General Physiology Practice Questions

Q: What is the diameter of Type C fibers?

0.5-2 micrometers. **Explanation:** The classification of nerve fibers is based on the **Erlanger-Gasser classification**, which categorizes fibers according to their diameter, myelination, and conduction velocity. **Why Option D is Correct:** **Type C fibers** are the smallest nerve fibers in the human body. They are unique because they are **unmyelinated**, which results in a very small diameter (typically **0.5–2 micrometers**) and the slowest conduction velocity (0.5–2 m/s). These fibers primarily carry sensations of slow/chronic pain, temperature, and post-ganglionic autonomic signals. **Analysis of Incorrect Options:** * **Option A (13–20 µm):** This corresponds to **Type A-alpha (Aα)** fibers. These are the largest, most heavily myelinated fibers, responsible for proprioception and somatic motor function. * **Option B (4–13 µm):** This range corresponds to **Type A-beta (Aβ)** and **Type A-gamma (Aγ)** fibers, which mediate touch, pressure, and motor supply to muscle spindles. * **Option C (3–6 µm):** This range is characteristic of **Type B** fibers (pre-ganglionic autonomic fibers) or smaller **Type A-delta (Aδ)** fibers (fast pain and cold temperature). **High-Yield Clinical Pearls for NEET-PG:** * **Susceptibility to Blockade:** Type C fibers are the **most sensitive to local anesthetics** (due to lack of myelin) but the **least sensitive to hypoxia** and pressure. * **Pain Transmission:** Remember the "Double Pain" phenomenon: **Aδ fibers** carry "fast" (sharp/localized) pain, while **C fibers** carry "slow" (dull/aching/diffuse) pain. * **Rule of Thumb:** Conduction velocity (in m/s) for Type A fibers is roughly $6 \times \text{diameter (in µm)}$. This rule does not apply to Type C fibers as they lack myelin.

Q: The magnitude of the electrical potential difference that exists across a membrane can be determined by which of the following equations?

Nernst equation. ### Explanation **Correct Answer: C. Nernst equation** The **Nernst equation** is the fundamental formula used to calculate the **equilibrium potential** (electromotive force) for a single ion across a semi-permeable membrane. It determines the electrical potential difference required to exactly balance the concentration gradient of that ion, such that there is no net movement. * **Formula:** $E = \frac{RT}{zF} \ln \frac{[Ion]_{out}}{[Ion]_{in}}$ (Simplified at body temperature: $E = \pm 61 \log \frac{[Ion]_{out}}{[Ion]_{in}}$). * In physiology, it explains why the resting membrane potential is close to the equilibrium potential of Potassium ($K^+$), as the membrane is most permeable to it at rest. **Analysis of Incorrect Options:** * **A. Gibbs-Donnan equation:** Describes the behavior of charged particles near a semi-permeable membrane when one ion is non-diffusible (e.g., plasma proteins). It explains the resulting unequal distribution of diffusible ions, not the magnitude of the potential itself. * **B. Henderson-Hasselbalch equation:** Used in acid-base physiology to calculate the **pH** of a buffer solution or the ratio of bicarbonate to carbon dioxide in the blood. * **D. Fick’s law:** Relates to 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. **High-Yield Clinical Pearls for NEET-PG:** * **Goldman-Hodgkin-Katz (GHK) Equation:** While Nernst is for a *single* ion, the GHK equation calculates the *resting membrane potential* by considering the permeability and concentration of *all* major ions ($Na^+, K^+, Cl^-$). * **Standard Potentials:** $E_{K^+} \approx -90\text{ mV}$, $E_{Na^+} \approx +60\text{ mV}$. * **Hypokalemia** makes the resting membrane potential more negative (hyperpolarization), making cells less excitable.

Q: Which type of muscle exercise involves the muscle changing length against a constant load?

