Anatomy
3 questionsWhich of the following is not a tributary of the cavernous sinus?
Medulla oblongata arises from which of the following?
Chorda tympani is a branch of which cranial nerve?
NEET-PG 2013 - Anatomy NEET-PG Practice Questions and MCQs
Question 331: Which of the following is not a tributary of the cavernous sinus?
- A. Central vein of retina
- B. Sphenoparietal sinus
- C. Inferior cerebral vein (Correct Answer)
- D. Superior ophthalmic vein
Explanation: Detailed anatomical knowledge of the dural venous sinuses is required to answer this question. Venous drainage from the brain by way of the deep veins and dural sinuses typically empties principally into the internal jugular veins, though blood also drains via the ophthalmic and pterygoid venous plexuses [1]. ***Inferior cerebral vein*** - The **inferior cerebral veins** drain the inferior surface of the cerebral hemispheres and typically empty into the **basal vein of Rosenthal**, **transverse sinus**, or other dural sinuses. - They do **not directly drain** into the cavernous sinus, making this the correct answer. - While some small inferior cerebral veins may occasionally communicate with the cavernous sinus, they are not considered standard tributaries. *Central vein of retina* - The **central vein of retina** drains the retina and exits the eye through the optic nerve. - It drains into the **superior ophthalmic vein**, which then empties into the cavernous sinus. - It is an **indirect tributary** via the superior ophthalmic vein, not a direct tributary itself. *Sphenoparietal sinus* - The **sphenoparietal sinus** is a dural venous sinus that runs along the posterior edge of the lesser wing of the sphenoid bone. - It is a **direct tributary** that drains anteriorly into the cavernous sinus. - This is one of the standard tributaries listed in anatomical texts. *Superior ophthalmic vein* - The **superior ophthalmic vein** is the **major tributary** draining orbital structures including the eyeball, extraocular muscles, and eyelids. - It passes posteriorly through the **superior orbital fissure** to drain directly into the cavernous sinus. - This is the most clinically significant tributary, as infections can spread from the face to the cavernous sinus via this route.
Question 332: Medulla oblongata arises from which of the following?
- A. Mesencephalon
- B. Myelencephalon (Correct Answer)
- C. Rhombencephalon
- D. None of the options
Explanation: ***Myelencephalon*** - The **myelencephalon** is the most caudal of the three primary brain vesicles and is the developmental origin of the **medulla oblongata**. - It differentiates from the **rhombencephalon** (hindbrain) and is responsible for vital autonomic functions. *Rhombencephalon* - The **rhombencephalon** is the hindbrain and is a primary brain vesicle that further divides into the **metencephalon** and **myelencephalon**. - While it is the parent structure, it does not directly give rise to the medulla oblongata as a final differentiated structure without further division. *Mesencephalon* - The **mesencephalon** is the midbrain, a primary brain vesicle that develops into structures like the **tectum** and **tegmentum** [1]. - It is located rostral to the rhombencephalon and is not involved in the development of the medulla oblongata [1]. *None of the options* - This option is incorrect because the **myelencephalon** is the direct embryonic precursor of the medulla oblongata.
Question 333: Chorda tympani is a branch of which cranial nerve?
- A. Vestibulocochlear nerve (CN VIII)
- B. Facial nerve (CN VII) (Correct Answer)
- C. Trigeminal nerve (CN V)
- D. Glossopharyngeal nerve (CN IX)
Explanation: ***Facial nerve (CN VII)*** - The **chorda tympani** is a branch of the **facial nerve (CN VII)**, carrying special sensory (taste) innervation to the anterior two-thirds of the tongue and preganglionic parasympathetic fibers to the submandibular and sublingual salivary glands. - It arises from the facial nerve within the **temporal bone**, passes through the middle ear, and then joins the lingual nerve. *Trigeminal nerve (CN V)* - The **trigeminal nerve** is primarily responsible for **sensory innervation of the face** and motor innervation of the muscles of mastication. - While the lingual nerve (a branch of the trigeminal nerve) carries the fibers of the chorda tympani, the chorda tympani itself originates from the facial nerve. *Vestibulocochlear nerve (CN VIII)* - The **vestibulocochlear nerve** is responsible for **hearing** and **balance**. - It does not have any branches that innervate taste buds or salivary glands. *Glossopharyngeal nerve (CN IX)* - The **glossopharyngeal nerve** innervates the posterior one-third of the tongue for **taste** and general sensation, the parotid gland for parasympathetic secretion, and the stylopharyngeus muscle. - It does not give rise to the chorda tympani.
Internal Medicine
1 questionsWhich of the following statements about Alport's syndrome is incorrect?
NEET-PG 2013 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 331: Which of the following statements about Alport's syndrome is incorrect?
