CH 3. Major divisions of the nervous system. SNS/ParaSNS originates as signals in the CNS, which result in physiological arousal/relaxation (CNS to PNS = efferent). Remember that efferent nerves carry impulses away from CNS to PNS nervous tissues - think of "effervescent" bubbling drinks. Afferent nerves carry signals from PNS receptors to the CNS.
