Proprioceptive Impulse Patterns during Contraction of Irtrinsic Laryngeal Muscles

In histological serial sections of four different laryngeal muscles in the dog no spindles were found. — Evidence of proprioceptive reflexes induced by displacement of laryngeal cartilages and mediated by afferent inflow via the internal laryngeal nerve prompted an analysis of the proprioceptive impulse discharges in this nerve. Twitch and tetanic contractions of slow and fast laryngeal muscles were used to induce ieproducible movement patterns in the larynx. Comparison with manually applied pressure stimulation indicated that the receptors activated during muscle contraction are located outside the muscles, mainly in ligament structures and around joints. During twitch contraction receptor activation was observed in the form of an acceleration of spontaneously active units or an initiation of discharges in initially silent units, and receptor inhibition in the form of a pause of pre‐existent activity. The duration of both types of responses could be related to the time course of contraction. The same types of effect were induced by tetanic contraction. Typical and atypical responses obtained during the dynamic and static phases of tetanic contraction of varying amplitude are described. Most units responded to contractions of two or three muscles, and some common combinations of excitatoiy and inhibitory effects in one and the same unit are presented. It is concluded that the impulse patterns of the receptors studied are differentiated enough to serve a proprioceptive control mechanism.