General visceral afferent fibers
|General visceral afferent fibers|
Scheme showing pathways of a typical spinal nerve.
6,7. Autonomic nervous system (ANS) afferent.
Note that this image merely depicts pathways in a schematic fashion – it is not anatomically correct. The efferent sympathetics exit in a loop – entering the more lateral White ramus communicans and either exiting the more medial Gray ramus communicans (grey) or traveling up/down the chain to exit grey at other ganglia.
The general visceral afferent fibers (GVA) conduct sensory impulses (usually pain or reflex sensations) from the
In the abdomen, general visceral afferent fibers usually accompany sympathetic efferent fibers. This means that a signal traveling in an afferent fiber will begin at sensory receptors in the afferent fiber's target organ, travel up to the ganglion where the sympathetic efferent fiber synapses, continue back along a
The only GVA nerves in the abdomen that do not follow the above pathway are those that innervate structures in the distal half of the sigmoid colon and the rectum. These afferent fibers, instead, follow the path of parasympathetic efferent fibers back to the vertebral column, where the afferent fibers enter the S2-S4 sensory (dorsal root) ganglia followed by the spinal cord.
The course of GVA fibers from organs in the pelvis, in general, depends on the organ's position relative to the pelvic pain line. An organ, or part of an organ, in the pelvis is said to be "above the pelvic pain line" if it is in contact with the peritoneum, except in the case of the large intestine, where the pelvic pain line is said to be located in the middle of the sigmoid colon. GVA fibers from structures above the pain line follow the course of the sympathetic efferent fibers, and GVA fibers from structures below the pain line follow the course of the parasympathetic efferents. Pain from the latter fibers is less likely to be consciously experienced.