Isotonic exercise. **Explanation:** The correct answer is **Isotonic exercise**. This type of muscle contraction occurs when the **tension remains constant** while the **muscle length changes** (either shortening or lengthening) to move a load. The term is derived from the Greek words *"iso"* (same) and *"tonos"* (tension). Isotonic exercises are further divided into **concentric** (muscle shortens, e.g., upward phase of a bicep curl) and **eccentric** (muscle lengthens under tension, e.g., controlled lowering of a weight). **Why other options are incorrect:** * **Isometric exercise:** In this type, the **length of the muscle remains constant** while the **tension increases**. No external work is performed (Work = Force × Displacement; here displacement is zero). An example is pushing against a stationary wall. * **Aerobic exercise:** This refers to the metabolic pathway used (oxidative phosphorylation) rather than the mechanics of muscle length or tension. While many isotonic exercises are aerobic, the terms are not synonymous. **High-Yield NEET-PG Pearls:** 1. **Isokinetic exercise:** A type of exercise where the muscle contracts at a **constant velocity** throughout the entire range of motion (requires specialized equipment). 2. **Energy Expenditure:** Isotonic contractions perform external work and consume more energy compared to isometric contractions. 3. **Clinical Correlation:** Isometric exercises cause a more significant rise in **mean arterial pressure (MAP)** due to the compression of blood vessels within the contracting muscle, leading to increased peripheral resistance. 4. **Golgi Tendon Organs:** These are sensitive to changes in muscle **tension** (prominent in isometric), whereas **Muscle Spindles** are sensitive to changes in muscle **length** (prominent in isotonic).

Q: What does the Golgi tendon organ primarily detect?

Muscle tension. **Explanation:** The **Golgi Tendon Organ (GTO)** is a high-threshold mechanoreceptor located in the tendons of skeletal muscles, arranged in **series** with the muscle fibers. Its primary function is to monitor and respond to **muscle tension** (force of contraction). When a muscle contracts, it pulls on the tendon, compressing the nerve endings within the GTO. This triggers an inhibitory signal via **Ib afferent fibers** to the spinal cord, causing the muscle to relax (the **Inverse Stretch Reflex**). This mechanism protects the muscle and tendon from damage due to excessive force. **Analysis of Options:** * **Option A & D (Static and Dynamic Muscle Length):** These are detected by **Muscle Spindles**, which are arranged in **parallel** with muscle fibers. Nuclear chain fibers detect static length, while nuclear bag fibers detect dynamic changes in length (velocity). * **Option B (Muscle Action):** This is a general term. While GTOs are active during muscle action, their specific physiological stimulus is the resulting tension, not the action itself. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** GTO is in **series**; Muscle Spindle is in **parallel**. * **Afferent Nerve:** GTO uses **Type Ib** fibers; Muscle Spindle uses **Type Ia** (primary) and **Type II** (secondary) fibers. * **Reflex:** GTO mediates the **Autogenic Inhibition** (Inverse Stretch Reflex), whereas the Muscle Spindle mediates the **Stretch Reflex** (DTRs). * **Function:** GTO prevents avulsion injuries; Muscle Spindles maintain muscle tone and posture.

Q: Oxidative capacity is high in which type of skeletal muscle fiber?

Type I fiber. **Explanation:** Skeletal muscle fibers are classified based on their contraction speed and primary metabolic pathway. The correct answer is **Type I fiber** because these fibers are specifically designed for endurance and continuous aerobic activity. **1. Why Type I is correct:** Type I fibers, also known as **Slow-Twitch (Red) fibers**, have a high oxidative capacity. This is due to a high density of **mitochondria**, high concentrations of **myoglobin** (which stores oxygen and gives the muscle its red color), and a rich capillary supply. They rely on aerobic metabolism (oxidative phosphorylation) to produce ATP, making them highly resistant to fatigue. **2. Why the other options are incorrect:** * **Type IIA (Fast-Twitch Oxidative-Glycolytic):** These are intermediate fibers. While they possess some oxidative capacity, they also rely significantly on anaerobic glycolysis. Their oxidative capacity is lower than Type I but higher than Type IIB. * **Type IIB (Fast-Twitch Glycolytic):** These are "White fibers" with **low oxidative capacity**. They have few mitochondria and low myoglobin. They rely almost exclusively on anaerobic glycolysis for rapid, powerful bursts of activity but fatigue very quickly. **High-Yield NEET-PG Clinical Pearls:** * **Postural Muscles:** Muscles like the *soleus* are predominantly Type I (endurance). * **Sprint Muscles:** Muscles like the *extraocular muscles* or *gastrocnemius* have a higher proportion of Type II fibers (speed). * **Mnemonic:** **"One Slow Red Ox"** (Type **I**, **Slow**-twitch, **Red** color, **Ox**idative). * **ATPase Activity:** Type II fibers have high myosin ATPase activity (fast contraction), whereas Type I has low activity.

Q: Which protein is shown in the thin filament as illustrated?

