1. No. 34 The Visceral Nervous System The Visceral Nervous System

2. Section 3 The Visceral Nervous System Introduction: Introduction: The visceral nervous system is a part of the whole nervous system. According to the distribution it can be divided into the central and peripheral part. The visceral nerves are mainly distributed in the viscera, cardiovascular system and secretary glands. As the somatic nerve, the visceral nerve also contains two groups of fibers, i.e. sensory (afferent) fibers and motor (efferent) fibers. The visceral nervous system is a part of the whole nervous system. According to the distribution it can be divided into the central and peripheral part. The visceral nerves are mainly distributed in the viscera, cardiovascular system and secretary glands. As the somatic nerve, the visceral nerve also contains two groups of fibers, i.e. sensory (afferent) fibers and motor (efferent) fibers.

3. The visceral motor nerves are also termed the autonomic nervous system or the vegetative nervous system because they regulate the common involuntary metabolic activities of the animal and vegetable. They manipulate the movements of the smooth muscle, cardiac muscle and the secretion of glands. The visceral motor nerves are also termed the autonomic nervous system or the vegetative nervous system because they regulate the common involuntary metabolic activities of the animal and vegetable. They manipulate the movements of the smooth muscle, cardiac muscle and the secretion of glands.

4. Ⅰ. The Visceral motor Nerves There are some obvious differences in both functions and structures between the visceral and somatic motor system. There are some obvious differences in both functions and structures between the visceral and somatic motor system. The main differences in structure are briefly described as follows: The main differences in structure are briefly described as follows: 1) Difference in effectors 1) Difference in effectors The somatic motor nerve innervates the skeletal muscles, the visceral motor nerve innervates the smooth muscle, cardiac muscle and glands. The somatic motor nerve innervates the skeletal muscles, the visceral motor nerve innervates the smooth muscle, cardiac muscle and glands. The responses of the somatomotor fibers are controlled voluntarily by consciousness, whereas the visceral motor fibers are to a large extent involuntary and unconscious. The responses of the somatomotor fibers are controlled voluntarily by consciousness, whereas the visceral motor fibers are to a large extent involuntary and unconscious.

5. 2) Difference in the fibrous components 2) Difference in the fibrous components The somatic motor nerve contains only one kind of fiber, but visceral motor nerve is divided into the sympathetic and parasympathetic nerves by which most of the visceral organs are innervated. The somatic motor nerve contains only one kind of fiber, but visceral motor nerve is divided into the sympathetic and parasympathetic nerves by which most of the visceral organs are innervated.

6. 3) Difference in number of neurons. 3) Difference in number of neurons. A single neuron is required to carry an impulse from the lower nervous centers through the somatic motor nerves to a skeletal muscle. A single neuron is required to carry an impulse from the lower nervous centers through the somatic motor nerves to a skeletal muscle. Whereas two neurons are required to transmit an impulse from the lower nervous centers through the visceral motor nerves to the active effector organ in the viscera. Whereas two neurons are required to transmit an impulse from the lower nervous centers through the visceral motor nerves to the active effector organ in the viscera. The first neurons, whose cell bodies are located in the brain stem and spinal cord, are termed preganglionic neurons which send out the preganglionic fibers. The first neurons, whose cell bodies are located in the brain stem and spinal cord, are termed preganglionic neurons which send out the preganglionic fibers. The second neurons, situated in the peripheral nerve ganglia, are called postganglionic neurons which give rise to postganglionic fibers. The second neurons, situated in the peripheral nerve ganglia, are called postganglionic neurons which give rise to postganglionic fibers. One preganglionic neuron usually synapses with one or more postganglionic neurons. One preganglionic neuron usually synapses with one or more postganglionic neurons.

7. 4) Differenct in onstruction of fiber 4) Differenct in onstruction of fiber The somatomotor fibers are all thick myelinated fibers, whereas the preganglionic fibers of visceral motor nerve are thin myelinated fibers and the postganglionic fibers are unmyelinated. The somatomotor fibers are all thick myelinated fibers, whereas the preganglionic fibers of visceral motor nerve are thin myelinated fibers and the postganglionic fibers are unmyelinated.

8. 5) Difference in distributed mood of postanglionic fibers 5) Difference in distributed mood of postanglionic fibers The somatomotor nerves are distributed peripherally in the form of nerve trunk, however, the postganglionic fibers of the nerves form the nerve plexuses around the viscera or blood vessels. The somatomotor nerves are distributed peripherally in the form of nerve trunk, however, the postganglionic fibers of the nerves form the nerve plexuses around the viscera or blood vessels. The visceral motor nerves are divided into the sympathetic and parasympathetic divisions on the basis of their features in function, shape and neurobiochemistry. The visceral motor nerves are divided into the sympathetic and parasympathetic divisions on the basis of their features in function, shape and neurobiochemistry.

