Somatic nervous system

The external stimulus from the environment sends the signal to the sensory neuron (afferent neuron). After that, the neuron send the information up to the central nervous system (CNS), which as an intermediate neuron. CNS intergrates and interprets all the information. The output signal is released and transmitted to the motor neuron (efferent neuron). Therefore, the somatic neurons are causing the voluntary movement of muscle, for instance, skeletal muscle. In contrast, the smooth muscle is having involuntary movement of muscle contraction. For examples, digestive system, respiratory tract, blood vessel and reproductive tract (uterus).