**Core Concept:** The internal capsule is a white matter tract in the brain that connects various brain regions. It consists primarily of myelinated axons from the corticospinal, corticobulbar, corticohypothalamic, and corticoreticular fibers.

**Why the Correct Answer is Right:** The correct answer, D (corticospinal fibers), is right because these fibers are primarily present in the genu of the internal capsule. Corticospinal fibers originate from the motor cortex and project to the spinal cord, playing a crucial role in voluntary movement control.

**Why Each Wrong Option is Incorrect:**
A (corticobulbar fibers) is incorrect because these fibers mainly connect the cortex and the brain stem, not the internal capsule.
B (corticohypothalamic fibers) is incorrect as these fibers connect the cortex and hypothalamus, not the internal capsule.
C (corticoreticular fibers) is incorrect because these fibers connect the cortex and the nucleus of the dorsolateral prefrontal cortex, not the internal capsule.

**Clinical Pearl / High-Yield Fact:** The internal capsule is essential for understanding neurological disorders involving the motor system, such as stroke and trauma, as disruption to these fibers can lead to various motor deficits.

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**Question:** Which of the following nerve fibers are present in the genu of internal capsule?

A. Corticobulbar fibers
B. Corticohypothalamic fibers
C. Corticoreticular fibers
D. Corticospinal fibers

**Correct Answer:** D. Corticospinal fibers