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Diencephalon

these lectures will cover some of the objects of the Central Nervous System ...
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Diencephalon

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Diencephalon

  1. 1. Diencephalon lecture 6 Abbas A. A. Shawka Medical student 2nd grade
  2. 2. Subjects • Diencephalon
  3. 3. Overview on CNS parts
  4. 4. Overview on CNS parts midbrainmidbrain hindbrainhindbrain ponspons Medulla oblongata Medulla oblongata CerebellumCerebellum 4th vemtricle 4th vemtricle ForebrainForebrain 2 Cerebral hemisphere+ 2 lateral cavity ( telencephalon ) 2 Cerebral hemisphere+ 2 lateral cavity ( telencephalon ) Deep portion (thalamus & hypothalamus) with their cavity ( the 3rd ventricle ) ( diencephalon ) Deep portion (thalamus & hypothalamus) with their cavity ( the 3rd ventricle ) ( diencephalon ) - Connect the forebrain with the hindbrain - composed of : - 1. Tectum“Corpora quadrigemina” - inferior colliculi - superior colliculi 2. cerebral peduncle - midbrain tegmentum - crus cerebri - substantia nigra * Also called mesencephalon “ - Connect the forebrain with the hindbrain - composed of : - 1. Tectum“Corpora quadrigemina” - inferior colliculi - superior colliculi 2. cerebral peduncle - midbrain tegmentum - crus cerebri - substantia nigra * Also called mesencephalon “ Aqueduct cerebellum Aqueduct cerebellum
  5. 5. Diencephalon • The diencephalon of the brain consists of structures that are lateral to the third ventricle ( structures that the 3rd ventricle is their cavity ). • Diencephalon includes 1. the thalamus 2. the hypothalamus 3. the subthalamus 4. Metathalamus 5. the epithalamus ForebrainForebrain 2 Cerebral hemisphere+ 2 lateral cavity ( telencephalon ) 2 Cerebral hemisphere+ 2 lateral cavity ( telencephalon ) Deep portion (thalamus & hypothalamus) with their cavity ( the 3rd ventricle ) ( diencephalon ) Deep portion (thalamus & hypothalamus) with their cavity ( the 3rd ventricle ) ( diencephalon )
  6. 6. Thalamus • Morphologically, the thalamus is a large ovoid nuclear mass, about 4 cm long, which borders the dorsal part of the third ventricle (1) • Its narrow anterior pole lies close to the midline and forms the posterior boundary of the interventricular foramen. • Posteriorly, an expansion, the pulvinar ( medial side of the posterior border of thalamus ) (2) , extends beyond the third ventricle to overhang the superior colliculus (3) . • The brachium of the superior colliculus (superior quadrigeminal brachium) separates the pulvinar above from the medial geniculate body (4) below. • A small oval elevation, the lateral geniculate body (5) , lies lateral to the medial geniculate. 1 2 3 4 5
  7. 7. Thalamus surfaces • The superior (dorsal) surface of the thalamus is covered by a thin layer of white matter, the stratum zonale. • This curved surface is separated from the overlying body of the fornix ( arrow ) by the choroid fissure with the choroid plexus within it. • More laterally, it forms part of the floor of the lateral ventricle. • The lateral border of the superior surface of the thalamus is marked by the stria terminalis (1) and overlying thalamostriate vein, which separate the thalamus from the body of the caudate nucleus (2) • Laterally, a slender sheet of white matter, the external medullary lamina, separates the main body of the thalamus from the reticular nucleus. • Lateral to this, the thick posterior limb of the internal capsule lies between the thalamus and the lentiform complex. 1 2
  8. 8. Thalamus surfaces • The medial surface of the thalamus is the superior (dorsal) part of the lateral wall of the third ventricle. • It is usually connected to the contralateral thalamus by an interthalamic adhesion (1) • The boundary with the hypothalamus is marked by a faint hypothalamic sulcus (2) , which curves from the upper end of the cerebral aqueduct to the interventricular foramen (3) . • The thalamus is continuous with the midbrain tegmentum, the subthalamus and the hypothalamus. 1 2 3
  9. 9. Blood supply to thalamus • The thalamus derives its blood supply from a number of arteries: the polar artery (posterior communicating artery), paramedian thalamic- subthalamic arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries. • These are all branches of the posterior cerebral artery. • Some people have the artery of Percheron, which is a rare anatomic variation in which a single arterial trunk arises from the posterior cerebral artery to supply both parts of the thalamus.
