General Physiology Practice Questions

Q: The Monro-Kellie doctrine is related to the doctrine of non-compressible contents within which part of the body?

Head. ### Explanation **The Monro-Kellie Doctrine (Hypothesis)** The correct answer is **Head (A)**. The Monro-Kellie doctrine states that the cranial vault is a rigid, non-expandable container with a fixed total volume. This volume is composed of three nearly incompressible components: 1. **Brain parenchyma** (~80%) 2. **Cerebrospinal fluid (CSF)** (~10%) 3. **Blood** (~10%) According to this principle, because the total volume is constant, an increase in any one of these components (or the addition of a pathological mass like a tumor or hematoma) must be compensated by an equal decrease in the volume of another. If compensation fails, **Intracranial Pressure (ICP)** rises sharply. **Why the other options are incorrect:** * **B. Abdomen & C. Chest:** Unlike the skull, the abdominal and thoracic cavities have flexible walls (diaphragm, intercostal muscles, and skin) that can expand to accommodate volume changes. * **D. Leg:** The limbs are not enclosed in a rigid bony vault; while they can experience compartment syndrome, they do not follow the specific volumetric constraints of the Monro-Kellie doctrine. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Compensatory Mechanisms:** When ICP rises, the body first displaces **CSF** into the spinal subarachnoid space and shunts **venous blood** out of the skull. * **Cushing’s Triad:** A late sign of increased ICP resulting from the Monro-Kellie doctrine failure, characterized by **Hypertension, Bradycardia, and Irregular Respiration.** * **Clinical Application:** This doctrine explains why even small intracranial hemorrhages can lead to rapid neurological deterioration and brain herniation.

Q: Inward flow of Na+ in heart leads to what?

Action potential. ### Explanation **Correct Answer: B. Action potential** In cardiac physiology, the **inward flow of Sodium (Na+)** ions through fast voltage-gated sodium channels is the primary driver for **Phase 0 (Depolarization)** of the action potential in non-pacemaker cells (atrial and ventricular myocytes). When the cell membrane reaches its threshold potential, these channels open rapidly, allowing a massive influx of Na+ down its electrochemical gradient. This sudden shift in membrane potential from negative to positive initiates the cardiac action potential. **Analysis of Incorrect Options:** * **A. Plateau phase:** This is **Phase 2** of the cardiac action potential. It is primarily maintained by the **inward flow of Calcium (Ca2+)** through L-type calcium channels, balanced by the outward flow of Potassium (K+). * **C. Repolarization:** This occurs during **Phases 1, 2, and 3**. The main driver for repolarization (returning the cell to a negative state) is the **outward flow of Potassium (K+)** ions. * **D. No change:** Inward Na+ flux causes a significant electrical change (depolarization), making this option incorrect. **High-Yield Clinical Pearls for NEET-PG:** * **Fast Response vs. Slow Response:** Fast Na+ channels are responsible for depolarization in myocytes and Purkinje fibers. In contrast, the **SA and AV nodes** (pacemaker cells) lack functional fast Na+ channels; their depolarization is driven by **inward Calcium (Ca2+)** flow. * **Class I Antiarrhythmics:** Drugs like Lidocaine or Flecainide work by blocking these fast Na+ channels, thereby slowing the rate of Phase 0 depolarization. * **Tetrodotoxin (TTX):** A potent toxin that specifically inhibits these voltage-gated Na+ channels, preventing action potential generation.

Q: Concurrent flexion of both wrists in response to electrical stimulation is characteristic of which area of the nervous system?

Supplementary motor cortex. **Explanation:** The **Supplementary Motor Area (SMA)**, located on the medial surface of the frontal lobe (Brodmann area 6), is primarily involved in the planning and coordination of complex, bilateral movements. Unlike the Primary Motor Cortex (M1), which controls discrete muscles on the contralateral side, electrical stimulation of the SMA typically results in **bilateral, synergistic movements** or postural adjustments, such as the concurrent flexion of both wrists or the raising of both arms. **Analysis of Options:** * **A. Postcentral Gyrus:** This is the Primary Somatosensory Cortex (S1). Stimulation here results in sensory perceptions (tingling, numbness) on the contralateral side of the body, not motor movements. * **B. Vestibulospinal Tract:** This is an extrapyramidal pathway responsible for maintaining equilibrium and muscle tone (primarily extensors) in response to head movements. It does not coordinate complex bilateral wrist flexion. * **C. Dentate Nucleus:** The largest of the deep cerebellar nuclei, it is involved in the planning and timing of movements. While it influences motor output, direct electrical stimulation does not produce the specific bilateral motor patterns characteristic of the SMA. **High-Yield Facts for NEET-PG:** * **SMA vs. Premotor Cortex:** SMA is for **internal cues** (complex sequences from memory), while the Premotor cortex is for **external cues** (sensory-guided movements). * **Jacksonian March:** Associated with the Primary Motor Cortex (M1), not the SMA. * **Alien Hand Syndrome:** Can occur with lesions involving the SMA and corpus callosum. * **Stimulation Threshold:** The SMA has a higher threshold for electrical stimulation compared to the Primary Motor Cortex.

