All of the following structures pass through the internal capsule EXCEPT:

Explanation

## Internal Capsule — Anatomical Organization The internal capsule is a V-shaped white matter structure that contains both ascending and descending fiber tracts. Understanding which fibers traverse which limb is critical for localizing stroke lesions. ### Anterior Limb **Key Point:** Contains thalamocortical radiations connecting the dorsomedial and anterior thalamic nuclei to the prefrontal cortex. Also carries some frontopontine fibers. ### Genu (Bend) **Key Point:** Carries corticobulbar (corticobulbar) tract fibers projecting from the motor cortex to the brainstem motor nuclei (CN III–XII). These fibers control facial, tongue, and pharyngeal muscles. ### Posterior Limb **Key Point:** Contains the major descending motor pathway — the corticospinal tract — which carries ~1 million axons from the motor cortex (M1, M2, premotor) to the spinal cord. Also carries sensory radiations (thalamocortical) from the VPL thalamus to the somatosensory cortex. ### Superior Longitudinal Fasciculus (SLF) **High-Yield:** The SLF is an association fiber tract that connects the frontal, parietal, and temporal lobes *within the cerebral hemisphere*. It does NOT pass through the internal capsule. It runs in the white matter of the corona radiata and superior longitudinal direction, but remains lateral to and separate from the internal capsule proper. **Clinical Pearl:** Lesions of the SLF cause conduction aphasia (preserved comprehension and repetition but impaired naming and fluency). Internal capsule lesions cause contralateral hemiplegia and hemisensory loss, not language deficits. ### Why the Distractor is Wrong | Structure | Location in IC | Function | |-----------|---|---| | Corticospinal tract | Posterior limb | Motor control to limbs | | Thalamocortical radiations | Anterior limb | Sensory relay | | Corticobulbar tract | Genu | Motor control to cranial nerves | | **Superior longitudinal fasciculus** | **NOT in IC** | **Association fiber — intra-hemispheric** | **Mnemonic:** **GAP** = Genu (corticobulbar), Anterior limb (thalamocortical), Posterior limb (corticospinal). The SLF is NOT part of this trio — it's a separate association bundle.