  10. 10. Thalamic nuclei • Medullary laminae of thalamus are layers of myelinated fibres that appear on cross sections of the thalamusThe specific layers are: 1. external ( lateral )medullary lamina the thalamus from the subthalamus and thalamic reticular nucleus ( covering the lateral surface ) 2. Internal ( medial ) medullary laminaY-shape lamina within the substance of the thalamus dividing it into three compartments: -The anterior part -The medial part -The lateral part; is the largest & includes the pulvinar Each part is further divided into nuclei which have their specific connections
  11. 11. Other thalamic nuclei ! • Intralaminar & reticular • Median • Posterior
  12. 12. Main connection of thalamus Group Connection Function Lesion Anterior • Limbic • hypothalamic • Emotion • Memory Emotional and learning proplems Medial • Frontal lobe ( prefrontal ) • Hypothalamus • Basal nuclei • Affections • Judgments • Somato-visceral and olfactory integrations Apathy ( does not response ) Lateral • Sensory pathway • Cortex • Basal nuclei • Mainly sensory action Crossed hemi anesthesia
  13. 13. Thalamus connections • The general idea that the thalamus is the “ main sensory “ do not mean definitely there is NO motor area in thalamus !! ( YOU HAVE MOTOR AREA IN THALAMUS ) • Thalamus is not only important in the primary motor movement, it is also important in the associated motor activites of the EXTRAPYRAMIDAL SYSTEM !! • If you removed the cortex ( you fell with it ) , they found that some sensations will be maintained ( especially pain ) !! • If we removed the 2 thalami from a person, it will enter in deep coma ( loss of function ) !!
  14. 14. Thalamus connections • The thalamus is an important relay station for sensory-motor axonal loops involving the cerebellum and the basal nuclei • The thalamus is manifoldly connected to the hippocampus via the mammillo-thalamic tract, this tract comprises the mammillary bodies and fornix. ( emotions !! ) • The thalamus is connected to the cerebral cortex via the thalamocortical radiations ( each part of thalaus send axon to cortex and each part of cortex send axon to thalamus so they can modefiy each other activites ) • The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch. There are two main parts: the lateral spinothalamic tract, which transmits pain and temperature, and the anterior (or ventral) spinothalamic tract, which transmits crude touch and pressure.
  15. 15. Thalamus connections • Role of thalamus in sensation: • 1- Sensory information of all types (except smell) converges on the thalamus and are integrated through the interconnections between the nuclei. The resulting information pattern is distributed to other parts of the central nervous system. • 2- It is known that following removal of the cortex, the thalamus can appreciate crude sensations. However, the cerebral cortex is required for the interpretation of sensations based on past experiences.
  16. 16. Thalamus functions 1. Sensory relay and integrative area . 2. Recognize pain , temperature and touch. 3. Influence motor action by its connections with cerebellum, cortex and basal nuclei 4. Sleep and wakefulness cycle ( regulation of consciousness ). 5. Mood regulation through the hypothalamic connections. 6. Emotion and recent memory circuts.
  17. 17. Thalamic disorders • Thalamic disorders :- 1. Contralateral hemianesthesia 2. Sensory ataxia ( problem in iput of thalamus 3. Phantom limb ( problem in the output of thalamus ) 4. Hyperesthesia and abnormal reaction to pain 5. Visual field defects
  18. 18. Hypothalamus • The hypothalamus is located below the thalamus and is part of the limbic system. • it forms the ventral part of the diencephalon.
