A text-book of physiology, for medical students and physicians . cord to terminate in the lower cervical region. From this pointthe path is continued by spinal neurons which leave the cord in theeighth cervical and the first and second thoracic spinal nerves andpass by way of the corresponding rami communicantes into thesympathetic chain at the level of the first thoracic ganglion. Fromthis point the fibers pass upward in the cervical sympathetic with-out terminating until they reach the superior cervical ganglion nearthe base of the skull. From this ganglion the path is continuedby sympatheti
A text-book of physiology, for medical students and physicians . cord to terminate in the lower cervical region. From this pointthe path is continued by spinal neurons which leave the cord in theeighth cervical and the first and second thoracic spinal nerves andpass by way of the corresponding rami communicantes into thesympathetic chain at the level of the first thoracic ganglion. Fromthis point the fibers pass upward in the cervical sympathetic with-out terminating until they reach the superior cervical ganglion nearthe base of the skull. From this ganglion the path is continuedby sympathetic (postganglionic) fibers which pass to the Gasserianganglion and unite with its ophthalmic branch. Subsequentlythey leave the ophthalmic nerve in the long ciliary branches. Thesefibers under normal conditions are in constant (tonic) activity, sothat if the path is interrupted at any point by section of the cervical Gasserian. v—N Ojbhttalmie branJiof£t^ Zona ciliary nerves. 6anSlior,.\ > VMotor jiupillae. Superior Ceruieal/Ganglion/ ~? / Q/ju/ialCord A. / 3°Cranial W/ nerve. CuwryGanjlvoru Short Ciliary heroes CeruiealSjmpaVietic Fig. 135.—Schema showing the path of the preganglionic and postganglionic fibersto the ciliary and to the sphincter and dilator muscles of the iris.—(Modified fromSchultz.) The course of the long ciliary nerves is represented very diagrammatically. sympathetic, for instance—the pupil is seen to contract. Thisconstant activity may be referred directly to the activity of thespinal neurons whose cells lie in the spinal cord in the lower cervicaland upper thoracic region. The cells in question constitute whatis sometimes called the lower ciliospinal center of Budge. The Accommodation Reflex and the Light Reflex of theSphincter When the eye is accommodated for a nearobject by the contraction of the ciliary muscle there is always asimultaneous contraction of the sphincter pupillse whereby thepupil is narrowed. The net is one of
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