Neuro: 11:00 - 12:00Scribe: Laura Adams

Thursday, January 15, 2009Proof: Brittney Wise

Dr. BanosDiencephalon (Thalamus/Hypothalamus)Page1 of 4

  1. Introduction [S1]:
  2. Thalamus plays a role in a lot of systems.
  3. Overview [S2]
  4. Parts of the diencephalon: the thalamus, the hypothalamus, and then a couple other parts wewill discuss.
  5. The diencephalon (Diagram) [S3]
  6. He pointed to the positions of the medulla, pons, midbrain, thalamus and hypothalamus
  7. The diencephalon [S4], [S5], [S6]
  8. Four major parts:Epithalamus, Dorsal thalamus, Subthalamus, and hypothalamus
  9. When we say dorsal thalamus that is the thalamus
  10. Epithalamus or the pineal glandis located on the back of the thalamus (sticks out the back) and it is an unpaired midline structure which is unusual in the nervous system, most things are bilateral. It is just rostral to superior colliculi. Supposedly it looks like a pine cone (“pineal” = pine cone), but it really looks like more like a mushy blob. It is an endocrine gland related to seasonal light cycles, and secretes melatonin
  11. Descartes [S7] JUST TRIVIA NOT ON TEST
  12. What did Descartes think?
  13. He thought it was a joystick, basically that your soul controls your physical body.
  14. Clinical Correlation [S8]
  15. Melatonin affects the sleep wake cycle that the pineal gland would usually be involved in. So there are melatonin pills you can take and use as a sleep aid, for jetlag, so on.
  16. [S9] Pineal tumors: they would cause hydrocephalus and eye movement abnormalities. Why? Where is the pineal gland located? Right by the cerebral aqueduct, so if you have a big space occupying lesion, you have a high probably of pinching off the cerebral aqueduct and causing hydrocephalus. You also have the superior colliculi nearby, so you could cause problems with reflexive eye movements that would be mediated by the superior colliculus.
  17. The diencephalon [S10], [S11] (lost audio for slides 10, 11), [S12], [S13], [S14]
  18. Dorsal thalamus has two thalamic hemispheres.
  19. The dorsal thalamus is 80% of the diencephalon.
  20. The subthalamusis the little area right below the thalamus. It includes the zona incerta, which is the rough area below thalamus, and the subthalamic nucleuswhich is below the zona incerta but above the midbrain and substantia nigra.
  21. A quick clinical application: Deep Brain stimulation is when they stick a tiny electrode in brain, usually in subthalamus, to dampen the effects of Parkinson’s disease.
  22. Hypothalamus: (“hypo” is sort of used here to describe “below”) it is anterior and below the dorsal thalamus, but it is a completely separate structure that does a lot of different things.
  23. If you look at the ventral surface of the hypothalamus you can see the optic chiasm, the optic nerve (or tract), mammilary bodies which are part of hypothalamus (hear mammilary and remember two little round structures), and the infundibulum or the stalk of the pituitary
  24. The infundibulum is very short or ripped off on the gross specimens; however you can see the hypothalamus grossly on the brain, around the interpeduncular cistern. Cranial nerve III will be on either side.
  25. Look at a mid-saggital of the brain to find the infundibulum and optic chiasm. These are easy to confuse and very close together. If the structure has a big optic nerve attached then obviously it is the optic chiasm.
  26. The pituitary gland is close to the optic chiasm, so if you have a pituitary tumor you can develop tunnel vision, because the chiasm has fibers that tend to be associated with peripheral vision.
  27. Dorsal Thalamus [S15]
  28. Don’t panic with all the little nuclei. Know the big picture, general organization, and general functional information.
  29. Functional Roles [S16]
  30. Thalamus has four basic functional roles:
  31. Sensory: People often say the thalamus “gates” the incoming sensory information. All sensory information (except olfaction) is relayed to the cortex via the thalamus. The recurring theme is that almost everything on its way to the cortex goes through the thalamus, not just sensory but other things as well.