  19. 19. Hypothalamus • Extends from the region of the optic chiasma (1) to the caudal border of the mammillary bodies (2) • It lies below the thalamus and forms the floor and the inferior part of the lateral walls of the third ventricle • Anterior to the hypothalamus, the preoptic area is regarded as functional component • Caudally, the hypothalamus merges into the tegmentum of the midbrain • The hypothalamus is bounded laterally by the internal capsule • tuber cinerem (3) is part of the hypothalamus located between the optic chiasma and the mamilary bodies 1 2 2 21 3 3
  20. 20. Hypothalamus cells 1. magnocellular neurosecretory cells in the paraventricular nucleus and the supraoptic nucleus of the hypothalamus produce neurohypophysial hormones, oxytocin and ADH hormones . These hormones are released into the blood in the posterior pituitary. 2. Much smaller parvocellular neurosecretory cells, neurons of the paraventricular nucleus, release corticotropin-releasing hormone and other hormones into the hypophyseal portal system, where these hormones diffuse to the anterior pituitary.
  21. 21. Hypothalamus connections • The hypothalamus receives information from the rest of the body through:- • • 1- Nervous connections • 2- Bloodstream • 3- Cerebrospinal fluid • The neurons of the hypothalamic nuclei respond and exert their control via the same routes • The cerebrospinal fluid may serve as a conduit between the neurosecretory cells of the hypothalamus and distant sites of the brain
  22. 22. Hypothalamus connections Nuclei Function Anterio • Parasymp. Control • Response to heat Posterior • Sympath. Control • Response to cold Lateral • Hunger center • Thirst center Medial • Satiety center Suprachiasmatic Sleep and circadian rhyhthme Supraoptic ADH secretion Paraventricular Oxytocin secretion Hypothalamus is mainly for autonomic endocrine system control !!
  23. 23. Hypothalamus connection to pituitary • The hypothalamus is connected to the hypophysis cerebri by two pathways: 1. Nerve fibers that travel from the supraoptic and paraventricular nuclei to the posterior lobe of the hypophysis 2. Long and short blood vessels that connect hypothalamus with capillary plexuses in the anterior lobe of the hypophysis.
  24. 24. Functions of the hypothalamus • 1- autonomic control center • controlling the sympathetic and parasympathetic systems .. • Hypothalamus control the activity of :- • CVS • Digestive system • Respiratory system • Glandular system • 2- memory • Mammillary body is the main part of hypothalamus which build and support memory.
  25. 25. Functions of the hypothalamus • 3- water balance • Secretion of ADH hormone • Diabetes insipidus : failure of ADH secretion • Excessive thirst, diluted urine with normal glucose level. • 4- hunger and food intake • Response to change in glucose , amino acid and salts the hypothalamus control this through hunger and satiety centers. • Anorexia nervosa ( fear of obesity so do not eat anything !! ) • Obesity
  26. 26. Functions of the hypothalamus • 5- circadian rhythm • By controlling hormones levels of ACTH and melatonin • Suprachiasmatic nuclei is connected to pineal gland which secrete melatonin ( responsible for sleep and wake cycle ) • 6- temperature control • Receive information from thermoreceptor in brain and body and respond to it by :-
  27. 27. Functions of the hypothalamus • 7- emotional control and affective control • Through communication with 1. Frontal lobe 2. Limbic lobe 3. Endocrine and autonomic centers
  28. 28. Subthtalamus • The subthalamus is located ventral to the thalamus, medial to the internal capsule and lateral to the hypothalamus. • It is a region formed by several grey matter nuclei and their associated white matter structures, namely: - 1. The subthalamic nucleus, whose neurons contain glutamate and have excitatory effects over neurons of globus pallidus and substantia nigra 2. Zona incerta, located between fields of Forel H1 and H2. It is continuous with the thalamic reticular nucleus and receives input from the precentral cortex. 3. Subthalamic fasciculus, formed by fibers that connect the globus pallidus with the subthalamic nucleus 4. Fields of Forel. 5. Ansa lenticularis.
