From an anatomic point of view, one normally distinguishes between:
- the central nervous system (CNS), consisting of brain and spinal cord, and
- the peripheral nervous system (PNS) to which the nervous pathways outside the CNS are numbered and which makes sure afferent and efferent information flows between the periphery and the CNS.
In the sense of a coping aid for studying the nervous system this is divided into two interrelated units that interact with each other:
- The central nervous system (CNS), or neuraxis, which arises from the neural tube. It comprises the brain (cerebral hemispheres, diencephalon, brain stem, cerebellum) and the spinal cord and is the subject of this module.
The peripheral nervous system (PNS) comprises an afferent or sensory branch as well as an efferent or motoric branch, both of which lie outside the CNS (**). Essentially, the PNS arises from the cells of the neural crests. The neural tube, though, delivers the somatomotoric fibers as well as the preganglionic fibers of the autonomous nervous systems (see below). In addition, the dura mater or pachymeninx and the connective tissue of the peripheral nerves develop from the mesoderm (in contrast, the leptomeninx, i.e., the arachnoïdea and pia mater, arise from the neural crest).
(**) The somatomotoric and preganglionic fibers of the autonomous nervous system form an exception in that, despite belonging to the PNS, the perikarya that belong to them are to be found in the spinal cord and brain stem and thus in the CNS!
The afferent sensory pathways comprise both somatic and also visceral neurons. These transmit the information that is collected by the receptors of the somatic (skin, muscles) and visceral organs (intestines, lungs, etc.) to the central nervous system. The cell bodies of the sensory neurons form the spinal ganglia and the paravertebral ganglia.
The efferent motoric pathways can be subdivided into:
- the somatomotoric pathway (SNS) that accompanies the cerebral nerves of the brain stem and the spinal nerves of the spinal cord.
- The visceromotoric pathway (VNS), which comprises all the efferents that regulate the internal milieu (homeostasis). They are responsible for the steering the cardiac muscles, the smooth muscles of the intestines and blood vessels as well as the glands. The preganglionic part accompany the cerebral nerves and the spinal nerves. The postganglionic part (the sympathetic) forms a plexus that continues periarterial or as fibers that accompany the larger peripheral nerves before they reach the target organ via a terminal branch.
The vegetative nervous system can be divided into two sections:
- the sympathetic and
- the parasympathetic
Generalizing, the parasympathetic is in the service of regeneration, the recuperation of the organism and the excitation of the digestive apparatus.
Responsible neurotransmitter: acetylcholin.
Correspondingly, the sympathetic cares for an elevated alertness and concentration of the organism and for preparing for physical and intellectual achievements (widening of the bronchia, elevation of the pulmonary frequency and cardiac activity, pupil dilation.
Responsible neurotransmitters: noradrenalin and adrenalin
The peripheral nervous system is treated in a separate module.