Chapter 13, End of Chapter, Review Questions, Exercise 1

The lower motor neurons are located within the ventral horn of the spinal cord. The upper motor neurons from the brain synapse with the lower motor neurons, and carry the motor information that is required to move the muscle. Thus, the lower motor neurons act as output for the motor system, and direct the contraction of the muscle it innervates. They also receive input from the sensory neurons that provide information about the length of muscle, and the interneurons that help communicate between sensory and motor neurons.  

The lower motor neurons are characterized into three types based on the muscle they innervate: visceral, branchial, and somatic. 

• Visceral motor neurons: These neurons innervate the smooth muscles forming the organs and blood vessels, the cardiac muscles and the glands. 
• Branchial motor neurons: These neurons innervate the muscles involved in mastication and facial expression. 
• Somatic Motor Neurons: These neurons innervate the skeletal muscles.