Answer
Wallace's hunting accident resulted in a specific pattern of sensory loss known as "dissociated sensory loss." The injury affected the spinal cord and specific sensory pathways, resulting in the sensory losses on opposite sides of his body. To understand this condition, we need to consider the spinal tracts involved and their functions.
**Affected Spinal Tracts:**
1. **Dorsal Column-Medial Lemniscus Pathway:** This pathway is responsible for transmitting sensations of fine touch, proprioception (limb position sense), and vibration from the body to the brain. It carries sensory information from the peripheral nerves to the brain via ascending fibers in the spinal cord's dorsal columns.
2. **Anterolateral (Spinothalamic) Pathway:** This pathway carries sensory information related to pain and temperature from the body to the brain. It consists of ascending fibers in the anterior and lateral columns of the spinal cord.
**Explanation of Sensory Loss:**
In Wallace's case, the injury involved the left half of his spinal cord at segments T8 through T10. Here's why he experiences dissociated sensory loss on opposite sides of his body:
1. **Left-Side Sensory Loss (Below the Injury):** The injury severed the left half of the spinal cord, affecting the dorsal columns and anterolateral pathway on the left side below the level of the injury (T8-T10). As a result, Wallace loses sensations of deep touch, limb position, and vibration on the left side of his body below the injury because the ascending fibers in the dorsal columns on the left side are damaged.
2. **Right-Side Sensory Loss (Pain and Heat Sensation):** The anterolateral (spinothalamic) pathway, responsible for transmitting pain and temperature sensations, crosses over to the opposite side of the spinal cord shortly after entering. This crossing is known as decussation. In Wallace's case, the injury has affected the right half of the spinal cord at the level of T8-T10, where these pain and temperature pathways are crossing. Consequently, he loses sensations of pain and heat on the right side of his body because the injury has damaged the crossing fibers in the anterolateral pathway.
This pattern of dissociated sensory loss occurs because the sensory pathways for different types of sensations (e.g., fine touch and proprioception vs. pain and temperature) cross over to the opposite side of the spinal cord at different levels. The injury selectively damages the pathways on the side and at the level of the injury, resulting in the distinct sensory losses observed in Wallace's case.
Work Step by Step
Wallace's hunting accident resulted in a specific pattern of sensory loss known as "dissociated sensory loss." The injury affected the spinal cord and specific sensory pathways, resulting in the sensory losses on opposite sides of his body. To understand this condition, we need to consider the spinal tracts involved and their functions.
**Affected Spinal Tracts:**
1. **Dorsal Column-Medial Lemniscus Pathway:** This pathway is responsible for transmitting sensations of fine touch, proprioception (limb position sense), and vibration from the body to the brain. It carries sensory information from the peripheral nerves to the brain via ascending fibers in the spinal cord's dorsal columns.
2. **Anterolateral (Spinothalamic) Pathway:** This pathway carries sensory information related to pain and temperature from the body to the brain. It consists of ascending fibers in the anterior and lateral columns of the spinal cord.
**Explanation of Sensory Loss:**
In Wallace's case, the injury involved the left half of his spinal cord at segments T8 through T10. Here's why he experiences dissociated sensory loss on opposite sides of his body:
1. **Left-Side Sensory Loss (Below the Injury):** The injury severed the left half of the spinal cord, affecting the dorsal columns and anterolateral pathway on the left side below the level of the injury (T8-T10). As a result, Wallace loses sensations of deep touch, limb position, and vibration on the left side of his body below the injury because the ascending fibers in the dorsal columns on the left side are damaged.
2. **Right-Side Sensory Loss (Pain and Heat Sensation):** The anterolateral (spinothalamic) pathway, responsible for transmitting pain and temperature sensations, crosses over to the opposite side of the spinal cord shortly after entering. This crossing is known as decussation. In Wallace's case, the injury has affected the right half of the spinal cord at the level of T8-T10, where these pain and temperature pathways are crossing. Consequently, he loses sensations of pain and heat on the right side of his body because the injury has damaged the crossing fibers in the anterolateral pathway.
This pattern of dissociated sensory loss occurs because the sensory pathways for different types of sensations (e.g., fine touch and proprioception vs. pain and temperature) cross over to the opposite side of the spinal cord at different levels. The injury selectively damages the pathways on the side and at the level of the injury, resulting in the distinct sensory losses observed in Wallace's case.
