1. THALAMUS

2. Objectives 1. Describe the location of the thalamus
2. List the different parts and nuclei of the thalamus
3. List the afferent input to different nuclei of the thalamus
4. List the efferent output from the different nuclei of the thalamus

3. Thalamus
Part of the diencephalon (The other parts are hypothalamus, subthalamus and epithalamus)
A midline symmetrical structure, formed of 2 oval masses of grey matter
Is the largest nuclear mass
Situated between the cerebral cortex and brainstem
Together with the hypothalamus, it forms the lateral wall of the 3rd ventricle T H
3rd ventricle

4. Thalamus
Functionally considered as the great sensory gateway to the cerebral cortex
It relays received information to the cerebral cortex from diverse brain regions.
Axons from every sensory system (except olfaction) synapse in the thalamus as the last relay site before the information reaches the cerebral cortex.
There are some thalamic nuclei that receive input from cerebellar nuclei, basal ganglia and limbic-related brain regions.
Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness.

5. Relations Lateral: Posterior limb of the internal capsule (IC)
Medial: Together with hypothalamus, forms the lateral wall of the 3rd ventricle
Superior: Caudate nucleus (C) fornix (F) & lateral ventricle (LV)
Inferior: Hypothalamus (H) anteromedially & Subthalamus (ST) posterolaterally.

6. External Features Ends : Anterior & Posterior Surfaces : Superior
Inferior
Medial
Lateral
Medial s.: frequently connected to the thalamus of the opposite side by the interthalamic adhesion (massa intermedia) S L M I

8. Thalamus has 2 ends.
*Anterior: Forms a projection called anterior tubercle which lies just behind the interventricular foramen.
*Posterior: Forms a projection called Pulvinar which lies above the superior colliculus and the lateral & medial geniculate bodies. * * *
Pulvinar. *
Interventricular
foramen.

10. Surfaces
4 Surfaces:
Superior
Inferior
Medial
Lateral S L M l

11. Superior Surface
- Bounded laterally by caudate nucleus, thalamostriate vein and a nerve fiber bundle called stria terminalis
- Lateral part lies in the floor of the lateral ventricle & is covered by ependyma
- Medial part is related to the choroid plexus of the 3rd ventricle
caudate nucleus
stria terminalis LV
thalamo-striate vein
ependyma
choroid plexus

12. Lateral Surface
Related to the internal capsule
Inferior Surface
Rests on the subthalamus & hypothalamus

13. Medial Surface Stria medullaris thalami
(a fascicle of nerve fibers) courses along its dorsomedial margin
Below is limited by hypothalamic sulcus
Forms the upper part of the lateral wall of the 3rd ventricle
Covered by ependyma
Hypothalamic sulcus

14. Internal Organization
Thalamus is composed of grey matter, interrupted by two vertical sheaths of white matter called medullary laminae.
External medullary lamina:
- Located laterally, separates reticular nucleus from the rest of the thalamic mass
- Contains thalamocortical & corticothalamic fibers

15. 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

16. Thalamic Nuclei Anterior nuclear group: Anterior nucleus
Medial nuclear group: Largest nucleus is medial dorsal nucleus (MD)
Intralaminar nuclei: Lie within the internal medullary lamina
Midline nuclei: Lie deep to ependyma of 3rd ventricle
Lateral Nuclear group

17. Thalamic Nuclei
Lateral nuclear group is divided into Dorsal & Ventral tiers.
Dorsal tier contains:
lateral dorsal n. (LD)
lateral posterior n. (LP)
pulvinar.
Ventral tier contains
ventral anterior (VA)
ventral lateral (VL)
ventral posterior (VP) nuclei, divided into lateral & medial parts
medial & lateral geniculate bodies.

