Wireless sensor networks are currently experiencing widespread enthusiasm in the field of research, mainly because of the great benefits they promise in terms of flexibility, cost, range and robustness. In addition, such networks find use in a wide variety of applications, for example in collecting remote data, type of climate monitoring, seismic activity, or in other areas such?as home automation and medical. Unfortunately, their disadvantages are up to their promises. Indeed, the sensor nodes are subjected to high energy consumption constraints due to their compact size as well as the deployment environment. Frequent replacement of batteries is excluded in a field that can be difficult to access. Therefore, the main challenge remains as a result of miniaturization and reduces power consumption to maximize network lifetime. The objective of this work is to make a thorough study of the energy consumption in wireless sensor networks. The study points are addressed at the media access protocol or MAC protocol.