]
});

Packer.toBuffer(doc).then(buffer => {
  fs.writeFileSync("/home/daytona/workspace/neuro-mcq-guide/Neurophysiology_MCQ_StudyGuide.docx", buffer);
  console.log("Done: Neurophysiology_MCQ_StudyGuide.docx");
});