Nasal Stimulation

As another way to assess head and face sensation and behavioral reaction to cranial stimulation, a blunt instrument or cotton-tipped applicator is gently inserted into each nostril while trying to blindfold the animal with the other hand. A normal response to this stimulation is an immediate retraction of the head from the stimulus.

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Touching the nasal mucosa with a blunt probe causes stimulation of the ophthalmic and the maxillary branches of the trigeminal nerve which then passes into the skull via the orbital fissure and the rostral alar foramen respectively from where the nerves enter the pons of the brainstem.  Projections from their synapse in the pons and medulla are to the contralateral cerebral cortex for conscious perception and result in neck muscle contraction and an avoidance movement.

Insertion of a blunt probe into a nostril can be seen to stimulate the ophthalmic branch of the trigeminal nerve (CN V). A behavioral response to this stimulus is mediated by the contralateral forebrain as with the menace response. The effect of conscious perception of nasal stimulation is contraction of the neck muscles via the brain stem causing an avoidance movement of the head and neck.

Stimulation of the trigeminal nerve branches is transmitted to the point of synapse in the pons and medulla. The pontine sensory nucleus of CN V and the nucleus of the spinal tract of CN V transmit a signal to the contralateral cerebral sensory cortex which results in stimulation of the motor fibers projecting from the adjacent motor cortex. Motor cortical stimulation results in neck muscle contraction.

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