The tongue has a lot of taste buds on it. These taste buds contain the sensory receptors that respond to the food particles. The sensory receptors emit an electrical signal that is carried by the sensory neurons present in the tongue to the brain. The brain has a lot of inter-neurons that help in processing the signal and form bridge between the sensory and motor neurons. The brain analyses and decodes the taste from the electrical signal and relays an output through the motor neurons to the muscles present in the tongue and the cheeks to spit the sour milk out.