Preganglionic fibre

It should be noted, as an apparent exception, that preganglionic fibres pass through the sympathetic chain, and tcift-out synapse, innervate the adrenal medulla. The cells of the latter may, however, be considered as modified postganglionic tissue. 

The parasympathetic nervous system. Here the postganglionic fibres are always short. The preganglionic fibres are long and pus almost up to the muscle or gland to be innervated. The preganglionic fibres arise from the brain stem (cranial nerves VII, IX and X), from the tectal region (cranial nerve III which supplies the eye, p. 38), and from the sacral region. 

Similar considerations would apply at the synapse between the preganglionic fibre and the nerve cell of the postganglionic fibre of the sympathetic and parasympathetic systems and curare is the blocking agent (fig. 7 A). 

Somatic nerves originate in the CNS and terminate at the neuromuscular junction where acetylcholine is the transmitter. Nerves of the autonomic system also use acetylcholine as the neurotransmitter at the end of the preganglionic fibres within the ganglia. With few exceptions, the postganglionic sympathetic fibres secrete noradrenaline (norepinephrine) whilst postganglionic parasympathetic fibres secrete acetylcholine. 

Langley, J.N. (1895) Note on regeneration of preganglionic fibres of the sympathetic. J. Physiol. (London) 18 280-284. 

AChE can be located on the postsynaptic as well as the presynaptic membrane. For example, in the cholinergic synapses of the autonomic ganglia AChE is located on the presynaptic membrane only it disappears after the degeneration of preganglionic fibres. In skeletal muscle, on the contrary, the major portion of the AChE is localized on the postsynaptic membrane and remains intact after denervation. 

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