NEET-PG 2012 - Physiology Practice Questions

Q: Which substrate is both secreted and filtered by the kidneys?

Uric Acid. ***Uric Acid*** - **Uric acid** is freely **filtered** at the glomerulus. - It undergoes both **secretion** and reabsorption in the renal tubules, making it a substrate that is both secreted and filtered. *Glucose* - **Glucose** is freely **filtered** at the glomerulus but is almost completely **reabsorbed** in the proximal tubule under normal physiological conditions. - It is not actively secreted by the renal tubules. *Urea* - **Urea** is freely **filtered** at the glomerulus. - It undergoes **reabsorption** (especially in the medullary collecting duct) and some facilitated diffusion, but significant active secretion is not its primary handling mechanism. *Na+* - **Sodium (Na+)** is freely **filtered** at the glomerulus in large quantities. - Its renal handling is dominated by extensive **reabsorption** throughout the nephron, which is crucial for fluid balance and blood pressure regulation, with no active secretion.

Q: Damage to the striatum primarily affects which type of memory?

Memory of how to perform tasks. ***Memory of how to perform tasks*** - The **striatum**, a component of the **basal ganglia**, is crucial for **procedural memory**, which is the memory of how to perform skills and habitual tasks. - Damage to this area can impair the ability to learn new motor skills or execute previously learned ones, even if the person remembers the task explicitly. *Memory for recent events* - This type of memory, often referred to as **episodic memory**, relies heavily on the **hippocampus** and medial temporal lobe structures. - Damage to the striatum typically does not directly affect the recall of recent events or experiences. *Memory for past experiences* - **Autobiographical memory**, which includes past experiences, primarily involves widespread cortical networks, particularly in the **temporal and frontal lobes**. - While broad brain damage can affect this, the striatum's primary role is not in the storage or retrieval of experiential memories. *Memory for facts and events* - This describes **declarative memory**, which is subdivided into **semantic memory** (facts) and **episodic memory** (events). - These are largely mediated by the **hippocampus**, **medial temporal lobes**, and various cortical areas, not primarily the striatum.

Q: Which of the following contains the PRIMARY central chemoreceptors responsible for detecting CO2 and pH changes in cerebrospinal fluid?

Medulla. ***Medulla*** - The **medulla oblongata** in the brainstem houses the primary central chemoreceptors. - These chemoreceptors are located on the **ventral surface of the medulla** and are highly sensitive to changes in the **pH of the cerebrospinal fluid (CSF)**, which is indirectly affected by the partial pressure of carbon dioxide (PCO2) in arterial blood. - CO2 diffuses across the blood-brain barrier, combines with water to form H+ ions, which directly stimulate these central chemoreceptors. *Baroreceptors in carotid sinus* - **Baroreceptors** primarily detect changes in **arterial blood pressure**, not CO2 or pH levels. - They are located in the carotid sinus and aortic arch and are involved in cardiovascular reflexes, not direct chemoreception for respiratory drive. *Peripheral chemoreceptors in carotid bodies* - **Peripheral chemoreceptors** in the carotid bodies (and aortic bodies) detect changes in **arterial blood O2, CO2, and pH**. - However, they are **peripheral**, not central chemoreceptors, and are the primary detectors of **hypoxemia**. - They contribute to respiratory drive but are secondary to central chemoreceptors for CO2 detection. *All of the above* - This option is incorrect because only the **medulla** contains the primary central chemoreceptors for CO2 and pH detection in CSF. - Baroreceptors detect blood pressure, and peripheral chemoreceptors are not central chemoreceptors.

Q: Which of the following factors increases the rate of particle diffusion across the cell membrane?

Maintaining a concentration gradient across the membrane. ***Maintaining a concentration gradient across the membrane*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration, driven by the **concentration gradient**. - A steeper gradient means a larger difference in concentration, leading to a faster rate of net diffusion until equilibrium is reached. - According to **Fick's Law**, the rate of diffusion is directly proportional to the concentration gradient across the membrane. *Decreasing the lipid solubility of the substance* - The cell membrane is primarily composed of a **lipid bilayer**, meaning that substances with **higher lipid solubility** can more easily pass through it via simple diffusion. - Decreasing lipid solubility would **hinder** the substance's ability to cross the membrane, thus slowing down or preventing diffusion. *Increasing the size of the opening in the cell membrane* - While increasing channel or pore diameter can increase diffusion rate for **channel-mediated transport**, this option is less comprehensive than maintaining a concentration gradient. - The concentration gradient is the **primary driving force** for diffusion across all types of membrane transport (simple diffusion through lipid bilayer, channel-mediated, and carrier-mediated). - Channel size is relevant only for specific facilitated diffusion pathways, not for general particle diffusion. *Increasing the size of the particle* - **Smaller particles** generally diffuse faster than larger particles because they have higher diffusion coefficients and can more easily navigate through the membrane. - According to the **Stokes-Einstein equation**, diffusion rate is inversely proportional to particle size. - Increasing particle size would therefore **decrease** the rate of diffusion.

