Pain Physiology — MCQs

10 questions

Slow, burning pain is primarily carried by which type of nerve fibers?

A person is able to sense fast, sharp pain and temperature normally. Which type of nerve fiber is primarily involved in carrying these fast pain and temperature sensations?

Free nerve endings carrying nociceptive fibers are seen in:

A woman with right-sided loss of sensations of both the upper and lower limb complains of shooting pain from her fingers to the right shoulder and a burning sensation when touching cold water. Motor functions are normal. Which of the following structures is likely to be involved?

Capsaicin acts on ______

Stimulation of which of the following areas of brain is experimentally used to control intractable pain -

Nerve endings sensitive to noxious stimuli are present in all except:

Pain and temperature are carried by:

An exaggerated pain response to a normally painful stimulus is called:

Q10

A ventrolateral cordotomy is performed to produce relief of pain from the right leg. It is effective because it interrupts the

Pain Physiology Indian Medical PG Practice Questions and MCQs

Question 1: Slow, burning pain is primarily carried by which type of nerve fibers?

A. Aα fibers
B. Aβ fibers
C. Aδ fibers
D. C fibers (Correct Answer)

Explanation: ***C fibers*** - **C fibers** are small, unmyelinated nerve fibers responsible for transmitting **slow, dull, burning, and aching pain** sensations. - They conduct impulses slowly due to their lack of **myelin sheath**, leading to the characteristic long-lasting and diffuse nature of the pain. *Aα fibers* - **Aα fibers** are the largest and most heavily myelinated nerve fibers, primarily responsible for **proprioception** (sense of body position) and **motor control**. - They conduct impulses at the highest speeds and are not involved in pain transmission. *Aβ fibers* - **Aβ fibers** are moderately myelinated and transmit sensations of **touch and pressure**, as well as vibration. - While they are involved in tactile sensation, they do not primarily convey pain signals, especially not the slow, burning kind. *Aδ fibers* - **Aδ fibers** are thinly myelinated fibers responsible for transmitting **fast, sharp, and localized pain** (the "first pain"). - They convey rapid pain signals, distinct from the slow, burning pain transmitted by C fibers.

Question 2: A person is able to sense fast, sharp pain and temperature normally. Which type of nerve fiber is primarily involved in carrying these fast pain and temperature sensations?

A. A-delta (Correct Answer)
B. C fibers
C. A-beta
D. A-alpha

Explanation: ***A-delta*** - **A-delta fibers** are **myelinated**, medium-diameter fibers responsible for transmitting **fast, sharp pain** and **cold temperature** sensations. - Their myelination allows for **rapid conduction** of nerve impulses, leading to the immediate perception of acute pain. *A-beta* - **A-beta fibers** are large-diameter, highly myelinated fibers primarily involved in transmitting **touch** and **pressure** sensations. - While they can transmit some non-painful signals from the skin, they are not the primary carriers of sharp pain or temperature. *C fibers* - **C fibers** are **unmyelinated**, small-diameter fibers that transmit **slow, dull, burning pain** and **warm temperature** sensations. - Their lack of myelination results in **slower conduction velocity**, which is why the duller pain is perceived after the sharp pain. *A-alpha* - **A-alpha fibers** are the **largest diameter**, most heavily myelinated fibers in the periphery. - They are primarily responsible for **proprioception** (sense of body position) and **motor control** to skeletal muscles, not pain or temperature.

Question 3: Free nerve endings carrying nociceptive fibers are seen in:

