Pain Physiology and Pathways — MCQs
A 10-year-old boy cuts his finger with a pocketknife and immediately applies pressure to the damaged area with his other hand to partially alleviate the pain. Inhibition of pain signals by tactile stimulation of the skin is mediated by which type of afferent neurons from mechanoreceptors?
Which substance enhances the sensitivity of pain receptors but does not directly excite them?
Stimulation of which of the following areas of brain is experimentally used to control intractable pain -
Pain and temperature are carried by:
Activation of which of the following fibers results in first pain, which helps to localize the site and intensity of the noxious stimulus?
A female developed pain and a sensation like insects crawling on her legs at night which is relieved by shaking her legs. Which of the following is the drug of choice for this condition?
Primary Dysmenorrhoea can be treated by which of the following? 1. Antiprostaglandin 2. Cyclic combined estrogen and progesterone preparations 3. Pre-sacral neurectomy 4. Uterine curettage
Which of the following anaesthetic agent lacks analgesic effect? A) N2O B) Thiopentone C) Methohexitone D) Ketamine E) Fentanyl
Which of the following is true about allodynia?
The Visual Analog Scale (VAS) is a type of:
Pain Physiology and Pathways Indian Medical PG Practice Questions and MCQs
Question 1: A 10-year-old boy cuts his finger with a pocketknife and immediately applies pressure to the damaged area with his other hand to partially alleviate the pain. Inhibition of pain signals by tactile stimulation of the skin is mediated by which type of afferent neurons from mechanoreceptors?
- A. Aδ
- B. Type C
- C. Aβ (Correct Answer)
- D. Aα
Explanation: ***Aβ*** - **Aβ (A-beta) fibers** are large, myelinated afferent neurons that transmit discriminative touch and proprioception. - According to the **gate control theory of pain**, activation of these Aβ fibers by tactile stimulation can inhibit the transmission of pain signals (carried by Aδ and C fibers) in the spinal cord, explaining why rubbing an injured area can reduce pain. *Aδ* - **Aδ (A-delta) fibers** are thinly myelinated afferent neurons that transmit sharp, localized, and fast pain, as well as cold and touch. - While they are involved in pain transmission, they do not primarily mediate the inhibition of pain signals through tactile stimulation, but rather the initial painful sensation. *Type C* - **Type C fibers** are unmyelinated afferent neurons that transmit slow, dull, aching, and burning pain, as well as warmth and some touch. - These fibers are primarily responsible for the prolonged, chronic pain sensation and are inhibited by Aβ fiber activity, not the mediators of the pain inhibition themselves. *Aα* - **Aα (A-alpha) fibers** are the largest and fastest myelinated afferent neurons, primarily responsible for proprioception from muscle spindles (sensory information about muscle length and stretch), and motor innervation to extrafusal muscle fibers. - They are not directly involved in the tactile inhibition of pain signals.
Question 2: Which substance enhances the sensitivity of pain receptors but does not directly excite them?
- A. Potassium ions
- B. Prostaglandins (Correct Answer)
- C. Bradykinin
- D. Serotonin
Explanation: ***Prostaglandins*** - **Prostaglandins** are lipid compounds that do not directly activate pain receptors, but they enhance the sensitivity of nociceptors to other painful stimuli. - They are released during **inflammation** and contribute to the sensation of pain by lowering the threshold for neuronal activation. *Potassium ions* - **Potassium ions** directly depolarize nociceptors, thereby **exciting them** and causing pain. - Tissue damage and cell lysis release intracellular potassium, leading to direct pain perception. *Bradykinin* - **Bradykinin** directly excites pain receptors via its specific receptors (B1 and B2 receptors), leading to rapid depolarization and pain signals. - It also contributes to inflammation and vasodilation. *Serotonin* - **Serotonin** (5-HT) can directly activate certain types of nociceptors (e.g., 5-HT3 receptors), thereby **directly exciting them**. - It is released by platelets at injury sites and contributes to both pain and inflammation.
