NEET-PG 2024 — Physiology
9 Previous Year Questions with Answers & Explanations
After ovulation, the oocyte is:
Which of the following prevents polyspermy?
Match the following receptors with their correct functions: Receptors: 1. Ruffini corpuscle 2. Merkel cells 3. Pacinian corpuscle 4. Meissner's corpuscle Functions: A. Vibration B. Sustained pressure C. Stretching D. Fine touch Select the option that correctly matches each receptor (1-4) with its function (A-D).
What are the effects of a lesion in Brodmann area 22?
Sour taste is mediated by which of the following receptors?
Select the correct option regarding the function of receptors:
A patient is experiencing phantom limb pain after the amputation of the right limb. What is observed on a PET scan in a patient with phantom limb pain?
Sequence the events in neuromuscular action potential conduction: 1. Sodium channels open in the end plate 2. Calcium enters at the nerve terminal 3. Release of acetylcholine
A woman suffered a sunburn while enjoying a vacation on the beach. Now, while taking a shower, the lukewarm water (40° C) touching her back caused her to feel pain. What types of receptors were activated by the lukewarm water, and why did she experience pain?
NEET-PG 2024 - Physiology NEET-PG Practice Questions and MCQs
Question 1: After ovulation, the oocyte is:
- A. Primary oocyte arrested in prophase II
- B. Secondary oocyte arrested in prophase II
- C. Secondary oocyte arrested in metaphase II (Correct Answer)
- D. Primary oocyte arrested in prophase I
Explanation: ***Secondary oocyte arrested in metaphase II*** - After ovulation, the **oocyte** has completed **meiosis I** and extruded the **first polar body**, becoming a secondary oocyte. - It then arrests in **metaphase II** and will only complete meiosis II upon fertilization by a sperm. *Primary oocyte arrested in prophase II* - A **primary oocyte** is the stage before meiosis I is completed, and it is arrested in **prophase I** at birth, not prophase II. - Oocytes do not arrest in **prophase II** during normal meiotic development. *Secondary oocyte arrested in prophase II* - While it is a **secondary oocyte** that is ovulated, it is arrested in **metaphase II**, not prophase II. - **Prophase II** is a transient stage that occurs just before metaphase II, and arrest at this stage is not typical for the ovulated oocyte. *Primary oocyte arrested in prophase I* - This describes the state of the oocyte from **fetal development** until just before ovulation. - A **primary oocyte** completes meiosis I only in response to the **LH surge** before ovulation.
Question 2: Which of the following prevents polyspermy?
- A. Acrosome reaction
- B. Cortical reaction (Correct Answer)
- C. Zona reaction
- D. Capacitation
Explanation: ***Cortical reaction*** - The **cortical reaction** is the primary mechanism that prevents **polyspermy** following sperm-oocyte fusion. - Upon fusion, **cortical granules** in the oocyte cytoplasm release their contents (including proteases and peroxidases) into the **perivitelline space**. - These enzymes modify the **zona pellucida** proteins, making it impermeable to additional sperm - this modification is called the **zona reaction**. - The cortical reaction represents both the **fast block** (depolarization of oocyte membrane) and **slow block** (zona pellucida hardening) to polyspermy. *Zona reaction* - The **zona reaction** is the biochemical and structural change that occurs in the zona pellucida as a **result** of the cortical reaction. - It involves hardening and altered permeability of the zona pellucida, making it resistant to sperm penetration. - While this is the ultimate barrier to polyspermy, it is a **consequence** rather than the active mechanism - the cortical reaction is the causative event. *Acrosome reaction* - The **acrosome reaction** is essential for fertilization, allowing sperm to penetrate the zona pellucida by releasing hydrolytic enzymes. - It **facilitates** sperm entry rather than preventing additional sperm from binding. - This reaction must occur for the first sperm to fertilize the egg but plays no role in preventing polyspermy. *Capacitation* - **Capacitation** is the physiological maturation of sperm in the female reproductive tract. - It enables sperm to undergo the acrosome reaction and achieve fertilization competence. - It is a preparatory process and has no role in preventing polyspermy.