9. Ⅰ ) The Sympathetic System Ⅰ ) The Sympathetic System 1. Lower level center 1. Lower level center The centers of the sympathetic system at the lower level (preganglionic neurons) are situated in the intermediolateral nuclei of lateral gray horns of T1 (or C8) ～ L2 (or L3) segments of the spinal cord. So the preganglionic nerve fibers arise from these nuclei. It is for this reason that the sympathetic division is also termed the thoracolumbar part of visceral motor nerve. The centers of the sympathetic system at the lower level (preganglionic neurons) are situated in the intermediolateral nuclei of lateral gray horns of T1 (or C8) ～ L2 (or L3) segments of the spinal cord. So the preganglionic nerve fibers arise from these nuclei. It is for this reason that the sympathetic division is also termed the thoracolumbar part of visceral motor nerve.

11. 2. Peripheral part 2. Peripheral part The peripheral part of the sympathetic nerve includes sympathetic trunks, sympathetic ganglia, the branches from the ganglia, and many sympathetic plexuses. The peripheral part of the sympathetic nerve includes sympathetic trunks, sympathetic ganglia, the branches from the ganglia, and many sympathetic plexuses. (1) Sympathetic ganglia (1) Sympathetic ganglia They are divided into paravertebral ganglia and prevertebral ganglia. They are divided into paravertebral ganglia and prevertebral ganglia.

12. 1) The paravertebral ganglia (ganglia of sympathetic trunk) 1) The paravertebral ganglia (ganglia of sympathetic trunk) They are arranged symmetrically on either side of the spinal column and are connected by interganglionic branches to form two sympathetic trunks that extend from the base of the skull to the coccyx and are divided into cervical, thoracic, lumbar, sacral and coccygeal portions. The cervical portion contains the superior, middle and inferior cervical ganglia. There are 11 or 12 thoracic, 3 or 4 lumbar and 4 or 5 sacral ganglia on each trunk. In the sacral portion, the two trunks gradually approach each other and fuse at the coccyx in the unpaired ganglion impar (coccygeal ganglion). So there are 19-24 in number on each side. They are arranged symmetrically on either side of the spinal column and are connected by interganglionic branches to form two sympathetic trunks that extend from the base of the skull to the coccyx and are divided into cervical, thoracic, lumbar, sacral and coccygeal portions. The cervical portion contains the superior, middle and inferior cervical ganglia. There are 11 or 12 thoracic, 3 or 4 lumbar and 4 or 5 sacral ganglia on each trunk. In the sacral portion, the two trunks gradually approach each other and fuse at the coccyx in the unpaired ganglion impar (coccygeal ganglion). So there are 19-24 in number on each side.

14. 2) The prevertebral ganglia 2) The prevertebral ganglia They are situated in front of the vertebral column, and are irregular ganglionic masses surrounding the visceral branches of the abdominal aorta. They are situated in front of the vertebral column, and are irregular ganglionic masses surrounding the visceral branches of the abdominal aorta. They include the celiac ganglia, the aorticorenal ganglia, the superior and inferior mesenteric ganglia. They include the celiac ganglia, the aorticorenal ganglia, the superior and inferior mesenteric ganglia.

15. (2) The communicating branches (2) The communicating branches They link the sympathetic ganglia with the corresponding spinal nerves and are divided into white and gray communicating branches. They link the sympathetic ganglia with the corresponding spinal nerves and are divided into white and gray communicating branches. 1) The white communicating branches (sympathetic preganglionic fibers) 1) The white communicating branches (sympathetic preganglionic fibers) They are the myelinated preganglionic fibers sent by the neurons in the intermediolateral nuclei of the lateral horns in all thoracic and the upper two or three lumbar segments (T1 to L3) via the anterior roots of the spinal nerve to communicate with the paravertebral ganglia. They are the myelinated preganglionic fibers sent by the neurons in the intermediolateral nuclei of the lateral horns in all thoracic and the upper two or three lumbar segments (T1 to L3) via the anterior roots of the spinal nerve to communicate with the paravertebral ganglia.

