Certified Rehabilitation Registered Nurse (CRRN) Practice Exam

A neurological exam of a patient with a complete lower motor neuron lesion would show which reflex activity?

1. Bulbocavernosus absent

2. Patellar reflex present

3. Triceps reflex exaggerated

4. Plantars flexor response preserved

The correct answer is: Bulbocavernosus absent

A patient with a complete lower motor neuron lesion typically demonstrates absent reflex activity rather than exaggerated or preserved reflexes. This absence reflects the loss of the lower motor neurons that are responsible for conveying signals to the muscle fibers. In this case, the bulbocavernosus reflex, which involves the contraction of pelvic floor muscles when the glans of the penis is stimulated, would be absent due to the damage to the lower motor neuron pathway. This is a key indicator of lower motor neuron lesions, highlighting the disruption in the spinal reflex arc that is essential for reflexive actions. The other options illustrate reflexes that would either be present or exaggerated in scenarios involving upper motor neuron lesions or intact reflex pathways, which do not apply to a complete lower motor neuron lesion context. Hence, the absence of the bulbocavernosus reflex serves as a significant diagnostic criterion in assessing such a condition.