Which of the following agents have been proposed as sensory neurotransmitters for the colon?

b. Substance P

c. Calcitonin gene-related peptide

Sensory neurons within the wall of the colon perceive mechanical and chemical stimuli from the luminal contents. Their axons project both to motor neurons as well as to prevertebral ganglia and higher neural centers. Mediators of such sensory input appear to be substance P and calcitonin-gene related peptide. The role of sensory neurons in transmitting information remains uncertain, but since they have been shown to synapse on the excitatory and inhibitory motor neurons, they probably play an important role in modulating spontaneous contractions.