Nucleus suprachiasmaticus

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A preparation was made from the area marked in red . In the middle is the III as a dark, vertical line. Ventricle can be seen (1) and below it two pear-shaped densities of stained cells (2), the SCN on each side. The dark horizontal area in the lower third of the image is the junction of the optic nerve (3).

The nucleus suprachiasmaticus ( suprachiasmatic nucleus ; English suprachiasmatic nucleus , SCN) is a core area in the brain , more precisely in the ventral hypothalamus , of mammals . It is on both sides under the III. Cerebral ventricle and above the junction of the optic nerves ( optic chiasm ). The core area is very cell-rich and contains many synapses . Cytoarchitectural two parts can be distinguished. All supplying nerve tracts ( afferents ) end in the pars ventrolateralis (ventrally and laterally lying part), which also shows a significantly stronger branching of the dendrites . Opposite it is the pars dorsomedialis (back and to the middle part).

It is now considered certain that the “master clock”, that is, the “internal clock” of mammals that controls the circadian rhythms , is located in this area. The suprachiasmatic nucleus is the most important, but not the only coordinator of the sleep-wake rhythm . In humans, the nucleus contains around 20,000 self-oscillating neurons, which maintain the species-specific daily rhythm even in absolute darkness. This rhythm is made possible by the synchronization of the individual suprachiasmatic neurons, which is realized through the intimate interconnection within this core area.

Interconnection

The nucleus receives light information from the retina via collaterals of the optic tract , namely via optical fibers from the lateral knee cusp ( corpus geniculatum laterale ) and the area hypothalami lateralis . In addition, there are afferent and efferent pathways to the retrochiasmatica area and the hypothalamus nucleus ventromedialis , which are also considered weak oscillators. The input from the external light conditions is necessary in particular to adapt the internal clock to the seasons or when changing time zones. On the other hand, any external influence must not overly modify the core's own oscillation, as otherwise every switching on or off of artificial light would disturb the internal clock and thus trigger jetlag . Only about a quarter of the neurons react to external light stimuli, the others are light-independent. There are also efferents to the preoptic region , the lateral septum , the interstitial nucleus of the medullary stria , the anterior hypothalamus nucleus and the paraventricular nucleus . The pineal gland is controlled by indirect efferents, the sympathetic neurons in the hypothalamus. The suprachiasmatic nucleus has no direct influence on other brain regions. The rhythmic discharges of its neurons and axons tend to indirectly influence other nuclei and the release of hormones.

Lesions of the suprachiasmatic nucleus lead to the loss of all biological rhythms. Animals with a destroyed suprachiasmatic nucleus still show waking and sleeping phases, but these are without a regular pattern. In addition to the suprachiasmatic nucleus, there are other subcortical structures that have a rhythm and interact with it by means of neurotransmitters and hormones in order to let the sleep and waking phases run in a rhythm.

Neurotransmitters and neuropeptides

Numerous neurotransmitters and neuropeptides are found in the neurons of the suprachiasmatic nucleus . The vasoactive intestinal polypeptide (VIP) is mainly found in the pars ventrolateralis in intrinsic neurons, which switch the afferent impulses to the efferents in the pars dorsomedialis . Nerve cell bodies expressing vasopressin and somatostatin are located in the pars dorsomedialis . In addition, neurons with γ-aminobutyric acid , substance P , cholecystokinin , neurotensin and corticotropin-releasing hormones can be detected in the suprachiasmatic nucleus .

Individual evidence

  1. ↑ a b c d Karlheinz Meier-Ewert, Hartmut Schulz: Sleep and sleep disorders . Springer, Berlin 2013, ISBN 978-3-642-84063-0 , pp. 18-23 .
  2. ^ A b c d e Robert F. Schmidt , Gerhard Thews : Physiologie des Menschen . 27th edition. Springer, Berlin 2013, ISBN 978-3-662-00485-2 , pp. 151 .
  3. ↑ a b C. G. Gu, P. Wang, TF Weng, HJ Yang, J. Rohling: Heterogeneity of neuronal properties determines the collective behavior of the neurons in the suprachiasmatic nucleus. In: Mathematical biosciences and engineering: MBE. Volume 16, number 4, March 2019, pp. 1893-1913, doi : 10.3934 / mbe.2019092 , PMID 31137191 .