A neuromonitoring system utilizes transcutaneous, trans-abdominal nerve root stimulation to monitor the health and status of the motor neural pathways of the lower extremities during the portions of a surgical procedure in which a tissue retraction assembly is used to maintain an operative corridor. A method of monitoring the status of nerve during a spinal surgical procedure delivers a transcutaneous, trans-abdominal stimulation signal to the spine. A determination is made of a stimulation threshold required to elicit a neuromuscular response from the stimulation signal.