Q: Which sensory modalities are most directly affected by lesions of the primary somatosensory cortex?

Localization and two-point discrimination. ***Localization and two-point discrimination*** - Lesions in the **primary somatosensory cortex** (S1) lead to profoundly impaired **discriminative touch**, which includes the ability to precisely localize tactile stimuli and distinguish between two closely spaced points. - These are the **most characteristic deficits** of S1 lesions, representing the cortex's unique role in processing **spatial discrimination and fine sensory analysis**. - S1 is essential for the **integrative functions** that allow precise spatial mapping of sensory inputs. *Pain, temperature, and touch* - Basic touch perception is affected, but **pain and temperature** are primarily mediated by the **spinothalamic tracts** with substantial processing in the thalamus, insular cortex, and anterior cingulate cortex rather than S1. - Crude touch sensation remains relatively preserved with S1 lesions; it is the **discriminative quality** that is lost. - These modalities are NOT the most directly affected by isolated S1 lesions. *Vibration and proprioception* - **Vibration** and **proprioception** are indeed significantly impacted by S1 lesions as S1 receives thalamic projections from the **dorsal column-medial lemniscus (DCML) pathway**. - However, these modalities have substantial **subcortical representation** in the thalamus and can be partially preserved even with cortical damage. - In contrast, **localization and two-point discrimination** are purely cortical functions with no subcortical processing, making them the MOST directly and exclusively dependent on S1 integrity. *All of the options* - This is incorrect because pain and temperature perception is NOT most directly affected by S1 lesions—these are primarily processed by other pathways and cortical areas (spinothalamic system, insular cortex).

Q: Which of the following statements is true regarding the function of the spinocerebellar tract?

Smoothens and coordinates movements. ***Smoothens and coordinates movements*** - The spinocerebellar tract provides the cerebellum with **unconscious proprioceptive information** from muscle spindles and Golgi tendon organs. - This information allows the cerebellum to compare intended movements with actual movements, thereby **smoothing and coordinating voluntary motor activity**. *Involved in planning and programming motor activities* - This function is primarily attributed to the **cerebral cortex** (e.g., premotor and supplementary motor areas) and the **basal ganglia**. - While the cerebellum is involved in motor learning and fine-tuning, the initial **planning and programming** of complex movements are cortical functions. *Involved in maintaining equilibrium* - Maintaining equilibrium and balance is primarily a function of the **vestibulocerebellum** (flocculonodular lobe), which receives input from the vestibular system. - While the spinocerebellum indirectly influences balance by coordinating limb movements, its direct role is less pronounced than that of the vestibulocerebellum. *Facilitates learning through vestibulo-ocular reflex changes* - This function is specific to the **vestibulocerebellum** and is crucial for adapting the vestibulo-ocular reflex (VOR) to maintain visual stability during head movements. - The spinocerebellar tract's primary role is proprioception for limb coordination, not VOR adaptation.

Q: What is the fixed length of a myosin filament?

1.6 micrometers. ***1.6 micrometers*** - Myosin filaments, also known as **thick filaments**, are integral components of muscle contraction and have a characteristic fixed length. This length is precisely **1.6 micrometers** in mammalian skeletal muscle. - This consistent length is crucial for the **sliding filament model** of muscle contraction, ensuring proper overlap with actin filaments and efficient force generation. *0.16 nm* - This value is significantly too small; **nanometers (nm)** are typically used for atomic or molecular distances, not for entire protein filaments like myosin. - A myosin filament is composed of hundreds of myosin molecules, making its overall length much larger than a fraction of a nanometer. *16 nm* - While nanometers are used for molecular structures, 16 nm is still too small for a myosin filament. The entire filament is roughly **100 times larger** than this value. - This dimension might be more appropriate for the diameter of a single myosin molecule's head region, but not the entire filament's length. *1.6 mm* - This value is significantly too large; **millimeters (mm)** are visible to the naked eye and represent macroscopic objects. - Muscle filaments are microscopic structures, and a length of 1.6 mm would imply they are many times longer than an entire muscle cell.

