NEET-PG 2020 — Physiology
20 Previous Year Questions with Answers & Explanations
Which of the following techniques is used to study current flow across a single ion channel?
A 35-year-old female experiences a tingling sensation in her arm after watching TV for long hours with her hands under her head. Which type of nerve fibers is most likely to be affected due to this position?
Which of the following is an estrogen-dependent pubertal change?
Which of the following is referred to as the "Window of the limbic system"?
Among the following, prolactin secretion is maximum:
When the value of V/Q is infinity, it means?
In multiple sclerosis, slow conduction of motor and sensory pathways is due to?
What is the main feature of chemotaxis as observed in white blood cells?
What is the reflex in which there is inhibition of gastric emptying when there is acid and hypertonic solution in the duodenum?
A 33-year-old man presents with a 5-week history of calf pain, swelling, and low-grade fever. Serum levels of creatinine kinase are elevated. A muscle biopsy reveals numerous eosinophils and he also has peripheral blood eosinophilia. Which of the following interleukins is primarily responsible for the increase in eosinophils in this patient?
NEET-PG 2020 - Physiology NEET-PG Practice Questions and MCQs
Question 1: Which of the following techniques is used to study current flow across a single ion channel?
- A. Galvanometry
- B. Voltage clamp
- C. Patch clamp (Correct Answer)
- D. Iontophoresis
Explanation: ***Patch clamp*** - The **patch clamp** technique allows for the direct measurement of **ion current flow** through a single ion channel or a small group of channels. - It involves isolating a small patch of cell membrane with a micropipette to record the electrical activity. *Voltage clamp* - The **voltage clamp** technique is used to maintain a constant membrane potential while measuring the **total ionic current** across the entire cell membrane. - It is not typically used for studying current across a *single* ion channel, but rather for analyzing whole-cell currents. *Iontophoresis* - **Iontophoresis** is a method used to introduce ionized substances, such as drugs or neurotransmitters, into tissues using a small electric current. - It is a technique for drug delivery or localized stimulation, not for directly measuring ion channel current. *Galvanometry* - **Galvanometry** is a general term for the measurement of small electric currents using a galvanometer. - While ion channel activity involves electric currents, galvanometry is not a specific technique for isolating and studying single ion channels.
Question 2: A 35-year-old female experiences a tingling sensation in her arm after watching TV for long hours with her hands under her head. Which type of nerve fibers is most likely to be affected due to this position?
- A. B - fibers (autonomic)
- B. C - fibers (pain and temperature)
- C. Sympathetic nerve fibers
- D. A-beta (Aβ) sensory nerve fibers (Correct Answer)
Explanation: ***A-beta (Aβ) sensory nerve fibers*** - The tingling sensation (paresthesia) described is a classic symptom of **A-beta fiber compression**. - **A-beta fibers** are large, myelinated sensory fibers that transmit light touch, pressure, vibration, and proprioception. - These fibers are **most susceptible to mechanical compression** due to their position and structure. - Positioning the hands under the head for extended periods compresses superficial nerves, causing temporary A-beta fiber dysfunction, which manifests as the characteristic "pins and needles" sensation. *B-fibers (autonomic)* - **B-fibers** are preganglionic autonomic fibers that mediate visceral functions, such as organ control and glandular secretions. - Compression of these fibers would lead to symptoms related to autonomic dysfunction (e.g., changes in sweating, blood pressure), not a tingling sensation in the arm. *C-fibers (pain and temperature)* - **C-fibers** are unmyelinated fibers that transmit slow, dull, aching pain and contribute to temperature sensation. - They are **less susceptible to compression** than larger myelinated fibers. - The primary sensation described (tingling/paresthesia) is characteristic of large myelinated fiber (A-beta) dysfunction, not C-fiber involvement. *Sympathetic nerve fibers* - **Sympathetic nerve fibers** regulate involuntary functions like heart rate, blood pressure, and sweating. - Their compression would cause symptoms such as changes in skin temperature, altered sweating, or blood vessel constriction (Horner's syndrome if severe), not a tingling sensation.
Question 3: Which of the following is an estrogen-dependent pubertal change?
