#Autonomic nervous system lens series

Most of the thoracic and abdominal organs are supplied by preganglionic neurons of the vagus nerve extending from the brainstem. The axons of the postganglionic neurons extend a relatively short distance from the terminal ganglia to the target organ. Preganglionic cell bodies of the parasympathetic division are located either within brainstem nuclei of the oculomotor nerve (III), facial nerve (VII), glossopharyngeal nerve (IX), or vagus nerve (X) or within the lateral part of the central gray matter of the spinal cord in the regions that give rise to spinal nerves S2 through S4.Īxons of the preganglionic neurons extend through spinal nerves or cranial nerves to terminal ganglia either located near effector organs in the head (figure 8.39) or embedded in the walls of effector organs in the thorax, abdomen, and pelvis. Postganglionic neurons in the collateral ganglia project to target tissues in the abdominal and pelvic regions. Preganglionic neurons synapse with postganglionic neurons in the collateral ganglia. Collateral ganglia are located nearer target organs and consist ofthe celiac, superior mesenteric, and inferior mesenteric ganglia. The axons of those preganglionic fibers that do not synapse in the sympathetic chain ganglia form splanchnic nerves that extend to collateral ganglia. The postganglionic axons form sympathetic nerves that innervate structures of the thoracic cavity. Some preganglionic fibers synapse with postganglionic fibers in the sympathetic chain ganglia. The sympathetic chain ganglia are connected to one another and are so named because they form a chain along both sides of the spinal cord. The axons of the preganglionic neurons exit through ventral roots and project to either sympathetic chain ganglia or collat-eral ganglia (figure 8.39). Increasedactivity in sympathetic neurons generally prepares the individual for physical activity, whereas parasympathetic stimulation gener-ally activates involuntary functions, such as digestion, that are normally associated with the body at rest.Ĭell bodies of sympathetic preganglionic neurons are in the lat-eral horn of the spinal cord gray matter (see figure 8.16) between the first thoracic (T1) and the second lumbar (L2) segments. The autonomic nervous system is composed of the sympa-thetic (sim-pă-thet′ik sympatheo,to feel with+ pathos,suf-fering) division and the parasympathetic (par-ă-sim-pa-thet′ ik para, alongside of) division(table 8.7 and figure 8.39). There, the postganglionic neurons are actually the hormone-secreting cells of the adrenal medulla. An exception is the preganglionic neuron that extends to the adrenal gland. The first is called the preganglionicneuron the second is the postganglionic neuron (figure 8.38).The neurons are so named because preganglionic neurons synapse with postganglionic neurons in autonomic ganglia outside the CNS.

#Autonomic nervous system lens series

In the autonomic nervous system, two neurons in series extend from the CNS to the effector organs. This is in contrast to somatic motor neurons, which extend axons from the CNS to skeletal muscle. Autonomic functions are largely controlled unconsciously.Īxons from autonomic neurons do not extend all the way from the CNS to target tissues. The autonomic neurons innervate smooth muscle, cardiac muscle, and glands.

The autonomic nervous system (ANS) comprises motor neurons that carry action potentials from the CNS to the periphery.