Saturday, October 29, 2011

Situated above the thalamus at its posterior end, the habenula is a pair of small nuclei with affarent and efferent pathways, forming a relay system in which olfactory impulses are transmitted to efferent (salivatory and motor) nuclei of the brain stem. In this way, olfactory sensation is thought to affect food intake. The habenular nucleus contains numerous peptidergic neurons.

The afferent pathways reach the habenular nuclei via the medullary stria of the thalamus; it contains fibers from the septal nuclei , the anterior perforated substance (olfactory area), and the preoptic region. Furthermore, it receives fibers from the amygdaloid body (amygdala) crossing over from the terminal stria.

The efferent pathways extend into the midbrain. The habenulotectal tract transmits olfactory impulses to the superior colliculi. The habenulotegmental tract terminates in the dorsal tegmental nucleus, from where there is a link to the posterior longitudinal fasciculus with connections to the salivatory and motor nuclei of the masticatory and deglutitory muscles (olfactory stimuli leading to secretion of saliva and gastric juice). The habenulo-interpeduncular tract, Meynert’s bundle, terminates in the interpeduncular nucleus which is connected to various nuclei of the reticular formation.