ABSTRACT
The autonomic nervous system is regarded both as an afferent and efferent system, since it is important to understand the autonomic reflexes when considering the pharmacology of drugs acting on the autonomic nervous system and its effectors. The description of the autonomic nervous system is divided into two components – the efferent pathways leaving the spinal cord or brain stem and the afferent pathways transmitting sensory data to the central nervous system (CNS). The efferent pathways originate in the brain stem and spinal cord. The cell bodies of neurones leaving the spinal cord are located in the lateral portion of the intermediate zone of the grey matter throughout the thoracic and the first two or three lumbar segments and in the second, third and fourth sacral segments. The sympathetic fibres originate from the upper three or four thoracic segments of the spinal cord.
