Autonomic nervous system parasympathetic division

Autonomic ganglia. Ganglionic stimulation occurs in both the sympathetic and parasympathetic divisions of the autonomic nervous system. Parasympathetic activation results in increased production of gastric juice (smoking ban in peptic ulcer) and enhanced bowel motility ( laxative effect of the first morning cigarette defecation diarrhea in the novice). 

Figure 9.1 The autonomic nervous system and its effector organs. The efferent pathways of this system consist of two neurons that transmit impulses from the CNS to the effector tissue, preganglionic neuron (solid line), and postganglionic neuron (dashed line). As illustrated, most tissues receive nervous input from both divisions of the ANS the sympathetic and the parasympathetic.

The autonomic nervous system (ANS) modifies contractile activity of both types of smooth muscle. As discussed in Chapter 9, the ANS innervates the smooth muscle layer in a very diffuse manner, so neurotransmitter is released over a wide area of muscle. Typically, the effects of sympathetic and parasympathetic stimulation in a given tissue oppose each other one system enhances contractile activity while the other inhibits it. The specific effects (excitatory or inhibitory) that the two divisions of the ANS have on a given smooth muscle depend upon its location. 

Muscarinic receptors are responsible for postganglionic parasympathetic neurotransmission and thus for control of a wide range of smooth muscle, cardiac muscle and secretory responses. Some responses originating in the sympathetic division of the autonomic nervous system, such as sweating and piloerection, also are mediated through muscarinic receptors. 

Forming part of the peripheral nervous system is the autonomic nervous system which controls the glands and non-skeletal muscles that are not under conscious control. This control is provided by two parts of this system the sympathetic and parasympathetic divisions which, in general, bring about antagonistic responses. 

Excitation of the parasympathetic division of the autonomic nervous system causes release of acetylchoUne at neuro-effector junctions in different target organs. The major effects are summarized in A (blue arrows). Some of these effects have therapeutic appUcations, as indicated by the clinical uses of parasympa-thomimetics (p. 102). 

Acetylcholine is the primary neurotransmitter in the parasympathetic division of the autonomic nervous system, which mainly innervates the gastrointestinal tract, eyes, heart, respiratory tract, and secretory glands. Although its receptors are crucial for maintaining all normal functions of the body, an extremely small number of illnesses can be explained by the dysfunction of cholinergic regions of the peripheral autonomic system. 

Many neurons of both divisions of the autonomic nervous system are tonicaUy active that is, they are continually carrying some impulse traffic. The moment-to-moment activity of an organ such as the heart, which receives a dual innervation by sympathetic (noradrenergic) and parasympathetic (cholinergic) neurons, is controlled by the level of tonic activity of the two systems. 

Erection involves a coordinated action of the autonomic nervous system, and certain drugs may interfere with either the sympathetic division (e.g., aj- receptors) or the parasympathetic division (e.g., noncholinergic neurotransmitters). 

The answer is d. (Hardman, pp 192-193.) Nicotine is a depolarizing ganglionic blocking agent that initially stimulates and then blocks nicotinic muscular (NM) (skeletal muscle) and nicotinic neural (NN) (parasympathetic ganglia) cholinergic receptors. Blockade of the sympathetic division of the autonomic nervous system (ANS) results in arteriolar vasodilation, bradycardia, and hypotension. Blockade at the neuromuscu-... 

Anatomy of the Autonomic Nervous System Sympathetic and Parasympathetic Divisions... 

The autonomic nervous system lends itself to division on anatomic grounds into two major portions the sympathetic (thoracolumbar) division and the parasympathetic (craniosacral)... 

CNS—brain and spinal cord—and two separate pathways within the peripheral nervous system (PNS) for two-way communication with the peripheral organs. The PNS subdivisions are the somatic and autonomic nervous systems (Figure 11.2). The latter is further divided into sympathetic and parasympathetic divisions (Figure 11.3). 

Q3 What are the anatomical differences between the sympathetic and parasympathetic divisions of the autonomic nervous system ... 

Q4 The ganglionic transmitter of both divisions of the autonomic nervous system is acetylcholine. The major postganglionic neurotransmitter of the sympathetic nervous system is norepinephrine (noradrenaline), but a small number of structures are innervated by sympathetic, cholinergic fibres. These fibres release acetylcholine and the structures innervated include the sweat glands and blood vessels supplying skeletal muscle. In the parasympathetic system the postganglionic neurotransmitter is acetylcholine. 

Previous studies have shown that accommodation mediated via ciliary smooth muscle activity also receives sympathetic innervation. Sympathetic nerves reach the ciliary muscle through the uveal blood vessels in close association with arteries and terminal arterioles. The distribution of the adrenergic fibers in the ciliary muscle appears to vary across species. In primates sympathetic nerve terminals, mainly 3 receptors, can generally be found in the anterior portion of the ciliary muscle. The accommodative amplitude significantly decreased in human subjects after instillation of phenylephrine (an a agonist) or hydroxyamphetamine (an a and (3 agonist). Such observations provide evidence that both sympathetic and parasympathetic divisions of the autonomic nervous system can affect accommodation but not equally. Furthermore, the nature of sympathetic innervation can be summarized as follows ... 

The parasympathetic division is the dominant portion of the pulmonary autonomic nervous system in all mammals. Airway smooth muscle is richly supplied with muscarinic receptors and stimulation of M3 receptors results in smooth muscle contraction and bronchoconstriction. Cholinergic stimulation is the primary mechanism of bronchospasm in horses with recurrent airway obstruction (Robinson et al 1996). Parasympathetic innervation can be demonstrated throughout the tracheobronchial tree of the horse but smooth muscle contraction evoked by stimulation of cholinergic nerves is more pronounced in the trachea than in the smaller bronchi. It is expected that parasympathetic blockade with a muscarinic antagonist will have the greatest effect in large, central airways. 

Neurologic pathways in the sympathetic nervous system originate from the thoracic (T1 to T12) and the upper lumbar segments (LI and L2) of the spinal cord. Neurologic pathways in the parasympathetic nervous system originate from cranial nerves III, VII, IX, and X, from the brainstem, and the sacral segments S2, S3, and S4 from the spinal cord. This is why the parasympathetic nervous system is also known as the craniosacral division of the autonomic nervous system. 

Biologically, the autonomic nervous system controls many physiological functions, including respiration, circulation, metabolism, digestion, secretions, and body tempera-ture. The sympathetic and parasympathetic systems are the two major divisions of the autonomic nervous system. In general, they are antagonistic (one stimulates while the other... 

ANS [Autonomic Nervous System] Part of die nervous system of vertebrates that controls involuntary actions of the smooth muscles, heart, and glands. The components of the peripheral and central nervous system concerned with the regulation of involuntary actions. It has two divisions the sympathetic and parasympathetic nervous systems. Anticholinergic Inhibiting or blocking the physiological action of acetylcholine at a receptor site. An agent that blocks the parasympathetic nerves. 

Figure 6-1. Schematic diagram comparing some features of the parasympathetic and sympathetic divisions of the autonomic nervous system with the somatic motor system. Parasympathetic ganglia are not shown as discrete structures because most of them are diffusely distributed in the walls of the organs innervated. ACh, acetylcholine Epi, epinephrine NE, norepinephrine, D, dopamine N, nicotinic M, muscarinic a, p, alpha and beta adrenoceptors D, dopamine, receptors. (Reproduced, with permission, from Katzung BG [editor] Basic Clinical Pharmacology, 8th ed. McGraw-Hill, 2001.)...

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