NEET-PG 2013 - Physiology Practice Questions

Q: Which receptor is primarily stimulated in response to moderate cold temperatures?

TRPM8 Receptor (Menthol Receptor). ***TRPM8 Receptor (Menthol Receptor)*** - The **TRPM8 receptor** is a **cold-sensitive ion channel** that is primarily activated by moderate cold temperatures (around 8–28°C) and by cooling compounds like **menthol** and **eucalyptol**. - Its activation leads to an influx of cations, primarily **calcium**, causing depolarization and generation of action potentials. *Vanilloid Receptor 1 (VR1)* - Vanilloid Receptor 1, also known as **TRPV1**, is primarily activated by noxious heat (temperatures above 43°C), low pH, and capsaicin. - It plays a significant role in **pain sensation** and inflammation, not moderate cold detection. *Vanilloid Receptor 2 (VR2)* - Vanilloid Receptor 2, or **TRPV2**, is activated by even higher temperatures than TRPV1, typically above 52°C, and is also involved in the detection of **intense heat** and mechanical stimuli. - It does not respond to cold temperatures at all. *Vanilloid Receptor-Like 1 (VRL-1)* - **VRL-1**, or **TRPV3**, is a heat-sensitive channel activated by warm temperatures (above 31°C) and plays a role in the sensation of warmth and heat hyperalgesia. - It is not involved in the detection of cold stimuli.

Q: What is the normal mean velocity of blood flow in the aorta?

40-50 cm/sec. ***40-50 cm/sec*** - This range represents the **normal mean velocity** of blood flow in the **aorta**, reflecting efficient cardiac output and systemic circulation. - Blood flow velocity can vary slightly based on factors like age, cardiac health, and physical activity, but this range is a common physiological benchmark. *100-150 cm/sec* - This velocity is significantly **higher** than normal for mean aortic flow and would typically indicate a state of **hyperdynamic circulation** or specific pathological conditions. - Such elevated velocities might be seen in conditions like severe **aortic stenosis**, where the heart works harder to push blood through a narrowed valve. *200-250 cm/sec* - This range is **pathologically high** for mean aortic blood flow and is not compatible with normal physiological function. - Velocities in this range would strongly suggest a severe **cardiovascular abnormality**, such as critical **aortic stenosis** or a significant **arteriovenous shunt**. *250-300 cm/sec* - This velocity is **extremely high** and far exceeds any normal or even most pathological mean aortic flow rates found in humans. - Such high velocities would likely be associated with a highly turbulent and severely compromised cardiovascular system, potentially leading to **acute circulatory failure**.

Q: Duration of maximum contraction depends upon?

Absolute refractory period. ***Absolute refractory period*** - The duration of **maximum (sustained) contraction** in skeletal muscle depends primarily on the **absolute refractory period** - The absolute refractory period (1-2 ms in skeletal muscle) is much **shorter than the contraction duration** (20-200 ms), allowing for **temporal summation** - When stimuli arrive after the refractory period but before complete relaxation, contractions **summate** to produce **tetanus** (sustained maximum contraction) - A shorter refractory period allows **higher frequency stimulation** → more complete summation → stronger and longer sustained contraction - This is why skeletal muscle can achieve **complete tetanus** at stimulation frequencies of 50-100 Hz *Relative refractory period* - While the relative refractory period affects excitability, it is the **absolute refractory period** that sets the fundamental limit on maximum stimulation frequency - The relative refractory period is less critical for determining the duration of maximum contraction *None of the two* - This is incorrect because the refractory period directly determines the **maximum frequency** at which muscle can be stimulated - Higher stimulation frequency (limited by refractory period) → better temporal summation → sustained maximum contraction (tetanus) - The refractory period is the key factor enabling or limiting the duration of maximum contraction *Both* - While both refractory periods influence excitability, the **absolute refractory period** is the primary determinant - It sets the absolute limit on stimulation frequency and thus the ability to achieve and maintain tetanic contraction

Q: What is the primary action observed in the withdrawal reflex?

