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  • 1. Thalamus“Gateway to cerebral cortex” 1
  • 2. Thalamus• Development • Anatomical & Functional• Functional Roles Divisions• parts • Functional Organization• Relations • Connections of nuclei• Internal Organization • Blood supply • Clinical correlation 2
  • 3. BRAIN:• Embryologically derived from 3 primary brain vesicles: – Prosencephalon (Forebrain) • 5th week, • subdivide into : – Telencephalon - Cerebrum – Diencephalon - Thalamus – Mesencephalon (Midbrain) – Rhombencephalon(Hindbrain) • subdivide into: – Metencephalon - Pons, Cerebellum – Myelencephalon - Medulla 3
  • 4. Diencephalon• Paired structure• Located between the brain stem and the cerebral hemisphere• Continuous with the mb rostral part of the p C midbrain mo• Forms the lateral wall of the 3rd ventricle 4
  • 5. • Almost entirely surrounded by cerebral hemispheres• A little part seen externally on base of brain caudal to optic chiasma• Other parts seen on sagittal & coronal sections 5
  • 6. • medial surface of diencephalon- – Subdivided by hypothalamic sulcus (indicated by black line) into: – Dorsal part – Ventral part 6
  • 7. Dorsal partThalamus & Epithalamus Subthalamus & Hypothalamus H Ventral part 7
  • 8. Thalamus Functional Roles• Four basic functional roles: – Sensory • All sensory information (except olfaction) is relayed to cortex via the thalamus – Motor • Motor system outputs from basal ganglia and cerebellum are relayed by thalamus – Emotion/memory • The thalamus is part of 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 8
  • 9. Thalamus• Large mass of grey matter• Shape and size, resembles – small hen’s egg• 80 percent of diencephalon• Forms lat wall of 3rd ventricle• Separated from hypothalamus – hypothalamic sulcus• May be connected to opposite thalamus – interthalamic adhesion (massa intermedia) 9
  • 10. Thalamus: In horizontal sections of brainLower Higherlevel level 10
  • 11. • Anterior pole – Narrow – Close to midline – Tubercle of thalamus – form posterior boundary of the interventricular foramen 11
  • 12. • posterior pole – Expanded – Pulvinar – Extend beyond 3rd ventricle – Overhang superior Colliculus – Sup quadrigeminal brachium separates from MGB 12
  • 13. Relations Dorsal: lateral ventricle Anterior: interventricular foramenLateral: Medial: 3rdInternal ventriclecapsule Ventral: Subthalamus & Hypothalamus Caudal: midbrain 13
  • 14. Surfaces• 4 Surfaces:• Superior• Inferior• Medial S• Lateral L M l 14
  • 15. Superior Surface caudate nucleus• Stratum zonale stria terminalis• Bounded laterally by – caudate nucleus – thalamostriate vein – stria terminalis LV• Lateral part – lies in the floor of lat ventricle – covered by ependyma• Medial part-related to : – choroid plexus of the 3rd ventricle thalamo- choroid plexus ependyma striate vein 15
  • 16. Lateral Surface• Related to the internal capsule Inferior Surface • Rests on the Subthalamus & hypothalamus 16
  • 17. Medial Surface Stria medullaris thalami• Stria medullaris thalami (a fascicle of nerve fibers) courses along its dorsomedial margin• hypothalamic sulcus• Interthalamic adhesion• Forms the upper part of the lateral wall of the 3rd ventricle Hypothalamic sulcus 17
  • 18. Internal Organization• composed of – grey matter – interrupted by two vertical sheaths of white matter - medullary laminae.• External medullary lamina: – Located laterally – separates reticular nucleus from rest of the thalamic mass – Contains thalamocortical & corticothalamic fibers 18
  • 19. Internal medullary lamina• Y- shaped band• divides thalamus into – Anterior – Medial – Lateral nuclear groups• Contains: – Fibers connecting thalamic nuclei with one another – Neuronal collections called intralaminar nuclei 19
  • 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 posterolateral (VPL) – Ventral posteromedial (VPM) 20
  • 21. Anatomical Divisions• Medial Geniculate Nucleus (MGN)• Lateral Geniculate Nucleus (LGN)• Intralaminar Nuclei – Centromedian (CM) – Parafascicular (PF)• Reticular Nucleus 21
  • 22. 22
  • 23. 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 23
  • 24. Functional Divisions• Association nuclei – Support areas of association cortex • Prefrontal cortex • Parietal-occipital-temporal cortex – Association cortex is involved in higher cognitive function 24
  • 25. 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 25
  • 26. 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 26
  • 27. Functional Organization• Thalamus is major route for- – Subcortical neuronal activity influences the cerebral cortex• All nuclei of thalamus except reticular nucleus, project to ipsilateral cerebral cortex• whole of cerebral cortex receives input from thalamus• All thalamic nuclei receive corticofugal fibers in a reciprocal fashion 27
  • 28. • Based on their connection with the cerebral cortex, the thalamic nuclei are divided into: Specific nuclei Nonspecific nuclei 28
