Developing a technology able to measure in-vivo and non-invasively the electrical activity of the human spinal cord would fulfill an important and still unmet need in both basic and clinical research. In this work, we describe a novel recording and analysis pipeline to obtain non-invasive, high-resolution images of the electrical activity of the spinal cord in humans (Electrical Spinal Imaging, ESI). Using this approach, we provide a detailed description and physiological characterization of the spatiotemporal dynamics of the peripheral, spinal and cortical activity elicited by somatosensory stimulation. We also demonstrate that attention modulates synaptic activity at spinal cord level. Specifically for the spinal cord activity, we obtained the following four results. (1) We identified three distinct responses in the time domain: sP9, sN13 and sP22. (2) The sP9 is a traveling wave reflecting the afferent volley entering the spinal cord through the dorsal root. (3) In contrast, the sN13 and sP22 reflect local, synaptic activity. (4) While the sP9 response is first seen on the dorsal electrodes ipsilateral to the stimulated side, the sN13 and sP22 were not clearly lateralised with respect to the side of stimulation. (5) Focusing attention on the stimulus strongly modulates the amplitude of the sP22, but not that of the sP9 and sN13. The proposed method, besides offering critical insights into the spatiotemporal dynamics of somatosensory processing within the spinal cord, paves the way for precise non-invasive monitoring of spinal cord functions and neural pathway integrity in basic and clinical neurophysiology.