Q: The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by which equation?

Nernst equation. **Explanation:** The correct answer is the **Nernst equation**. **1. Why the Nernst Equation is Correct:** The Nernst equation calculates the **equilibrium potential (electrochemical equilibrium)** for a **single ion**. It determines the electrical potential difference across a cell membrane that exactly balances the concentration gradient of that specific ion, resulting in no net movement of the ion across the membrane. * **Formula:** $E = \frac{RT}{zF} \ln \frac{[Ion]_{outside}}{[Ion]_{inside}}$ (Simplified at body temperature: $E = \frac{61}{z} \log \frac{[C]_{out}}{[C]_{in}}$). **2. Why Other Options are Incorrect:** * **Goldman-Hodgkin-Katz (GHK) Equation:** Unlike the Nernst equation, this accounts for **multiple ions** (Na⁺, K⁺, Cl⁻) simultaneously and considers their relative **membrane permeability**. It is used to calculate the actual Resting Membrane Potential (RMP). * **van't Hoff Equation:** This is used to calculate **osmotic pressure** ($\pi = MRT$). It relates the concentration of solutes to the pressure required to stop osmosis. * **Fick’s Law:** This describes the **rate of diffusion** of a gas or solute across a membrane. It states that the flux is proportional to the concentration gradient and surface area, but inversely proportional to membrane thickness. **3. High-Yield Clinical Pearls for NEET-PG:** * **Standard Equilibrium Potentials:** $E_{K^+}$ is approx. **-94 mV**; $E_{Na^+}$ is approx. **+61 mV**. * The Resting Membrane Potential (-70 to -90 mV) is closest to $E_{K^+}$ because the membrane is most permeable to Potassium at rest (via leak channels). * If permeability to an ion increases (e.g., Na⁺ during depolarization), the membrane potential shifts toward that ion's Nernst potential.

Q: Total lung capacity depends on which of the following?

Lung compliance. **Explanation:** **Total Lung Capacity (TLC)** is the maximum volume of air the lungs can hold after a maximal inspiratory effort. It is determined by the balance between the outward pull of the inspiratory muscles and the inward elastic recoil of the lungs and chest wall. **Why Lung Compliance is Correct:** Compliance refers to the "distensibility" or the ease with which the lungs expand under pressure. * **High Compliance:** In conditions like **Emphysema**, the loss of elastic tissue makes the lungs overly distensible, leading to an **increased TLC**. * **Low Compliance:** In **Restrictive Lung Diseases** (e.g., Pulmonary Fibrosis), the lungs become stiff and resist expansion, significantly **decreasing TLC**. Therefore, the elastic properties (compliance) are a primary determinant of the lung's maximum volume. **Analysis of Incorrect Options:** * **Size of Airway:** This primarily affects **airway resistance** and flow rates (like FEV1), not the total volume capacity of the lung parenchyma. * **Closing Tidal Volume:** This relates to the point during expiration when small airways in the dependent parts of the lung begin to close. It is a measure of airway stability, not total capacity. * **Residual Volume (RV):** While RV is a *component* of TLC (TLC = VC + RV), it is a sub-volume rather than a physiological determinant. TLC is the independent variable defined by the limits of expansion. **High-Yield Clinical Pearls for NEET-PG:** * **TLC Formula:** TLC = Vital Capacity (VC) + Residual Volume (RV). * **Helium Dilution/Body Plethysmography:** These are required to measure TLC, as spirometry cannot measure RV. * **Emphysema Paradox:** TLC increases due to high compliance, but effective gas exchange decreases due to alveolar destruction. * **Scoliosis/Kyphosis:** These decrease TLC by reducing **chest wall compliance**.

Q: Which muscle fiber type has a high glycogen content?

White fibers. **Explanation:** The classification of muscle fibers is based on their metabolic profile and contraction speed. **White fibers (Type IIb/IIx)** are designed for short bursts of high-intensity activity (anaerobic power). Because they have fewer mitochondria and less myoglobin, they rely primarily on **anaerobic glycolysis** for ATP production. To support this rapid energy demand, they store significantly **high amounts of glycogen** and have high glycolytic enzyme activity. **Analysis of Options:** * **White fibers (Correct):** These are "Fast-twitch" fibers. They have high glycogen content, high myosin ATPase activity, and fatigue rapidly. * **Red fibers / Type 1 fibers (Incorrect):** These are "Slow-twitch" fibers. They are rich in myoglobin and mitochondria, relying on aerobic oxidative phosphorylation. They have high triglyceride (fat) stores rather than high glycogen stores and are resistant to fatigue. * **Tonic fibers (Incorrect):** These are specialized fibers (like those in extraocular muscles) that do not follow the "all-or-none" law and have multiple nerve endings. They are not characterized by high glycogen content. **High-Yield NEET-PG Pearls:** 1. **Myoglobin Content:** Type 1 (Red) = High; Type 2 (White) = Low. 2. **Mitochondria/Capillaries:** Type 1 = High (for oxygen utilization); Type 2 = Low. 3. **ATPase Activity:** Type 2 fibers have high myosin ATPase activity, leading to faster contraction. 4. **Fatigability:** Type 1 is fatigue-resistant (postural muscles); Type 2 is easily fatigued (sprinter's muscles). 5. **Intermediate Fibers:** Type IIa fibers are "Fast-Oxidative Glycolytic," sharing characteristics of both types.