- A. Nerve deafness
- B. Glomerulonephritis
- C. Autosomal dominant (Correct Answer)
- D. X-linked
Explanation: ***Autosomal dominant*** - While there are rare autosomal dominant forms, the most common and classic presentation of **Alport's syndrome is X-linked recessive**, affecting males more severely. - This statement is incorrect because it implies that autosomal dominant inheritance is the primary or typical mode, which is not true for the majority of cases. *Nerve deafness* - **Sensorineural hearing loss**, particularly for high frequencies, is a common and characteristic extra-renal manifestation of Alport's syndrome. - This symptom typically progresses with age and is a key diagnostic feature. *Glomerulonephritis* - **Progressive glomerulonephritis** is the hallmark renal feature of Alport's syndrome, leading to hematuria, proteinuria, and eventually end-stage renal disease. - It is caused by mutations in collagen type IV genes, which disrupt the integrity of the glomerular basement membrane. *X-linked* - The majority of Alport's syndrome cases (about 85%) are **X-linked recessive**, caused by mutations in the *COL4A5* gene located on the X chromosome. - This explains why males are more severely affected and typically present with earlier onset and more rapid progression of renal disease.
Physiology
6 questionsWhat is the minimum fluid urine output for neutral solute balance?
Fever increases water loss by how much for each degree Celsius increase in body temperature?
Which equation is used to calculate physiological dead space?
Which of the following best describes hypoxic pulmonary vasoconstriction?
Which of the following stimuli is primarily responsible for triggering the Bezold-Jarisch reflex?
What physiological mechanism leads to an increase in cardiac output?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 331: What is the minimum fluid urine output for neutral solute balance?
- A. 300 ml
- B. 750 ml
- C. 500 ml
- D. 400 ml (Correct Answer)
Explanation: ***400 ml*** - The kidneys must excrete approximately **600 mOsm of solutes daily** to maintain neutral solute balance. - With a maximum urine concentrating ability of **1200-1400 mOsm/L**, the minimum volume required is calculated as: 600 mOsm ÷ 1400 mOsm/L = **428 ml**. - Therefore, **400 ml** is the conventionally accepted minimum urine output for neutral solute balance. - Below this volume, even with maximal concentration, solute excretion would be inadequate. *300 ml* - **300 ml** would be insufficient to excrete the 600 mOsm daily solute load even at maximal concentration (300 × 1400 = 420 mOsm only). - This volume would lead to accumulation of solutes and **azotemia** (elevated BUN and creatinine). *500 ml* - While **500 ml** would certainly be adequate for solute excretion, it exceeds the calculated minimum of ~428 ml. - The question asks for the *minimum* volume, making **400 ml** the more precise answer according to standard textbooks. *750 ml* - **750 ml** is well above the minimum required for neutral solute balance. - This volume represents normal physiological urine output but is not the minimum threshold for maintaining solute balance.
Question 332: Fever increases water loss by how much for each degree Celsius increase in body temperature?
- A. 100 ml/day
- B. 200 ml/day (Correct Answer)
- C. 400 ml/day
- D. 800 ml/day
Explanation: ***200 ml/day*** - For every 1-degree Celsius (or 1.8-degree Fahrenheit) increase in body temperature, there is an approximate **200 ml increase in insensible water loss** per day due to increased metabolism and sweating. - This value highlights the importance of **adequate fluid replacement** in febrile patients to prevent dehydration. *100 ml/day* - This value is **insufficient** to account for the increased insensible fluid losses associated with fever. - Using this estimate could lead to **underestimation of fluid requirements** and potential dehydration in febrile patients. *400 ml/day* - This value is **higher than the typical estimated increase** in water loss per degree Celsius of fever. - While extreme fever might cause higher losses, 200 ml/day is the standard clinical approximation for a 1-degree rise. *800 ml/day* - This value represents a **significant overestimation** of the fluid loss per degree Celsius increase in fever. - Such a high estimate would generally be seen only in very severe conditions or with much larger temperature increases.
Question 333: Which equation is used to calculate physiological dead space?
- A. Dalton's law
- B. Bohr equation (Correct Answer)
- C. Charles's law
- D. Boyle's law
Explanation: ***Bohr equation*** - The Bohr equation is used to calculate **physiological dead space**, which is the sum of anatomical dead space and alveolar dead space. - It relates the partial pressure of carbon dioxide in arterial blood to the partial pressure of carbon dioxide in expired air, along with **tidal volume** and expired volume. *Dalton's law* - Dalton's law states that the **total pressure** exerted by a mixture of non-reactive gases is equal to the **sum of the partial pressures** of individual gases. - It is used to calculate partial pressures of gases in a mixture, not dead space. *Charles's law* - Charles's law describes the relationship between the **volume and temperature** of a gas at constant pressure. - It states that the volume of a given mass of gas is directly proportional to its absolute temperature. *Boyle's law* - Boyle's law describes the inverse relationship between the **pressure and volume** of a gas at constant temperature. - It is fundamental to understanding mechanics of breathing, but not dead space calculation.
Question 334: Which of the following best describes hypoxic pulmonary vasoconstriction?
