Quiz 119 · Ascending Pathways

Answers to Quiz 118 · Sensory Communication to Spinal Cord

1. The Bell–Magendie law states that:

   Answer: The dorsal root is sensory and the ventral root is motor

   Afferents enter the cord by the dorsal root and efferents leave by the ventral root. The statements on compression and regrowth are true, but they are other points from the chapter, not the law. Revise afferent fibers, dorsal root and spinal laminae

2. A few afferent fibers break the Bell–Magendie law by running in the ventral root. What are most of them?

   Answer: Small unmyelinated nociceptors from the viscera

   Your book describes the ventral-root afferents as mostly small unmyelinated visceral nociceptors. Spindle, touch and cold afferents enter by the dorsal root like other sensory fibers. Revise afferent fibers, dorsal root and spinal laminae

3. In a skin nerve, fast pain and cold are carried mainly by:

   Answer: Small myelinated Aδ fibers

   Aδ fibers carry fast pain and cold, plus some mechanoreceptor signals. C fibers carry slow pain and temperature; Aα and Aβ carry mechanoreceptor signals. Revise afferent fibers, dorsal root and spinal laminae

4. A blood-pressure cuff is kept inflated on a volunteer's arm for 20 minutes. Which sensation in the hand is most likely to survive?

   Answer: Slow, burning pain

   Ischemia lasting over 15 minutes abolishes touch, temperature and fast pain. Slow pain usually survives because unmyelinated C fibers stand hypoxia best. Revise afferent fibers, dorsal root and spinal laminae

5. A local anesthetic is injected around a nerve. In what order are sensations lost?

   Answer: Pain first, then touch

   Small unmyelinated fibers are the most sensitive to local anesthetics, so pain goes first. Ischemia and compression show the reverse order, touch before pain. Revise afferent fibers, dorsal root and spinal laminae

6. In carpal tunnel syndrome, which fibers of the median nerve suffer earliest and most?

   Answer: Large fibers over 5 µm across

   Compression hits large fibers (over 5 µm) first and hardest, so touch goes early, while slow pain carried by C fibers is usually spared at first. Revise afferent fibers, dorsal root and spinal laminae

7. After an axon is cut, which change is seen in the part of the neuron still joined to the cell body?

   Answer: Swelling of the cell body with chromatolysis

   Proximally the cell body swells, shows chromatolysis and the axon retracts from the injury. Wallerian degeneration affects the part beyond the cut, and new sprouts grow from the proximal axon. Revise afferent fibers, dorsal root and spinal laminae

8. Which statement about regeneration after axotomy matches your book?

   Answer: Sensory fibers regenerate faster than motor fibers

   Peripheral axons regrow faster than central ones, and sensory fibers faster than motor fibers. Sprouts come from the proximal axon, not the distal part. Revise afferent fibers, dorsal root and spinal laminae

9. The area of skin supplied by a single dorsal root ganglion is called a:

   Answer: Dermatome

   A dermatome is the skin territory of one dorsal root ganglion. Myotome and sclerotome are the matching territories in muscle and bone. Revise afferent fibers, dorsal root and spinal laminae

10. A man with a slipped lumbar disc has pain, tingling and heightened sensitivity along one dermatome, but no numbness. What does this pattern point to?

    Answer: Irritation of the dorsal root

    Irritation of a dorsal root gives paresthesia or hyperesthesia in its dermatome. Damage to the root would give frank segmental anesthesia. Revise afferent fibers, dorsal root and spinal laminae

11. The substantia gelatinosa is Rexed lamina:

    Answer: II

    Lamina II, the substantia gelatinosa, gets mainly C-fiber input, and its axons end mostly locally. Lamina I takes both Aδ and C nociceptors; IX is the motor lamina. Revise afferent fibers, dorsal root and spinal laminae

12. Dorsal horn cells that respond to fine touch, vibration and proprioception lie mainly in laminae:

    Answer: III–VI

    Laminae III–VI receive myelinated A-fiber input and send axons up the dorsal column pathway. Laminae I and II deal mainly with nociceptive input. Revise afferent fibers, dorsal root and spinal laminae

13. Which Rexed lamina is the main motor lamina?

    Answer: IX

    Lamina IX is the motor lamina. VII and VIII count as motor laminae but hold mostly interneurons, and X is the intercommissural lamina. Revise afferent fibers, dorsal root and spinal laminae

14. Of the descending tracts your book lists, which ends in dorsal horn laminae III–VI but not in laminae I and II?

    Answer: Corticospinal

    Corticospinal fibers end in laminae III–VI. Raphespinal and medullary reticulospinal fibers reach I, II, V, VI and VII, and pontine reticulospinal fibers end in V, VII and VIII. Revise afferent fibers, dorsal root and spinal laminae

15 questions on chapter 119. 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. In the dorsal column–medial lemniscus pathway, the second-order fibers cross the midline:

In the midbrainIn the ponsIn the medullaIn the segment of entry

2. The fasciculus gracilis carries fibers from the:

Upper limb and upper trunk, same sideLower limb and lower trunk, opposite sideUpper limb and upper trunk, opposite sideLower limb and lower trunk, same side

3. The anterior spinothalamic tract carries:

Fine touchVibrationCrude touchPain and temperature

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

Lamina IX onlyLaminae I, II and VLaminae VII and VIIILaminae III and IV only

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?

PainVibrationCrude touchTemperature

6. Which pair are both slowly adapting touch receptors?

Merkel discs and Ruffini endingsMeissner's and Pacinian corpusclesPacinian corpuscles and Ruffini endingsMeissner's corpuscles and Merkel discs

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

10 mm3 mm30 mm65 mm

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

Impaired crude touch over the faceImpaired vibration sense over the ankleImpaired temperature sense in the handsImpaired pinprick sense over the trunk

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

Their fibers bypass the thalamusThey travel in the anterolateral systemThey are integrated in the cortexTheir receptors lie in the cortex

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

It damages the vestibular nuclei in the medullaIt destroys the motor neurons of the ventral hornIt cuts proprioceptive input relayed to the cerebellumIt interrupts the lateral spinothalamic tract

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:

PallanesthesiaAstereognosisStereoanesthesiaAlloesthesia

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

Touch fibers are unmyelinated and resist injuryPain fibers are larger and more easily crushedThe dorsal columns lie at the edge of the cordThe cavity forms only in the lateral white matter

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

SyringobulbiaSyringomyeliaComplete cord transectionIntramedullary tumor

14. A positive Romberg sign shows loss of:

Position sense in both legsCrude touch in both legsMotor power in both legsPain and temperature in both legs

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

AlloesthesiaAgraphesthesiaHyperpathiaParesthesia

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