Cranial nerves NCS

Nerve	Active	Reference	Ground	Stimulation	Lat Max (Onset)	Amp. (Min)
Facial nerve	Nasalis, on the lateral mid-nose. The subject may “wrinkle the nose” and the electrode is placed on the most prominent bulge of the muscle. Orbicularis oculi under the eye in line with the pupil. An alternate position is at the lateral border of the eye. Orbicularis oris lateral to the angle of the mouth	on the tip or bridge of the nose	over the base of the neck or on the cheek	Preauricular stimulation is performed with the cathode just anterior to the lower ear over the substance of the parotid gland and several centimeters superior to the angle of the mandible. Postauricular stimulation is performed by placing the cathode just behind the lower ear, below the mastoid process and behind the neck of the mandible. The anode is posterior	3.5 3.8	>50% difference is significant >90% indicate surgery
Cranial accessory	Over the upper trapezius, about 9 cm lateral to the 7th spinous process.	3 cm lateral to the active electrode.	between the stimulating and recording electrodes	In the posterior triangle of the neck, 1–2 cm posterior to the posterior border sternocleidomastoid muscle and slightly above the midpoint of this muscle. This is a point halfway between the mastoid process and the suprasternal notch. The anode is superior	3	3
Great auricular nerve	On the back of the ear lobe	2 cm above the active electrode	On the back of the neck.	8 cm from the active electrode along the lateral border of the sternocleidomastoid muscle, with the cathode superior	1.6
Blink reflex	Over the lower lateral orbicularis oculi muscle bilaterally	Over the temple or the lateral surface of the nose above the nasalis muscle	Under the chin or on the forehead or cheek	Cathode (C) over the supraorbital nerve at the supraorbital notch. The anode is superolateral. A ratio of R1 latency (R) to the direct response latency (D) can be calculated. This R/D ratio should not fall outside the range of 2.6 to 4.6. A larger ratio, with a normal D, is indicative of slowing of the trigeminal portion. If the R/D ratio is low, it is indicative of slowing of the facial nerve. A glabellar tap with a special hammer can be used instead of electrical stimulation	Direct latency: 4 Ipsilateral R1: 13 Ipsilateral R2: 40 Contralat R2: 41 Several blink responses should be tested and the shortest latencies chosen. Latency should be measured to the first deflection from the baseline