Dr. Bill Blessing
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Langley (1852-1925) coined the term autonomic nervous system. He continued the tradition whereby the ANS is seen as functioning in its own right, with independence from the CNS. Langley noted the absence of sensory (afferent) nerve cell bodies in autonomic ganglia and defined the ANS as a purely motor system. | Langley (1852-1925) coined the term autonomic nervous system. He continued the tradition whereby the ANS is seen as functioning in its own right, with independence from the CNS. Langley noted the absence of sensory (afferent) nerve cell bodies in autonomic ganglia and defined the ANS as a purely motor system. | ||
| − | Modern experiments have shown that neurons in autonomic ganglia do not have inbuilt patterns of discharge sufficiently integrated to regulate physiological functions. The classic description of [http://www. | + | Modern experiments have shown that neurons in autonomic ganglia do not have inbuilt patterns of discharge sufficiently integrated to regulate physiological functions. The classic description of [http://www.hexamethonium man.com] summarizes the state of an individual after drug-mediated separation of the ANS from functional control by the brain. Similarly, when brain control of spinal autonomic preganglionic neurons is removed (as in quadriplegia), cardiovascular, bowel and bladder functions are profoundly impaired. Thus the ANS is best seen as one of the three efferent outflows whereby the CNS controls bodily organs, so that “peripheral autonomic pathways” is a better term, but “autonomic nervous system” is well-established. |
ANS pathways are divided into sympathetic and parasympathetic (around the sympathetic) divisions and enteric plexuses. Preganglionic cell bodies for the sympathetic outflow are in the thoracic spinal cord. Preganglionic cell bodies for the parasympathetic outflow are in the brainstem (cranial) and in the sacral spinal cord (sacral). The idea that the divisions oppose each other is a misleading simplification. Neither division is ever activated in its entirety. Rather, each division consists of a series of discrete functional pathways that may be activated from the CNS either independently or in patterns, according to the particular requirement of the particular daily activity that is contributing to bodily homeostasis. The primacy of integrative brain control of all bodily functions was recognized by Walter Cannon, but his idea that the brain activates sympathetic nerves diffusely and non-specifically during bodily emergencies (“fight or flight reaction”) is an over simplification. Different emergency states require different patterns of autonomic activity, and normal daily life (apart from emergencies) also requires patterned autonomic activity. | ANS pathways are divided into sympathetic and parasympathetic (around the sympathetic) divisions and enteric plexuses. Preganglionic cell bodies for the sympathetic outflow are in the thoracic spinal cord. Preganglionic cell bodies for the parasympathetic outflow are in the brainstem (cranial) and in the sacral spinal cord (sacral). The idea that the divisions oppose each other is a misleading simplification. Neither division is ever activated in its entirety. Rather, each division consists of a series of discrete functional pathways that may be activated from the CNS either independently or in patterns, according to the particular requirement of the particular daily activity that is contributing to bodily homeostasis. The primacy of integrative brain control of all bodily functions was recognized by Walter Cannon, but his idea that the brain activates sympathetic nerves diffusely and non-specifically during bodily emergencies (“fight or flight reaction”) is an over simplification. Different emergency states require different patterns of autonomic activity, and normal daily life (apart from emergencies) also requires patterned autonomic activity. | ||
Sensory information (visceral afferent information) relevant to autonomic control (eg degree of bladder distention or level of blood pressure) travels in visceral afferent nerves and enters the CNS via spinal afferent pathways, or via vagal or glossopharyngeal afferents that project into the lower brainstem (see black arrows in Fig. 1). | Sensory information (visceral afferent information) relevant to autonomic control (eg degree of bladder distention or level of blood pressure) travels in visceral afferent nerves and enters the CNS via spinal afferent pathways, or via vagal or glossopharyngeal afferents that project into the lower brainstem (see black arrows in Fig. 1). | ||
Revision as of 02:53, 21 June 2007
Autonomic Nervous System
From Scholarpedia
Curators: Bill Blessing and Ian Gibbins, Departments of Human Physiology and Medicine, and Department of Anatomy and Histology, Centre for Neuroscience, Flinders University, Adelaide, Australia
The term autonomic nervous system (ANS) refers to groups of motor neurons (ganglia) situated in the head and neck, and in the thorax, abdomen and pelvis, outside the central nervous system (CNS) as shown in Fig. 1. Preganglionic axons, processes of preganglionic neurons in the CNS, innervate the ganglionic neurons. Axonal processes of these neurons (post-ganglionic axons) innervate bodily organs (eyes, salivary glands, heart, stomach, bladder, blood vessels, etc). Complex autonomic ganglia in the walls of the stomach and small intestine are separately classified as the enteric nervous system. Autonomic nerves, together with neuroendocrine pathways and the somatic motor nerves to skeletal muscle comprise the three motor outflows from the CNS.
History of the definition and functional conception of the ANS
Rational thought has traditionally been seen as distinct from the emotions. The brain, locked away in its bony case, was conceived as responsible for the rational thoughts and ideas that direct behavioral interactions with the external environment. Emotions,visceral rather than rational, were linked with the functions of the internal bodily organs. We have “gut feelings”, the heart is the “seat of love” and we “vent our spleen”. Bichat (1771-1802) divided life into two distinct forms, one (relational life) governed by the brain, and the other (organic life) by the abdominal ganglia. Organic life was seen as connected with the passions and independent of education, governed as it is by independently functioning abdominal ganglia, a chain of “little brains”. Phillipe Pinel one of the founders of modern psychiatry and Bichat’s teacher, even considered mental disease to be caused by abnormal function of these ganglia.
Langley (1852-1925) coined the term autonomic nervous system. He continued the tradition whereby the ANS is seen as functioning in its own right, with independence from the CNS. Langley noted the absence of sensory (afferent) nerve cell bodies in autonomic ganglia and defined the ANS as a purely motor system.
Modern experiments have shown that neurons in autonomic ganglia do not have inbuilt patterns of discharge sufficiently integrated to regulate physiological functions. The classic description of man.com summarizes the state of an individual after drug-mediated separation of the ANS from functional control by the brain. Similarly, when brain control of spinal autonomic preganglionic neurons is removed (as in quadriplegia), cardiovascular, bowel and bladder functions are profoundly impaired. Thus the ANS is best seen as one of the three efferent outflows whereby the CNS controls bodily organs, so that “peripheral autonomic pathways” is a better term, but “autonomic nervous system” is well-established.
ANS pathways are divided into sympathetic and parasympathetic (around the sympathetic) divisions and enteric plexuses. Preganglionic cell bodies for the sympathetic outflow are in the thoracic spinal cord. Preganglionic cell bodies for the parasympathetic outflow are in the brainstem (cranial) and in the sacral spinal cord (sacral). The idea that the divisions oppose each other is a misleading simplification. Neither division is ever activated in its entirety. Rather, each division consists of a series of discrete functional pathways that may be activated from the CNS either independently or in patterns, according to the particular requirement of the particular daily activity that is contributing to bodily homeostasis. The primacy of integrative brain control of all bodily functions was recognized by Walter Cannon, but his idea that the brain activates sympathetic nerves diffusely and non-specifically during bodily emergencies (“fight or flight reaction”) is an over simplification. Different emergency states require different patterns of autonomic activity, and normal daily life (apart from emergencies) also requires patterned autonomic activity.
Sensory information (visceral afferent information) relevant to autonomic control (eg degree of bladder distention or level of blood pressure) travels in visceral afferent nerves and enters the CNS via spinal afferent pathways, or via vagal or glossopharyngeal afferents that project into the lower brainstem (see black arrows in Fig. 1).