Q: Which isotope is used to measure RBC volume?

Cr 51. ***Cr 51*** - **Chromium-51** attaches irreversibly to the beta chain of hemoglobin, making it an ideal tracer for measuring **red blood cell volume** and survival. - After injection, the labeled red blood cells distribute throughout the circulation, and their dilution allows for the calculation of the total **RBC mass**. *H-3* - **Tritium (H-3)** is typically used as tritiated water to measure **total body water**, as it readily equilibrates throughout all fluid compartments. - It does not specifically bind to red blood cells for mass measurement. *D2O* - **D2O (heavy water)** is used to measure **total body water** content, similar to tritiated water. - It exchanges with water in the body and diffuses into all fluid compartments, rather than targeting red blood cells. *I-135* - While various **iodine isotopes** are used in medicine, such as **I-131** for thyroid imaging or therapy, **I-135** is not a commonly used isotope for measuring red blood cell volume. - Other tracers like **radio-iodinated human serum albumin** (e.g., I-125 HSA) can be used to measure plasma volume, not specifically RBC volume.

Q: What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

50 ml/min. ***50 ml/min*** - The body typically consumes about **250 ml/min of oxygen** at rest and produces approximately **200 ml/min of carbon dioxide**. - The difference between oxygen consumed and carbon dioxide produced is therefore **50 ml/min** (250 - 200 = 50). - This difference exists because the **respiratory quotient (RQ)** is approximately **0.8** (200/250), meaning less CO2 is produced than O2 consumed on a molar basis. *20 ml/min* - This value is **too low** and underestimates the physiological difference between oxygen consumption and carbon dioxide production. - With typical O2 consumption of 250 ml/min and RQ of 0.8, the difference cannot be this small. *75 ml/min* - This value represents an **overestimation** of the difference between oxygen consumption and carbon dioxide production under normal resting conditions. - This would imply an RQ of approximately 0.7, which is lower than the typical mixed diet RQ of 0.8. *100 ml/min* - This value is a significant **overestimation** of the physiological difference. - This would suggest an RQ of 0.6, which is not physiologically normal for resting conditions on a mixed diet.

Question 1

Which substrate is both secreted and filtered by the kidneys?

Accepted Answer

Uric Acid

Answer

Glucose

Answer

Urea

Answer

Na+

Question 2

Damage to the striatum primarily affects which type of memory?

Accepted Answer

Memory of how to perform tasks

Answer

Memory for recent events

Answer

Memory for past experiences

Answer

Memory for facts and events

Question 3

Which of the following contains the PRIMARY central chemoreceptors responsible for detecting CO2 and pH changes in cerebrospinal fluid?

Accepted Answer

Medulla

Answer

Baroreceptors in carotid sinus

Answer

Peripheral chemoreceptors in carotid bodies

Answer

All of the above

Question 4

Which one of the following is the CORRECT statement regarding coronary blood flow?

Accepted Answer

Coronary blood flow is directly related to perfusion pressure and inversely related to resistance

Answer

Coronary blood flow is inversely related to perfusion pressure and directly related to resistance

Answer

Coronary blood flow is directly related to perfusion pressure and also to resistance

Answer

Coronary blood flow is inversely related to both pressure and resistance

Question 5

Which of the following factors increases the rate of particle diffusion across the cell membrane?

Accepted Answer

Maintaining a concentration gradient across the membrane

Answer

Decreasing the lipid solubility of the substance

Answer

Increasing the size of the opening in the cell membrane

Answer

Increasing the size of the particle

Question 6

Which sensory modalities are most directly affected by lesions of the primary somatosensory cortex?

Accepted Answer

Localization and two-point discrimination

Answer

Pain, temperature, and touch

Answer

Vibration and proprioception

Answer

All of the options

Question 7

Which of the following statements is true regarding the function of the spinocerebellar tract?

Accepted Answer

Smoothens and coordinates movements

Answer

Involved in planning and programming motor activities

Answer

Involved in maintaining equilibrium

Answer

Facilitates learning through vestibulo-ocular reflex changes

Question 8

What is the fixed length of a myosin filament?

Accepted Answer

1.6 micrometers

Answer

0.16 nm

Answer

16 nm

Answer

1.6 mm

Question 9

Which isotope is used to measure RBC volume?

Accepted Answer

Cr 51

Answer

H-3

Answer

D2O

Answer

I-135

Question 10

What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

Accepted Answer

50 ml/min

Answer

20 ml/min

Answer

75 ml/min

Answer

100 ml/min

NEET-PG 2012 — Physiology