Autonomic nervous system efferent pathways

Figure 9.1 The autonomic nervous system and its effector organs. The efferent pathways of this system consist of two neurons that transmit impulses from the CNS to the effector tissue, preganglionic neuron (solid line), and postganglionic neuron (dashed line). As illustrated, most tissues receive nervous input from both divisions of the ANS the sympathetic and the parasympathetic.

The autonomic nervous system is by definition that part of the nervous system that innervates smooth muscle, cardiac muscle and glands. It is thus a motor system. Perception arising from the viscera involves pathways similar to those arising from the body surface and skeletal muscle. Thus there are visceral afferent fibres that pass from the viscera to the central nervous system. Such impulses then ascend the spinal cord to the thalamus and are thence relayed to the post-central gyrus of the brain (or sensory cortex). Visceral reflex arcs use visceral afferent fibres to convey impulses to the cord, but the efferent limb of such a visceral reflex is the autonomic nervous system. Although visceral reflexes are under higher central control, it is usually impossible to bring them under the control of the will. 

Before investigating two more detailed examples of potential misuse, it is necessary first to describe something of the structure of the human nervous system. This is divided into the central nervous system (brain and spinal cord) and the peripheral nervous system.46 Information from peripheral sense organs is received via afferent pathways and processed within the central nervous system. Output from the central nervous system is sent via efferent pathways to the somatic nervous system (muscles) and to the autonomic nervous system (heart, gut, glands, etc.). 

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