{"id":4470,"date":"2019-07-31T21:39:26","date_gmt":"2019-07-31T21:39:26","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-dutchess-anatomy-physiology\/?post_type=chapter&p=4470"},"modified":"2019-08-11T20:39:28","modified_gmt":"2019-08-11T20:39:28","slug":"the-diencephalon-thalamus-hypothalamus-epithalamus","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-dutchess-anatomy-physiology\/chapter\/the-diencephalon-thalamus-hypothalamus-epithalamus\/","title":{"raw":"The Diencephalon: Thalamus, Hypothalamus, Epithalamus","rendered":"The Diencephalon: Thalamus, Hypothalamus, Epithalamus"},"content":{"raw":"

The Diencephalon<\/h2>\r\nThe diencephalon is the one region of the adult brain that retains its name from embryologic development. The etymology of the word diencephalon translates to \u201cthrough brain.\u201d It is the\r\n\r\n[caption id=\"attachment_4473\" align=\"alignright\" width=\"600\"]\"This<\/a> Figure 1. The Diencephalon. <\/strong>The diencephalon is composed primarily of the thalamus, hypothalamus and epithalamus, which together define the walls of the third ventricle. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached. The epithalamus is located posterior to the thalamus.[\/caption]\r\n\r\nconnection between the cerebrum and the rest of the nervous system, with one exception. The rest of the brain, the spinal cord, and the PNS all send information to the cerebrum through the diencephalon. Output from the cerebrum passes through the diencephalon. The single exception is the system associated with\u00a0olfaction<\/strong>, or the sense of smell, which connects directly with the cerebrum. In the earliest vertebrate species, the cerebrum was not much more than olfactory bulbs that received peripheral information about the chemical environment (to call it smell in these organisms is imprecise because they lived in the ocean). The diencephalon is deep beneath the cerebrum and constitutes the walls of the third ventricle.\u00a0 The three major regions of the diencephalon are the thalamus, the hypothalamus, and the epithalamus (Figure 1). There are other structures, such as the\u00a0subthalamus, which includes the subthalamic nucleus that is part of the basal nuclei.\r\n\r\nThe cranial nerve associated with this area of the brain is the optic nerve (CN II) shown in Figure 3.\u00a0 The optic chiasm, where some axons of the optic nerves decussate, can be seen on Figure 2.\r\n

Thalamus<\/h3>\r\nThe\u00a0thalamus<\/strong>\u00a0is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. It has a left and right half, which are connected medially by the intermediate mass (Figure 2).\r\n\r\nSensory input to the thalamus comes from most of the special senses and ascending somatosensory tracts. Each sensory system is relayed through a particular nucleus in the thalamus. The thalamus is a required transfer point for most sensory tracts that reach the cerebral cortex, where conscious sensory perception begins. The one exception to this rule is the olfactory system. The olfactory tract axons from the olfactory bulb project directly to the cerebral cortex, along with the limbic system and hypothalamus.\r\n\r\nThe thalamus is a collection of several nuclei that can be categorized into three anatomical groups. White matter running through the thalamus defines the three major regions of the thalamus, which are an anterior nucleus, a medial nucleus, and a lateral group of nuclei. The anterior nucleus serves as a relay between the hypothalamus and the emotion and memory-producing limbic system. The medial nuclei serve as a relay for information from the limbic system and basal ganglia to the cerebral cortex. This allows memory creation during learning, but also determines alertness. The special and somatic senses connect to the lateral nuclei, where their information is relayed to the appropriate sensory cortex of the cerebrum.\r\n\r\nThe thalamus does not just pass the information on, it also processes that information. For example, the portion of the thalamus that receives visual information will influence what visual stimuli are important, or what receives attention.\u00a0 In this way, the thalamus helps the cerebrum to focus on specific stimuli while ignoring others.\r\n\r\nThe cerebrum also sends information down to the thalamus, which usually communicates motor commands. This involves interactions with the cerebellum and other nuclei in the brain stem. The cerebrum interacts with the basal nuclei, which involves connections with the thalamus. The primary output of the basal nuclei is to the thalamus, which relays that output to the cerebral cortex. The cortex also sends information to the thalamus that will then influence the effects of the basal nuclei.\r\n

Hypothalamus<\/h3>\r\n[caption id=\"attachment_4480\" align=\"alignright\" width=\"600\"]\"Sagittal<\/a> Figure 2<\/strong>. Sagittal view through the diencephalo and structures immediately superior to this region (septum pellucidum and corpous callosum).[\/caption]\r\n\r\nInferior and slightly anterior to the thalamus is the\u00a0hypothalamus <\/strong>(Figure 1,2), the another major region of the diencephalon.\u00a0 The hypothalamus is attached to the pituitary gland by a stalk called the\r\n\r\ninfundibulum.\u00a0 Inferior to the hypothalamus are a pair of bumps which are the mammillary bodies.\u00a0 While the function of the\u00a0mammillary bodies is not well understood, it is possible that they play a role in memory formation.\u00a0 The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. Functions of the hypothalamus to this end are numerous, and include:\r\n