- A. Vaginal Cornification (Correct Answer)
- B. Cervical mucus
- C. Menstruation
- D. Hair growth
Explanation: ***Vaginal Cornification*** - Vaginal cornification refers to the **maturation and stratification of the vaginal epithelium** under the direct influence of **estrogen**. - Estrogen stimulates the **proliferation of vaginal epithelial cells**, leading to thickening of the vaginal mucosa and increased glycogen content in the superficial cells. - This is a **purely estrogen-dependent change** and is one of the key markers of estrogenic activity during puberty. - The vaginal maturation index increases with estrogen exposure, making this a reliable indicator of estrogenic stimulation. *Menstruation* - While estrogen is important for endometrial proliferation, menstruation requires the **coordinated action of both estrogen AND progesterone**. - Estrogen builds the endometrium during the proliferative phase, but **progesterone** is essential for the secretory transformation. - Menstruation occurs due to the **withdrawal of both hormones**, not estrogen alone, making it dependent on both hormones rather than purely estrogen-dependent. *Cervical mucus* - Cervical mucus characteristics are influenced by **both estrogen and progesterone** throughout the menstrual cycle. - Estrogen makes mucus thin, watery, and stretchy (spinnbarkeit), while progesterone makes it thick and viscous. - This **dual hormonal regulation** means it is not purely estrogen-dependent. *Hair growth* - Pubertal hair growth, including **pubic and axillary hair**, is primarily stimulated by **androgens** (testosterone, DHEA-S from the adrenal glands). - This process is called **adrenarche** and is androgen-dependent, not estrogen-dependent.
Question 4: Which of the following is referred to as the "Window of the limbic system"?
- A. Hypothalamus
- B. Hippocampus
- C. Amygdala
- D. Thalamus (Correct Answer)
Explanation: ***Thalamus*** - The thalamus is often referred to as the **"relay station"** of the brain, processing and relaying most **sensory information** (except smell) to the cerebral cortex. - Due to its extensive connections with various limbic structures and its role in integrating and filtering emotional and motivational information before it reaches conscious awareness, it's considered the **"window of the limbic system"**. *Hypothalamus* - The hypothalamus primarily controls **autonomic functions** and maintains **homeostasis**, such as regulating temperature, hunger, thirst, and sleep cycles. - While it has strong connections with the limbic system, its main role is executive autonomic control rather than sensory integration. *Amygdala* - The amygdala is critically involved in processing **emotions**, particularly **fear** and **aggression**, and plays a key role in emotional memory. - It's a central component *within* the limbic system, but it doesn't serve as a general window or relay for the entire system's input. *Hippocampus* - The hippocampus is primarily responsible for **memory formation** (especially new episodic memories) and spatial navigation. - It is an important limbic structure, but its function is more specific to memory rather than being a gateway for broader limbic system activity.
Question 5: Among the following, prolactin secretion is maximum:
- A. During REM sleep
- B. After 2 hours of running
- C. 24 hrs after delivery (Correct Answer)
- D. 24 hours after ovulation
Explanation: ***Correct: 24 hrs after delivery*** - Prolactin levels are highest in the initial **24 hours postpartum**, especially during and after **breastfeeding sessions**, which act as a powerful stimulus for prolactin release. - This peak prolactin level is crucial for initiating and maintaining **lactation** following childbirth. - The postpartum prolactin surge represents the **maximum physiological level** of this hormone under normal circumstances. *Incorrect: During REM sleep* - While prolactin secretion does exhibit a **circadian rhythm** with nocturnal peaks, the highest levels do not specifically occur during **REM sleep**; rather, they are elevated throughout the sleep cycle. - Though prolactin does rise during sleep, the magnitudes are **not comparable** to the surges seen postpartum or after intense suckling. *Incorrect: After 2 hours of running* - Exercise, particularly prolonged and intense physical activity, can cause a transient increase in prolactin levels due to **stress response** and hormonal changes. - However, this exercise-induced increase is generally **modest** compared to the physiological surge observed after delivery. *Incorrect: 24 hours after ovulation* - Prolactin levels show a slight increase during the **luteal phase** of the menstrual cycle, which follows ovulation, primarily due to rising progesterone levels. - This elevation is significantly **lower** than the dramatic rise seen immediately postpartum needed for milk production.