Question 3: Stimulation of which of the following areas of brain is experimentally used to control intractable pain -
- A. Mesencephalon
- B. Subthalamic nucleus
- C. Periaqueductal grey matter (Correct Answer)
- D. Medial forebrain bundle
Explanation: ***Periaqueductal grey matter*** - The **periaqueductal grey (PAG)** is a key modulator of endogenous analgesia, and its stimulation activates descending pain inhibitory pathways. - Stimulation of the PAG leads to the release of **endogenous opioids** (e.g., endorphins, enkephalins) and other neurotransmitters that suppress pain transmission at the spinal cord level. *Mesencephalon* - While the PAG is located within the mesencephalon (midbrain), simply stimulating the broader mesencephalon is not as precise or effective for pain control. - The mesencephalon contains various structures with diverse functions, and non-specific stimulation could lead to unwanted side effects. *Subthalamic nucleus* - The **subthalamic nucleus (STN)** is primarily involved in motor control and is a common target for deep brain stimulation in Parkinson's disease. - Its direct stimulation is not a primary or established method for controlling intractable pain. *Medial forebrain bundle* - The **medial forebrain bundle (MFB)** is a complex pathway associated with reward, motivation, and pleasure, important in the limbic system. - While it plays a role in emotional aspects of pain, its direct stimulation is not a recognized technique for somatic pain management.
Question 4: Pain and temperature are carried by:
- A. Lateral spinothalamic tract (Correct Answer)
- B. Dorsal column pathway
- C. Anterior spinothalamic tract
- D. Ventral column pathway
Explanation: ***Lateral spinothalamic tract*** - The **lateral spinothalamic tract** is primarily responsible for transmitting **pain** and **temperature** sensations from the body to the brain. - This pathway decussates (crosses) at the level of the spinal cord segment where the sensory neuron enters, then ascends contralaterally. *Dorsal column pathway* - The **dorsal column pathway** (also known as the posterior column-medial lemniscus pathway) is responsible for **fine touch, vibration, and proprioception**. - It ascends ipsilaterally in the spinal cord and decussates in the medulla oblongata. *Anterior spinothalamic tract* - The **anterior spinothalamic tract** primarily carries information related to **crude touch** and **pressure**. - While part of the spinothalamic system, it does not carry pain and temperature as its primary function. *Ventral column pathway* - The term **ventral column pathway** is not a standard, precise neuroanatomical classification for a specific sensory tract. - While parts of the spinothalamic tracts (anterior and lateral) are located in the ventral/anterior funiculus of the spinal cord, "ventral column pathway" itself is not a primary sensory pathway.
Question 5: Activation of which of the following fibers results in first pain, which helps to localize the site and intensity of the noxious stimulus?
- A. A delta fiber (Correct Answer)
- B. A beta fiber
- C. C fiber
- D. B fiber
Explanation: ***A delta fiber*** - **A delta fibers** are **myelinated** and transmit signals rapidly, leading to the sharp, localized sensation known as **first pain**. - This rapid transmission allows for precise localization of the noxious stimulus and assessment of its initial intensity. *A beta fiber* - **A beta fibers** are primarily responsible for transmitting **light touch** and **vibration** sensations, not noxious stimuli. - While myelinated, their receptive fields and response characteristics do not align with the perception of first pain. *C fiber* - **C fibers** are **unmyelinated** and transmit signals slowly, resulting in a dull, aching, and poorly localized sensation known as **second pain**. - They are involved in the chronic and burning aspects of pain, not the initial, sharp localization. *B fiber* - **B fibers** are preganglionic autonomic fibers primarily involved in the **autonomic nervous system's** functions, not sensory perception of pain. - They are generally found in the autonomic ganglia and do not transmit somatic sensory information.
Question 6: A female developed pain and a sensation like insects crawling on her legs at night which is relieved by shaking her legs. Which of the following is the drug of choice for this condition?
