Traumatic brain injury (TBI) is a widespread debilitating condition which affects the brain at many architectural scales. The development of effective therapies for TBI is dependent on understanding and integrating mechanisms of injury across multiple spatial and temporal scales. In this thesis, we characterized the response to injury from the single cell scale to the level of small circuits of hundreds of neurons (islands), an ensemble size which has recently emerged as an important level of architecture for brain function. First, we developed an in vitro experimental platform for islands of primary cortical neuronal cultures, and combined it with Ca2+ imaging and a single-cell model of mechanical injury to non-invasively probe activity in neuronal circuits and their response to targeted inactivation of individual neurons. Our key finding that cellular density is a key modulator of island activity – likely through the excitatory/inhibitory balance modulation - which in turn dictates a circuit’s level of resilience to injury, highlights the importance of the structure-function relationship and understanding how single cell disruptions propagate to the network level. Second, we incorporated this knowledge into the study of a model of single-cell fluid shear injury to characterize the spatial and temporal scale of the network response to partial injury. We found that mild injury of as few as a quarter of the neurons in a circuit triggers immediate network-wide activity changes which progress to long-term activity and network degradation by the chronic period (20 hrs). The response spreads beyond the individual cells and islands injured, pointing to a different set of regulatory mechanisms which emerge at the network level to guide the global response of the circuit to injury. Taken together, our studies provide a robust experimental platform to investigate the role of single-cell connectivity in the physiological function of more complex topologies and their response to injury. Furthermore, our longitudinal and spatial assessment of network function following targeted injury, albeit in a simplified model, highlights the long-lasting, far-reaching alterations in circuit function that can result from mild-mechanical injury, thus beginning to suggest some cellular correlates for the long-lasting alterations in cognition experienced by TBI patients.