Flexion. ***Flexion*** - The **withdrawal reflex** is a protective reflex that causes the affected limb to **flex** and withdraw from a painful stimulus. - This **flexion** is mediated by the contraction of flexor muscles and relaxation of extensor muscles, moving the limb away from danger. *Extension* - **Extension** is the opposite of flexion and would move the limb closer to or maintain its position relative to the painful stimulus. - This action is typically observed in the **crossed extensor reflex**, where the contralateral limb extends to support the body, not in the direct withdrawal of the stimulated limb. *Flexion followed by extension* - While **flexion** is the primary action, it is not typically followed immediately by extension within the same limb in a simple withdrawal reflex. - If a coordinated movement were to occur, such as shifting weight, the **crossed extensor reflex** would involve extension in the opposite limb. *Not applicable* - The withdrawal reflex involves a clear and defined muscle action which is **flexion**, making "not applicable" incorrect. - This reflex is a fundamental component of the nervous system's response to noxious stimuli.

Q: Which type of muscle fibers has fewer mitochondria?

Type IIb fibers (Fast-twitch fibers). ***Type IIb fibers (Fast-twitch fibers)*** - These fibers rely primarily on **anaerobic glycolysis** for ATP production, which is a less efficient process than aerobic respiration and therefore requires fewer mitochondria. - Their primary function is rapid, powerful contractions over short durations, leading to quick fatigue. *Type IIa fibers* - These fibers are **fast-twitch oxidative-glycolytic** fibers, meaning they have a moderate number of mitochondria to support both aerobic and anaerobic metabolism. - They are capable of generating strong contractions and are more fatigue-resistant than Type IIb fibers but less so than Type I fibers. *Type I fibers (Red fibers)* - Known as **slow-twitch oxidative fibers**, they have a high density of mitochondria to support continuous **aerobic respiration** for sustained, low-intensity contractions. - Their rich blood supply and high myoglobin content give them their characteristic red color and make them highly fatigue-resistant. *Type IIx fibers (Intermediate fibers)* - These fibers are very similar to Type IIb fibers in their metabolic profile, often considered an intermediate or even functionally equivalent type depending on the species. - They also primarily utilize **anaerobic glycolysis** and have a relatively low mitochondrial content, making them prone to fatigue.

Q: Which of the following statements is true about red muscle fibers?

Exhibit more oxidative capacity. ***Exhibit more oxidative capacity*** - **Red muscle fibers**, also known as **slow-twitch fibers**, are rich in **mitochondria** and enzymes for aerobic respiration, allowing for sustained contractions and high oxidative capacity. - Their high oxidative capacity is crucial for activities requiring **endurance**, such as long-distance running or maintaining posture through efficient **ATP production** via the **electron transport chain**. *Contain fewer mitochondria than white muscle fibers* - **Red muscle fibers** contain **more mitochondria** than white muscle fibers to support their greater reliance on **aerobic metabolism** for sustained energy production. - **Mitochondria** are the primary sites of **oxidative phosphorylation**, which is essential for the continuous ATP supply needed by these endurance specialized fibers. *Utilize glycolytic metabolism* - While red fibers can perform some glycolysis, their primary metabolic pathway is **oxidative phosphorylation**, utilizing **fatty acids** and **glucose** aerobically. - **Glycolytic metabolism** is more characteristic of **white muscle fibers (fast-twitch)**, which rely on anaerobic pathways for rapid, high-intensity contractions. *Have less myoglobin than white muscle fibers* - **Red muscle fibers** are characterized by a **high content of myoglobin**, which gives them their characteristic red color and high oxygen storage capacity. - **Myoglobin** is crucial for oxygen delivery to the mitochondria, supporting the sustained aerobic metabolism of these fibers, in contrast to white fibers which have less myoglobin.

Q: Integration center of tonic labyrinthine reflex is?

Medulla. ***Medulla*** - The **tonic labyrinthine reflex** is a primitive reflex originating in the **vestibular system**, specifically the otolith organs, which respond to head position changes. - Its integration center lies in the **medulla oblongata**, a part of the brainstem responsible for essential involuntary functions. *Spinal cord* - The spinal cord integrates simpler reflexes like **stretch reflexes** and **withdrawal reflexes**. - It does not process the complex vestibular input required for the tonic labyrinthine reflex. *Midbrain* - The **midbrain** is involved in integrating reflexes related to visual and auditory stimuli, such as the **startle reflex** and **pupillary light reflex**. - It is superior to the primary integration center for the tonic labyrinthine reflex. *Cerebral cortex* - The **cerebral cortex** is responsible for higher cognitive functions, voluntary movements, and conscious sensation. - Reflexes like the tonic labyrinthine reflex are subcortical and operate without conscious control.

Q: Which part of the brain is primarily responsible for the righting reflex?

