Final answer:
The correct statement about spinal nerves is that they are all mixed, containing both sensory and motor fibers. The correct answer is option a.
Step-by-step explanation:
A true statement about spinal nerves is that they are all mixed, meaning they contain both sensory and motor fibers. Spinal nerves are critical components of the nervous system, transmitting information to and from the spinal cord. The sensory fibers carry sensory information into the brain, targeting specific sensory nuclei, while motor fibers arise from motor neurons in the spinal cord and target skeletal muscles for movement.
The arrangement of spinal nerves is highly organized, with each nerve giving rise to two roots: the dorsal and the ventral root. The dorsal root harbors the sensory axons, with their cell bodies located in the dorsal root ganglia. Sensory neurons receive input from the periphery, such as the skin or sensory organs. On the other hand, the ventral root contains the motor fibers, emanating from the ventral gray matter of the spinal cord and responsible for stimulating muscle contractions.
Together, these roots combine to form a mixed nerve that can both perceive sensory information and create motor responses. Consequently, the correct answer to the question is option 'a': All spinal nerves are mixed.