This chapter explores the topic of voluntary and reflex action and the autonomic nervous system. It begins by discussing the function of the central nervous system and discusses voluntary movement and reflex action. The chapter considers the two parts of the autonomic nervous system: the sympathetic nervous system and the parasympathetic nervous system. Voluntary movement occurs as a result of stimuli produced at will in the motor centres of the brain. Reflex action occurs as a result of the stimulation of the motor cells by stimuli transmitted by afferent neurones from the tissues. The reason for the reflex being more marked when the cord is cut off from the brain is that central centres have an inhibiting effect on reflex action. The autonomic nervous system supplies nerves to all the internal organs of the body and blood vessels. The autonomic nervous system consists of two parts: the sympathetic and parasympathetic systems.