**Core Concept:** Innervation of joints is essential for joint motion, sensation, and reflexes. Joints are innervated by somatic and autonomic nerves, primarily from the ventral root of spinal nerves.

**Why the Correct Answer is Right:** The correct answer (D) refers to the spinal nerves, which are involved in somatic innervation, responsible for voluntary movement and sensation. Joints receive their innervation from the ventral roots of spinal nerves, which carry information about touch, pain, and temperature.

**Why Each Wrong Option is Incorrect:**

A. Autonomic nerves: While some joints (e.g., carpal tunnel) do have autonomic innervation, this option is incorrect because the majority of joint innervation comes from spinal nerves.

B. Vagus nerve: The vagus nerve is part of the autonomic nervous system and does not innervate joints directly. Joints primarily receive their innervation from the spinal nerves.

C. Sympathetic nerves: Similar to option B, sympathetic nerves are part of the autonomic nervous system and do not directly innervate joints.

**Innervated structures of joints are all except:**

- Spinal nerves (ventral roots) innervate joints for somatic sensation and movement.

**Clinical Pearl:** A thorough understanding of joint innervation is essential for clinical practice, as it helps to appreciate the role of nerves in joint function, pain, and reflexes. This knowledge may guide appropriate diagnosis and treatment of joint-related conditions.