Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What is the main action tested for the L3 motor nerve root?

1. Flexion of the hip

2. Extension of the leg

3. Dorsiflexion of the foot

4. Plantar flexion of the foot

The correct answer is: Extension of the leg

The main action tested for the L3 motor nerve root is the extension of the leg. The L3 nerve root is primarily associated with the innervation of muscles involved in the extension of the knee, which is predominantly facilitated through the quadriceps femoris muscle. This muscle extends the leg at the knee joint and is crucial for actions such as standing up from a seated position, walking, and running. The option involving extension of the leg aligns with the neurological assessment for L3, which typically includes testing the strength of knee extension. In clinical examinations, the assessment of the L3 nerve root often involves evaluating the patellar reflex, which further highlights its role in knee extension. In contrast, the other actions mentioned do not directly relate to the primary function of the L3 nerve root, as they involve different nerve roots and muscle groups. These details highlight the specificity of the L3 motor function in relation to lower limb movements and clarify the importance of knowing which nerve root corresponds to which muscle action in the context of neurological assessments.