Quiz 120 · Physiology of Pain, Itch and Temperature

Answers to Quiz 119 · Ascending Pathways

1. In the dorsal column–medial lemniscus pathway, the second-order fibers cross the midline:

   Answer: In the medulla

   They start in the nucleus gracilis and cuneatus, cross in the medulla and climb in the medial lemniscus to the opposite thalamus. Crossing in the segment of entry is what the anterolateral system does. Revise ascending tracts: dorsal column and anterolateral system

2. The fasciculus gracilis carries fibers from the:

   Answer: Lower limb and lower trunk, same side

   The medial gracile fasciculus carries the lower limb and lower trunk, and the lateral cuneate fasciculus the upper limb and upper trunk. Dorsal column fibers climb on the side they entered, so both are same-side. Revise ascending tracts: dorsal column and anterolateral system

3. The anterior spinothalamic tract carries:

   Answer: Crude touch

   The anterior (ventral) spinothalamic tract carries crude touch. Pain and temperature run in the lateral spinothalamic tract, and fine touch and vibration in the dorsal columns. Revise ascending tracts: dorsal column and anterolateral system

4. In the anterolateral system, the cell bodies of the second-order neurons lie mainly in which laminae of the dorsal horn?

   Answer: Laminae I, II and V

   First-order pain, temperature and touch fibers end on second-order neurons of the same-side dorsal horn, mainly in laminae I, II and V. Their axons then cross in the same segment. Revise ascending tracts: dorsal column and anterolateral system

5. A stab wound cuts the left half of the spinal cord at T8. Below the lesion, which sensation is lost on the LEFT side?

   Answer: Vibration

   Dorsal column fibers climb on the side they enter, so vibration, fine touch and position sense go on the side of the lesion. Spinothalamic fibers have already crossed, so pain, temperature and crude touch go on the opposite side. Revise ascending tracts: dorsal column and anterolateral system

6. Which pair are both slowly adapting touch receptors?

   Answer: Merkel discs and Ruffini endings

   Merkel discs and Ruffini endings adapt slowly; Meissner's and Pacinian corpuscles adapt rapidly. The last two pairs each mix one rapid and one slow receptor. Revise pathways for specific sensations

7. On the fingertips, the two-point discrimination threshold can be as small as:

   Answer: 3 mm

   The fingertips are packed with touch receptors and have a large cortical area, so two points about 3 mm apart are felt as two. On the back they must be 65 mm or more apart. Revise pathways for specific sensations

8. A 60-year-old with pernicious anemia is being examined. Which finding is likely to appear first?

   Answer: Impaired vibration sense over the ankle

   Vitamin B12 deficiency degenerates the dorsal columns, and a dulled vibration sense, tested with a tuning fork on a bony prominence, is an early sign. Pinprick and temperature travel in the spinothalamic tracts instead. Revise pathways for specific sensations

9. Two-point discrimination, tactile localization and stereognosis are called cortical sensations because:

   Answer: They are integrated in the cortex

   All three reach the brain by the dorsal column pathway and are put together in the cortex, so a cortical lesion impairs them severely even when simple touch is intact. Revise pathways for specific sensations

10. According to your book, why does disease of the dorsal columns cause ataxia?

    Answer: It cuts proprioceptive input relayed to the cerebellum

    A large proprioceptive projection runs from the nucleus gracilis and cuneatus to the cerebellum. Dorsal column disease interrupts it, so movement loses its sensory guidance. Revise pathways for specific sensations

11. After a lesion of the sensory cortex, a patient with normal touch and pressure sense cannot name a key placed in his hand while his eyes are closed. This is:

    Answer: Astereognosis

    Failing to recognize a familiar object by handling it, with basic touch intact, is astereognosis, a sign of cortical disease. In stereoanesthesia a cord or brainstem lesion cuts off the touch and position input itself. Revise abnormalities of dorsal column sensations

12. In syringomyelia, pain and temperature are lost but touch is preserved because:

    Answer: The dorsal columns lie at the edge of the cord

    The cavity destroys the grey matter around the central canal, where the spinothalamic fibers cross, so pain and temperature go. Dorsal column fibers run at the periphery of the cord and escape, so touch stays. Revise abnormalities of dorsal column sensations

13. Which of these is NOT a cause of dissociated anesthesia?

    Answer: Complete cord transection

    Complete transection cuts every tract, so all sensation is lost below the level of the lesion. Syringomyelia, syringobulbia and intramedullary tumors take pain and temperature but spare touch. Revise abnormalities of dorsal column sensations