  32. Motor: The descending motor pathways and the corticospinal tract don’t go through the thalamus, but when you get to the basal ganglia and cerebellar systems, which are adjunct motor systems, these have feedback loops that go back to the cortex and these go through the thalamus. So you can argue that the thalamus has a motor function in this respect.
  33. Emotion/memory: The thalamus is part of the Papez circuit which helps control some emotional and memory information going to limbic cortex (cingulate gyrus).
  34. Vegetative: The thalamus has some intrinsic nuclei associated with alertness and arousal. Can be associated with disorders of consciousness. The thalamus is part of the ascending reticular activating system as information is relayed to the cortex.
  35. Thalamus trivia! [S17]
  36. What is the single largest source of input to the thalamus? The cortex! The thalamus is way more than just a sensory gate of info coming from below.
  37. Functional Roles [S18]
  38. Thalamus doesn’t just send information to the cortex. It receives cortical feedback. It wouldn’t serve much good to just send info up and get no feedback about what is going on. This signal helps regulate what is coming to the cortex. Cortical input is a feedback inhibition loop, letting the thalamus know that information has been received and inhibiting further relaying of the information.
  39. You have sensory things that you are aware of, like holding your pen. There is a lot of repetitive info coming in that your cortex says ok I got it, and you stop consciously processing that info anymore. The cortex can use that as a way of controlling the amount of info it has to deal with. So to redundant sensory info the cortex says “that is enough”, the things that change the thalamus puts importance on.
  40. Anatomic Divisions [S19]
  41. Internal medullary lamina(lamina means sheet). This is a thin sheet of myelinated fibers that divides the thalamus into four major divisions, each containing specific nuclei:Anterior, medial, lateral, plus the others that don’t fit into those three.
  42. The intralaminar nuclei and The Reticular nucleusdo not belong to one of the first three groups.
  43. Picture of slices of the thalamus (see page 395 in the book) [S20]
  44. Anterior, Medial, lateral
  45. Anatomical Divisions [S21] (know that these are in the thalamus, not necessarily what they do)
  46. Within each of these divisions you have one or more nuclei. You should know that they are in the thalamus, but you don’t have to know what each of them do. Note that the abbreviations are commonly used.
  47. Anterior Division: Anterior nucleus
  48. Medial Division: Dorsomedial Nucleus (DM)
  49. Lateral Division: you have two tiers: Dorsal Tier and Ventral Tier.
  50. Dorsal Tier: Lateral dorsal (LD), Lateral Posterior (LP), and Pulvinar
  51. Ventral Tier: Ventral Anterior (VA), Ventral Lateral (VL), Ventral Posterior (VP). The ventral posterior has two divisions the Ventral posteriolateral (VPL) and Ventral posteriomedial (VPM).
  52. The laminas are not clean divisions of anterior, medial, and lateral. The nuclei names are not even as intuitive as they seem, so do not get caught up in these maybe just know the divisions and the way they are organized.
  53. Anatomical Divisions (continued from previous) [S22]
  54. Aside from these divisions you have the Medial Geniculate Nucleus (MGN), Lateral Geniculate Nucleus (LGN), Intralaminar Nuclei[which has two parts Centromedian (CM) and Parafascicular (PF)] and the Reticular Nucleus.
  55. Do know the functions of the lateral geniculate nucleus which is part of the visual pathway and medial geniculate nucleus which plays a role in the auditory pathway.
  56. Intralaminar nuclei are located in the medullary lamina.
  57. No Title (see page 395 in book) [S23]
  58. Rough divisions, then they break up into the nuclei, but the names don’t always make sense. So just understand how they are divided up at least.
  59. Functional Divisions [S24], [S25], [S26], [S27], [S28]
  60. Another way to think of this is to group by the nuclei functions.
  61. So you have relay nuclei (i.e., relay to the cortex), Association nuclei, and “Other” nuclei including the Interlaminar and Reticular.
