The midbrain ( large mesencephalon ) is part of the brain stem and lies between the bridge ( pons ) and the interbrain ( diencephalon ). While the midbrain in fish and reptiles still largely performs the functions of the endbrain in mammals and the visual, auditory and surface sensory tracts end here, in mammals it is the connection between the hindbrain and the diencephalon and, above all, responsible for the coordination of motor functions but largely controlled by higher-level centers. The midbrain controls most of the eye muscles and is an important part of the extrapyramidal system .
The midbrain can be divided into three layers. The cerebral legs ( crura cerebri ) lie in the front base of the midbrain, followed by the midbrain hood ( tegmentum mesencephali ) dorsally . Both together are called Pedunculi cerebri ("cerebral stalks"). This is followed by the roof of the midbrain ( tectum mesencephali or lamina tecti ). Between the tegmentum and the tectum lies the cerebral water canal of the midbrain ( aqueductus mesencephali ) about 1.5 cm long in adults , which is surrounded by the central gray cave .
The cerebral legs ( crura cerebri , singular crus cerebri ) are the front part of the midbrain. Both cerebral legs form the brain stem ( Pedunculus cerebri ). Crura cerebri and pedunculi cerebri are also used synonymously by some authors.
The cerebral crura are bounded laterally by shallow furrows ( sulcus lateralis mesencephali ) and towards the middle (medial). In front there is a pit ( interpeduncular fossa ) between the legs of the cerebrum . In this area, some structures of the diencephalon ( corpus mamillare , pituitary stalk ) push themselves between the cerebral legs. Caudally, the legs of the cerebrum border the pons .
The legs of the cerebrum contain, among other things, the long tracts from the internal capsule . These nerve fiber strands can be further subdivided from the outside to the inside into the fibers corticospinales, corticonucleares, corticopontinae, parietotemporopontinae and frontopontinae. At the medial groove ( sulcus oculomotorius ) occurs the III. Cranial nerve ( oculomotor nerve ) to the surface of the brain.
The midbrain dome ( tegmentum mesencephali ) is the largest part of the midbrain and consists of white and gray matter.
It contains the ruber nucleus as an important switching core for the basal motor system as well as the cranial nerve nuclei nucleus nervi oculomotorii , nucleus nervi trochlearis , nucleus accessory nervi oculomotorii (Edinger-Westphal nucleus) and nucleus mesencephalicus nervi trigemini . The substantia nigra , which is functionally an important core area of motor skills , lies on the border with the cerebral thighs . Further structures of the tegmentum are the central tegmental tract , the dorsal and medial longitudinal fasciculus and parts of the reticular formation . The ventral tegmental area is part of the mesolimbic system .
The roof of the midbrain ( tectum mesencephali ) is the dorsal part of the midbrain. It consists of a thin plate called the four-hill plate ( Lamina quadrigemina or Lamina tecti ). The two mounds towards the mouth ( Colliculi rostrales ) are also known as upper hills ( Colliculi superiores ) in humans . Analogously, the two mounds distant from the mouth ( colliculi caudales ) are referred to as lower mounds ( colliculi inferiores ) in humans . In animal anatomy one speaks instead of front or rear hills due to the non-upright posture. The superior colliculi are important for the optical reflexes , the inferior colliculi are the switching station of the auditory pathway . The area pretectalis lies towards the mouth (rostral) of the four-hill plate .
In birds , only the front mounds are formed and very developed. This is where the birds' primary visual center lies; it is also known as the optic tectum . In fish and amphibians, the midbrain still largely takes on the function of the mammalian ape.
Core areas and pathways in the midbrain
The following important core areas are in the midbrain:
- Nucleus nervi oculomotorii
- Nucleus nervi trochlearis
- Nucleus accessorius nervi oculomotorii (Edinger-Westphal-Kern)
- Nucleus mesencephalicus nervi trigemini
- Nucleus ruber
- Substantia nigra
- Formatio reticularis
Important pathways of the midbrain are:
- Corticospinal tract
- Spinothalamic tract
- Central tegmental tract
- Lemniscus medialis and lateralis
- Fasciculus longitudinalis medialis and dorsalis
- Corticopontinae fibers
- Corticonuclear fibers
- Fibrae temporopontinae
- Gerhard Böhme: Textbook of the anatomy of domestic animals . tape 4 . Georg Thieme, Stuttgart, ISBN 978-3-8304-4150-2 , p. 110-117 .
- T.H. Schiebler, W. Schmidt: Textbook of the entire human anatomy: cytology, histology, history of development, macroscopic and microscopic anatomy . 3. Edition. Springer, Berlin 2013, ISBN 978-3-662-22083-2 , pp. 668 .
- Wolfgang Dauber: Feneis' Bild-Lexikon der Anatomie . Georg Thieme, Stuttgart 2005, ISBN 978-3-13-330109-1 , p. 348-356 .
- Herbert Lippert: Anatomy compact . Springer, Berlin 2013, ISBN 978-3-642-95726-0 , pp. 317-318 .
- Norbert Ulfig: Kurzlehrbuch Neuroanatomie . Georg Thieme, Stuttgart 2008, ISBN 978-3-13-152721-9 , pp. 100 .