Where are interneurons, sensory neurons and motor neurons found in the human body?

The three basic types of neurons are represented in the Reflex Arc above.

The Afferent Neuron or Sensory Neuron receives information from the sensory receptors and carries the impulse from the sense receptors to the central nervous system. In this example the touch receptors in the skin are relaying information through the Afferent "Sensory" Neuron from the environment to the spinal cord.

The Interneuron or the Associative Neuron is the transfer station or the decision making neuron. In the case of the reflex arc, the Interneuron would make a decision to respond or not respond based upon the intensity of the stimulus.

The Efferent Neuron of Motor Neuron would then return the impulse back to the muscle or gland that would need to respond.

We have all had the doctor strike our patellar tendon with a rubber hammer. The Afferent "Sensory" Neuron receives the information of the force of the strike on our tendon. This information is relayed quickly up the neuron to the spinal cord where the Interneuron would decide if the stimulus warrants a response. If a response is necessary the Efferent "Motor" Neuron returns the impulse to the muscle of the legs causing the lower leg to react.