How is the nervous system able to respond to changes in the environment so quickly?

When a receptor detects a stimulus, the information is sent through a sensory neuron to the brain which sends information back to the effector through a motor neuron and effector produces a response. The processes in the nervous system, which allows the body to respond to changes in the environment, are usually coordinated by the brain. However, if a rapid reaction is needed, the response is not coordinated by the brain and this reaction is called a reflex action.