Question 6: When the value of V/Q is infinity, it means?
- A. Dead space (Correct Answer)
- B. The PO2 of alveolar air is 159mmHg and PCO2 is 0mmHg
- C. Partial pressure of O2 and CO2 are equal
- D. No O2 goes from alveoli to blood and no CO2 goes from blood to alveoli
Explanation: ***Dead space*** - A V/Q ratio of infinity indicates that there is **ventilation (V) without perfusion (Q)**. This represents alveolar dead space, where air enters the alveoli but no blood flow is available for gas exchange. - In this scenario, the ventilating air does not participate in gas exchange, essentially behaving like dead space in the respiratory system. *The PO2 of alveolar air is 159mmHg and PCO2 is 0mmHg* - When V/Q approaches infinity (dead space), alveolar gas composition approaches that of **inspired air**, with PO2 around 150-159 mmHg and PCO2 near 0 mmHg. - However, this describes the gas composition consequence rather than the fundamental physiological concept, which is "dead space." - Normal alveolar air (with normal V/Q) has PO2 around 100-104 mmHg and PCO2 around 40 mmHg. *Partial pressure of O2 and CO2 are equal* - The partial pressures of O2 and CO2 are **never normally equal** in the alveoli or blood; they always maintain a concentration gradient for efficient gas exchange. - When V/Q is infinite, alveolar gas tensions approach those of inspired air (high O2, very low CO2), not equal partial pressures. *No O2 goes from alveoli to blood and no CO2 goes from blood to alveoli* - While it is true that **no gas exchange occurs** (no O2 goes from alveoli to blood, and no CO2 goes from blood to alveoli) due to the absence of blood flow (Q=0), the primary physiological term for this condition is "dead space." - This option describes the consequence of an infinite V/Q ratio rather than the fundamental concept it represents.
Question 7: In multiple sclerosis, slow conduction of motor and sensory pathways is due to?
- A. Loss of myelin sheath (Correct Answer)
- B. Dysfunction of sodium channels
- C. Dysfunction of calcium channels
- D. Defect in the nodes of Ranvier
Explanation: ***Loss of myelin sheath*** - Multiple sclerosis (MS) is characterized by **demyelination**, which is the destruction of the **myelin sheath** surrounding nerve fibers in the central nervous system. - Myelin acts as an electrical insulator, facilitating rapid, **saltatory conduction** of nerve impulses; its loss directly leads to **slowed or blocked signal transmission**. *Dysfunction of sodium channels* - While sodium channel dysfunction can occur secondary to demyelination, it is not the primary cause of slow conduction in MS but rather a downstream effect or an adaptive change. - The initial and fundamental problem leading to slowed conduction in MS is the **loss of the myelin sheath**, which renders the exposed axon less efficient at propagating action potentials. *Dysfunction of calcium channels* - Dysfunction of calcium channels is not the primary pathological mechanism responsible for the slowed conduction in MS. - While calcium dysregulation can play a role in **axonal damage** and neurodegeneration in MS, it is not the direct cause of the characteristic **slowed nerve impulse propagation**. *Defect in the nodes of Ranvier* - The **nodes of Ranvier** are uncovered gaps in the myelin sheath that are crucial for **saltatory conduction**. While their integrity is important, a primary "defect" in the nodes themselves is not the initial cause of slowed conduction in MS. - Slowed conduction occurs because the **myelin surrounding the axons** is lost, leading to longer distances for the action potential to travel and exposing segments of the axon unprepared for continuous conduction.
Question 8: What is the main feature of chemotaxis as observed in white blood cells?
