Afferent Fibres in the Hypoglossal Nerve of Cat

Hanson, J. and L. Widén. Afferent fibres in the hypoglossal nerve of cat. Acta physiol. scand. 1970. 79. 24–36. Electrical stimulation of the hypoglossal nerve in cat elicited bilateral twitching of the vibrissae and suppression of shivering. The afferent fibres which mediate these reflexes have a higher stimulus threshold than the motor fibres. They travel to the brain stem via anastomoses between the hypoglossal nerve and the vagus group in the region of the ganglion nodosum. Unitary activity was recorded in the spinal trigeminal nucleus after stimulation of the hypoglossal nerve. The reflexes are probably nociceptive reactions since similar reflexes can be evoked from the greater part of the body surface by pain stimuli. Stimulation of a peripheral branch of the hypoglossal nerve also elicited a local reflex response in the styloglossus muscle. The reflex is polysynaptic. Any tonic background activity in the muscle is inhibited by the stimulation. It is shown that this inhibition is probably not recurrent but mediated by afferent fibres via anastomoses to the vagus group. Afferent impulses evoked by stretching the tongue were recorded in the proximal part of the hypoglossal nerve trunk. These units behaved like muscle spindles. In cat these units are sparse and probably of secondary importance for movements of the tongue.