16. A preganglionic fiber of a white communicating branch, after entering the sympathetic trunk, may terminate in three ways: A preganglionic fiber of a white communicating branch, after entering the sympathetic trunk, may terminate in three ways: ① Some fibers terminate in the corresponding paravertebral ganglia and synapse with their neurons. ① Some fibers terminate in the corresponding paravertebral ganglia and synapse with their neurons. ② Some fibers pass up or down in the sympathetic trunk for a considerable distance before terminating in the superior and inferior paravertebral ganglia. ② Some fibers pass up or down in the sympathetic trunk for a considerable distance before terminating in the superior and inferior paravertebral ganglia. ③ The others pass through the paravertebral ganglia and terminate in the prevertebral ganglia via the splanchnic nerves. ③ The others pass through the paravertebral ganglia and terminate in the prevertebral ganglia via the splanchnic nerves.

18. 2) The gray communicating branches (sympathetic postganglionic fibers) 2) The gray communicating branches (sympathetic postganglionic fibers) They are the unmyelinated postganglionic fibers, emitted by neurons of the paravertebral ganglia and are situated between the sympathetic trunk and the 31 pairs of spinal nerve. They are the unmyelinated postganglionic fibers, emitted by neurons of the paravertebral ganglia and are situated between the sympathetic trunk and the 31 pairs of spinal nerve.

19. They also course in three ways: They also course in three ways: ① Accompany with the corresponding spinal nerve to the peripheral blood vessels, sweat gland and arrectores pilorum; ① Accompany with the corresponding spinal nerve to the peripheral blood vessels, sweat gland and arrectores pilorum; ② Surround the artery as a layer of nerve plexus to innervate the organs accompanying the corresponding arteries. ② Surround the artery as a layer of nerve plexus to innervate the organs accompanying the corresponding arteries. ③ Terminate directly in certain organs from the paravertebral ganglia. ③ Terminate directly in certain organs from the paravertebral ganglia.

20. 3. The general distributions of the sympathetic nerves 3. The general distributions of the sympathetic nerves 1) The cervical portion 1) The cervical portion The cervical sympathetic trunk consists of three ganglia, superior, middle and inferior. The cervical sympathetic trunk consists of three ganglia, superior, middle and inferior. The superior cervical ganglion: largest one, situating in front of the transverse processes of the C2 and C3. The superior cervical ganglion: largest one, situating in front of the transverse processes of the C2 and C3. The middle cervical ganglion: the smallest of the three cervical ganglia, at the level of the transverse process of the C6. The middle cervical ganglion: the smallest of the three cervical ganglia, at the level of the transverse process of the C6. The inferior cervical ganglion: at the level of the C7, may be fused with the first thoracic ganglion to form the cervicothoracic ganglion (stellate ganglion). The inferior cervical ganglion: at the level of the C7, may be fused with the first thoracic ganglion to form the cervicothoracic ganglion (stellate ganglion). The postganglionic fibers arising from the three cervical ganglia are distributed in the following ways. The postganglionic fibers arising from the three cervical ganglia are distributed in the following ways.

21. ① They communicate with the eight cervical nerves through the gray communicating branches to the blood vessels, sweat glands and arrectores pilorum of the head, neck and upper limbs, are distributed in the following ways: ① They communicate with the eight cervical nerves through the gray communicating branches to the blood vessels, sweat glands and arrectores pilorum of the head, neck and upper limbs, are distributed in the following ways: ② The fibers surround the internal and external carotid arteries to form the internal carotid plexus, external carotid plexus, to innervate the glands (lacrimal gland, salivary glands, mucous glands in the oral and nasal cavities, thyroid gland), arrectores pilorum, blood vessels, dilator pupillae of the head and neck. ② The fibers surround the internal and external carotid arteries to form the internal carotid plexus, external carotid plexus, to innervate the glands (lacrimal gland, salivary glands, mucous glands in the oral and nasal cavities, thyroid gland), arrectores pilorum, blood vessels, dilator pupillae of the head and neck. The internal carotid plexus sends a branch to the iris to control the activity of the dilator pupillae. The internal carotid plexus sends a branch to the iris to control the activity of the dilator pupillae. ③ The fibers, with the cardiac branch of the vagus nerve, comprise the cardiac plexus at the base of the heart. ③ The fibers, with the cardiac branch of the vagus nerve, comprise the cardiac plexus at the base of the heart.

22. 2) The thoracic portion 2) The thoracic portion The thoracic sympathetic trunk is situated in front of the heads of the ribs and contains a series of ganglia, 10 ～ 12 in number on each side. The thoracic sympathetic trunk is situated in front of the heads of the ribs and contains a series of ganglia, 10 ～ 12 in number on each side. The postganglionic fibers arising from the thoracic sympathetic trunk are distributed in the following ways. The postganglionic fibers arising from the thoracic sympathetic trunk are distributed in the following ways.

