General Medical Information

Innervation of the Nasal Mucosa

Richard L. Mabry

Nasal innervation is composed of sensory, parasympathetic, and sympathetic components. The olfactory (first cranial) nerve and the first and second division of the trigeminal (fifth cranial) nerve supply sensory innervation to the nose. The autonomic nervous system supplies both parasympathetic and sympathetic fibers, which regulate the degree of vascular tone, turbinate congestion, and nasal secretions. Presynaptic parasympathetic fibers travel along the facial nerve as far as the geniculate ganglion and continue in the greater superficial petrosal nerve before joining the deep petrosal nerve to form the vidian nerve. The fibers travel with the vidian nerve to the sphenopalatine ganglion, where they synapse with the postganglionic neurons, which innervate the nasal mucosa. Postsynaptic sympathetic fibers pass through the sphenopalatine ganglion before terminating in the nasal mucosa. Fibers from the trigeminal nerve also pass through the sphenopalatine ganglion and transmit sensations of pain, temperature, and touch.

The location of olfactory neuroepithelium varies among individuals, and the neuroepithelium may shrink with increasing age. Olfactory neuroepithelium is generally situated on the roof of the nasal vault at the cribriform plate, superolateral aspects of the septum, and medial surfaces of the superior turbinates. Neuroepithelium can be a composite region (1 to 4 cm2) with interspersed patches of respiratory epithelium. This specialized epithelium usually is thicker (approximately 200 mm) than respiratory epithelium (approximately 70 mm), and although it contains cilia, the cilia lack dynein arms and functional ciliary beat. Excess particles overlying the olfactory neuroepithelium are removed by the ciliary beat from adjacent functional respiratory epithelia. That is, nearby cilia mobilize the mucous sheet with its entrapped particles away from the olfactory neuroepithelium.

Sensory innervation is responsible for olfaction and reflexes that elicit sneezing, laryngeal constriction, bronchoconstriction, and cardiovascular responses. Parasympathetic and sympathetic stimulation of nasal mucosa results in direct alterations of nasal flow. Parasympathetic innervation affects the nasal mucosa primarily through vasodilator or secretomotor activity leading to obstruction, whereas sympathetic innervation is primarily vasoconstrictive, which decongests the nose. Relative to nasal obstruction, parasympathetic and sympathetic effects can dramatically alter the function of the nasal mucosa.

Specific to nasal flow, nervous reflexive airflow monitoring is most sensitive at the nasal vestibule, where tactile hair (associated with the vibrissae), Iggo dome, Pacinian, and Meissner receptors abound. Afferent impulses transmitted via the trigeminal (fifth cranial) nerve allow assessment of nasal airflow from tactile, thermal, and possibly chemical sensation. Interpretation of these sensory data allows perturbation of the nasal passage through changes in mucosal hypertrophy. In healthy persons, regulation by the nasal valve, which is just posterior to the alar cartilages, is most apparent at high air velocity.