Functions of the autonomic nervous system

Tissue Sympatheticreceptor Sympathetic stimulation Parasympathetic stimulation 

Ciliary muscle P2 Relaxation for far vision Contraction for near vision 

Heart Pi/ P2 Increased heart rate Increased contractility Decreased heart rate 

Salvivary glands i, P Small volume K + and water secretion Large volume K + and water secretion Amylase secretion 

Inspection of the retina during an ophthalmoscopic examination is greatly facilitated by mydriasis, or the dilation of the pupil. Parasympathetic stimulation of the circular muscle layer in the iris causes contraction and a decrease in the diameter of the pupil. Administration of a muscarinic receptor antagonist such as atropine or scopolamine prevents this smooth muscle contraction. As a result, sympathetic stimulation of the radial muscle layer is unopposed, causing an increase in the diameter of the pupil. These agents are given in the form of eye drops that act locally and limit the possibility of systemic side effects. 

The autonomic nervous system consists of central connections, visceral afferent fibers, and visceral efferent fibers. The hypothalamus is where the principal integration of the entire autonomic nervous 

Comparison of Somatic Nervous System and Autonomic Nervous System 

Cell bodies of somatic efferent neurons are found at all levels of the spinal cord 

The neurons have voluntary and involuntary (reflex) regulation 

Target tissues (effectors) receive only one efferent neuron 

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Action potentials are generated in single-unit smooth muscle. Simultaneous depolarization of 30 to 40 smooth muscle cells is required to generate a propagated action potential the presence of gap junctions allows this to occur readily. Because single-unit smooth muscle is self-excitable and capable of generating action potentials without input from the autonomic nervous system, it is referred to as myogenic. In this muscle, the function of the autonomic nervous system is to modify contractile activity only. Input is not needed to elicit contraction. 

The concept of chemical transmission in the nervous system arose in the early years of the century when it was discovered that the functioning of the autonomic nervous system was largely dependent on the secretion of acetylcholine and noradrenaline from the parasympathetic and sympathetic nerves respectively. The physiologist Sherrington proposed that nerve cells communicated with one another, and with any other type of adjacent cell, by liberating the neurotransmitter into the space, or synapse, in the immediate vicinity of the nerve ending. He believed that transmission across the synaptic cleft was unidirectional and, unlike conduction down the nerve fibre, was delayed by some milliseconds because of the time it took the transmitter to diffuse across the synapse and activate a specific neurotransmitter receptor on the cell membrane. 

In general terms, the function of the autonomic nervous system is to maintain the constancy of the internal environment (homeostasis). This includes the regulation of the cardiovascular system, digestion, body... 

In addition, numerous drugs such as neuroleptics and antidepressants produce side effects by modifying the function of the autonomic nervous system. 

It was only after the role of acetylcholine in the functioning of the autonomic nervous system, in neuroeffector transmission to the various entitles Innervated by that system and to skeletal muscles (3-11), and In synaptic transmission within some areas of the central and peripheral nervous systems (12-17) had been demonstrated that the proximate mechanism of action of atropine, scopolamine, and ocher compounds of similar activity could be understood, niese c[Pg.133]

While Western scientific study of meditation is limited and typically focuses on the mental and emotional benefits of relaxation, pain management, and stress reduction, meditation is integrally linked to the function of the autonomic nervous system, which regulates many organs and muscles in our bodies. It plays a role in how our heart beats, how we breathe and sweat, and how effectively our digestive system works. 

Dysautonomias are conditions in which altered function of the autonomic nervous system adversely affects health. Such conditions range from more common transient episodes in otherwise healthy people (e.g., neurocardiogenic syncope), to progressive neurodegenerative diseases (e.g., multiple system atrophy), and to even more rare genetic disorders, such as dopamine P-hydroxylase deficiency (Table 29-5). 

Another chemical approach to modification of the functioning of the autonomic nervous system was the development of compounds whose primary... 

This classic in the field of pharmacology provides detailed information on anatomy and functions of the autonomic nervous system. Although primarily concerned with drugs and how they act upon the body, there are also excellent sections on the toxicity of gases and vapors and heavy metals. Goodman and Gilman thoroughly evaluate many of the more widely used compounds utilized by the pharmaceutical industry. 

Maintaining blood pressure within a narrow range is one of the major functions of the autonomic nervous system. The symptom, called orthostatic hypotension was described in 1826 by the distinguished French physician, Pierre Piorry. He was called to see a patient who had lost consciousness. His pulse was feeble, and he had to be supported in a sitting position by his friends. When Piorry laid him down, he immediately opened his eyes, his breathing became normal, and color came back to his face. He was suffering from a precipitous fall in blood pressure whenever he stood up. 

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