  • 29. • Specific nuclei: • Non-specific Nuclei: – Have well-defined – Receive less sensory and motor functionally distinct functions afferent input – Have highly organized – Connect with wider point-to-point area of cortex, connection with including associative sensory & motor and limbic regions regions of cerebral – Include nuclei of cortex dorsal tier of lateral – Lie within the ventral group, and whole of group of the lateral ant and med group nuclear group 29
  • 30. Anterior Nuclear Groups• Enclosed bn arms of int medullary lamina• 3 parts: – Anteroventral – Anteromedial – Anterodorsal 30
  • 31. Mammillary body of Ant limbic areahypothalamus via cingulate gyrusmammillothalamic tract Parahippocampal gyrus•Functionally part of the limbic system•Involved in control of alertness & attention•Acquisition of memory 31
  • 32. Medial Nuclear Group Integrates emotion, thought, and judgmentMediodorsal nucleus &Nucleus reuniens Hypothalamus, amygdala, other thalamic nuclei, prefrontal cortex Prefrontal cortex post parietal cortex limbic structures 32
  • 33. Lateral Nuclear Group Ventral Tier• Ventral anterior• Ventral lateral• Ventral posterior: • VPL • VPM• Lateral geniculate• Medial geniculate 33
  • 34. Ventral Anterior Nucleus Influences motor activityIpsilateral globuspallidus &substantia nigrapremotor cortexFrontal eye field Premotor & supplementary motor cortex 34
  • 35. Ventral Lateral Nucleus Planning & modulation of commandsIpsilateral globus pallidus &substantia nigraContralateral dentate nucleusSpinothalamic tract & vestibular nuPrecentral motor cortical area Primary motor cortex Supplementary motor area 35
  • 36. Ventral Posterior Nucleus principal thalamic relay for somasensory pathwaysC/L Gracile &Cuneate nu,C/L Dorsal horn of spinal cordPrimarysomatosensorycortex C/L trigeminal sensory nuclei 36
  • 37. Medial Geniculate BodyPart of the Auditory Pathway Inferior Colliculus Primary auditory cortex 37
  • 38. Lateral Geniculate BodyPart of the Visual Pathway Ipsilateral temporal hemiretina Contralateral nasal hemiretina Primary visual cortex 38
  • 39. Lateral Nuclear Group Dorsal Tier• Lateral Dorsal• Lateral Posterior• Pulvinar 39
  • 40. Lateral dorsal nucleus Memory, interpretation of visual stimuliHappocampal formationPretectal areaSuperior ColliculusCingulate gyrusVisual association cortex 40
  • 41. Lateral posterior nucleus Interpretation of visual & other sensory stimuliSuperior ColliculusParietal, temporal,& occipitalassociation cortex 41
  • 42. Pulvinar Visual, perceptive, cognition & memoryPretectal area, superior Colliculus,retinasAssociation area of parietotemporal cortexVisual areas in occipital &post temporal lobe 42
  • 43. Intralaminar Nuclei Cortical activation, Sensorimotor integrationBrainstem reticular formationSpinothalamic tractCerebellar nuPallidumFrontal & parietal lobesstriatum 43
  • 44. Midline Nuclei Part of limbic system, memory & arousalBrainstem reticular formationHypothalamusSpinothalamic tractmidbrainHippocampal formationAmygdalaNucleus accumbensCingulate gyrus 44
  • 45. Reticular Nucleus Inhibitory modulation of thalamocortical transmissionCollaterals of Thalamocortical,Corticothalamic , thalamostriatal, pallidothalamic fibersBody of thalamusC/L thalamus 45
  • 46. Blood supply of thalamus•Perforating branches of post cerebral a. •Posteromedial group(thalamo- perforating a) supply medial and anterior part. •Posterolateral group ( thalamo- geniculate br) supply posterior and lateral part of thalamus.•Also receives br from- •posterior communicating •anterior choroidal •posterior choroidal •middle cerebral a. 46
  • 47. Clinical correlation• Thalamus – important relay and integrative center – lesions will have profound effects• 3 common etiologies: – Invasion of neoplasm – Degeneration following disease of its arterial supply – Damage by Hemorrhage 47
  • 48. • Manifestations: 1. Sensory loss • damage to the VPM and VPL nucleus – loss of all forms of sensation » light touch » tactile localization & discrimination » muscle joint sense from opposite side of body 2. Thalamic pain • may be aroused by light touch or by cold – occurs on the opposite side of the body 48
  • 49. 3. Abnormal involuntary movements-4. Thalamic hand- • due to altered muscle tone: – wrist is pronated and flexed – metacarpophalangeal joints are flexed – interphalangeal joints are extended 49
  • 50. Thalamic syndrome•Also known as "Dejerine-Roussy disease", afterJoseph jules dejerine & Gustave Roussy.•Vascular lesion- •ventral post part of thalamus (PCA)•Disturbance of •somatosensory aspect•C/L impairment of- •Proprioception •Touch •Pain & temp. 50
  • 51. Thalamic syndrome•Sensation is- •Exaggerated •Painful &perverted •exceptionally disagreeable•Development of spontaneous pain•Emotional instability •spontaneous or forced •laughing or crying 51
  • 52. Fatal familial insomnia •Caused by prions •Mediodorsal & ventral ant nu •Dementia & other neurological symptoms 52
  • 53. Thalamic cauterization •Surgical relief of pain in terminal cancer •Intralaminar nu –relay of pain to cortex 53
  • 54. 54