A. Spleen
B. Liver
C. Mesentery (Correct Answer)
D. Intestine

Explanation: ***Mesentery*** - The mesentery is **richly innervated with free nerve endings** that carry nociceptive (pain) fibers, making it highly sensitive to painful stimuli [1]. - These nerve endings respond to **stretch, traction, ischemia, and inflammation**, transmitting visceral pain signals via **sympathetic pathways** (T5-L2) [2]. - The mesentery's abundant nociceptive innervation is why **peritoneal irritation** and **mesenteric traction** during surgery cause significant pain [4]. - Free nerve endings in the mesentery are a key component of **visceral pain perception** in abdominal pathologies [1]. *Intestine* - The intestinal **mucosa and muscle layers** have relatively **few pain receptors** and are insensitive to cutting, burning, or crushing [1]. - Pain from the intestine primarily arises from the **serosal surface** (peritoneal covering) and associated mesentery, not from the intestinal wall itself [4]. - Intestinal pain is typically due to **distension, ischemia, or inflammation** affecting the serosa or mesentery [2]. *Liver* - The liver parenchyma is **devoid of pain receptors** - it has no free nerve endings for nociception [3]. - Hepatic pain originates only from **stretching of Glisson's capsule** (the fibrous covering), not from the liver tissue itself [3]. - This capsular pain may be referred to the right upper quadrant or shoulder via phrenic nerve (C3-C5) [4]. *Spleen* - The spleen has **sparse nociceptive innervation** and is relatively insensitive to pain. - Splenic pain, when present, typically results from **capsular distension or rupture**, not from the splenic parenchyma itself. - Pain from splenic pathology is often referred to the left shoulder (Kehr's sign) [4].

Question 4: A woman with right-sided loss of sensations of both the upper and lower limb complains of shooting pain from her fingers to the right shoulder and a burning sensation when touching cold water. Motor functions are normal. Which of the following structures is likely to be involved?

A. Anterior spinothalamic tract
B. Spinocerebellar tract
C. Lateral spinothalamic tract (Correct Answer)
D. Posterior column

Explanation: ***Lateral spinothalamic tract*** - The symptoms described, such as **loss of sensations**, **shooting pain** (neuropathic pain), and **burning sensation** with cold water (dysesthesia/allodynia), are characteristic of damage to the **spinothalamic tract**, which carries **pain and temperature** sensations. - Involvement of the **right-sided upper and lower limb** indicates a lesion affecting sensory pathways on the ipsilateral side of the body before decussation, or more commonly a contralateral lesion above the level of decussation for the specific tract. Given the symptoms affecting pain and temperature, the lateral spinothalamic tract is the primary candidate. *Anterior spinothalamic tract* - This tract primarily transmits **crude touch** and **pressure** sensations. - While loss of sensation is present, the prominent **shooting pain** and **burning sensation with cold water** are not typically associated with isolated anterior spinothalamic tract lesions. *Spinocerebellar tract* - This tract is responsible for transmitting **proprioceptive information** to the cerebellum for motor coordination. - Damage to the spinocerebellar tracts would manifest as **ataxia** and **incoordination**, not pain or loss of touch/temperature sensation, and motor functions are stated as normal in the patient. *Posterior column* - The posterior column (dorsal column-medial lemniscus pathway) transmits **fine touch**, **vibration**, and **proprioception**. - While a loss of sensation is present, the specific complaints of **shooting pain** and **burning sensation to cold water** are not characteristic of posterior column damage, which would typically present with deficits in discriminative touch, vibratory sense, and position sense.

Question 5: Capsaicin acts on ______

A. Vanilloid receptor (Correct Answer)
B. Capsaicoid receptor
C. AMPA receptor
D. NMDA receptor

Explanation: ***Vanilloid receptor*** - Capsaicin is the active component of chili peppers and exerts its effects primarily through activation of the **transient receptor potential vanilloid 1 (TRPV1) receptor**, also known as the vanilloid receptor. - Activation of **TRPV1** by capsaicin leads to an influx of **calcium ions**, causing depolarization and firing of nociceptive neurons, which is perceived as burning pain. *Capsaicoid receptor* - This term is **not a recognized scientific receptor name** for capsaicin's primary target. - It might be a colloquial or misnomer derived from the mechanism of action of capsaicin. *AMPA receptor* - **AMPA receptors** are **ionotropic glutamate receptors** that mediate fast synaptic transmission in the central nervous system. - They are primarily involved in learning, memory, and synaptic plasticity, not directly activated by capsaicin. *NMDA receptor* - **NMDA receptors** are another type of **ionotropic glutamate receptor** that plays a crucial role in synaptic plasticity and learning. - Although also involved in pain processing, they are distinct from the **TRPV1 receptor** and are not directly activated by capsaicin.