24. ① The postganglionic fibers communicate with the 12 pairs of thoracic nerves through the gray communicating branches, are distributed in the blood vessels, sweat glands, arrectores pilorum of the thoracic and abdominal walls. ① The postganglionic fibers communicate with the 12 pairs of thoracic nerves through the gray communicating branches, are distributed in the blood vessels, sweat glands, arrectores pilorum of the thoracic and abdominal walls. ② The postganglionic fibers arising from the upper 5 paires of thoracic ganglia, with the branches of the vagus nerve, form the pulmonary plexus whose filaments innervate the trachea, bronchi, lungs and other thoracic viscera. ② The postganglionic fibers arising from the upper 5 paires of thoracic ganglia, with the branches of the vagus nerve, form the pulmonary plexus whose filaments innervate the trachea, bronchi, lungs and other thoracic viscera.

25. ③ The greater splanchnic nerve is formed by the preganglionic fibers from the 5th (6th) to the 9th (or 10th) thoracic ganglia, which terminate in the celiac ganglion. ③ The greater splanchnic nerve is formed by the preganglionic fibers from the 5th (6th) to the 9th (or 10th) thoracic ganglia, which terminate in the celiac ganglion. ④ The lesser splanchnic nerve is formed by the preganglionic fibers from the ninth and tenth thoracic ganglia, which end in the aorticorenal ganglion. ④ The lesser splanchnic nerve is formed by the preganglionic fibers from the ninth and tenth thoracic ganglia, which end in the aorticorenal ganglion. The postganglionic fibers of the celiac and aorticorenal ganglia, with the branches of the vagus nerve, comprise the celiac plexus in front of the beginning of the abdominal aorta and surrounding the roots of the celiac and superior mesenteric artery. The bundles and filaments of the celiac plexus branches of the abdominal aorta to the liver, spleen, kidney and the alimentary tract as far as the left colonic flexure. The postganglionic fibers of the celiac and aorticorenal ganglia, with the branches of the vagus nerve, comprise the celiac plexus in front of the beginning of the abdominal aorta and surrounding the roots of the celiac and superior mesenteric artery. The bundles and filaments of the celiac plexus branches of the abdominal aorta to the liver, spleen, kidney and the alimentary tract as far as the left colonic flexure.

26. 3) The lumbar portion 3) The lumbar portion The lumbar sympathetic trunk includes 4 or 5 sympathetic ganglia which are situated ventrally to the bodies of the lumbar vertebrae, along the medial margin of the psoas major. The lumbar sympathetic trunk includes 4 or 5 sympathetic ganglia which are situated ventrally to the bodies of the lumbar vertebrae, along the medial margin of the psoas major.

28. ① Some of the postganglionic fibers of the lumbar trunk, which are the gray communicating branches, accompany the lumbar nerves to the blood vessels, sweat glands and arrectores pilorum of the anteromedial surface of the lower limbs. ① Some of the postganglionic fibers of the lumbar trunk, which are the gray communicating branches, accompany the lumbar nerves to the blood vessels, sweat glands and arrectores pilorum of the anteromedial surface of the lower limbs. ② The lumbar splanchnic nerves are composed of the preganglionic fibers penetrating the lumbar ganglia, terminate the prevertebral ganglia in the abdominal aortic plexus and the inferior mesenteric plexus. The postganglionic fibers are distributed to the alimentary tracts below the left colonic flexure, pelvic visceral organs and the lower limbs. ② The lumbar splanchnic nerves are composed of the preganglionic fibers penetrating the lumbar ganglia, terminate the prevertebral ganglia in the abdominal aortic plexus and the inferior mesenteric plexus. The postganglionic fibers are distributed to the alimentary tracts below the left colonic flexure, pelvic visceral organs and the lower limbs.

29. 4) The pelvic portion 4) The pelvic portion The pelvic sympathetic trunk lies against the ventral surface of the sacrum, medial to the sacral foramina. It is a direct continuation of the lumbar portion and contains 2 or 3 sacral sympathetic ganglia and the ganglion impar. The pelvic sympathetic trunk lies against the ventral surface of the sacrum, medial to the sacral foramina. It is a direct continuation of the lumbar portion and contains 2 or 3 sacral sympathetic ganglia and the ganglion impar. The postganglionic fibers arising from the pelvic sympathetic trunk are distributed in the following ways. The postganglionic fibers arising from the pelvic sympathetic trunk are distributed in the following ways.