Question 3: Match the following receptors with their correct functions: Receptors: 1. Ruffini corpuscle 2. Merkel cells 3. Pacinian corpuscle 4. Meissner's corpuscle Functions: A. Vibration B. Sustained pressure C. Stretching D. Fine touch Select the option that correctly matches each receptor (1-4) with its function (A-D).
- A. 1C 2D 3B 4A
- B. 1C 2B 3A 4D (Correct Answer)
- C. 1D 2C 3B 4A
- D. 1B 2A 3D 4C
Explanation: ***1C 2B 3A 4D*** - **Ruffini corpuscles** (1) detect **stretching** (C) of the skin. They are **slow-adapting Type II mechanoreceptors** located deep in the dermis, responding to sustained skin stretch and contributing to proprioception. - **Merkel cells** (2) detect **sustained pressure** (B) and fine texture discrimination. They are **slow-adapting Type I mechanoreceptors** with the highest spatial resolution, providing detailed information about touch. - **Pacinian corpuscles** (3) detect **vibration** (A), particularly high-frequency vibrations (200-300 Hz). They are **rapidly adapting receptors** with an onion-like lamellated structure located deep in the dermis and subcutaneous tissue. - **Meissner's corpuscles** (4) detect **fine touch** (D) and light pressure. They are **rapidly adapting receptors** located in dermal papillae of glabrous (hairless) skin, particularly abundant in fingertips and lips. *1C 2D 3B 4A* - Incorrectly assigns Merkel cells to fine touch (should be sustained pressure) and Pacinian corpuscles to sustained pressure (should be vibration). - Meissner's corpuscles are mismatched with vibration instead of fine touch. *1D 2C 3B 4A* - Incorrectly assigns Ruffini corpuscles to fine touch (should be stretching) and Merkel cells to stretching (should be sustained pressure). - Pacinian corpuscles are mismatched with sustained pressure (should be vibration). - Meissner's corpuscles are mismatched with vibration (should be fine touch). *1B 2A 3D 4C* - Completely incorrect matching: Ruffini to sustained pressure, Merkel to vibration, Pacinian to fine touch, and Meissner's to stretching. - Demonstrates fundamental misunderstanding of mechanoreceptor functions.
Question 4: What are the effects of a lesion in Brodmann area 22?
- A. Expressive aphasia
- B. Receptive aphasia (Correct Answer)
- C. Poor repetition of language
- D. Poor naming
Explanation: ***Receptive aphasia*** - A lesion in **Brodmann area 22**, specifically in **Wernicke's area**, leads to **receptive aphasia** (Wernicke's aphasia). - This condition is characterized by **impaired comprehension** of spoken and written language, **fluent but paraphasic speech**, and **poor repetition**. - This is the most comprehensive answer as it describes the entire clinical syndrome. *Expressive aphasia* - **Brodmann areas 44 and 45** (Broca's area) in the frontal lobe are associated with expressive aphasia (Broca's aphasia). - Patients have good comprehension but struggle to produce fluent speech, with effortful, telegraphic output. *Poor repetition of language* - While poor repetition is indeed a feature of Wernicke's aphasia, this option describes only one component of the syndrome rather than the complete clinical picture. - **Conduction aphasia** (from arcuate fasciculus lesions) is characterized by poor repetition with **relatively preserved** comprehension and fluent speech, distinguishing it from Wernicke's aphasia. - "Receptive aphasia" is the more complete answer. *Poor naming* - Difficulty with naming, or **anomia**, is a common feature across various types of aphasia, including both receptive and expressive aphasia. - It reflects disruption in language networks involving the **temporal and parietal lobes** but is not specific to Brodmann area 22 lesions.
Question 5: Sour taste is mediated by which of the following receptors?