- A. Increased random movement of neutrophils
- B. Increased adhesiveness to intima
- C. Increased phagocytosis
- D. Unidirectional locomotion of neutrophils (Correct Answer)
Explanation: ***Unidirectional locomotion of neutrophils*** - **Chemotaxis** refers to the **directional movement** of cells, such as neutrophils, towards a chemical attractant. - This process is crucial for recruiting immune cells to sites of infection or inflammation. *Increased random movement of neutrophils* - While neutrophils do exhibit random movement, **chemotaxis** specifically describes **directed movement** along a chemical gradient, not merely an increase in random motion. - **Random movement** without a specific direction does not effectively guide immune cells to a specific target. *Increased adhesiveness to intima* - **Adhesion to the intima** (endothelial cells) is an initial step in the process of leukocyte extravasation, allowing cells to roll and stick to vessel walls. - However, it is primarily mediated by adhesion molecules and is distinct from the **directional migration** defined by chemotaxis. *Increased phagocytosis* - **Phagocytosis** is the process by which cells engulf pathogens or cellular debris. - While essential for immune function, it is a separate function that occurs **after** the cell has migrated to its target via chemotaxis.
Question 9: What is the reflex in which there is inhibition of gastric emptying when there is acid and hypertonic solution in the duodenum?
- A. Enterogastric (Correct Answer)
- B. Gastroileal
- C. Gastrocolic
- D. Myenteric
Explanation: ***Enterogastric*** - The **enterogastric reflex** is initiated when the duodenum detects the presence of acid and hypertonic solutions, signifying that the chyme is not yet ready for further digestion and absorption. - This reflex inhibits **gastric emptying** to allow more time for the stomach to process its contents and for the duodenum to neutralize the acid and dilute the hypertonic solution. *Gastroileal* - The **gastroileal reflex** increases motility in the ileum when the stomach is distended, facilitating the movement of chyme into the large intestine. - This reflex does not primarily involve the inhibition of gastric emptying due to duodenal contents. *Gastrocolic* - The **gastrocolic reflex** increases the motility of the colon in response to the stretching of the stomach by food. - Its main function is to prepare the large intestine for upcoming chyme and does not directly inhibit gastric emptying. *Myenteric* - The **myenteric plexus** (Auerbach's plexus) is a network of neurons located between the longitudinal and circular layers of the muscularis propria throughout the gastrointestinal tract. - While it plays a crucial role in controlling gut motility and is involved in numerous reflexes, it refers to a neural plexus rather than a specific reflex mechanism for inhibiting gastric emptying due to duodenal stimuli.
Question 10: A 33-year-old man presents with a 5-week history of calf pain, swelling, and low-grade fever. Serum levels of creatinine kinase are elevated. A muscle biopsy reveals numerous eosinophils and he also has peripheral blood eosinophilia. Which of the following interleukins is primarily responsible for the increase in eosinophils in this patient?
- A. IL-4
- B. IL-5 (Correct Answer)
- C. IL-6
- D. IL-2
Explanation: ***IL-5*** - **Interleukin-5 (IL-5)** is the **most potent and direct cytokine** responsible for the **differentiation, maturation, activation, and survival of eosinophils**. - IL-5 is produced primarily by **Th2 cells**, mast cells, and eosinophils themselves, and acts directly on eosinophil progenitors in the bone marrow. - In this patient with eosinophilic myositis (likely parasitic infection such as trichinosis), **IL-5 is the primary mediator** of the peripheral blood eosinophilia and tissue eosinophil infiltration. - **Clinical correlation:** Anti-IL-5 therapies (mepolizumab, reslizumab) are used to treat hypereosinophilic conditions, confirming IL-5's central role. *IL-4* - **Interleukin-4 (IL-4)** is produced by Th2 cells and mast cells and promotes the **differentiation of naive T cells into Th2 cells**. - While IL-4 initiates the Th2 immune response that eventually leads to IL-5 production, it does **not directly stimulate eosinophil production or recruitment**. - IL-4 is more involved in IgE class switching and allergic inflammation rather than direct eosinophil regulation. *IL-6* - **Interleukin-6 (IL-6)** is a pleiotropic cytokine involved in the **acute phase response**, inflammation, and hematopoiesis. - While it has broad effects on immune cells, it is **not primarily responsible** for eosinophil production or recruitment. - Elevated in many inflammatory conditions but not specific for eosinophilia. *IL-2* - **Interleukin-2 (IL-2)** is primarily involved in the **proliferation and differentiation of T lymphocytes** and activation of natural killer (NK) cells. - It plays no significant direct role in eosinophil production or recruitment. - More important for T cell-mediated immunity rather than eosinophilic responses.