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The Diencephalon

The Diencephalon. Basic Neuroscience James H. Baños, Ph.D. Overview. Parts of the diencephalon Thalamus Hypothalamus. The Diencephalon. The Diencephalon. Four major parts: Epithalamus Dorsal Thalamus Subthalamus Hypothalamus. The Diencephalon. Epithalamus Pineal gland

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The Diencephalon

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  1. The Diencephalon Basic Neuroscience James H. Baños, Ph.D.

  2. Overview • Parts of the diencephalon • Thalamus • Hypothalamus

  3. The Diencephalon

  4. The Diencephalon • Four major parts: • Epithalamus • Dorsal Thalamus • Subthalamus • Hypothalamus

  5. The Diencephalon • Epithalamus • Pineal gland • A few nearby structures Pineal Gland

  6. The Diencephalon • Pineal Gland • Unpaired midline structure • Just rostral to superior colliculi • Looks like a pine cone (“pineal”) • Endocrine gland related to seasonal light cycles • Secretes melatonin

  7. Clinical Correlation • What did Descartes think?

  8. Clinical Correlation

  9. Clinical Correlation • Pineal Tumor • Hydrocephalus. Why? • Eye movement abnormalities. Why?

  10. The Diencephalon • Dorsal Thalamus • Thalamic hemispheres • 80% of diencephalon

  11. The Diencephalon • Subthalamus • Zona incerta • Subthalamic nucleus

  12. The Diencephalon • Hypothalamus

  13. The Diencephalon • Hypothalamus Mammilary Bodies Infundibulum

  14. Dorsal Thalamus

  15. Functional Roles • Thalamus has four basic functional roles: • Sensory • All sensory information (except olfaction) is relayed to the cortex via the thalamus • Motor • Motor system outputs from the basal ganglia and cerebellum are relayed by the thalamus • Emotion/memory • The thalamus is part of the Papez circuit and helps control some emotional and memory information going to limbic cortex (cingulate gyrus) • Vegetative • The thalamus has some intrinsic nuclei associated with alertness and arousal. Can be associated with disorders of consciousness

  16. Thalamus Trivia!! • What is the single largest source of input to the thalamus?

  17. Functional Roles • Thalamus doesn’t just send information to the cortex. It receives cortical feedback • 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

  18. Anatomic Divisions • Internal medullary lamina • Thin sheet of myelinated fibers • Divides the thalamus into four major divisions, each containing specific nuclei: • Anterior • Medial • Lateral • Not included in these divisions are • The intralaminar nuclei • The Reticular nucleus

  19. Anterior Medial Lateral See p. 392

  20. Anatomical Divisions • Anterior Division • Anterior nucleus • Medial Division • Dorsomedial Nucleus (DM) • Lateral Division • Dorsal Tier • Lateral dorsal (LD) • Lateral Posterior (LP) • Pulvinar • Ventral Tier • Ventral Anterior (VA) • Ventral Lateral (VL) • Ventral Posterior (VP) • Ventral posteriolateral (VPL) • Ventral posteriomedial (VPM)

  21. Anatomical Divisions …But wait…there’s more… • Medial Geniculate Nucleus (MGN) • Lateral Geniculate Nucleus (LGN) • Intralaminar Nuclei • Centromedian (CM) • Parafascicular (PF) • Reticular Nucleus

  22. LD A Pulv DM VL A Ret CM PF VPL VL VA VPM MGN LGN Pulv DM VPL A VL VA Ret See p. 392

  23. Functional Divisions • Another way to think of this • Relay nuclei (i.e., relay to the cortex) • Association nuclei • “Other” nuclei • Interlaminar • Reticular

  24. Functional Divisions

  25. Functional Divisions • Relay Nuclei • Relay specific information from a particular tract or modality • This is not just sensory information • Relay nuclei are part of several important modulatory loops in the CNS • This is not simple “passing on” of the signal • Relay nuclei engage in some complex condensing and processing of the incoming raw information

