Editing Brainstem (section)

===Midbrain===
{{Main|Midbrain}}
[[File:Brainstem and thalamus ja ja 135.png|thumb|upright=1.4|Diagram showing the position of the colliculi. Superior shown in green and inferior in orange.]]
[[File:Midbrain-axial-showing-tectum-and-tegmentum.jpg|thumb|View of the midbrain showing covering tectum and tegmental floor]]
The [[midbrain]] is further subdivided into three parts: [[tectum]], [[tegmentum]], and the [[ventral tegmental area]].  The [[tectum]] forms the ceiling. The tectum comprises the paired structure of the [[superior colliculus|superior]] and [[inferior colliculus|inferior colliculi]] and is the dorsal covering of the [[cerebral aqueduct]]. The [[inferior colliculus]] is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei, as well as inputs from the auditory cortex. Its inferior brachium (arm-like process) reaches to the [[medial geniculate nucleus]] of the [[diencephalon]]. The [[superior colliculus]] is positioned above the inferior colliculus, and marks the rostral midbrain. It is involved in the special sense of vision and sends its superior brachium to the [[lateral geniculate body]] of the diencephalon.

The [[tegmentum]] which forms the floor of the midbrain, is ventral to the [[cerebral aqueduct]].  Several [[Nucleus (neuroanatomy)|nuclei]], [[neural tract|tracts]], and the [[reticular formation]] are contained here.

The [[ventral tegmental area]] (VTA) is composed of paired [[cerebral peduncle]]s. These transmit axons of [[upper motor neuron]]s.

====Midbrain nuclei====
The midbrain consists of:
*[[Periaqueductal gray]]:  The [[gray matter]] around the [[cerebral aqueduct]] contains neurons involved in the [[pain]] desensitization pathway.  Neurons synapse here. When stimulated by a signal, the synaptic connections activate neurons in the [[nucleus raphe magnus]]. The pathway then projects down into the [[posterior grey column]] of the spinal cord, inhibiting pain sensation transmission.
*[[Oculomotor nerve]] nucleus:  This is the third [[cranial nerve nucleus]].
*[[Trochlear nerve]] nucleus:  This is the fourth cranial nerve.
*[[Red nucleus]]: This is a motor nucleus that sends a descending tract to the [[lower motor neuron]]s.
*[[Substantia nigra pars compacta]]: This is a concentration of neurons in the ventral portion of the midbrain that uses [[dopamine]] as its [[neurotransmitter]] and is involved in both motor function and emotion. Its dysfunction is implicated in [[Parkinson's disease]].
*[[Reticular formation]]: This is a large area in the [[midbrain]] that is involved in various important functions of the midbrain. In particular, it contains lower motor neurons, is involved in the pain desensitization pathway, is involved in the arousal and consciousness systems, and contains the [[locus coeruleus]], which is involved in intensive [[alertness]] modulation and in [[Autonomic nervous system|autonomic]] reflexes.
*[[Central tegmental tract]]: Directly anterior to the floor of the [[fourth ventricle]], this is a pathway by which many tracts project up to the cortex and down to the spinal cord.
*[[Ventral tegmental area]]: A [[dopaminergic]] [[nucleus (neuroanatomy)|nucleus]], known as [[Dopaminergic cell groups#Cell group A10|group A10 cells]]<ref name="Hegarty">{{cite journal |last1=Hegarty |first1=SV |last2=Sullivan |first2=AM |last3=O'Keeffe |first3=GW |title=Midbrain dopaminergic neurons: a review of the molecular circuitry that regulates their development. |journal=Developmental Biology |date=15 July 2013 |volume=379 |issue=2 |pages=123–38 |doi=10.1016/j.ydbio.2013.04.014 |pmid=23603197|doi-access=free }}</ref> is located close to the midline on the floor of the midbrain.
*[[Rostromedial tegmental nucleus]]: A [[GABAergic]] nucleus located adjacent to the ventral tegmental area.

<gallery>

Midbrain - superior colliculus.svg|Cross-section of the midbrain at the level of the superior colliculus
Midbrain - inferior colliculus.svg|Cross-section of the midbrain at the level of the inferior colliculus
</gallery>