The spinal nerves that innervate the whole body connect to the spinal cord through two roots on each side. Essentially, the dorsal roots carry sensory information while the ventral roots contain motor neuron axons. These two roots together form a spinal nerve.
You can also spot an enlargement on the dorsal root, called the dorsal root ganglion, which contains the cell body of the sensory neuron that enters the dorsal horn.
Figure 1: Internal Structure of the Spinal Cord