  26. Functional Divisions • Association nuclei • Support areas of association cortex • Prefrontal cortex • Parietal-occipital-temporal cortex • Association cortex is involved in higher cognitive function

  27. Other Nuclei • Intralaminar nuclei • Inputs are diverse! • Cortex, basal ganglia, cerebellum, brainstem reticular formation, spinothalamic tract • Project to • Widespread areas of cortex • Basal ganglia • Produce general changes in cortical function

  28. Other Nuclei • Reticular nucleus • Sheet-like layer of neurons partially covering the thalamus • Receives input from widespread cortical areas • Only thalamic nucleus with no projections to the cortex • Inhibitory projections to specific thalamic nuclei • Regulates the activity of the thalamus in the form of cortical feedback

  29. Clinical Correlation • Thalamic Stroke - What’s the number one symptom you might predict?

  30. Clinical Correlation • Thalamic Stroke • Loss of consciousness/coma • Attention/arousal problems • Widespread disruption of cortical function • Severe cognitive deficits

  31. Clinical Correlation • Anterior nucleus • Part of the Papez Circuit in the limbic system • Involved in memory • Unilateral Damage: Encoding deficit • Bilateral Damage: Severe encoding deficit

  32. Hypothalamus

  33. Hypothalamus Caudate Ventricle Thalamus Putamen & Globus pallidus Hypothalamus Amygdala

  34. Hypothalamus Pituitary Stalk

  35. Hypothalamus • Hypothalamus Coordinates Drive-Related Behaviors • What are “Drive-related behaviors?”

  36. Hypothalamus • Behaviors follow the principal of homeostasis • “Drive” refers to drive to correct homeostatic imbalance • Hunger/satiety • Thirst • Sexual behavior • Temperature regulation • Sleep

  37. Hypothalamus • Hypothalamus is also the integrative link between the external and internal environment External Environment Hypothalamus Internal Environment

  38. Hypothalamus • Interaction with external environment occurs through integration with the cortex • Interaction with the internal environment occurs through: • “Sampling” of blood and CSF • Release of hormones (via the pituitary) • The position of the hypothalamus is not a coincidence

  39. Anatomic Considerations • Can be divided into three regions • Each region includes medial and lateral zones Posterior Anterior Tuberal

  40. Anatomic Considerations • Three regions X two zones = six areas containing nuclei

  41. Anatomic Considerations See p. 563

  42. Anatomic Considerations • Inputs • Widespread! • Cortex • Limbic system • Helps integrate autonomic responses with emotional state • Brain Stem and Spinal cord • Visceral somatic information

  43. Anatomic Considerations • Inputs • Hypothalamus also has intrinsic sensory neurons • Directly responsive to physical stimuli • Temperature • Blood osmolality • Glucose

  44. Anatomic Considerations • Outputs • Neural • Reciprocate inputs • Hippocampus • Amygdala • Thalamus • Brain Stem • Spinal Cord • Hormonal • Pituitary gland

  45. Anatomic Considerations • Two parts of the pituitary gland • Neurohypophysis • Direct neural control of hormone release into blood via neurosecretory cells • Adenohypophysis • Not a direct neural link • Vascular connection with hypothalamus

  46. Anatomic Considerations Adenohypophysis Neurohypophysis

  47. Clinical Correlation • Suprachiasmatic Nucleus • Center for circadian rhythm regulation • Has a natural 25 hour set cycle • Daylight cues and melatonin from the pineal gland “train” it to a 24-hour cycle • Important in sleep/wake cycle

  48. Clinical Correlation • Mammillary Bodies • Part of the limbic Papez Circuit • Crucial for memory function • Mammillary bodies are damaged by chronic alcohol abuse

  49. Clinical Correlation

  50. Clinical Correlation • Long-term chronic alcoholics end up with alcohol induced dementia • Temporally graded severe memory loss

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