Final answer:
An injury at L2, L3, or L4 would affect the patellar tendon reflex, or knee, which involves the quadriceps muscle. Testing this reflex is important in a neurological exam to assess the integrity of the lower motor neurons that control leg movement.
Step-by-step explanation:
An injury at the L2, L3, or L4 levels of the spinal cord would likely affect the patellar tendon reflex, which is also known as the knee reflex. This reflex involves the quadriceps muscle of the thigh. When the patellar tendon is struck, sensory neurons transmit a signal to the spinal cord at these lumbar segments, and a response is elicited that causes the quadriceps muscle to contract, resulting in the extension of the knee. An injury at these levels may diminish or eliminate this reflex, thus, it is an important indicator in a neurological exam to assess the functioning of the lower motor neurons (LMN) that serve the leg muscles. In the context of a neurological exam, testing reflexes is crucial. For example, the ankle reflex that involves the gastrocnemius and soleus muscles, requires the proper functioning of nerve signals within the lumbar and sacral segments of the spinal cord. A compromised reflex could indicate an issue with the respective spinal segment or nerve pathway.