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Epithalamus – Epithalamus
The dorsal part of the diencephalon is composed of the unpaired pineal gland ,responsible for the circadian and circannual cycles, and the paired habenulae containing the habenular nuclei which are involved in the limbic system circuits and emotional integration.
• 1 Pineal gland (glandula pinealis) – a neuroendocrine gland
synthesizing the hormone called melatonin, it communicates reciprocally with the suprachiasmatic nucleus of hypothalamus – is involved in circadian and circannual biorhythms – has impact on sleep, vigilance, and sexual activity and its regulation 2 Habenular trigone (trigonum habenulare) – follows the stria medullaris of thalamus – the habenular nuclei are situated under it 1 3 Habenular nuclei (nuclei habenulares) – the nuclei of the limbic system localized in the habenular trigone 2 – receive afferents from the amygdaloid body, 1 hippocampal formation, septum verum, hypothalamus, Sagittal and cross-section of the brain and olfactory tubercle via the stria medullaris of thalamus 2 5 – efferents goes to the interpeduncular nucleus, 3 tectum of midbrain, thalamus, and reticular formation – represent a center for emotional integration of olfactory, 4 somatosensory, and viscerosensory information 1 4 Habenular commissure (commissura habenularum) Scheme of the epithalamus – a connection between the right and left habenular trigone (detail of the frontal section) 5 Posterior commissure (commissura posterior) – Commissural fibers: connecting the posterior thalamic nuclei, superior colliculus, and pretectal nuclei – Decussation fibers: projection fibers carrying information from the interstitial nucleus of Cajal and elliptic nucleus of Darkschewitsch then continue into the medial longitudinal fasciculus, which represents a tract of the vestibulo-oculo-motor reflexes
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6.2
Subthalamus – Subthalamus
The subthalamus is the basal part of the diencephalon connected via the subthalamic nucleus with the motor circuit of basal nuclei. It also contains the zona incerta (the rostral-most part of the reticular formation). The white matter of subthalamus is formed mainly by the pallido-thalamic tract of basal nuclei. Nuclei
• 1 Subthalamic nucleus of Luys (nucleus subthalamicus)
– functionally it represents a component of the basal nuclei loops – receives afferents from the lateral globus pallidus and precentral gyrus – efferents go to the lateral and medial globus pallidus 2 Reticular nuclei and zona incerta 2 – the nuclei are described as the reticular nuclei (nuclei reticulares) 1 but they are not related to the ascending reticular activation system (ARAS) – receive afferents via the excitation collaterals from the specific thalamic nuclei – efferents are dominantly inhibitory (GABA-ergic) and go into the thalamus and basal nuclei – these nuclei are responsible for determining new impulses and distinguishing them from known stimuli, they are also involved in body temperature control
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Frontal section of the brain
Tracts and pathways
• 3 Thalamic fasciculus / Forel´s field H1 (fasciculus thalamicus)
– the white matter between the thalamus and zona incerta containing the pallido-thalamic fibers – a part of the motor basal nuclei loops 4 Lenticular fasciculus / Forel´s field H2 (fasciculus lenticularis) – the white matter between the zona incerta and subthalamic nucleus containing the pallido-thalamic fibers 5 Ansa lenticularis / Forel´s field H – the fibers running around the posterior part of the internal capsule containing the pallido-thalamic tracts 6 Subthalamic fasciculus (fasciculus subthalamicus) – contains connections of the globus pallidus and subthalamic nucleus
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Frontal section of the diencephalon (detail)
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