BRS

298

BRS Neuroanatomy

Glutamate and aspartate

Striatum

x

e

Septal nuclei

r t

c o

e o

N

Sup. colliculus

Fornix

MN

Septal area

Climbing fibers

Dentate gyrus

Hippocampus Perforant pathway Entorhinal area (area 28)

Granule cells of cerebellar cortex Olivocerebellar tract

Subiculum

Inf. olivary nucleus

FIGURE 21.11. Distribution of glutamate- and aspartate-containing neurons and their projections. Glutamate is con sidered the major excitatory transmitter of the central nervous system. Cortical glutamatergic neurons project to the striatum; hippocampal and subicular glutamatergic neurons project via the fornix to the septal area and hypothalamus. Neurons of the inferior olivary nucleus project aspartatergic fibers to the cerebellum. The granule cells of the cerebellum are glutamatergic. MN, mammillary nucleus.

IX. NITRIC OXIDE

■ a gaseous neurotransmitter that is produced when nitric oxide synthase converts arginine to citrulline. ■ located in the olfactory system, striatum, cortex, hippocampal formation, supraoptic nucleus of the hypothalamus, and cerebellum. ■ responsible for the smooth muscle relaxation of the corpus cavernosum and thus penile erection. ■ believed to play a role in memory formation (long-term potentiation in the hippocampal formation).

X. FUNCTIONAL AND CLINICAL CONSIDERATIONS

A. Endogenous pain control system 1. Ascending pathway

■ spinoreticular pain impulses project to the periaqueductal gray of the midbrain. 2. Descending raphespinal pathway ■ excitatory neurons of the periaqueductal gray project to the nucleus raphe magnus of the pons. ■ excitatory neurons of the nucleus raphe magnus project serotonergic fibers to enkeph alinergic inhibitory neurons of the substantia gelatinosa. ■ enkephalinergic neurons of the substantia gelatinosa inhibit afferent pain fibers (sub stance P) and tract neurons that give rise to the spinoreticular and spinothalamic tracts.

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