Tonic and Phasic (image) Picower Institute at MIT Share Print E-Mail Caption The left panel shows the "tonic" neuron (stained green) innervating just one muscle on the right of the panel. In the next panel, one can see the phasic neuron (also stained green) connecting to more than one muscle. Credit Nicole Aponte-Santiago/MIT Picower Institute Usage Restrictions with credit Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.