Editing Midbrain (section)

===Cerebral aqueduct===
[[File:Brain-ventricle-anatomy-diagram.jpg|thumb|upright=1.5|Ventricular system anatomy showing the cerebral aqueduct, labelled centre right.]]

The [[cerebral aqueduct]] is the part of the [[ventricular system]] which links the [[third ventricle]] (rostrally) with the [[fourth ventricle]] (caudally); as such it is responsible for continuing the circulation of [[cerebrospinal fluid]]. The cerebral aqueduct is a narrow channel located between the tectum and the tegmentum, and is surrounded by the [[periaqueductal grey]],<ref name="Martin">Martin. Neuroanatomy Text and Atlas, Second edition. 1996, pp. 522-525.</ref> which has a role in analgesia, quiescence, and bonding. The [[dorsal raphe nucleus]] (which releases [[serotonin]] in response to certain neural activity) is located at the ventral side of the periaqueductal grey, at the level of the inferior colliculus.

The nuclei of two pairs of [[cranial nerve]]s are similarly located at the ventral side of the periaqueductal grey – the pair of [[oculomotor nucleus|oculomotor nuclei]] (which control the eyelid, and most eye movements) is located at the level of the superior colliculus,<ref>{{cite book|last=Haines|first=Duane E.|title=Neuroanatomy : an atlas of structures, sections, and systems|url=https://archive.org/details/neuroanatomyatla00hain_570|url-access=limited|publisher=Wolters Kluwer/ Lippincott Williams & Wilkins Health|location=Philadelphia|isbn=978-1-60547-653-7|pages=[https://archive.org/details/neuroanatomyatla00hain_570/page/n55 42]|edition=8th|year=2012}}</ref> while the pair of [[trochlear nucleus|trochlear nuclei]] (which helps focus vision on more proximal objects) is located caudally to that, at the level of the inferior colliculus, immediately lateral to the dorsal raphe nucleus.<ref name="Martin"/> The oculomotor nerve emerges from the nucleus by traversing the ventral width of the tegmentum, while the trochlear nerve emerges via the tectum, just below the inferior colliculus itself; the trochlear is the only cranial nerve to exit the brainstem dorsally. The [[Edinger-Westphal nucleus]] (which controls the shape of the lens and size of the pupil) is located between the oculomotor nucleus and the cerebral aqueduct.<ref name="Martin"/>