- A. Iron supplementation (if deficient)
- B. Pramipexole (Correct Answer)
- C. Gabapentin
- D. Vitamin B12 supplementation
Explanation: ***Pramipexole*** - **Pramipexole** is a **dopamine agonist** and is considered a first-line treatment for Restless Legs Syndrome (RLS) due to its efficacy in reducing symptoms. - It works by stimulating **dopamine receptors**, which are thought to play a role in the pathophysiology of RLS. *Iron supplementation (if deficient)* - While **iron deficiency is a common reversible cause of RLS**, iron supplementation is primarily indicated when serum ferritin levels are low. In the absence of confirmed deficiency, it is not the initial drug of choice. - Correcting iron deficiency can improve RLS symptoms, but it's a treatment for the underlying cause rather than a symptomatic drug of choice when iron status is unknown. *Gabapentin* - **Gabapentin** is an alpha-2-delta ligand and is an effective second-line or alternative treatment for RLS, especially when patients do not respond to dopamine agonists or have comorbid pain or anxiety. - Although effective, it is generally not considered the primary drug of choice over dopamine agonists for most RLS patients. *Vitamin B12 supplementation* - **Vitamin B12 deficiency** can cause neurological symptoms, but it is not typically associated with Restless Legs Syndrome (RLS) or an "insect crawling" sensation specifically relieved by movement. - Supplementation is only indicated if a **diagnosed deficiency is present**, and it would not be the drug of choice for RLS symptoms as described.
Question 7: Primary Dysmenorrhoea can be treated by which of the following? 1. Antiprostaglandin 2. Cyclic combined estrogen and progesterone preparations 3. Pre-sacral neurectomy 4. Uterine curettage
- A. 1, 2, 3 and 4
- B. 1, 2 and 4
- C. 2, 3 and 4
- D. 1, 2 and 3 (Correct Answer)
Explanation: ***1, 2 and 3*** - **Antiprostaglandins (NSAIDs)** are the first-line treatment for primary dysmenorrhea as they inhibit prostaglandin synthesis, reducing uterine contractions and pain. - **Cyclic combined estrogen and progesterone preparations (oral contraceptives)** are second-line therapy that suppress ovulation, leading to a thinner endometrium and reduced prostaglandin production, thereby alleviating dysmenorrhea. - **Pre-sacral neurectomy** is a surgical procedure that may be considered for severe, refractory primary dysmenorrhea that has failed medical management, though it is more commonly used for secondary dysmenorrhea and chronic pelvic pain. *1, 2, 3 and 4* - This option incorrectly includes **uterine curettage**, which is not a treatment for primary dysmenorrhea. - Uterine curettage is a diagnostic or therapeutic procedure for conditions like abnormal uterine bleeding or retained products of conception, not for menstrual pain management. *1, 2 and 4* - This option incorrectly includes **uterine curettage** while excluding pre-sacral neurectomy. - Curettage has no role in primary dysmenorrhea treatment, whereas the other interventions target the underlying pathophysiology. *2, 3 and 4* - This option incorrectly excludes **antiprostaglandins (NSAIDs)**, which are the cornerstone first-line therapy for primary dysmenorrhea. - It also incorrectly includes uterine curettage, which has no role in dysmenorrhea management.
Question 8: Which of the following anaesthetic agent lacks analgesic effect? A) N2O B) Thiopentone C) Methohexitone D) Ketamine E) Fentanyl
- A. N2O
- B. Methohexitone
- C. Ketamine
- D. Fentanyl
- E. Thiopentone (Correct Answer)
Explanation: ***Thiopentone*** - Thiopentone is a **barbiturate** anesthetic primarily used for inducing anesthesia. - It provides significant **hypnosis** and sedation but lacks intrinsic **analgesic properties**, meaning it does not relieve pain. *N2O* - **Nitrous oxide** (N2O) is an inhalation anesthetic that provides good **analgesia** at sub-anesthetic concentrations. - It is often used as an adjunct to other anesthetic agents to enhance pain relief during procedures. *Methohexitone* - Methohexitone is another **barbiturate** similar to thiopentone, used for induction of anesthesia. - While it provides rapid **hypnosis**, it also lacks significant **analgesic effects**. *Ketamine* - Ketamine is a **dissociative anesthetic** known for its potent **analgesic properties**. - It works by blocking **NMDA receptors**, providing pain relief even at sub-anesthetic doses. *Fentanyl* - Fentanyl is a powerful **opioid analgesic** that is commonly used in anesthesia for its strong pain-relieving effects. - It acts on **opioid receptors** in the central nervous system to reduce pain perception.
