What are the functions of efferent fibers

Nervous system

Belong to the nervous system brain and Spinal cord (= CNS) as well as that peripheral nervous system (= PNS) which includes all the nerves emanating from the CNS. In the brain are Thousands of nerve cellswho have favourited signals from the Sense organs and other endogenous receptors filter, analyze and convert into response signals for the peripheral nervous system. The central nervous system receives oxygen and nutrients via a large vascular network. The skull and the Spine, three Connective tissue layers as well as the brain- and Spinal fluid, as buffer serves.


The CNS arises from one Ectoderm zone, the neural plate, which first forms a tube through neurulation. This neural tube changes its shape enormous growth,Bulges and Kink. The following structure of the CNS can be carried out in adults:

Structure of the CNS
Main section Subsection caves
  • Telencephalon
  • Diencephalon
  • Lateral ventricle
  • 3. Ventricle


  • Metencephalon with cerebellum and pons
  • Myelencephalon with medulla oblongata
  • 4. Ventricle

  • Central canal

The peripheral nervous system includes PNS afferent and efferent Fibers that connect the nervous center to the periphery. Such fibers are in the Spinal nerves and in the Cranial nerves contain. One distinguishes one animales of a autonomous or vegetative NS.

 Fig. 1 - Overview of the structure of the peripheral NS Legend   Fig. 1
The autonomous control of the organs takes place via 2 neurons: a pre- and a postganglionic neuron. The cell bodies of the preganglionic neurons are located in the CNS, the axons of which are myelinated. As the disease progresses, a synapse outside the CNS is formed in a peripheral ganglion.
The neuron after the synapse is called postganglionic, the axon of which is marrowless and runs into the end organ.

The development of a spinal cord nerve can be summarized as follows:

  1. The cells of the spinal ganglion, which originate from the neural crest cells, send fibers to the center and to the periphery:
    > Dorsal afferent roots of the spinal cord
  2. Cells of the lamina basalis of the neural tube send processes to the periphery
    > ventrally efferent roots of the spinal cord

Together they make that Spinal nerve, but still autonomousafferent and efferentFibers attached. Therefore, the spinal nerve contains the following 4 functional fiber types:

  • somatoafferente (somatosensitive) fibers
  • viszeroafferente (viscerosensitive) fibers
  • viszeroefferente (parasympathetic) fibers
  • somatoefferente (somatomotor) fibers
 Fig. 2 - Overview of the origin of the peripheral NS Legend   Fig. 2
Overview of the different types of fibers in the spinal cord nerve. The visceroefferent fibers (parasympathetic nervous system) are not shown here. It belongs to the craniosacral system because the preganglionic fibers originate on the one hand from the medulla oblongata (e.g. N. vagus) and on the other hand from the sacral segments.
1. Spinal cord  8.Gaglion sympathetic
2.Spinal ganglion  9.postganglionic fibers
3. Spinal nerve 10.Central canal
4.Ramus posterior 11.Radix posterior
5.autochthonous back muscles 12.Radix anterior
6.Ramus ventralis 13.Ramus communicans griseus
7. Ramus communicans albus    

 with legend
without legend

The autonomic nervous system (ANS) is part of the peripheral NS and is included in the parasympathetic and sympathetic system structured. The sympathetic system has its origin in the preganglionic neurons the thoraco-lumbar section of the spinal cord (intermediolateral zone of the mantle layer). The axons (largely myelinated) arrive as Ramus communicans albus to the boundary line. The postganglionic neurons are either in the paired sympathetic ganglia (Border line) or in the unpaired prevertebral ganglia and send out their fibers as postganglionic fibers (mostly unmyelinated). Part arrives as Ramus communicans griseus back to the spinal nerves for the innervation of sweat glands, blood vessels and Mm arrectores pilorum.

The parasympathetic NS comes from the preganglionic neurons of the Medulla oblongata and the Sacral segments ab (craniosacral system). The axons are mostly unmyelinated and, in contrast to the sympathetic preganglionic fibers, very long (cf. N. vagus). The cells with the postganglionic fibers are either in the Terminal ganglia of the head or in the Intramural ganglia various viscera and in the pelvis near the successor organs. In contrast to the sympathetic ones postganglionic fiber are the parasympathetic ones much shorter.

The so-called enteric NS (ENS) of the viscera, which controls reflex activity for the viscera, represents the most extensive and complex area of ​​the peripheral NS. The CNS exercises through the autonomic nervous system a modulating effect on the ENS out.

In contrast to the animal NS is the autonomous through an additional circuit, which leads into a ganglion or a plexus is interrupted. Fig. 3 - Neural control of the ENS Legend   Fig. 3
The ENS has about the same number of neurons as in the spinal cord (100 million). It consists of the Meisser and AuerbachPlexus and basically works autonomously.