Final answer:
The statement is true; all spinal nerves contain both sensory and motor axons, classifying them as mixed nerves.
Step-by-step explanation:
The statement that all spinal nerves are mixed nerves is true. Spinal nerves are composed of both sensory and motor axons, making them mixed nerves. Specifically, the sensory axons enter the spinal cord through the dorsal nerve root, while the motor fibers, which include both somatic and autonomic nerves, emerge from the ventral nerve root. These nerves are vital as they transmit sensory and motor information between the spinal cord and the rest of the body, playing a crucial role in the nervous system's function.