Both preganglionic sympathetic fibers and preganglionic parasympathetic fibers are cholinergic. Within the ganglion the axons synapse onto the postganglionic parasympathetic neurons. The vagus nerve activity reflects the physiological modulation of the parasympathetic and sympathetic nervous system. The insula controls autonomic functions through the regulation of the sympathetic and parasympathetic systems. Pelvic splanchnic nerves are the primary source for parasympathetic innervation. These ganglia are both parasympathetic and sensory ganglia. Input from the parasympathetic nervous system occurs via the vagus nerve. Acetylcholine is the primary neurotransmitter of the parasympathetic nervous systems. It does this by influencing the sympathetic and parasympathetic nervous systems via the vagus nerve. This inhibition causes an increase in synaptic acetylcholine and over-stimulation of the parasympathetic nervous system. X. There are also a number of parasympathetic cranial nerve ganglia. The vagus gives no parasympathetic to the cranium. This can cause a spontaneous release of neurotransmitters via sympathetic or parasympathetic nerve channels. Its contraction is inhibited by parasympathetic fiber stimulation. Atropine's actions on the parasympathetic nervous system inhibit salivary and mucus glands.