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Wireless sensor network (WSN) consists of tiny sensor nodes with sensing, computation and wireless communication capabilities. Now a days, it is finding wide applicability and increasing deployment, as it enables reliable monitoring and analysis of environment. The design of routing protocols for WSN is influenced by many challenging factors like fault tolerance, energy efficiency, scalability, latency, power consumption and network topology. In this paper, we mainly focus on minimizing end to end latency and energy efficiency as primary design objectives of routing protocols for WSN without overshadowing the other design factors. We present a survey of low latency, energy efficient and time critical routing protocols. TEEN (threshold-sensitive energy efficient sensor network protocol), a reactive network protocol which is well suited for time critical data sensing applications is quite efficient in terms of energy consumption and response time. APTEEN (adaptive periodic threshold-sensitive energy efficient sensor network protocol), a hybrid network protocol which gives the overall picture of the network at periodic intervals in a very energy efficient manner. SPEED is a stateless, highly efficient and scalable protocol for sensor networks which achieves end to end soft real time communication by maintaining a desired delivery speed across the network through a novel combination of feedback control and non deterministic geographic forwarding. RAP, a real-time communication architecture for large scale sensor networks which significantly reduces the end to end latency by using velocity - monotonic scheduling (VMS). RPAR, real-time power aware routing protocol which supports energy efficient real-time communication by dynamically adapting transmission power and routing decisions. We also discuss the advantages and performance issues of each routing protocol.