Which spinal cord pathway is responsible for transmitting sharp, well-localized pain and temperature sensation to the contralateral thalamus?

Explanation

## Ascending Pain Pathways: Spinothalamic Tract **Key Point:** The lateral spinothalamic tract (also called the neospinothalamic tract) is the primary pathway for sharp, well-localized (first) pain and temperature sensation. It crosses at the spinal cord level and ascends to the ventral posterolateral (VPL) nucleus of the thalamus. ### Anatomical Organization of Pain Pathways | Feature | Lateral Spinothalamic | Ventral Spinothalamic | Spinoreticular | | --- | --- | --- | --- | | **Pain type** | Sharp, well-localized (first pain) | Diffuse, burning (second pain) | Emotional/affective pain | | **Crossing level** | 1–2 segments above entry | 1–2 segments above entry | Multiple levels | | **Thalamic target** | VPL nucleus | VPL/intralaminar | Intralaminar/medial | | **Cortical projection** | Primary/secondary somatosensory | Insular cortex | Anterior cingulate | | **Fiber type** | Aα, Aδ (fast) | C fibers (slow) | Mixed | ### Three-Neuron Relay in Spinothalamic Pathway ```mermaid flowchart TD A[First-order neuron: nociceptor in periphery]:::outcome --> B[Synapse in dorsal horn laminae I & V]:::outcome B --> C[Second-order neuron: crosses at spinal cord]:::action C --> D[Ascends contralateral spinothalamic tract]:::action D --> E[VPL nucleus of thalamus]:::outcome E --> F[Third-order neuron to primary somatosensory cortex]:::outcome ``` **High-Yield:** The spinothalamic tract crosses at the spinal cord level (unlike dorsal columns which cross in the medulla). This is why a hemisection of the spinal cord causes contralateral loss of pain/temperature below the lesion (Brown-Séquard syndrome). **Mnemonic:** **STAB** — **S**pinothalamic crosses at **S**pinal cord; **D**orsal columns cross in **M**edulla (medial lemniscus). **Clinical Pearl:** Syringomyelia affecting the crossing fibers in the dorsal horn causes a "cape-like" distribution of pain/temperature loss (suspended sensory level) while preserving dorsal column function (proprioception/vibration intact).