CHAPTER XXXVIII 



Peripheral autonomic mechanisms 



NILS-AKE HILLARP i University oj Lund, Lund, Sweden 



CHAPTER CONTENTS 



General Organization of Peripheral Autonomic Nervous System 

 Sympathetic Division 

 Parasympathetic Division 

 Fiber Types and Their Functional Significance 

 Structure of Autonomic Ganglia 

 Types of Ganglion Cells 



Connections Between Preganglionic and Postganglionic 

 Neurons 

 Physiological Discharge Rate in Peripheral Autonomic Nervous 



System 

 Activities of Peripheral Autonomic Nervous System Inde- 

 pendent of Central Nervous System 

 'Spontaneous' Activity 

 Axon Reflexes 



Other Types of Reflexes Mediated by Autonomic Ganglia 

 Effects of Decentralization or Denervation on Autonomic 

 Effectors 

 Effects on Structure and Activity of Effectors 

 Supersensitivity of Autonomic Effector Cells 

 Degeneration and Regeneration in Peripheral Autonomic 

 Nervous System 

 Degeneration 

 Regeneration 



Heterogeneous Regeneration 

 Structure and Functional Organization of Autonomic Effector 



Junctions 

 Functional Significance of Autonomic Nervous System and Its 

 Subdivisions 



THE CLASSICAL EXPERIMENTS OF Langlev gave strong 

 evidence for the view that the peripheral autonomic 

 nervous system is principally organized as a two- 

 neuron pathway. Nerve cells situated in the central 

 nervous system give rise to fibers, the preganglionic 

 fibers, which run via cranial nerves and ventral roots 

 of the spinal cord to the peripheral autonomic ganglia 

 where they are synaptically connected to nerve cells 

 constituting the second neuron link. The axons emerg- 



ing from the ganglia, the postganglionic fibers, then 

 give innervation to smooth muscle, heart and glands. 

 This conception of the general organization of the 

 autonomic nervous system is now — although severely 

 criticized by some neurohistologists — generally ac- 

 cepted in physiology. 



Mainly on the basis of differences in the action of 

 drugs on the craniosacral and on the thoracolumbar 

 autonomic neuroeffector systems, Langley proposed 

 that these systems should be recognized as two differ- 

 ent divisions of the autonomic nervous system. He 

 therefore restricted the name sympathetic to the 

 thoracolumbar division and called the craniosacral 

 division the parasympathetic system. 



As evidence accumulated that the autonomic nerve 

 fibers acted on their effector cells by liberating acetyl- 

 choline or an epinephrine-like mediator, a classifica- 

 tion of the fibers on this physiological basis was indi- 

 cated. Dale (91) proposed the names cholinergic and 

 adrenergic,. The classification of autonomic nerves 

 into sympathetic-parasympathetic and adrenergic- 

 cholinergic is now generally accepted anatomical and 

 physiological nomenclature. 



Acetylcholine seems to be the synaptic transmitter 

 in sympathetic (145, 147) as well as in parasympa- 

 thetic ganglia (133, 340). Accordingly all pregangli- 

 onic fibers are cholinergic. There is good evidence 

 that the postganglionic parasympathetic fibers also 

 are cholinergic, but exceptions have been claimed 

 to exist (253). In general the sympathetic postgangli- 

 onic nerves have been shown to be adrenergic, but it 

 has become highly probable that the sudomotor 

 fibers in man and cat (93) and the v^asodilators to 

 voluntary mijscle in cat and dog (61, 153, 426) are 

 cholinergic. It has also been claimed that a fraction 

 of the sympathetic fibers to the nictitadng membrane 

 of the cat are cholinergic (12, 66). A detailed discus- 



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