  62. Relay Nuclei:
  63. Note that there is a table in the book that may break these relay nuclei down and be helpful to you.
  64. When we say the thalamus is a sensory gate, this means it has relay function.
  65. Relay specific information from a particular tract or modality
  66. This is not just sensory information (anything going through the cortex will be relayed by the thalamus). So you will have specific relay nuclei that relay specific information from a particular tract or modality, so you will specific nuclei that take the information from the basal ganglia send it back to the cortex and you will have specific nuclei that take information from the cerebellum output and send it back to the cortex. So these relay nuclei are part of several important modulatory loops in the CNS. This is not simple passive “passing on” of the signal, the thalamus is sophisticated. The relay nuclei engage in some complex condensing and processing of the incoming raw information.
  67. The Relay Nuclei are as follows:
  68. Anterior & Lateral Dorsal (LD): Hippocampus to Cingulate Gyrus
  69. Ventral Anterior (VA)/Ventral Lateral (VL): Basal Ganglia/cerebellum to motor areas
  70. Ventral Posterolateral (VPL): Medial Lemniscus & Spinothalamic Tract to somatosensory cortex (body)
  71. Ventral Posteromedial (VPM):Medial Lemniscus & Spinothalamic Tract to somatosensory cortex (face)
  72. Medial Geniculate (MGN): Inferior colliculus to auditory cortex
  73. Lateral Geniculate (LGN):Optic Tract to visual cortex
  74. Association nuclei (these are a little harder)
  75. Support areas of association cortexspecifically the Prefrontal cortex and Parietal-occipital-temporal cortex.
  76. Association cortex is where a lot of your real thinking is going on. It is involved in higher cognitive function. Sothese loops between the thalamus, the cortex, and the association nuclei help us think in a higher level, the thalamus processes a little and bounces it back to the cortex; the cortex does the same and so on.
  77. Other Nuclei [S29], [S30]
  78. Intralaminar nuclei
  79. Inputs are diverse: from the Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic tract
  80. Project to widespread areas of cortex (gets info from everyway and sends it everywhere) and the Basal ganglia.
  81. They produce general changes in cortical functionincluding arousal, alertness, and cortical tone. This is brain stem reticular formation input.
  82. Reticular nucleus
  83. Reticular means net-like, so this is a sheet-like layer of neurons partially covering the thalamus. It receives some of the feedback from the cortex and it will send inhibitory projections to specific thalamic nuclei. So the cortex can shut of the signal by saying, “enough” and reticular formation can selective inhibit thalamic nuclei to stop that info from constantly being sent to the cortex. It is the only thalamic nucleus with no projections to the cortex. So in summary they regulate the activity of the thalamus in the form of cortical feedback.
  84. Clinical Correlation [S31], [S32]
  85. Thalamic Stroke – What’s the number one symptom you might predict? A lot of things.
  86. Loss of consciousness/coma (Other strokes, like a cortical stroke, the patient can tell you what happened during the stroke, these patients cannot.)
  87. Attention/Arousal problems
  88. Widespread disruption of cortical function.
  89. Severe cognitive deficits
  90. Clinical Correlation [S33]
  91. Anterior nucleus
  92. Part of the Papez Circuit in the limbic system (another one that might be good to know)
  93. Involved in memory. Unilateral damage would cause an encoding deficit in memory. You can have a encoding or retrieval deficits. If you hit anything in the Papez circuit you cause an encoding deficit and you cannot store memory into the system. Bilateral Damage would cause severe encoding deficit, almost completely wiped out. This patient you could meet and then 5 minutes later they would not know who you are because they do not remember.
  94. Hypothalamus [S34], [S35], [S36], [S37], [S38]
  95. Hypothalamus coordinates Drive-related behaviors: Behaviors follow the principal of homeostasisand “drive” refers to drive to correct homeostatic imbalance.