- A. T1R1
- B. T1R2
- C. T1R3
- D. OTOP1 (Correct Answer)
Explanation: ***OTOP1*** - The **OTOP1** receptor, an **otopetrin protein**, is responsible for detecting the **sour taste** sensation by mediating proton influx. - It functions as a **proton channel**, allowing hydrogen ions (H+) from acidic substances to enter taste receptor cells. *T1R1* - **T1R1** is a component of the **umami (savory) taste receptor**, forming a heterodimer with T1R3 to detect glutamate. - It does not directly detect sourness but is involved in the perception of amino acids. *T1R2* - **T1R2** is a component of the **sweet taste receptor**, forming a heterodimer with T1R3 to detect sugars. - This receptor is not involved in the transduction of sour taste. *T1R3* - **T1R3** is a common subunit that combines with **T1R1** for umami taste and with **T1R2** for sweet taste. - While essential for sweet and umami, it does not directly mediate the perception of sourness.
Question 6: Select the correct option regarding the function of receptors:
- A. Merkel cells - slow vibration
- B. Meissner's corpuscle - stretch
- C. Pacinian corpuscle - fast vibration (Correct Answer)
- D. Ruffini corpuscle - light touch
Explanation: ***Pacinian corpuscle - fast vibration*** - **Pacinian corpuscles** are rapidly adapting mechanoreceptors that are highly sensitive to **vibrations** and **deep pressure**. - Their layered structure allows them to detect even slight deformations and transmit information about **rapid changes** in mechanical stimuli. *Merkel cells - slow vibration* - **Merkel cells** are slow-adapting mechanoreceptors primarily responsible for sensing **light touch**, **texture**, and sustained pressure. - They are not associated with the detection of vibrations, whether slow or fast. *Meissner's corpuscle - stretch* - **Meissner's corpuscles** are rapidly adapting mechanoreceptors that detect **light touch**, **low-frequency vibration**, and discriminatory touch. - **Stretch sensation** is primarily mediated by Ruffini corpuscles and muscle spindle organs. *Ruffini corpuscle - light touch* - **Ruffini corpuscles** are slow-adapting mechanoreceptors that respond to **sustained pressure**, skin **stretch**, and joint position. - **Light touch** is primarily detected by Merkel cells and Meissner's corpuscles.
Question 7: A patient is experiencing phantom limb pain after the amputation of the right limb. What is observed on a PET scan in a patient with phantom limb pain?
- A. Neighboring cortical areas extending into the hand representation area (Correct Answer)
- B. Expansion of right somatosensory cortex
- C. Expansion of hand representation in the left somatosensory cortex into neighboring areas
- D. General expansion of left somatosensory cortex
Explanation: ***Neighboring cortical areas extending into the hand representation area*** - Phantom limb pain is associated with **cortical remapping** in the somatosensory cortex, where neighboring body part representations (face, upper arm) **invade the deafferented cortex zone** previously occupied by the amputated limb. - This reorganization is observed on PET scans as **increased metabolic activity in areas adjacent to the hand representation**, extending into the hand area that lost its sensory input. - This cortical reorganization correlates with the **intensity of phantom limb pain** and is a well-established finding in neuroimaging studies. *General expansion of left somatosensory cortex* - While the left somatosensory cortex (contralateral to the right amputated limb) does undergo changes, the key finding is **not a general expansion** of the entire cortex. - The characteristic observation is **specific reorganization** where neighboring representations invade the deafferented zone, rather than a diffuse enlargement. *Expansion of right somatosensory cortex* - Since the **right limb was amputated**, the **left somatosensory cortex** (which processes right-sided body sensations) is where reorganization occurs. - The right somatosensory cortex processes the left (intact) side and would not show the characteristic remapping associated with phantom limb pain. *Expansion of hand representation in the left somatosensory cortex into neighboring areas* - This describes the **opposite direction** of cortical remapping. - In phantom limb pain, **neighboring areas (face, upper arm) expand INTO the hand area**, not the hand area expanding outward. - The hand representation has lost its peripheral input due to amputation and is invaded by adjacent cortical representations.
