The nerves that control voluntary responses like those connected to your muscles are part of the nervous system.

SOMATIC NERVOUS SYSTEM

The neuron, a cell that composes the nervous system. For example a brain, an organ composed of thousands of neural fibers and glial cells that performs many important organismic functions. 
Neurons are specialised cells that have dendrites, axons and terminal buttons that sends and receives stimuli from the environment and transduces it into a meaningful information and understand the complexities which the brain now functions. 

From the sensory organ received by the sensory neuron the message is sent to the brain and then back to the motor neuron to the muscle or organ responsible.