  29. 29. • During development the subthalamus is continuous with the hypothalamus, but is separated by white matter fibres mainly from the internal capsule. • Caudally, the subthalamus or prethalamus is separated from the thalamus by the zona limitans intrathalamica. • Postnatally, the subthalamus lies beneath the thalamus, hence 'sub' (meaning below) 'thalamus'. It also lies dorsolateral to the hypothalamus.
  30. 30. Subthalamus connections 1. The subthalamus develops efferent (output) connections to the striatum (caudate nucleus and putamen) in the telencephalon, to the dorsal thalamus (medial and lateral nuclear groups) in the diencephalon, and to the red nucleus and substantia nigra in the mesencephalon. 2. It receives afferent (input) connections from the substantia nigra and striatum.
  31. 31. Metathalamus • 1- Medial geniculate body: - - Oval body lies under cover of the pulvinar - Connected to the inferior colliculus by inferior brachium - Receives most of the fibers of lateral lemniscus - It is one of the main stations in the auditory pathway
  32. 32. Metathalamus • 2- Lateral geniculate body: - Oval elevation on the lateral part of the posterior end of the thalamus - Connected with the superior colliculus by the superior brachium - Receives numerous fibers from the optic tract - It is a major station in the visual pathway
  33. 33. Metathalamus • Defect in MGB 1. Partial senory-neuronal hearing loss 2. Disturbed acoustic reflexes • Defect in LGB 1. Crossed homonymous Hemianopsia 2. Disturbed visual reflexes
  34. 34. epithalamus • The epithalamus is a (dorsal) posterior segment of the diencephalon. • The epithalamus includes the habenula and their interconnecting fibers the habenular commissure, the stria medullaris and the pineal gland. • The function of the epithalamus is to connect the limbic system to other parts of the brain. Some functions of its components include the secretion of melatonin and secretion of hormones from pituitary gland by the pineal gland (involved in circadian rhythms), and regulation of motor pathways and emotions.
  35. 35. Components of epitheliums • 1- habenula - Locate between the pineal gland and thalamus - he habenula receives input from the brain via the stria medullaris thalami and outputs to many midbrain areas involved in releasing neurotransmitters, such as dopamine, norepinephrine, and serotonin. - Habenula of each side are connected together by habenular commissure - The habenula receives input from the brain via the stria medullaris thalami and outputs to many midbrain areas involved in releasing neurotransmitters, such as dopamine, norepinephrine, and serotonin.
  36. 36. Components of epitheliums • 2- stria medularis - The stria medullaris is a part of the epithalamus. - It is a fiber bundle containing afferent fibers from the thalamus to the habenula. - It forms a horizontal ridge on the medial surface of the thalamus,and is found on the border between dorsal and medial surfaces of thalamus. - Superior and lateral to habenular trigone. - It projects to the habenular nuclei, from anterior perforated substance and hypothalamus, to habenular trigone, to habenular commissure, to habenular nucleus.
  37. 37. Components of epitheliums • 3- pineal gland - The pineal gland, also known as epiphysis cerebri, is a small endocrine gland in the vertebrate brain. - The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. - The pineal gland produces melatonin, a serotonin derived hormone which modulates sleep patterns in both circadian and seasonal cycles - Functions 1. Regulation of the pituitary gland 2. Drug metabolism 3. Regulation of bone metabolism
  38. 38. Pineal gland function • Retina ( day and night ) Hypothalamus SCN  PVN Sympathetic system Day : melatonin Night : melatonin
  39. 39. Summary for epitheliums structures 1. Pineal gland 2. Hebenaula ( with commissure ) 3. Stria medularis 4. Posterior commissure 5. Hebenular trigone 2 1 45 3 1
  40. 40. Thank youThank you

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