- Primary afferents from the thermorecptors responsive to the sensation of warmth (C fibers) enter the cord in the most lateral part of the dorsal root entry zone. A delta fibers, with recepors sensitive to cold, enter slightly more medially. Both may run up or down the cord for several segments before turning deeply to terminate on second order neurons in laminae I, II, and III. Neurons in these laminae (only one in laminae II is shown in the diagram) project by a multisynaptic route to lamina V.
- Second order neurons in lamina V send axons across the midline in the Anterior White Commissure to join the anterolateral pathway, as shown below.
- The fibers ascend through the tegmentum of the brainstem to terminate in the VPL and intralaminar nuclei of the thalamus.