  96. This would include Hunger/satiety, Thirst, Sexual behavior, Temperature regulation, and Sleep. A lot of these vegetative type things that are drive related you want to think hypothalamus.
  97. Hypothalamus is also the integrative link between the external (the world) and internal (what is going on in your body) environment
  98. Interaction with external environment occurs through integration with the cortex. So your cortex gets all the sensory information, and it is thinking all your thoughts about what is going on around you, so indirectly the hypothalamus gets that information and knows what is going on.
  99. Interaction with the internal environment occurs through: “Sampling” of blood or CSF and Release of hormones (via the pituitary). The position of the hypothalamus is not a coincidence, borders the third ventricle so a good bit of the hypothalamus in direct contact with CSF so it can figure out what is going on. It is also connected to the pituitary by the infundibulum so it can exert response to the body.
  100. Anatomic Considerations [S39]
  101. Can be divided into three regions: Posterior, Anterior, and Tuberal
  102. Each region includes medial and lateral zones. Medial and lateralalso include Periventricular Zone.
  103. Don’t get caught up in this, it will be more important for you to learn the thalamic nuclei than the hypothalamic nuclei so we are not listing them today. They just want us to be aware that the hypothalamus is not just unitary structure.
  104. [S40] and [S41] Inputs: are very Widespread
  105. From the Cortex, Limbic system (Helps integrate autonomic responses with emotional state), as well as the Brain Stem and Spinal cord, (Visceral somatic information).
  106. Also have intrinsic sensory neurons that are directly responsive to physical stimuli such as Temperature, Blood osmolality, and Glucose. Remember it gets this information by “Sampling” the blood and CSF.
  107. [S42] Outputs (reciprocal outputs)
  108. Neural: Reciprocate inputs that go to Hippocampus, Amygdala, Thalamus, Brain Stem, and Spinal Cord
  109. Hormonal: Pituitary gland (this is unique to the hypothalamus)
  110. Anatomic Considerations – Pituitary Gland [S43]
  111. Two parts of the pituitary gland: Neurohypophysis and Adenohypophysis
  112. The neurohypophysis has direct neural control of hormone release into blood via neurosecretory cells, neuronal signal means release of hormones into the blood
  113. Adenohypophysis is not a direct neural link but it has a vascular connection with hypothalamus that have hormones released into them, which can then go to parts of the endocrine system and cause other hormones to be released.
  114. Anatomic Considerations [S44] picture where he added the pituitary so you can see its position
  115. Find the Adenohypophysis and the neurohypophysis. The gross brains will not have the pituitary on it.
  116. Clinical Correlation [S45]
  117. Suprachiasmatic Nucleus is the center for circadian rhythm regulation and has a natural 25 hour set cycle. Daylight cues and melatonin from the pineal gland “train” it to a 24-hour cycle. This is important in sleep/wake cycle. So the melatonin pills are working on the suprachiasmatic nucleus. This nucleus is located above the chiasm.
  118. Clinical Correlation [S46]
  119. Mammillary Bodies are part of the limbic Papez Circuit and are crucial for memory function
  120. If the Mammillary bodies are damaged you can get the same memory deficit that you get when you damage the anterior thalamus. A specific way you can damage the mammillary bodies is by chronic alcohol abuse. With years of alcoholism, they start to erode and hemorrhage, you end up with alcohol induced dementia which causes a temporally graded severe memory loss; as they degrade the memories get weaker and weaker. So if you drink a lot for four decades your memories of the first decade will be the best and it will decrease every decade.
  121. TV test: Show patients list of real and fake TV shows; ask them to identify which are real. Patients could identify shows from the 50s and 60s, but could not in the 70s and 80s. You could identify the temporal gradient.
  122. Conclusion[S48], [S49]
  123. Dr. Lester is going to lecture about Motivation, reward, and addiction which will clear up how these things fit in with the hypothalamus
  124. For questions you can email Dr. Banos at

[end 31 min]