Energy and communication bandwidth are scarceresources in wireless sensor and actuator networks. Recentresearch efforts considered the control of physical processes oversuch resource limited networks. Most of the existing literatureaddressing this topic is dedicated to periodically sampled controlloops and scheduled communication, because it simplifies theanalysis and the implementation. We propose instead an aperiodicnetwork transmission scheme that reduces the number oftransmission instances for the sensor and control nodes, therebyreducing energy consumption and increasing network lifetime,without sacrificing control performance. As an added benefit,we show the possibility of dynamically allocating the networkbandwidth based on the physical system state and the availableresources. In order to allow timely, reliable, and energy efficientcommunication, we propose a new co-design framework forthe wireless medium access control, compatible with the IEEE802.15.4 standard. Furthermore, we validate our approach in areal wireless networked control implementation.