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Transcript
Dr. Mustafa Neuroanatomy lectures (8) Diencephalon The diencephalon is an interbrain structure lies between the two cerebral hemispheres. The cavity of the diencephalon is the third ventricle. Divisions of diencephalon: 1- Two thalami. 2- Hypothalamus. 3- Subthalamus. 4- Epithalamus. Thalamus: It is an important relay station has an egg shaped and it represents a large mass of gray matter. The two thalami are Dr. Mustafa situated on each side of the midline slit like cavity (the third ventricle). Lateral to each thalamus is the internal capsule (white matter). The nuclei of the thalamus: The thalamus is divided into numbers of nuclei. The division of the thalamus is done by the Y- shaped white matter bundle and it is called the internal medullary lamina which divides the thalamus into: a- Anterior nucleus anteriorly. b- Medial nucleus medially. c- Lateral group of nuclei laterally. The lateral group of nuclei includes the following: 1- Pulvinar is the rounded posterior part of the lateral group of nuclei of the thalamus. 2- Dorsal tire of nuclei. 3- Ventral tire of nuclei which is further subdivided into ventro-anterior (VA), ventro-lateral (VL) and ventro- posterior (VP). d- Medial and lateral geniculate bodies which are two nuclei that are situated at the posterior part of each thalamus. Dr. Mustafa Dr. Mustafa Connections of the thalamic nuclei: ●the anterior nucleus sent information to the limbic system (that is responsible for emotion and reaction). ●the medial nucleus sent information to prefrontal cortex (that is responsible for thinking, behaviors and mode). ●the pulvinar and dorsal tire of nuclei send together output to the association cortex of the temporal, parietal and occipital lobes. ●the ventroposterior nucleus is the main sensory nucleus that receives input from all of the sensory systems except olfaction. It receives input from: 1- Spinothalamic tract (for pain, temperature and touch pathway). 2- Medial lemniscus (for vibration and proprioception pathway). 3- Trigeminothalamic tract (for pain and temperature pathway). 4- Nucleus of tractus solitarius (for visceral sensation and taste). The output of the ventroposterior nucleus is to the primary sensory areas. ●the ventroanterior and ventrolateral nuclei are motor nuclei. They receive from: the cerebellum, red nucleus, substantia nigra and the globus pallidus. The output of the ventroanterior and ventrolateral nuclei are to the motor areas. Dr. Mustafa ●the medial and lateral geniculate bodies. The medial geniculate body is connected to the auditory area. While the lateral geniculate body is connected to the visual area. Thus, the sensory, motor and emotional systems are all pass through the thalamus for processing in the thalamus. Dr. Mustafa Dr. Mustafa The subthalamus: It is a transitory part of the diencephalon. It lies between the mid brain and the thalamus. The substantia nigra, red nucleus and superior colliculi have extensions inside the subthalamus. The subthalamus has an important motor nucleus that has connection with the basal ganglia which is called the subthalamic nucleus of Luys. The epithalamus: It has two parts: 1- Pineal gland. 2- Habenular nuclei. The pineal gland: It secrets the melatonin hormone that is secreted in response to darkness. It lies between the two superior colliculi. The pineal gland or body is frequently calcified with age and this calcification is a useful radiological landmark. Its displacement may indicate an intracranial space occupying lesion. Dr. Mustafa Dr. Mustafa The habenular: They are small nuclei that responsible for visceral and emotional response to smell. 1- Visceral response to smell like nausea and vomiting to certain smell. 2- Emotional response to smell like increase or decrease the emotional desire (attractive or non-attractive response). These visceral and emotional responses to smell are differing from one person to another. Hypothalamus: It is a small area lies anterior-inferior to the thalamus. It is about 5 grams in weight, its neurons have specialized features that make them participate in a wide range of activity. These Dr. Mustafa neurons will control food intake, water intake, body temperature, biological O'clock or circadian rhythm of sleep pattern; it also controls the sexual behaviors and reproduction. The hypothalamus controls the endocrine functions through its connections with the pituitary gland (hypophysis cerebri). The hypothalamus will control the pituitary gland through: 1- The hypothalamo-hypophyseal portal circulation, in which venous capillary bed in hypothalamus while the other venous capillary bed in the anterior lobe of the hypophysis cerebri (pituitary gland) to carry the stimulatory or inhibitory factors to pituitary gland. 2- The neural pathway through tuber cinnerum → median eminence → infundibulum that pass through opening in the diaphragma sellae to end in the posterior lobe of the pituitary gland. Thus, the neuronal bodies (perikaryons) are situated within the hypothalamus and their axons are extended to end within the posterior lobe of pituitary gland. This neural pathway between hypothalamus and posterior lobe will started from the two groups of nuclei in the hypothalamus; the paraventricular nucleus and supraoptic nucleus. These nuclei will produce anti diuretic hormone (ADH) and oxytocin hormone, then these hormones will be carried by axons of these two nuclei to be stored in posterior lobe of the pituitary gland and then release from the posterior lobe of the pituitary gland on need into circulation. Paraventricular and supraoptic nuclei of hypothalamus → tuber cinnerum → median eminence → infundibulum that Dr. Mustafa pierces through the opening of the diaphragma sellae → posterior lobe of pituitary gland. Limbic system This system controls the emotional aspect of behavior and it is composed of interconnected centers surrounding the regions where the Dr. Mustafa two hemispheres join the diencephalon. The limbic system is divided into two major parts: 1- The limbic cortex. 2- The subcortical structures. The limbic cortex: it includes: 1- Cingulate gyrus which is responsible for: a- Emotional response to pain. b- Emotional response to touch and vision. The emotional response to pain, touch and vision is controlled through the autonomic nervous system. 2- Parahippocampal gyrus. 3- Hippocampal formation which is medial to parahippocampal gyrus and has the following parts: • hippocampus. •dentate gyrus. •subicullum. The hippocampal formation is responsible for recording the memory and then these will be carried by the parahippocampal gyrus to different areas of the CNS. Thus, damage to hippocampal formation will lead to improper storage of the recent memory. Dr. Mustafa Dr. Mustafa Subcortical structures: it includes: 1- Fornix and mamillary body. The fornix is a bundle of white matter from the hippocampal formation then loop and end in the mamillary body. The fornix and mamillary body are responsible to transmit the memory traces from place to place within CNS. Damage to mamillary body will lead to Korsakoff psychosis in which there is patchy amnesia and confabulation. 2- Amygdaloid body. It presents in the anterior aspect of the temporal lobe inside the uncus. It has the following functions: a- Responsible for olfaction. b- Emotion of aggressiveness, fear and anger. c- Emotional control of sexual desire and tendency. Damage to amygdaloid body will lead to Klüver-Bussy syndrome. 3- Septal area. It is very small region in the anterior part of the cerebrum near septum palliucidum. They are responsible for control of sense of pleasure. The stimulation of this area leads to euphoria. 4- Habenular nuclei. They are responsible for visceral and emotional response to smell. Dr. Mustafa Applied anatomy of limbic system is the following psychiatric illnesses: 1- Schizophrenia. 2- Anxiety (fear of unknown). 3- Phobia (fear of no normal ground). 4- Depression (the value of things becoming less). The limbic system is responsible for emotional responses which are done through the autonomic nervous system. Dr. Mustafa