The cranial nerve that accounts for about 80% of parasympathetic outflow is the:

The cranial nerve that accounts for about 80% of parasympathetic outflow is the:

• A. Vagus Nerve
• B. Optic Nerve
• C. Trigeminal Nerve
• D. Hypoglossal Nerve

Answer: (A)

Parasympathetic outflow from the brainstem is carried mainly by a single cranial nerve, the vagus nerve, which provides about 80% of the parasympathetic input to the body. The vagus carries preganglionic parasympathetic fibers that innervate the heart, lungs, and most of the gastrointestinal tract, with synapses occurring in ganglia near or within the target organs. The other nerves listed do not contribute meaningful parasympathetic efferents: the optic nerve is purely sensory for vision; the trigeminal nerve is primarily sensory (and motor to muscles of mastication) with little to no parasympathetic output; the hypoglossal nerve is a somatic motor nerve to the tongue. Because of its broad distribution and dominant role in autonomic control of thoracic and abdominal organs, the vagus nerve accounts for the majority of parasympathetic outflow.

Parasympathetic outflow from the brainstem is carried mainly by a single cranial nerve, the vagus nerve, which provides about 80% of the parasympathetic input to the body. The vagus carries preganglionic parasympathetic fibers that innervate the heart, lungs, and most of the gastrointestinal tract, with synapses occurring in ganglia near or within the target organs. The other nerves listed do not contribute meaningful parasympathetic efferents: the optic nerve is purely sensory for vision; the trigeminal nerve is primarily sensory (and motor to muscles of mastication) with little to no parasympathetic output; the hypoglossal nerve is a somatic motor nerve to the tongue. Because of its broad distribution and dominant role in autonomic control of thoracic and abdominal organs, the vagus nerve accounts for the majority of parasympathetic outflow.