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Penile erection is a part of the human male sexual response, involving desire, excitation (erection), orgasm (ejaculation), and resolution, and autonomic nerves are involved in all phases. Autonomic innervation of smooth-muscle cells of the erectile tissue is provided by the cavernous nerve. Motor and sensory innervation is derived from the pudendal nerves and their terminal branches, that is, the dorsal nerves of the penis, which carry impulses from receptors harbored in the penile skin, prepuce, and glans. Erection begins with an increased flow in the pudendal arteries and dilatation of the cavernous arteries and helicine arterioles in association with relaxation of the smooth muscles of the trabecular network, causing engorgement of blood in the corpora. This leads to compression of subtunical venules by the resistant tunica albuginea and erection. During detumescence these events are reversed.

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Talita de Melo e Silva, Catherine Miriam Czeisler, and José Javier Otero

Breathing is essential for survival and is precisely regulated by the nervous system. From a neuroanatomical perspective, the respiratory tract is innervated by afferent and efferent autonomic nerves, which regulate aspects of airway function and ensure appropriate tissue oxygenation. The general concepts of how the peripheral nervous system (PNS) develops as it relates to lung function are reviewed. The vagus (cranial nerve X), a mixed motor and sensory nerve, supplies parasympathetic and sensory fibers to the airways. During development, preganglionic visceromotor efferent neurons of the cranial nerves arise in the hindbrain basal plate and later migrate dorsally through the neuroepithelium. The neural crest is a migratory and multipotent embryonic cell population that develops at the dorsal portion of the neural tube, which delaminates from the neuroepithelium to enter distinct pathways, forming various derivatives, among which include the peripheral nervous system. Neural crest cells emerging from the vagal region migrate into the ventral foregut and give rise to intrinsic ganglia in the respiratory tract that are innervated from the vagus and send out postganglionic fibers. The lung is innervated by sympathetic nerves derived from the upper thoracic and cervical ganglia. The sympathetic preganglionic neurons are derived from trunk neural crest cells that migrate, forming two chains of sympathetic ganglia referred to as the lateral vertebral sympathetic chains. Neural crest cells that migrate along defined pathways to generate sympathetic ganglia also derivate the dorsal root ganglia that send somatosensory afferent innervations to the respiratory tract.