Which fiber type carries sensory information, such as from chemoreceptors and mechanoreceptors, to the brainstem?

Afferent fibers are responsible for transmitting sensory information from peripheral receptors, such as chemoreceptors, which detect changes in chemical concentrations, and mechanoreceptors, which respond to mechanical pressure or distortion, to the central nervous system. The sensory data gathered by these receptors is crucial for the brain to interpret and respond to the surrounding environment.

In contrast, efferent fibers carry signals away from the central nervous system to effectors, such as muscles and glands, thereby controlling movements and functions. Autonomic fibers are a subset of efferent fibers specifically involved in involuntary bodily functions. Contractile fibers, on the other hand, refer to muscle fibers responsible for muscle contraction and movement, rather than the transmission of sensory information.

Overall, it is the afferent fibers that play the essential role in relaying sensory information to the brainstem, making this the correct answer.