Question 6: 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 7: Nerve endings sensitive to noxious stimuli are present in all except:

A. Intestine
B. Stomach
C. Liver (Correct Answer)
D. Mesentery

Explanation: ***Liver*** - The **liver parenchyma** itself is notable for its lack of **pain receptors**; therefore, sensations like cutting or burning of the liver tissue do not evoke direct pain. - Pain associated with the liver typically arises from the stretching of its **fibrous capsule (Glisson's capsule)** or involvement of surrounding structures, rather than from within the organ. *Intestine* - The intestine contains abundant **nociceptors** that respond to a variety of noxious stimuli, including **distention**, **ischemia**, and **chemical irritants**. - These nerve endings play a crucial role in mediating **visceral pain** experienced during conditions such as inflammatory bowel disease or irritable bowel syndrome. *Stomach* - The stomach is richly innervated with **nociceptors** that detect painful stimuli such as extreme **distension**, potent **chemical irritants**, and **ischemia**. - These nerve endings contribute to the sensation of **gastric pain** associated with conditions like gastritis, ulcers, and gastroesophageal reflux disease. *Mesentery* - The mesentery contains numerous **nociceptors** that are highly sensitive to **stretching**, **ischemia**, and **inflammation**. - Pain originating from the mesentery can be intense and is often implicated in conditions like **mesenteric ischemia** or **peritonitis**.

Question 8: 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 9: An exaggerated pain response to a normally painful stimulus is called:

A. Causalgia
B. Allodynia
C. Hypersensitivity
D. Hyperalgesia (Correct Answer)

Explanation: ***Hyperalgesia*** - This term describes an **increased sensitivity to pain** where a stimulus that is normally painful is perceived as even more painful than usual. - It often results from **damage to nociceptive afferent pathways** or central sensitization. *Causalgia* - This is an older term now largely replaced by complex regional pain syndrome type II (**CRPS II**), characterized by severe, burning pain following a **nerve injury**. - Unlike hyperalgesia, it specifically refers to a **syndrome of severe pain** after nerve trauma, not just an increased response to noxious stimuli. *Allodynia* - This refers to pain caused by a stimulus that **does not normally provoke pain**, such as light touch or brushing of the skin. - It differs from hyperalgesia, which is an exaggerated response to a **normally painful stimulus**. *Hypersensitivity* - This is a **general term** meaning an increased physical or allergic sensitivity to a substance or condition. - It is a **broader concept** and not as specific to pain perception as hyperalgesia or allodynia.

Question 10: A ventrolateral cordotomy is performed to produce relief of pain from the right leg. It is effective because it interrupts the

A. Left Dorsal Column
B. Left Lateral Spinothalamic Tract (Correct Answer)
C. Right Corticospinal Tract
D. Right Lateral Spinothalamic Tract

Explanation: ***Left Lateral Spinothalamic Tract*** - A ventrolateral cordotomy is a surgical procedure that specifically targets the **spinothalamic tract** to relieve chronic, intractable pain. - Pain signals from the right leg cross over in the spinal cord and ascend via the **contralateral (left) lateral spinothalamic tract**. Therefore, interrupting this tract on the left side relieves pain from the right leg. *Left Dorsal Column* - The dorsal columns (fasciculus gracilis and cuneatus) primarily carry information about **fine touch, vibration, and proprioception**, not pain. - Interrupting the dorsal column would lead to deficits in these sensory modalities, not pain relief. *Right Corticospinal Tract* - The corticospinal tract is a **descending motor pathway** responsible for voluntary movement, originating from the cerebral cortex. - Interrupting this tract would result in **motor deficits** (paresis or paralysis), not pain relief. *Right Lateral Spinothalamic Tract* - The lateral spinothalamic tract carries pain and temperature sensation, but the fibers **cross over** at the segmental level of entry into the spinal cord. - Therefore, pain from the right leg ascends in the **left** lateral spinothalamic tract, making the right tract irrelevant for right leg pain relief through cordotomy.

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