31. ① The postganglionic fibers communicate with the thoracic and coccygeal nerves through the gray communicating branches, are distributed in the blood vessels, sweat glands, arrectores pilorum of the lower limbs and the perineum. ① The postganglionic fibers communicate with the thoracic and coccygeal nerves through the gray communicating branches, are distributed in the blood vessels, sweat glands, arrectores pilorum of the lower limbs and the perineum. ② The some small branches of the sacral sympathetic ganglia and ganglion impar join the pelvic plexus, and are supplied through it to the pelvic viscera. ② The some small branches of the sacral sympathetic ganglia and ganglion impar join the pelvic plexus, and are supplied through it to the pelvic viscera.

32. The regularity of the distribution of the preganglionic and postganglionic fibers. The regularity of the distribution of the preganglionic and postganglionic fibers. ① After the preganglionic fibers from the intermediolateral nuclei of the 1st to 5th thoracic segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the visceral organs of the head, neck, and thoracic cavity, blood vessels, sweat glands, and arrectores pilorum of the upper limbs. ① After the preganglionic fibers from the intermediolateral nuclei of the 1st to 5th thoracic segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the visceral organs of the head, neck, and thoracic cavity, blood vessels, sweat glands, and arrectores pilorum of the upper limbs. ② After the preganglionic fibers from the intermediolateral nuclei of the 5th to 12th thoracic segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the liver, spleen, and kidney, and the alimentary tract upper the left colonic flexure. ② After the preganglionic fibers from the intermediolateral nuclei of the 5th to 12th thoracic segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the liver, spleen, and kidney, and the alimentary tract upper the left colonic flexure.

33. ③ After the preganglionic fibers from the intermediolateral nuclei of the 1st to 3rd lumbar segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the alimentary tracts below the left colonic flexure, pelvic visceral organs and blood vessels, sweat glands, and arrectores pilorum of the lower limbs. ③ After the preganglionic fibers from the intermediolateral nuclei of the 1st to 3rd lumbar segments of spinal cord interchange neurons, the postgnglionic fibers are distributed in the alimentary tracts below the left colonic flexure, pelvic visceral organs and blood vessels, sweat glands, and arrectores pilorum of the lower limbs.

34. Ⅱ ) The Parasympathetic System Ⅱ ) The Parasympathetic System The lower level center of the parasympathetic system: The lower level center of the parasympathetic system: The centers of the parasympathetic system at the lower level (preganglionic neurons) are situated in certain cranial parasympathetic nuclei and in the sacral parasympathetic nuclei 2-4 segments of sacral portion of the spinal cord. It is for this reason that the parasympathetic division is also termed the craniosacral portion of visceral motor nerve. The centers of the parasympathetic system at the lower level (preganglionic neurons) are situated in certain cranial parasympathetic nuclei and in the sacral parasympathetic nuclei 2-4 segments of sacral portion of the spinal cord. It is for this reason that the parasympathetic division is also termed the craniosacral portion of visceral motor nerve.

35. 1. The cranial portion of the parasympathetic system 1. The cranial portion of the parasympathetic system The cranial outflow includes fibers in the oculomotor, facial, glossopharyngeal and vagus nerves. The cranial outflow includes fibers in the oculomotor, facial, glossopharyngeal and vagus nerves. These nerves have been described in previous pages and the details will be repeated here only as far as the supply to the visceral efferent fibers. These nerves have been described in previous pages and the details will be repeated here only as far as the supply to the visceral efferent fibers.

37. 1) The parasympathetic preganglionic fibers in the oculomotor nerve 1) The parasympathetic preganglionic fibers in the oculomotor nerve They arise from neurons in the Edinger- Westphal nucleus (or accessory nucleus of oculomotor nerve) and form synapses with the ciliary ganglion cells after entering the orbit. They arise from neurons in the Edinger- Westphal nucleus (or accessory nucleus of oculomotor nerve) and form synapses with the ciliary ganglion cells after entering the orbit. The postganglionic fibers proceed in the short ciliary nerves to the eyeball, penetrate the sclera, and reach the ciliary muscle and sphincter pupillae. The postganglionic fibers proceed in the short ciliary nerves to the eyeball, penetrate the sclera, and reach the ciliary muscle and sphincter pupillae.

