Thalamus, Hypothalamus,Epithalamus Dr. Nimir Dr. Safaa

Describe the location of the thalamus . List the different parts and nuclei of the thalamus . List the afferent input to different nuclei of the thalamus. List the efferent output from the different nuclei of the thalamus. Describe the structure of hypothalamus, epithalamus , and subthalamus. List the nuclei of the hypothalamus. List the afferent connections of the hypothalamus. List the efferent connections of the hypothalamus List the functions of hypothalamus.

The thalamus is an egg-shaped gray matter situated rostral (superior) to brainstem, one in each cerebral hemisphere. Between them is third ventricle. They may connect with interthalamic connection (adhesion). It is an important relay and integrative station for information passing to: All areas of cerebral cortex. Basal ganglia. Hypothalamus. Brainstem.

Subdivisions of the thalamus: Internal medullary lamina is a Y shape sheet of white matter dividing the thalamus into 3 parts: Anterior part that contains anterior thalamic nuclei which receive mammillothalamic tract & also receive reciprocal connections with the cingulate gyrus and hypothalamus. Its function is concerned with emotion & recent memory.

Medial part that contains dorsomedial nucleus & several smaller nuclei Medial part that contains dorsomedial nucleus & several smaller nuclei. Dorsomedial nucleus has two-way connections with prefrontal cortex, hypothalamic nuclei & thalamic nuclei. Its function is integration of somatic, visceral, and olfactory informations, and relating them to one's emotional feelings and subjective states.

Lateral Part which is subdivided into dorsal tier & ventral tier. Dorsal tier includes lateral dorsal nucleus, lateral posterior nucleus, and pulvinar. They are interconnected with other thalamic nuclei , parietal lobe, cingulate gyrus, occipital and temporal lobes. Their function is not well known & mostly associated with emotions, sensory integration & vision.

Ventral tier consists of the following nuclei in a craniocaudal sequence: Ventral anterior nucleus which is connected to reticular formation, substantia nigra, corpus striatum, premotor cortex and thalamic nuclei. It influences motor activity. Ventral lateral nucleus has similar connections to that of ventral anterior nucleus plus input from cerebellum & red nucleus.

Ventral posterior nucleus is subdivided into ventral posteromedial nucleus and ventral posterolateral nucleus. Ventral posteromedial receives ascending trigeminal and gustatory pathways. Ventral posterolateral receives the important ascending sensory tracts, the medial and spinal lemnisci. Both nuclei relay common sensations to consciousness.

Other Nuclei of the Thalamus: Intralaminar nuclei are within the internal medullary lamina & they influence the levels of consciousness and alertness. Midline nuclei adjacent to the third ventricle. Reticular nucleus is between external medullary & internal capsule. It regulates thalamus by cerebral cortex.

Medial geniculate body forms part of the auditory pathway. Lateral geniculate body forms part of the visual pathway.

Hypothalamus: Is the part of diencephalon that extends from the region of the optic chiasma to mammillary bodies. When observed from below it is related to optic chiasma, tuber cinereum, infundibulum and mammillary bodies. Hypothalamic nuclei are divided into medial and lateral zones.

Medial zone include from anterior to posterior: Part of the preoptic nucleus. Anterior nucleus. Part of suprachiasmatic nucleus. Paraventricular nucleus. Dorsomedial nucleus. Ventromedial nucleus. Infundibular (arcuate) nucleus. Posterior nucleus.

Lateral zone include from anterior to posterior: Part of the preoptic nucleus. Part of suprachiasmatic nucleus. Supraoptic nucleus. Lateral nucleus. Tuberomammillary nucleus. Lateral tuberal nuclei.

Hypothalamus receives information from the body through: Nervous connections. Bloodstream. Cerebrospinal fluid. Hypothalamic nuclei respond and exert their control via the same routes. Afferents: Somatic and visceral afferents. Visual afferents. Olfaction. Auditory. Corticohypothalamic from frontal lobe. Hippocampohypothalamic Amygdalohypothalamic. Thalamohypothalamic. Tegmental.

Efferent: Descending fibers to the brainstem and spinal cord. Mammillothalamic tract. Mammillotegmental tract. Multiple pathways to the limbic system.

Functions of the Main Hypothalamic Nuclei Presumed Function Hypothalamic Nucleus Synthesizes vasopressin (antidiuretic hormone) Supraoptic nucleus Synthesizes oxytocin Paraventricular nucleus Control parasympathetic system Preoptic and anterior nuclei Control sympathetic system Posterior and lateral nuclei Regulate temperature (response to heat) Anterior hypothalamic nuclei Regulate temperature (response to cold) Posterior hypothalamic nuclei Initiate eating and increase food intake (hunger center) Lateral hypothalamic nuclei Inhibit eating and reduce food intake (satiety center) Medial hypothalamic nuclei Increase water intake (thirst center) Controls circadian rhythms Suprachiasmatic nucleus

The epithalamus consists of habenular nuclei and their connections and pineal gland. Habenular nuclei are medial to the posterior surface of the thalamus. Receive afferents from: Amygdaloid nucleus through the stria medullaris thalami ( some cross to form habenular commissure). Hippocampal formation through the fornix. Send efferents to: Interpeduncular nucleus. Tectum of the midbrain. Thalamus. Reticular formation of the midbrain.

Pineal gland is behind thalami & above superior colliculi. Its stalk base contains habenular commissure above & posterior commissure below. Receives afferents from superior cervical sympathetic ganglia. Its secretions(melatonin) reach target organs (pituitary, pancreas, parathyroids, adrenals and gonads) via the bloodstream or through the cerebrospinal fluid.