- A. Reversible pulmonary vasoconstriction due to hypoxia (Correct Answer)
- B. Irreversible pulmonary vasoconstriction due to hypoxia
- C. Redirects blood to well-ventilated areas
- D. Occurs immediately in response to hypoxia
Explanation: ***Reversible pulmonary vasoconstriction due to hypoxia*** - Hypoxic pulmonary vasoconstriction (HPV) is a physiological response in which **pulmonary arterioles constrict** in areas of the lung with low oxygen levels. - This mechanism is **reversible**, meaning that when oxygen levels improve, the constricted vessels will dilate again. - The underlying mechanism involves hypoxia-induced inhibition of voltage-gated K⁺ channels in pulmonary arterial smooth muscle, leading to membrane depolarization, Ca²⁺ influx, and smooth muscle contraction. *Irreversible pulmonary vasoconstriction due to hypoxia* - This statement is incorrect because HPV is fundamentally a **reversible process**, designed to adapt to transient changes in alveolar oxygen. - Irreversible vasoconstriction typically occurs in chronic hypoxia, leading to **pulmonary hypertension** and structural remodeling (vascular remodeling with medial hypertrophy), which is a pathological state rather than the acute physiological response of HPV. *Redirects blood to well-ventilated areas* - While this is the **physiological purpose** and overall effect of hypoxic pulmonary vasoconstriction, it describes the functional outcome rather than what HPV fundamentally is. - The redirection of blood flow is the **consequence** of vasoconstriction in hypoxic areas, which optimizes ventilation-perfusion matching. *Occurs immediately in response to hypoxia* - While HPV does begin rapidly in response to hypoxia (within seconds to minutes), this describes the **timing characteristic** rather than what HPV is. - This statement is also somewhat imprecise, as the response involves intracellular signaling pathways that take time to manifest fully, though the onset is relatively quick compared to other vascular responses.
Question 335: Which of the following stimuli is primarily responsible for triggering the Bezold-Jarisch reflex?
- A. Parasympathetic withdrawal
- B. Decreased venous return
- C. Increased sympathetic stimulation
- D. Activation of cardiac C-fiber afferents (Correct Answer)
Explanation: ***Activation of cardiac C-fiber afferents*** - The **Bezold-Jarisch reflex** is primarily triggered by stimulation of **cardiac mechanoreceptors and chemoreceptors** located in the ventricles, particularly the inferoposterior wall of the left ventricle. - These receptors have **unmyelinated vagal C-fiber afferents** that transmit signals to the medullary cardiovascular centers. - Activation of these afferents leads to the characteristic triad: **bradycardia, hypotension, and vasodilation** via increased parasympathetic activity and withdrawal of sympathetic tone. - Common triggers include vigorous ventricular contraction with decreased filling, certain drugs (veratridine), myocardial ischemia (especially inferior wall MI), and reperfusion. *Decreased venous return* - While **decreased venous return** creates the hemodynamic context (ventricular underfilling) that can lead to vigorous contraction of a relatively empty ventricle, it is not itself the *trigger* of the reflex. - The actual trigger is the activation of the ventricular receptors sensing this abnormal contraction pattern, which then signal via C-fiber afferents. - Decreased venous return alone, without receptor activation, would not produce the reflex. *Parasympathetic withdrawal* - **Parasympathetic withdrawal** would cause tachycardia and is opposite to the Bezold-Jarisch reflex, which involves **increased parasympathetic activity**. - This is a compensatory response seen in other reflexes like the baroreceptor reflex during hypotension. *Increased sympathetic stimulation* - **Increased sympathetic stimulation** produces tachycardia, increased contractility, and vasoconstriction—effects opposite to the Bezold-Jarisch reflex. - The reflex actually causes **sympathetic withdrawal** along with parasympathetic activation.
Question 336: What physiological mechanism leads to an increase in cardiac output?
- A. Inhalation
- B. Increased myocardial contractility (Correct Answer)
- C. Increased parasympathetic activity
- D. Transitioning from a supine to a standing position
Explanation: ***Increased myocardial contractility*** - **Increased myocardial contractility** directly leads to a greater **stroke volume** (the amount of blood pumped with each beat), thus increasing cardiac output (Cardiac Output = Stroke Volume × Heart Rate). - This can be stimulated by factors such as **sympathetic nervous system activation** or positive inotropic agents. *Inhalation* - While inhalation can temporarily affect venous return and intrathoracic pressure, it does not directly or consistently lead to a sustained increase in **cardiac output**. - Its primary effect is on **respiration**, not cardiac performance. *Increased parasympathetic activity* - Increased parasympathetic activity, primarily via the **vagus nerve**, acts to **decrease heart rate** and myocardial contractility. - This effect would typically **reduce cardiac output**, not increase it. *Transitioning from a supine to a standing position* - Transitioning to a standing position usually causes a **temporary decrease in venous return** and a brief drop in cardiac output as blood pools in the lower extremities. - The body then compensates by increasing heart rate and peripheral vascular resistance to maintain blood pressure, but the initial effect on cardiac output is generally a transient decrease.