The Question is from neet-zoology neural-control-and-coordination neural-system, and it was created by the author K SUNKANNA

Question

A patient presents with impaired tactile discrimination and proprioception in the left leg but retains pain and temperature sensation.  The lesion is most likely located in which spinal cord tract?

K SUNKANNA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Spinal cord tracts and their functions
 **Related Topics**: Sensory pathways, dorsal column-medial lemniscus pathway, spinothalamic tract, neurological examination
 **Prerequisites**: Understanding of the organization of sensory pathways in the spinal cord.
## SOLUTION PATHWAY
**Given Information**:
  * Impaired tactile discrimination and proprioception in the left leg.
  * Pain and temperature sensation are preserved in the left leg.
**Method & Steps**:
 1. Identify the sensory modalities affected.
  Reasoning: Tactile discrimination and proprioception are carried by the dorsal column-medial lemniscus pathway. Pain and temperature are carried by the spinothalamic tract.
  Formula/Rule: None directly applicable, this is a qualitative analysis based on anatomical knowledge.
 2. Determine which pathway is affected based on the symptoms.
  Working: Since tactile discrimination and proprioception are lost in the left leg, while pain and temperature are preserved, the lesion must be in the dorsal column pathway on the left side.  The dorsal columns contain the fasciculus gracilis (carrying information from the lower body) and the fasciculus cuneatus (carrying information from the upper body). Since the problem is in the leg, the fasciculus gracilis is implicated.
  Key Point:  The sensory pathways decussate (cross over) at different levels of the central nervous system.  For the dorsal column-medial lemniscus pathway, this occurs in the medulla oblongata; for the spinothalamic tract, it occurs at the spinal cord level.
 3. Pinpoint the location of the lesion.
  Result: The lesion is most likely in the left fasciculus gracilis.  Because the symptoms are only in the left leg, the lesion is likely located in the spinal cord on the left side, affecting the ascending fibers of the fasciculus gracilis that carry sensory information from that leg.
  Verification: The preserved pain and temperature sensation support the conclusion that the spinothalamic tract is intact. The loss of proprioception and tactile discrimination specifically in the left leg confirms the lesion is in the left fasciculus gracilis.
 ## OPTION ANALYSIS
[A] ✓: Left fasciculus gracilis: This is correct because the left fasciculus gracilis carries sensory information for fine touch, vibration, and proprioception from the left leg.  A lesion here would cause the described symptoms.
[B] :x: Right fasciculus gracilis: This is incorrect. A lesion in the right fasciculus gracilis would affect the right leg.
[C] :x: Left lateral spinothalamic tract: This is incorrect. The lateral spinothalamic tract carries pain and temperature sensation, which are preserved in this patient.
[D] :x: Right lateral spinothalamic tract: This is incorrect. A lesion here would affect pain and temperature sensation on the left side, which is not the case.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the sensory modalities carried by the dorsal column and spinothalamic tracts:  Carefully review the specific sensory information carried by each pathway.
  2.Incorrectly interpreting the side of the lesion: Remember the decussation points of the sensory pathways to correctly correlate the side of the lesion with the side of the symptoms.
 **Quick Tips**:
  1.Use a diagram of the spinal cord tracts to help visualize the pathways and their locations.
  2.Memorize the key sensory modalities carried by each major tract:  dorsal column (proprioception, fine touch, vibration) and spinothalamic (pain, temperature).

K SUNKANNA · Answer

The correct Option is "Left fasciculus gracilis"

K SUNKANNA · Answer

Right fasciculus gracilis

K SUNKANNA · Answer

Left lateral spinothalamic tract

K SUNKANNA · Answer

Right lateral spinothalamic tract

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