Question 9: Which of the following is true about allodynia?
- A. Hyperalgesia
- B. Loss of sensory sensations
- C. Perception of a non-painful stimulus as pain (Correct Answer)
- D. Hyperesthesia
Explanation: **Explanation:** **Allodynia** is defined by the International Association for the Study of Pain (IASP) as **pain due to a stimulus that does not normally provoke pain**. It is a hallmark of neuropathic pain and central sensitization. In this condition, the threshold for pain is lowered such that innocuous stimuli (like a light touch, the brush of clothing, or a breeze) are perceived as painful. **Analysis of Options:** * **Option C (Correct):** This directly matches the definition. It involves a change in the *quality* of sensation, where a non-noxious stimulus triggers a pain response. * **Option A (Incorrect):** **Hyperalgesia** is an *increased* response to a stimulus that is *normally* painful (e.g., a pinprick feeling like a stab). While both involve sensitization, allodynia involves a non-painful trigger, whereas hyperalgesia involves a painful one. * **Option B (Incorrect):** Loss of sensory sensation is termed **anesthesia** or **hypesthesia**. Allodynia is a positive sensory phenomenon (gain of function), not a loss. * **Option D (Incorrect):** **Hyperesthesia** is a broad term referring to increased sensitivity to any stimulus (touch, thermal, etc.), not specifically the conversion of a non-painful stimulus into pain. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Allodynia is primarily mediated by **A-beta fibers** (normally responsible for light touch) "shunting" signals into the pain pathways due to central sensitization in the spinal cord dorsal horn. * **Dynamic vs. Static:** Allodynia can be **mechanical** (moving a cotton wisp) or **thermal** (mild warmth feeling like a burn). * **Common Clinical Scenarios:** Post-herpetic neuralgia, Migraine (scalp tenderness), and Complex Regional Pain Syndrome (CRPS).
Question 10: The Visual Analog Scale (VAS) is a type of:
- A. Pain assessment scale (Correct Answer)
- B. Pressure assessment scale
- C. Vision assessment scale
- D. Auditory assessment scale
Explanation: **Explanation:** The **Visual Analog Scale (VAS)** is one of the most commonly used tools in clinical practice for the **subjective assessment of pain intensity**. It typically consists of a 10 cm (100 mm) horizontal line, anchored by two extremes: "No pain" at the 0 cm mark and "Worst imaginable pain" at the 10 cm mark. The patient marks a point on the line that represents their current pain level, and the distance is measured to provide a numerical value. **Analysis of Options:** * **Option A (Correct):** VAS is a validated psychometric response scale used to quantify pain. It is highly sensitive to changes in pain intensity, making it ideal for monitoring the efficacy of analgesic interventions. * **Option B (Incorrect):** Pressure assessment (e.g., compartment pressure or intracranial pressure) requires objective manometry or transducers, not subjective visual scales. * **Option C (Incorrect):** Vision is assessed using tools like the Snellen chart or Jaeger card. While the name "Visual" in VAS refers to the patient looking at the scale, it does not measure visual acuity. * **Option D (Incorrect):** Auditory function is assessed via audiometry or tuning fork tests (Rinne/Weber). **NEET-PG High-Yield Pearls:** * **Unidimensional vs. Multidimensional:** VAS is a **unidimensional** scale (measures only intensity). The McGill Pain Questionnaire is an example of a **multidimensional** scale (measures quality and emotional impact). * **Pediatric Use:** For children (usually >3 years), the **Wong-Baker FACES Pain Rating Scale** is preferred over the VAS. * **FLACC Scale:** Used for infants or non-verbal patients (Face, Legs, Activity, Cry, Consolability). * **Gold Standard:** The patient’s self-report is considered the "gold standard" for pain assessment.
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