38. 2) The parasympathetic preganglionic fibers in the facial nerve 2) The parasympathetic preganglionic fibers in the facial nerve They arise from the cells in the superior salivatory nucleus. They arise from the cells in the superior salivatory nucleus. ① Certain of the preganglionic fibers pass through the greater petrosal nerve to synapse with the cells in the pterygopalatine ganglion. ① Certain of the preganglionic fibers pass through the greater petrosal nerve to synapse with the cells in the pterygopalatine ganglion. Some of the postganglionic fibers reach the lacrimal gland via the maxillary, zygomatic, and lacrimal nerves successively; others accompany the branches of the maxillary nerve to the glands in the mucosa of the nasal cavity and palate. Some of the postganglionic fibers reach the lacrimal gland via the maxillary, zygomatic, and lacrimal nerves successively; others accompany the branches of the maxillary nerve to the glands in the mucosa of the nasal cavity and palate.

39. ② Other preganglionic fibers accompany the chorda tympani and join the lingual nerve to reach the submandibular ganglion. Then, they form synapses with the cells in the ganglion. The postganglionic fibers form the secretomotor supply to the submandibular and the sublingual glands. ② Other preganglionic fibers accompany the chorda tympani and join the lingual nerve to reach the submandibular ganglion. Then, they form synapses with the cells in the ganglion. The postganglionic fibers form the secretomotor supply to the submandibular and the sublingual glands.

40. 3) The parasympathetic preganglionic fibers contained in the glossopharyngeal nerve 3) The parasympathetic preganglionic fibers contained in the glossopharyngeal nerve They arise from the inferior salivatory join the tympanic plexus through the tympanic nerves. The lesser petrosal nerve arises from this plexus and form synapses in the otic ganglion. The postganglionic fibers join the auriculotemporal nerve, and are distributed to the parotid gland. They arise from the inferior salivatory join the tympanic plexus through the tympanic nerves. The lesser petrosal nerve arises from this plexus and form synapses in the otic ganglion. The postganglionic fibers join the auriculotemporal nerve, and are distributed to the parotid gland.

41. 4) The parasympathetic preganglionic fibers contained in the vagus nerve 4) The parasympathetic preganglionic fibers contained in the vagus nerve They arise from the cells in the dorsal nucleus of vagus in the medulla oblongata, and run in the vagus nerve to the ganglia which are situated in or near the organs innervated. They arise from the cells in the dorsal nucleus of vagus in the medulla oblongata, and run in the vagus nerve to the ganglia which are situated in or near the organs innervated.

42. 2. The sacral portion of the parasympathetic nerve 2. The sacral portion of the parasympathetic nerve The cells which give rise to the sacral outflow are in the second to fourth sacral segments of the spinal cord, and pass out with the corresponding sacral nerves. The cells which give rise to the sacral outflow are in the second to fourth sacral segments of the spinal cord, and pass out with the corresponding sacral nerves. They leave the sacral nerve as a pelvic splanchnic nerve and join the pelvic plexus whose branches synapse with the scattered ganglia in or near the walls of the pelvic organs and of the descending and sigmoid colon and rectum. They leave the sacral nerve as a pelvic splanchnic nerve and join the pelvic plexus whose branches synapse with the scattered ganglia in or near the walls of the pelvic organs and of the descending and sigmoid colon and rectum. The postganglionic fibers are distributed to the organs mentioned above. The postganglionic fibers are distributed to the organs mentioned above.

44. Ⅲ ) The Main Differences between the Sympathetic and Parasympathetic Systems Ⅲ ) The Main Differences between the Sympathetic and Parasympathetic Systems 1. The different lower center 1. The different lower center The lower centers of the sympathetic nerve are situated in the lateral horn of the thoracolumbar segments of the spinal cord. The lower centers of the sympathetic nerve are situated in the lateral horn of the thoracolumbar segments of the spinal cord. The lower centers of the parasympathetic nerve are in the brain stem and gray matter of the 2nd -4th of sacral segments of the spinal cord. The lower centers of the parasympathetic nerve are in the brain stem and gray matter of the 2nd -4th of sacral segments of the spinal cord.

47. 2. The different locations of the peripheral ganglia 2. The different locations of the peripheral ganglia The sympathetic ganglia are divided into paravertebral and prevertebral. The sympathetic ganglia are divided into paravertebral and prevertebral. The parasympathetic ganglia are situated in or near the walls of the innervated organs. The parasympathetic ganglia are situated in or near the walls of the innervated organs. So, the preganglionic fibers of the parasympathetic nerve are longer than those of the sympathetic nerve, vice versa, the postganglionic fibers of the parasympathetic are shorter than those of the sympathetic. So, the preganglionic fibers of the parasympathetic nerve are longer than those of the sympathetic nerve, vice versa, the postganglionic fibers of the parasympathetic are shorter than those of the sympathetic.

