USA Biology Olympiad (USABO) Practice Exam

Where are the cell bodies of afferent (sensory) nerves involved in somatic reflexes located?

1. Ventral root ganglion

2. Dorsal root ganglion

3. Cerebellum

4. Spinal cord

The correct answer is: Dorsal root ganglion

The cell bodies of afferent (sensory) nerves that are involved in somatic reflexes are located in the dorsal root ganglion. This structure is a collection of sensory neurons' cell bodies found just outside the spinal cord. When a stimulus occurs, such as touching a hot surface, sensory receptors in the skin detect this change and send signals through afferent nerves. These signals travel towards the spinal cord, where they enter through the dorsal roots. The dorsal root ganglion serves as the relay point for these sensory signals before they ascend to the brain or are processed for reflexive actions. This arrangement enables a quick response to stimuli because the reflex arc can involve direct connections between the sensory neurons and motor neurons, allowing for immediate reactions without the involvement of higher brain centers for initial processing. Therefore, the correct answer is based on the anatomical understanding of where sensory neuron cell bodies reside and how they contribute to the reflex pathways in the nervous system.