accumulations of grey matter inside the inner and outer tubercles of the medulla on the back of the medulla. The nuclei are switching stations for the signal flow in the back strings, i.e. sensory information from the skin and muscles that allows us to know how different body parts move and where they are and to determine the nature of different objects with the help of touch (e.g. when you separate a paper ball from a coin with your hand in your pocket).
The nerve fibers leaving the hind cord nuclei cross over the midline, form the medial lemnic and go up to the thalamus.