48. 3. The different ratio of the preganglionic fibers to the postganglionic fibers 3. The different ratio of the preganglionic fibers to the postganglionic fibers A preganglionic sympathetic fiber synapses with many more postganglionic neurons than the parasympathetic, so its effect is more widespread than that of the parasympathetic. A preganglionic sympathetic fiber synapses with many more postganglionic neurons than the parasympathetic, so its effect is more widespread than that of the parasympathetic.

49. 4. The different distributions 4. The different distributions The peripheral distribution of the sympathetic nerve is much wider than that of the parasympathetic. The peripheral distribution of the sympathetic nerve is much wider than that of the parasympathetic. It is generally believed that the blood vessels, sweat glands, arrectores pilorum and medullary part of the suprarenal gland are supplied only by the sympathetic nerve. It is generally believed that the blood vessels, sweat glands, arrectores pilorum and medullary part of the suprarenal gland are supplied only by the sympathetic nerve.

50. 5. The different actions to a visceral organ 5. The different actions to a visceral organ The viscera receives a dual autonomic supply. In most cases, the two sets of nerves function antagonistically to one another. However, in some cases, the action of the two divisions may not be antagonistic. The viscera receives a dual autonomic supply. In most cases, the two sets of nerves function antagonistically to one another. However, in some cases, the action of the two divisions may not be antagonistic.

51. The sympathetic division is thrown into activity in preparation of the organism for “ flight or fight ”. In action, it tends to produce vasoconstriction of the skin and viscera, shifting more blood to the brain and skeletal muscles, increasing the rate of the heart beating and respiration, the wider opening of the pupil, the elevation of the blood pressure and the dilatation of the bronchi. The sympathetic division is thrown into activity in preparation of the organism for “ flight or fight ”. In action, it tends to produce vasoconstriction of the skin and viscera, shifting more blood to the brain and skeletal muscles, increasing the rate of the heart beating and respiration, the wider opening of the pupil, the elevation of the blood pressure and the dilatation of the bronchi. While, the actions of parasympathetic division to the above mentioned organs, are on the contrary. While, the actions of parasympathetic division to the above mentioned organs, are on the contrary.

52. Ⅳ ) The Autonomic Plexuses Ⅳ ) The Autonomic Plexuses The fibers of two divisions of the autonomic system are combined into extensive plexuses in the thorax, abdomen and pelvis. The fibers of two divisions of the autonomic system are combined into extensive plexuses in the thorax, abdomen and pelvis. 1. The cardiac plexus 1. The cardiac plexus Superficial cardiac part and deep cardiac part. Superficial cardiac part and deep cardiac part. 2. pulmonary plexus 2. pulmonary plexus 3. The celiac plexus 3. The celiac plexus Secondary plexus, such as: Secondary plexus, such as: Hepatic plexus, Hepatic plexus, Splenic plexus, Splenic plexus, Pancreatic plexus, Pancreatic plexus, Superior and inferior mesenteric plexuses. Superior and inferior mesenteric plexuses. 4. The abdominal aortic plexus 4. The abdominal aortic plexus 5. The hypogastric plexus 5. The hypogastric plexus Superior hypostric plexus Superior hypostric plexus Inferior hypogastric plexus (pelvic plexus) Inferior hypogastric plexus (pelvic plexus)

54. Ⅱ. The Visceral Sensory Nerves Ⅱ. The Visceral Sensory Nerves They conduct the impulses from interoceptors of the viscera to the central nervous system. They conduct the impulses from interoceptors of the viscera to the central nervous system. Sensory fibers, myelinated or unmyelinated, from the thoracic, abdominal and pelvic viscera traverse sympathetic and splanchnic nerves to reach the sympathetic trunk. Sensory fibers, myelinated or unmyelinated, from the thoracic, abdominal and pelvic viscera traverse sympathetic and splanchnic nerves to reach the sympathetic trunk. Some of them pass uninterrupted through the trunk and white communicating branch to their perikarya of origin in the spinal ganglia whose central processes enter the spinal cord and end in the dorsal horn. Some of them pass uninterrupted through the trunk and white communicating branch to their perikarya of origin in the spinal ganglia whose central processes enter the spinal cord and end in the dorsal horn.

