**Core Concept**
An Upper Motor Neuron (UMN) lesion refers to damage to the motor pathways above the level of the anterior horn cells in the spinal cord, typically involving the corticospinal tracts. UMN lesions result in a specific set of clinical features that distinguish them from Lower Motor Neuron (LMN) lesions.

**Why the Correct Answer is Right**
A UMN lesion typically presents with spasticity, increased muscle tone, and a positive Babinski sign due to the loss of inhibitory control over the spinal cord. This is because the corticospinal tracts, which are responsible for motor control, are affected. The corticospinal tracts are composed of large, myelinated axons that carry signals from the motor cortex of the brain to the spinal cord, where they synapse with interneurons and motor neurons.

**Why Each Wrong Option is Incorrect**
* **Option A:** Spasticity - This is a feature of UMN lesions, not a characteristic that distinguishes them from LMN lesions.
* **Option B:** Weakness - While weakness may be present in some cases of UMN lesions, it is not a defining feature that distinguishes them from LMN lesions.
* **Option C:** Fasciculations - Fasciculations are more characteristic of LMN lesions, which involve damage to the anterior horn cells of the spinal cord.

**Clinical Pearl / High-Yield Fact**
UMN lesions typically present with a "positive" sign, meaning that the affected patient may exhibit increased muscle tone, spasticity, or a positive Babinski sign, whereas LMN lesions typically present with a "negative" sign, such as weakness, atrophy, or hyporeflexia.

**Correct Answer: C. Fasciculations**