Depending on where the "message" originates, it would generally be the periphrial nervous system carrying the message to the central nervous system, which is then processed by the appropriate neurons in the brain. The class of these nerves are the "efferent" nerves.
the olfactory nerve
The cochlea is the inner ear. It transforms sound into a message the nerves can carry to the brain.
Mostly nerves, although the blood can carry "messages" such as hormones.
Afferent nerves carry messages to and from the brain.
The Brain
afferent
The cochlea is the inner ear. It transforms sound into a message the nerves can carry to the brain.
Mostly nerves, although the blood can carry "messages" such as hormones.
Afferent nerves carry messages to and from the brain.
Sensory nerves.
neurotransmitters
It sends the message to your brain of what your seeing
The Brain
carry messages to the brain
nerves
afferent
It sends the message to your brain of what your seeing
muscle nerves carry messages from the brain to tell the muscle to contract.