Final answer:
The ventral and dorsal roots of a spinal nerve carry only motor and sensory fibers respectively, while the ventral and dorsal rami contain mixtures of both motor and sensory fibers, with the dorsal ramus innervating the back and the ventral ramus the front and limbs.
Step-by-step explanation:
The difference between ventral and dorsal roots versus ventral and dorsal rami of a spinal nerve lies in their function and the types of fibers they carry. The ventral roots contain only the axons of motor neurons that emerge from the anterior or lateral horns of the spinal cord and are responsible for transmitting motor commands from the central nervous system to the muscles or other effector organs. On the other hand, the dorsal roots contain only the axons of sensory neurons that convey sensory information from the periphery to the central nervous system.
After the spinal nerve exits the intervertebral foramen, it then divides into the dorsal and ventral rami. The dorsal ramus innervates the skin and muscles of the back, while the ventral ramus provides sensory and motor innervation to the anterior and lateral parts of the trunk as well as the limbs. Both the dorsal and ventral rami contain mixtures of sensory and motor fibers, unlike the strictly function-separated dorsal and ventral roots.