What part of runners and nervous system gets her ready to go at the sound of the starting gun -apex

Sympathic nervous system is part of Autonomic nervous system  control the function.it control  and ready the runners for fight and flight conditions.

The sympathetic nervous system can accelerate heart rate, widen bronchial passages, decrease motility of the large intestine, constrict blood vessels, increase peristalsis in the esophagus, cause pupillary dilation, piloerection  and perspiration (sweating), and raise blood pressure.

The sympathetic nervous system connects the internal organs to the brain by spinal nerves. sympathetic nervous system are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.

chordata is the answer