18. NUCLEUS
FUNCTIONS
VPM
Relay station for impulses from face, head & taste buds
VPL
Relay Station for exteroceptive& proprioceptive from all body EXCEPT head & face VA
Relay station for Striatal impulses (attention & recent memory )
VL (VI)
Relay station for cerebellar impulses
MGB
Relay station for Auditory impulses
LGB
Relay station for Visual(Optic) impulses

19. Attention & recent Memory
NUCLEUS
FUNCTIONS
Anterior
Attention & recent Memory
Medial
dorsal
Associated with mood & emotional balance
Lateral Dorsal
Integrates Sensory information
Lateral Posterior
Pulvinar
Correlates auditory & visual information with sensations

20. Forms part of ascending reticular activating system
NUCLEUS
FUNCTIONS
Reticular
Forms part of ascending reticular activating system
Intralaminar (Including centromedian)
Awareness of painful stimuli at thalamic level

21. Functional Organization
All the nuclei of the thalamus except reticular nucleus, project to ipsilateral cerebral cortex
The whole of the cerebral cortex receives input from the thalamus
All thalamic nuclei receive corticofugal fibers in a basically reciprocal fashion

22. Based on their connection with the cerebral cortex, the thalamic nuclei are divided into:
Specific nuclei
Nonspecific nuclei

23. Specific nuclei: Non-specific Nuclei:
Have well-defined sensory and motor functions
Have highly organized point-to-point connection with sensory & motor regions of cerebral cortex
Lie within the ventral group of the lateral nuclear group
Non-specific Nuclei:
Receive less functionally distinct afferent input
Connect with wider area of cortex, including associative and limbic regions
Include nuclei of the dorsal tier of lateral group, and whole of the anterior and medial group

24. Classification of thalamic nuclei according to their projection
They could be classified into 3 groups, each group contains 4 nuclei:
A)Simple sensory relay nuclei: receive well defined sensory impulses, and relay them to functionally distinct areas of the sensory cortex. 1. Ventral posterolateral nucleus (VPL). 2. Ventral posteromedial nucleus (VPM). 3. Lateral geniculate body (LGB). 4.Medial geniculate body (MGB).

25. B) Circuit relay nuclei: receive impulses from different areas of CNS and relay them to specific areas in cerebral cortex. They include:
Lateral ventral nucleus (projects to primary motor cortex).
Anterior ventral nucleus (projects to premotor cortex).
Anterior nucleus (projects to cingulate gyrus).
Part of dorsomedial nucleus.
C) Associative nuclei: receive impulses from other thalamic nuclei and relay these impulses to the association areas of the cerebral cortex, They include:
Pulvinar.
Lateral dorsal nucleus.
Lateral posterior nucleus.

26. Functions of Thalamus
Sensory integration and relay station for all the sensory pathways except Olfactory
Recognition of crude pain, temperature & touch
Influences voluntary movements by receiving impulses from basal ganglia & cerebellum & relaying them to motor cortex , influence LMN
Participates in maintenance of state of wakefulness & alertness through RAS
Role in emotions & recent memory

27. Functional Connections
Lesion: contralateral loss of pain/temp, discrim touch
Globus Pallidus
Substantia Nigra
Mammillary Body
Premotor Cortex
Prefrontal Cortex
Cingulate Gyrus VA GP SN
Cerebellum (Dentate)
Anterior VL
Primary Motor Cortex (4)
Supplementary Motor Cortex (5_
Cingulate LD
Spinothalamic and LL/ML
Sensory Cortex (3,1,2) DM
Superior Parietal Cortex
(5,7)
VPM
VPL LP
, Solitary Nucleus
Amygdala
Hypothalamus
Olfactory Cortex
Sensory Cortex
Lesion: contralateral loss of pain/temp, discrim touch in head; ipsilateral loss of taste
Prefrontal Cortex
Pulvinar
LGN
Right Optic Tract
Lesion: memory loss (Wernicke-Korsakoff)
MGN
Primary visual Cortex (17)
(lingual gyrus, cuneus)
Lesion: Left Homonymous Hemianopsia
Lesion: Sensory Aphasia
Primary Auditory Cortex (41,42)
LGN, Superior Colliculus
Brachium of Inferior Colliculus
Association areas of temporal, occipital, parietal lobes

28. Thalamic syndrome
Due to vascular lesion (thrombosis of thalamogeniculate artery)
Threshold for pain, touch & temperature decreased on opposite side of body
When threshold reached then exaggerated
Emotional instability, spontaneous laughing & crying

29. Thalamic hand Opposite hand shows abnormal posture
Forearm is pronated, wrist flexed, metacarpophalangeal joints flexed & interphalangeal joints extended
Fingers can move actively, but movements are slow
Due to altered muscle tone in different muscle groups