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DIENCEPHALON Diencephalon: Thalamus, Pituitary and Pineal Glands Learning Objectives 1. To become familiar with the four major anatomical divisions of the diencephalon. 2. To understand the main structure, connections and functions of the various parts of the diencephalon. Orientation Orientation EXPLORING THE BRAIN EXPLORING THE BRAIN EXPLORING THE BRAIN EXPLORING THE BRAIN EXPLORING THE BRAIN CAT Photography PET MRI Source: modified from Posner & Raichle, Images of Mind EXPLORING THE BRAIN MRI studies brain anatomy. Functional MRI (fMRI) studies brain function. EXPLORING THE BRAIN Brodmann’s Areas Brodmann (1905): Based on cytoarchitectonics: study of differences in cortical layers between areas Most common delineation of cortical areas More recent schemes subdivide Brodmann’s areas into many smaller regions Monkey and human Brodmann’s areas not necessarily homologous GENERAL INFORMATION 1. Commissural tracts 2. Association tracts 3. Projection tracts Neural development at 4 weeks Diagram depicting the main subdivisions of the embryonic vertebrate brain. These regions will later differentiate into forebrain, midbrain and hindbrain structures. FORAMINA OF CSF diencephalon The region of the human brain, specifically the human forebrain, that includes the thalamus, the hypothalamus, the epithalamus, the prethalamus or subthalamus, and the pretectum. Functions of the Diencephalon • The diencephalon ("interbrain") is the region of the vertebrate neural tube that gives rise to posterior forebrain structures. • In development, the forebrain develops from the prosencephalon , the most anterior vesicle of the neural tube that later forms both the diencephalon and the telencephalon. • In adults, the diencephalon appears at the upper end of the brain stem, situated between the cerebrum and the brain stem. • Organization diencephalon mid-diencephalic territory prethalamus zona limitans intrathalamica thalamus hypothalamus epithalamus pretectum pineal gland metathalamus The diencephalon is the region of the embryonic vertebrate neural tube that gives rise to posterior forebrain structures including the thalamus, hypothalamus, posterior portion of the pituitary gland, and pineal gland. • Distinct parts of diencephalon perform numerous vital functions, from regulating wakefulness to controlling the autonomic nervous system. Midbrain The midbrain plays major roles in both wakefulness and regulation of homeostasis. • Caudally the mesencephalon adjoins the pons (metencephalon) and rostrally it adjoins the diencephalon (Thalamus, hypothalamus, etc.). • It does not split into other brain areas while the prosencephalon, for example, divides into the telencephalon and the diencephalon. MIDBRAIN KEY POINTS • The midbrain or mesencephalon is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation. • Anatomically, the midbrain comprises the tectum (or corpora quadrigemina), tegmentum, ventricular mesocoelia (or "iter"), and the cerebral peduncles, as well as several nuclei and fasciculi. • During embryonic development, the midbrain arises from the second vesicle, also known as themesencephalon, of the neural tube. • The mesencephalon is considered part of the brainstem. Thalamus The thalamus is a small structure in the center of the brain that acts as a relay center for sensory and motor information. Thalamus KEY POINTS • The thalamus's functions include relaying sensory and motor signals to the cerebral cortex and the regulation of consciousness, sleep, and alertness. • The thalamus is the largest structure derived from the embryonic diencephalon. • Together, the two halves of the thalamus are a prominent bulb-shaped mass, about 5.7 cm in length, located obliquely and symmetrically on each side of the third ventricle. • The thalamus has a system of myelinated fibers that separate the different thalamic subparts. These areas are defined by distinct clusters of neurons. • Every sensory system (with the exception of the olfactory system) has a thalamic nucleus that receives sensory signals and sends them to the associated primary cortical area. THALAMIC NUCLEI • Nuclear groups of the thalamus include: • anterior nuclear group • • • • anteroventral nucleus anterodorsal nucleus anteromedial nucleus superficial ("lateral dorsal") • medial nuclear group (or dorsomedial nucleus) • parvocellular part • magnocellular part • midline nuclear group or paramedian • • • • paratenial nucleus parventricular nucleus reuniens nucleus rhomboidal nucleus • Intralaminar nuclear group (Intralaminar nuclei) • anterior (rostral) group • paracentral nucleus • central lateral nucleus • central medial nucleus • posterior (caudal) intralaminar group • centromedian nucleus • parafascicular nucleus • lateral nuclear group in fact a false entity replaced by posterior region pulvinar lateral posterior nucleus belongs to pulvinar (lateral dorsal nucleus) belongs to anterior group ventral nuclear group ventral anterior nucleus ventral lateral nucleus ventral posterior nucleus ventral posterolateral ventral posteromedial • metathalamus no more used for the geniculate group medial geniculate body lateral geniculate body • thalamic reticular nucleus part of the ventral thalamus Functions of the Diencephalon KEY POINTS Distinct parts of diencephalon perform numerous vital functions, from regulating wakefulness to controlling the autonomic nervous system. Diencephalon is made up of four distinct components: the thalamus, the subthalamus, the hypothalamus, and the epithalamus. The hypothalamus is an integral part of the endocrine system, with one of the most important functions being to link the nervous system to the endocrine system via the pituitary gland. The thalamus is critically involved in a number of functions including relaying sensory and motor signals to the cerebral cortex, and regulating consciousness, sleep, and alertness. The epithalamus functions as a connection between the limbic system to other parts of the brain. Some functions of its components include the secretion of melatonin by the pineal gland (involved in circadian rhythms) and regulation of motor pathways and emotions. Epithalamus KEY POINTS The epithalamus connects the limbic system to other parts of the brain. The epithalamus is a dorsal posterior segment of the diencephalon, which includes the habenula and their interconnecting fibers the habenular commissure, the stria medullaris, and the pineal body. A main function of the epithalamus is the secretion of melatonin by the pineal gland. The epithalamus is connected with both the limbic system and the basal ganglia. Epithalamus • The epithalamus is a dorsal posterior segment of the diencephalon. • The diencephalon ("interbrain") is the region of the vertebrate neural tube that gives rise to posterior forebrain structures. • In development, the forebrain develops from the prosencephalon, the most anterior vesicle of the neural tube which later forms both the diencephalon and the telencephalon. • In adults, the Diencephalon appears at the upper end of the brain stem, situated between the cerebrum and the brain stem. • The habenular commissure is a brain commisure (a band of nerve fibers) situated in front of the pineal gland that connects the habenular nuclei on both sides of the diencephalon. Epithalamus bent asparagus Egyptian Eye of Horus (or Eye of Ra) Egyptian Eye of Horus (or Eye of Ra) 3rd EYE! Holy of Holies