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Section through Superior Colliculus showing path of Oculomotor Nerve (Periaqueductal gray visible but not labeled)
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Periaqueductal+Gray
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(PAG; also called the "central gray") is the
Midbrain Grey Matter that is located around the
Cerebral Aqueduct within the
Midbrain . It plays a role in the descending modulation of
Pain and in defensive behavior. The ascending pain and temperature fibers of the
Spinothalamic Tract also send information to the PAG via the ''spinomesencephalic tract''. The spinomesencephalic tract is so-named because the fibers orginate in the
Spine and terminate in the
Mesencephalon , another name for the midbrain, which is the part of the brain in which the PAG resides.
Stimulation of the periaqueductal grey matter of the midbrain results in release of
Serotonin in the dorsal horn of the
Spinal Cord , profound
Analgesia , activation of interneurons containing
Enkephalin , and release of
Norepinephrine in the dorsal horn of the spinal cord.
Neuron s of the PAG are excited by
Endorphins and by
Opiate Analgesic s. It also plays a role in
Female copulatory behavior (see
Lordosis Behavior ) via a pathway from the ventromedial nucleus of the
Thalamus .
