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• Parasympathetic afferent and efferent innervation of the bladder and urethra. The preganglionic efferents originate in the sacral parasympathetic nucleus (SPN) of the S2-S4 spinal cord. Preganglionics synapse in the pelvic plexus or within the bladder or urethra. Neurons conveying afferent signal to the spinal cord dorsal horn have the cell bodies located in the S2-S4 dorsal root ganglia (DRG). Both afferent and efferent pathways are necessary for micturition and pain travel in the pelvic nerve. • Sympathetic afferent and efferent innervation of the bladder and urethra. The preganglionic efferents originate in the interomediolateral cell column (IMLC) of the T11-L2 spinal cord. Preganglionics can synapse on postganglionics in the sympathetic chain or pelvic plexus. Afferents have their cell bodies located in the T11-L2 DRG. The hypogastric nerve conveys sympathetic afferents and efferents. Note that the pelvic nerve also contains sympathetic fibers from the chain ganglia. • Somatic afferent and efferent innervation of the bladder and urethra. Efferent neurons reside in Onuf's nucleus (ON) of the S2-S4 spinal cord. The efferents supply the innervation of the external urethral sphincter through the pudendal nerve. Data indicate that the external urethral sphincter is both autonomically and somatically innervated (see text). Somatic afferents are conveyed to the dorsal horn of the spinal cord with their cell bodies in S2-S4 DRG. • A, Storage reflexes. During the storage of urine, distention of the bladder produces low-level bladder afferent firing. Afferent firing in turn stimulates the sympathetic outflow to the bladder outlet (base and urethra) and pudendal outflow to the external urethral sphincter. These responses occur by spinal reflex pathways and represent “guarding reflexes,” which promote continence. Sympathetic firing also inhibits detrusor muscle and transmission in bladder ganglia. • B, Voiding reflexes. At the initiation of micturition, intense vesical afferent activity activates the brainstem micturition center, which inhibits the spinal guarding reflexes (sympathetic and pudendal outflow to the urethra). The pontine micturition center also stimulates the parasympathetic outflow to the bladder and internal sphincter smooth muscle. Maintenance of the voiding reflex is through ascending afferent input from the spinal cord, which may pass through the periaqueductal gray matter (PAG) before reaching the pontine micturition center. • The upper motor neuron refers to injuries that are above the level of the anterior horn cell. This results in a spastic type of paralysis. Conversely, the lower motor neuron injury refers to an injury at or below the anterior horn cell that results in the flaccid type paralysis. This is usually seen in nerve root injuries or in the cauda equina syndrome