Question 8: Sequence the events in neuromuscular action potential conduction: 1. Sodium channels open in the end plate 2. Calcium enters at the nerve terminal 3. Release of acetylcholine
- A. $1 \rightarrow 2 \rightarrow 3$
- B. $1 \rightarrow 3 \rightarrow 2$
- C. $3 \rightarrow 2 \rightarrow 1$
- D. $2 \rightarrow 3 \rightarrow 1$ (Correct Answer)
Explanation: ***Correct: $2 \rightarrow 3 \rightarrow 1$*** - **Calcium entry at the nerve terminal** is the initial trigger - when an action potential reaches the presynaptic nerve terminal, voltage-gated calcium channels open, allowing Ca²⁺ influx - **Acetylcholine release** follows - the increased intracellular calcium causes synaptic vesicles containing acetylcholine to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft - **Sodium channels open in the end plate** last - acetylcholine binds to nicotinic receptors on the motor end plate, opening ligand-gated sodium channels, which depolarizes the muscle membrane and triggers muscle contraction *Incorrect: $1 \rightarrow 2 \rightarrow 3$* - Places sodium channel opening first, which is physiologically impossible - Sodium channels at the motor end plate only open in response to acetylcholine binding - Cannot occur before acetylcholine is released from the nerve terminal *Incorrect: $1 \rightarrow 3 \rightarrow 2$* - Incorrectly sequences sodium channel opening before calcium entry - Violates the fundamental principle that calcium influx is required for neurotransmitter release - Acetylcholine cannot be released without prior calcium entry *Incorrect: $3 \rightarrow 2 \rightarrow 1$* - Places acetylcholine release before calcium entry, which is impossible - Calcium-triggered exocytosis is an absolute requirement for neurotransmitter release - Without calcium influx, vesicles cannot fuse with the presynaptic membrane
Question 9: A woman suffered a sunburn while enjoying a vacation on the beach. Now, while taking a shower, the lukewarm water (40° C) touching her back caused her to feel pain. What types of receptors were activated by the lukewarm water, and why did she experience pain?
- A. Thermal nociceptors & nociceptive pain
- B. Thermal nociceptors & allodynia (Correct Answer)
- C. Innocuous thermal receptors and hyperalgesia
- D. Innocuous thermal receptors and allodynia
Explanation: ***Thermal nociceptors & allodynia*** - Sunburn causes tissue damage, leading to the sensitization of **thermal nociceptors** (e.g., TRPV1 channels), making them responsive to normally innocuous thermal stimuli. - **Allodynia** is the perception of pain from a stimulus that does not ordinarily cause pain, such as lukewarm water after a sunburn, due to increased sensitivity of the pain pathways. *Thermal nociceptors & nociceptive pain* - While thermal nociceptors are involved, **nociceptive pain** typically refers to pain caused by direct tissue damage from a noxious (harmful) stimulus. Here, the lukewarm water itself is not noxious. - The pain experienced from the lukewarm water is not due to a *new* noxious stimulus but rather an exaggerated response to a *non-noxious* one. *Innocuous thermal receptors and hyperalgesia* - **Innocuous thermal receptors** (e.g., TRPM8 for cold, TRPV3/TRPV4 for warmth) normally detect non-painful temperature changes, not pain from sunburn. - **Hyperalgesia** is an increased response to a stimulus that *is* normally painful, but applied at a lower intensity. The lukewarm water is not normally painful. *Innocuous thermal receptors and allodynia* - As mentioned, **innocuous thermal receptors** are not primarily responsible for pain transmission, even in a sensitized state, as they are not nociceptors. - While **allodynia** is an accurate description of the pain type, the primary receptors activated for the pain sensation are sensitized nociceptors, not innocuous thermal receptors.