Substantia nigra
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Location of the substantia nigra (blue arrow, 29), frontal section |
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Substantia nigra (also Soemmerring ganglion after Samuel Thomas von Soemmerring ) describes a part of the brain . This is a core complex in the area of the midbrain ( mesencephalon ), which isdarkly colored ( Latin niger (fem. Nigra ), black ')due to a high intracellular content of iron and melanin .
anatomy
The substantia nigra is located in the mesencephalon dorsal to the cerebral legs . Morphologically, a distinction is made between a dark pars compacta ( SNc ) with densely packed, melanin-containing nerve cells and a reddish pars reticulata ( SNr ), whose nerve cells stand out due to their particularly high iron content.
Nerve fibers ( afferents ) supplying the substantia nigra run from the motor cortex and the premotor cortex, which are referred to as the corticonigrales fibers . In addition, there are afferents from the caudate nucleus and the putamen , which are called strionigrales fibers .
The nerve fibers leading out ( efferents ) run over the nigrostriatal fibra to the striatum (= caudate nucleus and putamen combined) and to the thalamus . Various neurotransmitters can be detected histochemically in the neurons of the substantia nigra. A particularly high dopamine content is impressive in the pars compacta .
physiology
The substantia nigra is incorporated into various circuits of the extrapyramidal motor system and is in this way connected to the cerebral cortex , striatum , subthalamic nucleus , thalamus and other brain structures. Signals are transmitted via their dopaminergic neurons that have a particular effect on planning and the beginning of a movement (“starter function”).
Pathophysiology
A failure of the dopaminergic system leads to the loss of the inhibition of other components of the circuit and thus to the symptoms of Parkinson's disease . In contrast, failure of the subthalamic nucleus or the external parts of the globus pallidus leads to a relative hyperfunction of the neurons of the substantia nigra and thus to diseases such as Huntington's disease (pallidum) or hemiballism (subthalamic nucleus).
literature
- Martin Trepel: Neuroanatomy - Structure and Function . 4th edition. Urban & Fischer , Munich 2008, ISBN 978-3-437-41298-1 , midbrain (mesencephalon), p. 153 ff .
