**Core Concept**
The question is testing the understanding of the neural pathway controlling voluntary muscle movement. The anterior horn cells in the spinal cord are motor neurons responsible for transmitting signals to skeletal muscles. The question specifically asks about the relay via interneurons, which implies a complex neural circuit involving both motor and interneurons.

**Why the Correct Answer is Right**
The correct answer involves the reflex arc, specifically the monosynaptic stretch reflex. In this reflex, the afferent (sensory) neuron stimulates an interneuron, which in turn synapses with the anterior horn cell (motor neuron). This interneuron relay allows for fine-tuning and modulation of the reflex response. The monosynaptic stretch reflex is a fundamental concept in neurophysiology, and understanding its neural circuit is crucial for medical students.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because the monosynaptic stretch reflex does not involve a relay via interneurons, but rather a direct synapse between the afferent neuron and the motor neuron.

**Option B:** This is incorrect because the polysynaptic reflex does involve interneurons, but it is not the specific example being asked about in the question.

**Option C:** This is incorrect because the autonomic nervous system, particularly the sympathetic and parasympathetic divisions, do not directly involve interneurons in the same way as the monosynaptic stretch reflex.

**Option D:** This is incorrect because the cerebellum plays a role in motor coordination and learning, but it is not directly involved in the relay via interneurons on anterior horn cells.

**Clinical Pearl / High-Yield Fact**
The monosynaptic stretch reflex is a classic example of a spinal reflex that can be used to assess the integrity of the motor neuron pathway. This reflex is often tested clinically by assessing the knee jerk reflex, which is a monosynaptic stretch reflex involving the quadriceps muscle.

**Correct Answer: B. Polysynaptic reflex.**