All of the following statements regarding the corticospinal tract are correct EXCEPT:

Explanation

## Anatomy of the Corticospinal Tract **Key Point:** The corticospinal tract is the major voluntary motor pathway, but its anatomical location in the spinal cord is critical for clinical correlation. ### Origin and Course 1. **Origin**: Motor cortex (Brodmann area 4) and premotor cortex (Brodmann area 6) 2. **Descent**: Passes through the internal capsule (genu and posterior limb) 3. **Decussation**: ~90% of fibres cross at the **pyramids of the medulla** (pyramidal decussation) 4. **Spinal Cord Location**: The crossed fibres form the **lateral corticospinal tract** in the **lateral funiculus** (NOT dorsal column) ### Why Each Statement Is Correct (Except One) | Statement | Validity | Explanation | | --- | --- | --- | | Majority decussate at pyramids | ✓ Correct | 85–90% of fibres cross here; 10–15% remain ipsilateral (ventral corticospinal tract) | | Originates from areas 4 & 6 | ✓ Correct | Primary motor cortex (M1) and supplementary motor area (SMA) | | Located in **dorsal column** | ✗ **WRONG** | Lateral corticospinal tract is in the **lateral funiculus**, NOT dorsal column. Dorsal columns carry proprioception and vibration (fasciculus gracilis and cuneatus) | | Internal capsule damage → contralateral hemiparesis | ✓ Correct | Lesion here affects all descending motor fibres before decussation | **High-Yield:** The **lateral corticospinal tract** occupies the **lateral funiculus** (white matter region), making it vulnerable in lateral cord syndromes (e.g., Brown-Séquard). The dorsal columns are strictly sensory (fasciculi gracilis and cuneatus). **Clinical Pearl:** A patient with a lacunar stroke affecting the internal capsule presents with pure motor hemiparesis on the contralateral side, confirming the tract's anatomical integrity from cortex to spinal cord. ### Anatomical Diagram ```mermaid flowchart TD A["Motor Cortex<br/>(Brodmann 4 & 6)"]:::outcome --> B["Internal Capsule<br/>(genu & post. limb)"]:::action B --> C["Cerebral Peduncle<br/>(midbrain)"]:::action C --> D["Basis Pontis<br/>(pons)"]:::action D --> E["Pyramids<br/>(medulla)"]:::action E --> F{"Decussation?"}:::decision F -->|"~90% cross| G["Lateral Corticospinal Tract<br/>(lateral funiculus)"]:::outcome F -->|"~10% uncrossed| H["Ventral Corticospinal Tract<br/>(ventral funiculus)"]:::outcome G --> I["Contralateral Motor Neurons<br/>(anterior horn)"]:::action H --> J["Ipsilateral Motor Neurons<br/>(anterior horn)"]:::action ``` **Mnemonic:** **LCSF** = **Lateral Corticospinal** tract is in the **Lateral Funiculus** (crossed); **VCSF** = **Ventral Corticospinal** tract is in the **Ventral Funiculus** (mostly uncrossed).