Figure 3.

Schematic on the putative connection between the sensory branch of the trigeminal nerve (ophthalmic division), the spinal trigeminal nucleus, the facial nucleus, and the trigeminal motor nucleus. In some abnormal circumstances potentially leading to central plasticity and unmasking of silent synapses (see text), the activation of the corneal receptors and the trigeminal nerve may activate TTM motoneurons, thereby triggering TTM contraction. The TTM contraction can be objectified measuring middle ear admittance (Londero et al., 2017).