澳洲阳光海岸大学论文代写:神经节纤维

节前交感神经纤维出现在脊柱节段T1-L3的侧角中。大多数前神经节纤维在脊神经中行进很短的距离，之后分支为交感神经节，其被布置为从颈部延伸到骶骨区域的两个椎旁链（截断交感神经）。一些纤维仅穿过这些交感神经节链，在独立的颈（子宫颈或星状）或腹部（髂或肠系膜）神经节中突触。交感神经前神经末梢中的化学神经递质是乙酰胆碱。在大多数神经节后神经末梢，发射器也不是肾上腺素。

一些前神经节纤维穿过大肠系膜神经突触与肾上腺髓质中的嗜铬细胞。这些胆碱能神经节前纤维的刺激导致肾上腺素和较少程度的肾上腺素释放到血流中。肾上腺素和肾上腺素的作用由细胞表面上的特异性G蛋白偶联的肾上腺素能受体介导。

副交感流出在脑干中的颅神经III，VII，IX和X的运动核以及从脊柱节段S2-S4中产生。前神经节纤维与效应器官内或接近效应器官的神经节后纤维突触。前和后神经节副交感神经末梢中的化学神经递质是乙酰胆碱（胆碱能神经纤维）。乙酰胆碱的作用通过烟碱和muscarnic乙酰胆碱受体介导。烟碱受体是配体门控离子通道，介导乙酰胆碱在自主神经节中的作用。毒蕈碱受体是G蛋白偶联受体，介导对副作用器器官的副交感神经冲动。

澳洲阳光海岸大学论文代写:神经节纤维

Preganglionic sympathetic fibres arise in the lateral horns of the spinal segments T1 – L3. Most preganglionic fibres travel only a short distance in the spinal nerve, before branching off into the sympathetic ganglia which are arranged as two paravertebral chains (truncus sympatheticus) extending from the cervical to the sacral region. Some fibres only traverse these sympathetic ganglionic chains, synapsing in separate cervical (the cervical or the stellate) or abdominal (the iliac or mesenteric) ganglia. The chemical neurotransmitter in sympathetic preganglionic nerve endings is acetylcholine. In most post ganglionic nerve endings, the transmitter is nor adrenaline.

A few preganglionic fibres traversing through the greater mesenteric nerve synapse with chromaffin cells in the adrenal medulla. Stimulation of these cholinergic preganglionic fibres results in the release of adrenaline and to a lesser extent nor adrenaline into the bloodstream. The actions of adrenaline and nor adrenaline are mediated by specific G-protein coupled adrenergic receptors on the surface of the cell.

Parasympathetic outflow arises in the motor nuclei of cranial nerves III, VII, IX and X in the brainstem and from the spinal segments S2 – S4. Preganglionic fibers synapse with the postganglionic fibers within or close to the effector organ. The chemical neurotransmitter in both pre and post ganglionic parasympathetic nerve endings is acetylcholine (cholinergic nerve fibres). The actions of acetylcholine are mediated through nicotinic and muscarnic acetylcholine receptors. The nicotinic receptors are ligand – gated ion channels, mediating the effects of acetylcholine in the autonomic ganglia. The muscarnic receptors are G-protein coupled receptors, mediating the parasympathetic impulses to the effectors organs.

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