Troponin. ***Troponin*** - **Troponin** is a regulatory protein complex located on the **thin filament** (actin), consisting of **troponin C** (calcium-binding), **troponin I** (inhibitory), and **troponin T** (tropomyosin-binding). - Functions in **calcium-mediated muscle contraction** by regulating the interaction between **actin and myosin** through conformational changes in the **troponin-tropomyosin complex**. *Titin* - **Titin** is primarily associated with the **thick filament** (myosin) and acts as a **molecular spring** providing elasticity to muscle fibers. - It spans from the **Z-line to M-line** in the sarcomere but is not a component of the thin filament regulatory system. *Nebulin* - **Nebulin** is present on thin filaments but serves as a **molecular ruler** that determines **actin filament length** during muscle development. - Unlike troponin, it does not function as a **regulatory protein** for calcium-mediated contraction and is not part of the excitation-contraction coupling mechanism. *Dystrophin* - **Dystrophin** is a **cytoskeletal protein** that links intracellular **actin** to the **extracellular matrix** through the **dystrophin-glycoprotein complex**. - It provides **structural support** to muscle fibers but is not involved in the **thin filament regulatory mechanism** or direct contraction processes.

Q: During skeletal muscle contraction, which bands shorten?

Both H and I bands shorten. ### Explanation The mechanism of skeletal muscle contraction is best explained by the **Sliding Filament Theory** (Huxley and Hanson). According to this theory, muscle contraction occurs when thin (actin) filaments slide over thick (myosin) filaments toward the center of the sarcomere. #### Why the Correct Answer is Right: * **I Band (Isotropic):** This band contains only thin filaments. As actin filaments slide toward the M-line, they overlap more with thick filaments, causing the I band to **shorten**. * **H Zone (Heller):** This is the central part of the A band containing only thick filaments. As thin filaments move inward, they occupy the H zone, causing it to **shorten or even disappear** during maximal contraction. * **Sarcomere:** The distance between two Z-discs decreases, meaning the overall sarcomere shortens. #### Why Other Options are Wrong: * **A Band (Anisotropic):** This band represents the entire length of the thick (myosin) filament. Since the thick filaments themselves do not change length or move, the **A band remains constant** during contraction. * Options A, C, and D are incorrect because they suggest the A band shortens, which is physiologically impossible during normal contraction. #### High-Yield NEET-PG Pearls: * **The "Constant" Rule:** During contraction, the **A band** and the length of individual **thick and thin filaments** remain unchanged. * **The "Shortening" Rule:** The **I band, H zone, and Sarcomere** length all decrease. * **Structural Proteins:** Titin (the largest protein in the body) acts as a spring to maintain the central position of myosin, while Nebulin regulates the length of actin filaments. * **Calcium Source:** In skeletal muscle, calcium for contraction is derived exclusively from the **Sarcoplasmic Reticulum** (unlike cardiac muscle, which requires extracellular calcium).

Q: Which statement is true regarding Type-2 muscle fibers?

Increased Isoenzyme ATPase activity. ### Explanation **Correct Answer: C. Increased Isoenzyme ATPase activity** Skeletal muscle fibers are classified into Type 1 (Slow-twitch) and Type 2 (Fast-twitch) based on their metabolic profile and contraction speed. The speed of muscle contraction is directly proportional to the **Myosin ATPase activity**. Type 2 fibers possess a specific isoenzyme of myosin ATPase that hydrolyzes ATP rapidly, allowing for fast cross-bridge cycling and quick, powerful contractions. **Analysis of Options:** * **Option A & B (Incorrect):** These describe **Type 1 (Slow Oxidative) fibers**. Type 1 fibers are rich in myoglobin (giving them a red color) and mitochondria to support aerobic metabolism for endurance. Type 2 fibers have low myoglobin content and appear pale/white. * **Option D (Incorrect):** Type 2 fibers (specifically Type 2b) have a **high glycolytic capacity**, not moderate. They rely on anaerobic glycolysis for rapid energy production, making them prone to early fatigue due to lactic acid accumulation. --- ### High-Yield Clinical Pearls for NEET-PG: * **Type 1 Fibers (Slow-twitch):** "One Slow Red Ox" (Type **1**, **Slow**-twitch, **Red** color, **Ox**idative metabolism). Found in postural muscles like the **Soleus**. * **Type 2 Fibers (Fast-twitch):** "Two Fast White Sugar" (Type **2**, **Fast**-twitch, **White** color, **Sugar**/Glycolytic metabolism). Found in muscles used for sprinting or weightlifting, such as the **Gastrocnemius**. * **Intermediate Fibers (Type 2a):** These are fast-twitch but have both oxidative and glycolytic capacities (Fast Oxidative Glycolytic). * **Order of Recruitment:** According to **Henneman’s Size Principle**, smaller Type 1 motor units are recruited first, followed by larger Type 2 units as force requirements increase.