55. Others are the peripheral processes of the inferior ganglia of glossopharyngeal and vagus nerves whose central processes accompany these two nerves to terminate in the solitary nucleus of the brain stem. Others are the peripheral processes of the inferior ganglia of glossopharyngeal and vagus nerves whose central processes accompany these two nerves to terminate in the solitary nucleus of the brain stem. The afferent visceral fibers are important in the initiation of various visceral and viscerosomatic reflexes mediated through the spinal cord and brain stem. The afferent visceral fibers are important in the initiation of various visceral and viscerosomatic reflexes mediated through the spinal cord and brain stem. Although the viscera are insensitive to cutting, crushing or burning, the excessive tension and contraction of smooth muscle and certain pathological conditions can produce visceral pain. Although the viscera are insensitive to cutting, crushing or burning, the excessive tension and contraction of smooth muscle and certain pathological conditions can produce visceral pain.

56. The afferent impulses also give rise to distress, nausea, hunger and other poorly localized visceral sensations, and are responsible for the general feeling of internal well being. The afferent impulses also give rise to distress, nausea, hunger and other poorly localized visceral sensations, and are responsible for the general feeling of internal well being. The visceral afferent fibers have their own features in morphology which are different activities are at the subconscious level. The visceral afferent fibers have their own features in morphology which are different activities are at the subconscious level.

57. 1. The number of the visceral sensory fibers is less than that of the somatosensory fibers and have a high pain threshold, which may be the reason that most of the visceral activities are at the subconscious level. 1. The number of the visceral sensory fibers is less than that of the somatosensory fibers and have a high pain threshold, which may be the reason that most of the visceral activities are at the subconscious level. 2. The sensory fibers from a visceral organ pass through several segments of spinal nerves to the central centers, and a spinal nerve may contain the sensory fibers from several organs. 2. The sensory fibers from a visceral organ pass through several segments of spinal nerves to the central centers, and a spinal nerve may contain the sensory fibers from several organs.

58. Ⅲ. The Central Centers of Visceral Nerves Ⅰ ) The limbic lobe of the cerebrum is closely related to the visceral activities, in which there are representative motor areas of respiration, gastrointestine, bladder, blood pressure, pupil etc. Ⅰ ) The limbic lobe of the cerebrum is closely related to the visceral activities, in which there are representative motor areas of respiration, gastrointestine, bladder, blood pressure, pupil etc. Ⅱ ) The hypothalamus is believed to have close relationship with the visceral nerve, through which the limbic lobe regulates the visceral activities. Ⅱ ) The hypothalamus is believed to have close relationship with the visceral nerve, through which the limbic lobe regulates the visceral activities. Ⅲ ) The brain stem and cerebellum also play the important roles in regulation of the visceral activities. Ⅲ ) The brain stem and cerebellum also play the important roles in regulation of the visceral activities.

59. Ⅳ. The Referred Pain Although many and perhaps most of the physiological impulses carried by visceral afferent fibers fail to reach the level of consciousness, pathological conditions or excessive stimulation may bring into action of sensory fibers which carry pain. Although many and perhaps most of the physiological impulses carried by visceral afferent fibers fail to reach the level of consciousness, pathological conditions or excessive stimulation may bring into action of sensory fibers which carry pain. The central nervous system has a poorly developed power for localizing the source of such pain, and by some mechanism not clearly understood, the pain may be referred to the region innervated by somatic afferent fibers whose central connections are the same as those of the visceral afferents. The central nervous system has a poorly developed power for localizing the source of such pain, and by some mechanism not clearly understood, the pain may be referred to the region innervated by somatic afferent fibers whose central connections are the same as those of the visceral afferents.

60. For example, when patient suffers from angina pectoris, the visceral afferent from the heart enter the upper thoracic nerves, and impulses traversing them may cause pain on the medial side of the left arm, and in the precordial region. For example, when patient suffers from angina pectoris, the visceral afferent from the heart enter the upper thoracic nerves, and impulses traversing them may cause pain on the medial side of the left arm, and in the precordial region. The patient suffering from hepatic or cystic diseases may feel pain in the right shoulder. The patient suffering from hepatic or cystic diseases may feel pain in the right shoulder.

63. The study of clinical cases of referred pain has been very useful in tracing the path of the afferent fiber from the various viscera, and a knowledge of those paths may be of great assistance to the diagnostician in locating a pathological process. The study of clinical cases of referred pain has been very useful in tracing the path of the afferent fiber from the various viscera, and a knowledge of those paths may be of great assistance to the diagnostician in locating a pathological process.