The Argyll Robertson pupil, also known as the pupillary light reflex, can be absent in patients with tertiary syphilis affecting the central nervous system. This condition is characterized by the pupil's failure to respond to light but maintaining a normal accommodation response. The exact mechanism is controversial, but it is believed that optic tract fibers projecting to the pretectal area in the midbrain may be damaged in syphilitic meningitis. These fibers can be affected by the presence of spirochetes in the subarachnoid space. It is important to note that the pretectal area connects to the Edinger-Westphal nucleus, which controls the parasympathetic innervation of the eye and regulates the pupillary sphincter muscle. Although input to the olivary pretectal nucleus may be interrupted, the optic tract fibers projecting to the lateral geniculate nucleus remain intact, allowing for maintained vision and pupillary constriction during accommodation.

The urinary bladder's control involves both reflex pathways in the spinal cord and a supraspinal center. Sympathetic innervation originates from preganglionic sympathetic neurons in the upper lumbar segments of the spinal cord. These neurons inhibit the smooth muscle of the bladder, known as the detrusor muscle, throughout its body. However, they excite the smooth muscle in the trigone region and the internal urethral sphincter. During bladder filling, the detrusor muscle is tonically inhibited, preventing urine from being voided. This inhibition is mediated by the action of norepinephrine on β receptors. On the other hand, norepinephrine's action on α receptors results in excitation of the trigone and internal urethral sphincter.

The voiding process also involves the external sphincter of the urethra, which is a striated muscle. It receives innervation from motor axons in the pudendal nerves, which are somatic nerves. The motor neurons responsible for controlling the external sphincter are located in the Onuf nucleus, situated in the ventral horn of the sacral spinal cord.

Parasympathetic preganglionic neurons controlling the bladder are found in the sacral spinal cord, specifically the S2 and S3 or S3 and S4 segments. These cholinergic neurons project through the pelvic nerves and distribute to ganglia in the pelvic plexus and the bladder wall. Postganglionic parasympathetic neurons within the bladder wall innervate the detrusor muscle, as well as the trigone and sphincter. Parasympathetic activity results in contraction of the detrusor muscle and relaxation of the trigone and internal sphincter, ultimately leading to micturition or urination. Among these postganglionic neurons, some are cholinergic while others are purinergic, releasing ATP.

The micturition reflex plays a significant role in the control of micturition.
Thepupillarylightreflexissometimesabsentinpatientswithtertiary(advanced)syphilis,whichaffectstheCNS(i.e.,intheformoftabesdorsalis).Althoughthepupilfailstorespondtolight,ithasanormalaccommodationresponse.ThisconditionisknownastheArgyll Robertson pupil. Theexactmechanismiscontroversial.Oneexplanationrestsonthefactthatsomeoptictractfibersprojecttothepretectalareainthemidbrain.Thesefiberscanbedamagedinsyphiliticmeningitis,possiblybythepresenceofspirochetesinthesubarachnoidspace.NotethatthepretectalareaprojectstotheEdinger-Westphalnucleus,alsointhemidbrain,whosecellsoriginatetheparasympatheticinnervationoftheeye,whichcontrolsthepupillarysphinctermuscle.Althoughinputtotheolivarypretectalnucleusisinterrupted,theoptictractfibersprojectingtothelateralgeniculatenucleusarenotdestroyed,andthusvisionismaintained,asispupillaryconstrictionduringaccommodation.
The urinary bladder is controlled by reflex pathways in the spinal cord and also by a supraspinal center (
Fig. 11.3 ). The sympathetic innervation originates from preganglionic sympathetic neurons in the upper lumbar segments of the spinal cord. Postganglionic sympathetic axons act to inhibit the smooth muscle (detrusor muscle) throughout the body of the bladder, and they also act to excite the smooth muscle of the trigone region and the internal urethral sphincter.
•Fig. 11.3 Illustration of Descending and Efferent Pathways for Reflexes That Control the Urinary Bladder. Forclarity,onlysomeofthemajorinvolvedpathwaysareshown.(RedrawnfromdeGroatWC,BoothAM.InDyckPJ,etal[eds].Peripheral Neuropathy. 2nded.Philadelphia:WBSaunders;1984.)
The detrusor muscle is tonically inhibited during filling of the bladder, and such inhibition prevents urine from being voided. Inhibition of the detrusor muscle is mediated by the action of norepinephrine on β receptors, whereas excitation of the trigone and internal urethral sphincter is elicited by the action of norepinephrine on α receptors.
The external sphincter of the urethra also helps control voiding. This sphincter is a striated muscle, and it is innervated by motor axons in the pudendal nerves, which are somatic nerves. The motor neurons are located in the Onuf nucleus, in the ventral horn of the sacral spinal cord.
The parasympathetic preganglionic neurons that control the bladder are located in the sacral spinal cord (the S2 and S3 or S3 and S4 segments). These cholinergic neurons project through the pelvic nerves and are distributed to ganglia in the pelvic plexus and the bladder wall. Post-ganglionic parasympathetic neurons in the bladder wall innervate the detrusor muscle, as well as the trigone and sphincter. The parasympathetic activity contracts the detrusor muscle and relaxes the trigone and internal sphincter. These actions result in micturition, or urination. Some of the postganglionic neurons are cholinergic and others are purinergic (they release ATP).
Micturition is normally controlled by the micturition reflex (see