Q: Which of the following statements is true about Nissl granules?

Involves in protein synthesis. **Explanation:** **Nissl granules** (also known as Nissl bodies) are large, granular structures found in the cytoplasm of neurons. They are composed of **Rough Endoplasmic Reticulum (RER)** and associated **free ribosomes**. 1. **Why Option C is correct:** The primary function of ribosomes and RER is translation. Therefore, Nissl granules are the primary sites of **protein synthesis** in the neuron, producing proteins required for intracellular transmission and the renewal of structural components. 2. **Why other options are incorrect:** * **Option A:** RNA synthesis (transcription) occurs within the **nucleus** (specifically the nucleolus for rRNA), not in the Nissl granules. * **Option B:** Nissl granules are found in the **cyton (cell body)** and **dendrites**, but they are characteristically **absent in the axon** and the **axon hillock**. This is a classic anatomical landmark used to identify the start of an axon. * **Option D:** While they contain RER, stating they are "structurally endoplasmic reticulum" is incomplete. They are a complex of **RER plus free ribosomes**. (Note: In many competitive exams, "Protein Synthesis" is the more functional and definitive answer). **High-Yield Clinical Pearls for NEET-PG:** * **Chromatolysis:** When a neuron is injured (axonal injury), Nissl granules undergo hypertrophy, fragment, and disperse. This process is called chromatolysis, indicating an active attempt at protein synthesis for regeneration. * **Staining:** They are highly basophilic and are best visualized using basic dyes like **Cresyl Violet** or **Methylene Blue**. * **Location Tip:** Always remember: **D**endrites have them, **A**xons do not (**D** yes, **A** no).

Question 1

What is the diameter of Type C fibers?

Accepted Answer

0.5-2 micrometers

Answer

13-20 micrometers

Answer

4-13 micrometers

Answer

3-6 micrometers

Question 2

The magnitude of the electrical potential difference that exists across a membrane can be determined by which of the following equations?

Accepted Answer

Nernst equation

Answer

Gibbs-Donnan equation

Answer

Henderson-Hasselbalch equation

Answer

Fick's law

Question 3

Which type of muscle exercise involves the muscle changing length against a constant load?

Accepted Answer

Isotonic exercise

Answer

Isometric exercise

Answer

Aerobic exercise

Answer

None of the above

Question 4

What does the Golgi tendon organ primarily detect?

Accepted Answer

Muscle tension

Answer

Static muscle length

Answer

Muscle action

Answer

Dynamic muscle length

Question 5

Oxidative capacity is high in which type of skeletal muscle fiber?

Accepted Answer

Type I fiber

Answer

Type IIA fiber

Answer

Type IIB fiber

Answer

All of the above

Question 6

Which protein is shown in the thin filament as illustrated?

Accepted Answer

Troponin

Answer

Titin

Answer

Nebulin

Answer

Dystrophin

Question 7

Positive feedback is seen in which of the following?

Accepted Answer

Stimulation of gastric secretion of histamine and gastrin

Answer

LH Surge

Answer

Entry of Ca++ into sarcoplasmic reticulum

Answer

Thrombolytic activity in the coagulation cascade

Question 8

During skeletal muscle contraction, which bands shorten?

Accepted Answer

Both H and I bands shorten

Answer

A band shortens

Answer

Both A and I bands shorten

Answer

Both A and H bands shorten

Question 9

Which statement is true regarding Type-2 muscle fibers?

Accepted Answer

Increased Isoenzyme ATPase activity

Answer

Increased myoglobin content

Answer

Slow oxidative and red in color

Answer

Moderate glycolytic capacity

Question 10

Which of the following statements is true about Nissl granules?

Accepted Answer

Involves in protein synthesis

Answer

Involves in RNA synthesis

Answer

Present in the axon

Answer

Structurally, they are endoplasmic reticulum

General Physiology — MCQs

General Physiology — MCQs

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