14. A positive Romberg sign shows loss of:

    Answer: Position sense in both legs

    Swaying or falling with the feet together and the eyes closed shows that position sense from both legs is missing: a sensory ataxia. It must be told apart from cerebellar and vestibular ataxia. Revise abnormalities of dorsal column sensations

15. A touch given on the side of a hemisensory loss is felt at the matching spot on the opposite side. This is called:

    Answer: Alloesthesia

    Alloesthesia (allesthesia) is seen with a right putamen hemorrhage or an anterolateral lesion of the cervical cord. Agraphesthesia is the loss of the ability to recognize figures written on the skin. Revise abnormalities of dorsal column sensations

15 questions on chapter 120. Pick one answer for each, then save. Your answers stay in this browser, and the right ones are shown at the top of the next quiz.

1. Slow pain reaches the spinal cord along:

C fibers that end in lamina IIAβ fibers that end in lamina IIIAδ fibers that end in laminae I and VAα fibers that end in lamina IX

2. Besides capsaicin, the VR-1 receptor at C fiber endings is activated by:

Menthol applied to the skinA rise in temperature above 43°CA fall in temperature below 10°CA rise in temperature above 50°C

3. In the lateral spinothalamic tract, the fibers coming from sacral segments lie:

Scattered evenly through the tractMost medially, next to the grey matterIn the dorsal part of the lateral funiculusMost laterally, at the outer edge of the tract

4. The second order neurons of the paleospinothalamic pathway end mainly in which thalamic nuclei?

The ventrobasal complexThe midline and intralaminar nucleiThe anterior nuclear groupThe posterior nuclear complex

5. Which substance, released by the primary afferent fiber itself from its C fiber endings in skin, sensitizes nociceptors and heightens pain perception?

Substance PSerotoninGlutamateHistamine

6. A man with an acute myocardial infarction feels pain running down the inner border of his left arm. The best explanation is:

Referred pain, because heart and inner arm arise from the same embryonic segmentIschemia of the arm muscles exciting their own nociceptorsSpread of the pain impulse along the brachial plexusConduction of cardiac pain in the dorsal column pathway

7. The convergence theory of referred pain holds that:

Viscus and skin arise from the same embryonic dermatomeVisceral collaterals only raise the excitability of somatic neuronsPain is felt where the patient has been hurt on an earlier occasionVisceral and somatic afferents synapse on the same second order neuron

8. Which of these is NOT a feature of visceral pain?

It is often referred to a somatic structureIt is accompanied by autonomic symptomsIts afferents run in somatic sensory nervesIt is diffuse and poorly localized

9. Which statement about the endogenous opioid system is NOT correct?

Morphine acts as a powerful agonist at the µ receptorOpiate receptors belong to the G protein coupled familyNaloxone binds the µ receptor and reverses opioid effectsOpioids inhibit the postsynaptic neuron by lowering its K⁺ conductance

10. The dorsal horn interneurons of the descending analgesia system release enkephalin, which relieves pain by:

Blocking serotonin receptors on the afferent terminalIncreasing glutamate release from the primary afferent endingDepolarizing the second order neuronPreventing the release of substance P from the primary afferent ending

11. The gate control theory of pain proposes that:

Collaterals of large tactile afferents presynaptically inhibit Aδ and C fibers in the dorsal hornSympathetic fibers growing into the dorsal root ganglion silence the pain fibersSerotonergic fibers from the nucleus raphe magnus inhibit the second order neuronβ-endorphin from the pituitary occupies and blocks the opiate receptors

12. Pain produced by a stimulus that should not hurt at all, such as light touch, is called:

HyperalgesiaHyperpathiaHypoalgesiaAllodynia

13. A young man has continuous burning pain in the hand after a nerve injury in the forearm. It persists although the nerve has recovered fully, and it settles after sympathectomy. This is:

Inflammatory painCausalgiaThalamic syndromeTic douloureux

14. The receptors for itch are:

The same polymodal C fibers that carry slow painEndings of the cutaneous warmth receptorsEndings of unmyelinated C fibers, separate from the pain C fibersEndings of Aδ mechanical nociceptors in the epidermis

15. Cold receptors in the skin respond over a temperature range of about:

10 to 40°C20 to 45°C5 to 30°C30 to 50°C

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