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 part
Thalamus & 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 brain
Lower Higher
level 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
foramen
Lateral: Medial: 3rd
Internal ventricle
capsule
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 area
hypothalamus via cingulate gyrus
mammillothalamic 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 judgment
Mediodorsal 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 activity
Ipsilateral globus
pallidus &
substantia nigra
premotor cortex
Frontal eye field
Premotor &
supplementary
motor cortex
34

35. Ventral Lateral Nucleus
Planning & modulation of commands
Ipsilateral globus pallidus &
substantia nigra
Contralateral dentate nucleus
Spinothalamic tract & vestibular nu
Precentral motor cortical area
Primary motor cortex
Supplementary motor area
35

36. Ventral Posterior Nucleus
principal thalamic relay for somasensory pathways
C/L Gracile &Cuneate nu,
C/L Dorsal horn of spinal cord
Primary
somatosensory
cortex
C/L trigeminal sensory nuclei
36

37. Medial Geniculate Body
Part of the Auditory Pathway
Inferior Colliculus
Primary auditory cortex
37

38. Lateral Geniculate Body
Part 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 stimuli
Happocampal formation
Pretectal area
Superior Colliculus
Cingulate gyrus
Visual association cortex
40

41. Lateral posterior nucleus
Interpretation of visual & other sensory stimuli
Superior Colliculus
Parietal, temporal,& occipital
association cortex
41

42. Pulvinar
Visual, perceptive, cognition & memory
Pretectal area, superior Colliculus,
retinas
Association area of parietotemporal cortex
Visual areas in occipital &post temporal lobe
42

43. Intralaminar Nuclei
Cortical activation, Sensorimotor integration
Brainstem reticular formation
Spinothalamic tract
Cerebellar nu
Pallidum
Frontal & parietal lobes
striatum
43

44. Midline Nuclei
Part of limbic system, memory & arousal
Brainstem reticular formation
Hypothalamus
Spinothalamic tract
midbrain
Hippocampal formation
Amygdala
Nucleus accumbens
Cingulate gyrus
44

45. Reticular Nucleus
Inhibitory modulation of thalamocortical transmission
Collaterals of Thalamocortical,
Corticothalamic , thalamostriatal
, pallidothalamic fibers
Body of thalamus
C/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", after
Joseph 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
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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

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