Farther back in the brain is the spinal cord, which is the hollow dorsal nerve cord that chordates have. The spinal cord is protected by the vertebral column. Between each set of vertebrae, a pair of spinal nerves exits the cord and connects to the internal organs and muscles. Most fish have well designed sense organs. Chemoreceptors (chemical) are located all over the head and much of the body surface. Most fish have ears inside their heads, but they do not hear well. However, a series of pores connected to canals beneath the skin cover the head and the sides of their body. This system, called the lateral line system, detects movement.