Midbrain. ***Midbrain*** - The **midbrain** plays a crucial role in regulating posture and movement, including the **righting reflex**. - It integrates sensory information from the **vestibular system**, eyes, and proprioceptors to maintain upright posture. *Pons* - The pons is primarily involved in relaying signals between the **cerebrum** and **cerebellum** and regulating respiration and sleep. - While it contributes to motor control, it is not the primary center for the righting reflex. *Spinal cord* - The spinal cord mediates **reflex arcs** and transmits sensory and motor information, but it does not independently control complex postural reflexes like the righting reflex. - It contains the circuits for basic reflexes such as the **stretch reflex** and **withdrawal reflex**. *Cortex* - The cerebral cortex is responsible for **voluntary movements**, higher cognitive functions, and conscious perception. - While it can influence posture, the righting reflex is a subcortical, involuntary process.

Q: Cushing reflex is associated with all except?

Hypotension. ***Hypotension*** - The **Cushing reflex** is a compensatory response to increased intracranial pressure (ICP) aiming to maintain cerebral perfusion, which typically involves **hypertension**, not hypotension. - While prolonged or severe ICP can lead to decompensation and eventual hypotension, it is not a direct component of the reflex itself. *Increased intracranial pressure* - The **Cushing reflex** is triggered by an elevation in **intracranial pressure (ICP)**, as the body attempts to maintain blood flow to the brain. - This increased ICP reduces cerebral perfusion pressure, prompting a systemic response to raise mean arterial pressure. *Bradycardia* - **Bradycardia** is a classic component of the **Cushing reflex**, occurring as a compensatory response to the reflex hypertension. - The increased arterial blood pressure stimulates carotid and aortic baroreceptors, leading to a vagal response that slows the heart rate. *Irregular respiration* - **Irregular respiration** is another key component of the **Cushing reflex**, often manifesting as **Cheyne-Stokes breathing** or **ataxic breathing**. - This respiratory dysregulation is due to direct compression and dysfunction of the brainstem, specifically the medullary respiratory centers, caused by increased ICP.

Question 1

Which of the following statements about breathing is incorrect?

Accepted Answer

Normal breathing occurs when transpulmonary pressure is 5-8 cm H2O

Answer

Inspiration is an active process

Answer

Expiration during quiet breathing is passive

Answer

Compliance is influenced by multiple factors including surfactant.

Question 2

Which receptor is primarily stimulated in response to moderate cold temperatures?

Accepted Answer

TRPM8 Receptor (Menthol Receptor)

Answer

Vanilloid Receptor 1 (VR1)

Answer

Vanilloid Receptor 2 (VR2)

Answer

Vanilloid Receptor-Like 1 (VRL-1)

Question 3

What is the normal mean velocity of blood flow in the aorta?

Accepted Answer

40-50 cm/sec

Answer

100-150 cm/sec

Answer

200-250 cm/sec

Answer

250-300 cm/sec

Question 4

Duration of maximum contraction depends upon?

Accepted Answer

Absolute refractory period

Answer

Both

Answer

None of the two

Answer

Relative refractory period

Question 5

What is the primary action observed in the withdrawal reflex?

Accepted Answer

Flexion

Answer

Extension

Answer

Flexion followed by extension

Answer

Not applicable

Question 6

Which type of muscle fibers has fewer mitochondria?

Accepted Answer

Type IIb fibers (Fast-twitch fibers)

Answer

Type I fibers (Red fibers)

Answer

Type IIa fibers

Answer

Type IIx fibers (Intermediate fibers)

Question 7

Which of the following statements is true about red muscle fibers?

Accepted Answer

Exhibit more oxidative capacity

Answer

Contain fewer mitochondria than white muscle fibers

Answer

Have less myoglobin than white muscle fibers

Answer

Utilize glycolytic metabolism

Question 8

Integration center of tonic labyrinthine reflex is?

Accepted Answer

Medulla

Answer

Spinal cord

Answer

Midbrain

Answer

Cerebral cortex

Question 9

Which part of the brain is primarily responsible for the righting reflex?

Accepted Answer

Midbrain

Answer

Pons

Answer

Spinal cord

Answer

Cortex

Question 10

Cushing reflex is associated with all except?

Accepted Answer

Hypotension

Answer

Irregular respiration

Answer

Increased intracranial pressure

Answer

Bradycardia

NEET-PG 2013 — Physiology