Q: Pantothenic acid is associated with which of the following moieties?

coenzyme A. **Explanation:** **Pantothenic acid (Vitamin B5)** is a water-soluble vitamin that serves as an essential precursor for the synthesis of **Coenzyme A (CoA)**. 1. **Why Coenzyme A is correct:** Pantothenic acid consists of pantoic acid and $\beta$-alanine. In the body, it is phosphorylated and combined with ATP and cysteine to form Coenzyme A. CoA is a vital cofactor for the metabolism of carbohydrates, lipids, and proteins. It acts as an acyl group carrier (forming Acetyl-CoA), which is the entry point for the TCA cycle and is crucial for fatty acid synthesis and oxidation. 2. **Why the other options are incorrect:** * **Carboxyl (B):** Biotin (Vitamin B7) is the cofactor associated with carboxylation reactions (e.g., Pyruvate carboxylase). * **Hydroxyl (C):** Vitamin C (Ascorbic acid) is the primary vitamin associated with hydroxylation, specifically of proline and lysine residues in collagen synthesis. * **H+ (D):** Niacin (B3) and Riboflavin (B2) act as hydrogen/electron carriers in the form of NAD+/NADH and FAD/FADH2. **High-Yield Clinical Pearls for NEET-PG:** * **Active Form:** The active form of Vitamin B5 is Coenzyme A and **Acyl Carrier Protein (ACP)**. * **Deficiency:** Extremely rare but manifests as **"Burning Feet Syndrome"** (Gopalan’s syndrome), characterized by paresthesia and burning sensations in the lower extremities. * **Key Reaction:** It is a component of the **Pyruvate Dehydrogenase Complex**, which converts Pyruvate to Acetyl-CoA. * **Mnemonic:** B5 makes the "A" (Coenzyme A).

Question 1

Which of the following is NOT an example of a feedforward control system?

Accepted Answer

Blood pressure regulation

Answer

Temperature regulation

Answer

Cephalic phase of gastric secretion

Answer

Increased heart rate before the start of exercise

Question 2

The Monro-Kellie doctrine is related to the doctrine of non-compressible contents within which part of the body?

Accepted Answer

Head

Answer

Abdomen

Answer

Chest

Answer

Leg

Question 3

Inward flow of Na+ in heart leads to what?

Accepted Answer

Action potential

Answer

Plateau phase

Answer

Repolarization

Answer

No change

Question 4

Concurrent flexion of both wrists in response to electrical stimulation is characteristic of which area of the nervous system?

Accepted Answer

Supplementary motor cortex

Answer

Postcentral gyrus

Answer

Vestibulospinal tract

Answer

Dentate nucleus

Question 5

The repolarization phase of an action potential is due to which of the following ionic changes?

Accepted Answer

Decreasing sodium permeability and a delayed increase in potassium permeability

Answer

Increasing sodium permeability and increasing potassium permeability

Answer

Increasing sodium permeability and decreasing potassium permeability

Answer

Decreasing sodium permeability and an immediate increasing potassium permeability

Question 6

The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by which equation?

Accepted Answer

Nernst equation

Answer

Goldman equation

Answer

van't Hoff equation

Answer

Fick's law

Question 7

Total lung capacity depends on which of the following?

Accepted Answer

Lung compliance

Answer

Size of airway

Answer

Closing tidal volume

Answer

Residual volume

Question 8

All of the following statements about Hepcidin are true EXCEPT:

Accepted Answer

Mice with enhanced hepcidin expression have elevated body iron stores.

Answer

It is a 25-amino acid peptide secreted by Kupffer cells.

Answer

It decreases duodenal absorption of iron.

Answer

It regulates the activity of transporters DMT-1 and ferroportin-1.

Question 9

Which muscle fiber type has a high glycogen content?

Accepted Answer

White fibers

Answer

Red fibers

Answer

Type 1 fibers

Answer

Tonic fibers

Question 10

Pantothenic acid is associated with which of the following moieties?

Accepted Answer

coenzyme A

Answer

Carboxyl

Answer

Hydroxyl

Answer

H+

General Physiology — MCQs

General Physiology — MCQs

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