1. GETTING TO AND FROM THE
CEREBRAL CORTEX

2. THALAMUS

3. THALAMUS
• Oval, nuclear mass
• Forms 80% 0f diencephalon
• Anterior extent- interventricular foramen
• Superiorly- transverse cerebral fissure, floor of
3rd ventricle
• Inferiorly- hypothalamic sulcus
• Posteriorly- overlaps midbrain

11. Picture 2

12. • All sensory pathways relay in thalamus.
• Many circuits used by cerebellum, basal nuclei
and limbic system involve thalamus.
• These utilize more or less separate portions of
thalamus, which has been subdivided into a
series of nuclei.

13. • Nuclei can be distinguished from each other
by topographical locations within thalamus
and by input/output patterns.
• Thalamus is divided into medial and lateral
nuclear groups by a thin curved sheet of
myelinated fibres called internal medullary
lamina..

14. • It splits anteriorly to enclose a group of nuclei,
collectively called anterior nucleus, which is
close to interventricular foramen
• Medial group contains one large nucleus
called dosomedial nucleus
• Lateral group is subdivided into a dorsal and
ventral tier

17. • Dorsal tier consists of lateral dorsal, lateral
posterior nuclei and pulvinar.
• Lateral posterior nucleus and pulvinar have
almost similar connections

18. Nuclei of ventral tier
• Ventral anterior, ventral lateral- concerned
with motor control; are connected to basal
nuclei and cerebellum
• Ventral posterior is subdivided into ventral
posterolateral[ smatosensory input from
body] and ventral posteromedial
[somatosensory input from head]

19. • Lateral and medial geniculate nuclei / bodies
are considered as posterior extensions of
ventral tier
Intralaminar nuclei
• Embedded in internal medullary lamina
• Largest of this group are centromedian and
parafascicular nuclei

20. Reticular nucleus
• Lies between lateral thalamic surface and
external medullary lamina
• Reticular nucleus is developmentally not a
part of thalamus.
• It has distinct anatomical and physiological
properties.
• Considered a part of thalamus because of
location and extensive involvement in
thalamic function.

21. Midline nuclei
• Rostral continuation of periaqueductal gray
matter
• Form interthalamic adhesion [when present]

22. Role of thalamic nuclei
• Pipelines for flow of information to cerebral
cortex
• Site where decisions are implemented about
which information should reach cerebral
cortex for processing
• Any particular type of information affected by
any thalamic nucleus is a function of its input
and output connections

23. Inputs
• Specific - Regulatory
• Specific inputs convey information that a
given nucleus may pass to cerebral cortex
[and for some nuclei to additional sites].
• Examples; Medial lemniscus specifically to
VPL. Optic tract to LGB

24. • Regulatory inputs contribute to decisions
about whether or in what form information
leaves a thalamic nucleus

26. Sources
• cortical area to which the nucleus projects
• thalamic reticular nucleus
• diffuse cholinergic, noradrenergic,
serotonergic endings from brainstem reticular
formation

27. Categories of nuclei depending on pattern of
inputs
Relay nuclei
• receive well defined specific input fibres and
project to specific functional areas of cerebral
cortex
• deliver information from specific functional
systems to appropriate cortical areas
Intralaminar and midline nuclei seem to have
special role in function of basal nuclei and
limbic system

28. Association nuclei
• project to association areas of cerebral cortex
• receive major inputs from cerebral cortex and
subcortical structures
• probably important in distribution and gating
of information between cortical areas

29. SCHEME OF THALAMIC ORGANIZATION
• Every nucleus of the thalamus except the
reticular nucleus sends axons to the cerebral
cortex, either to a sharply defined area or
diffusely to a large area.
• Every part of the cortex receives afferent
fibers from the thalamus, probably from at
least two nuclei.

30. • Every thalamocortical projection is faithfully
copied by a reciprocal corticothalamic
connection.
• Thalamic nuclei receive other afferent fibers
from subcortical regions.
• Probably only one noncortical structure, the
striatum , receives afferent fibers from the
thalamus.
• .

31. • The thalamocortical and corticothalamic
axons give collateral branches to neurons in
the reticular nucleus, whose neurons project
to and inhibit the other nuclei of the thalamus
• No connections exist between the various
nuclei of the main mass of the thalamus,
although each individual nucleus contains
interneurons

32. • The synapses of the interneurons are
inhibitory, and most are dendrodendritic.
• Other synapses in the thalamus are excitatory,
with glutamate as the transmitter, and so are
thalamocortical projections

35. CONNECTIONS AND FUNCTIONS OF
THALAMIC NUCLEI

36. RETICULAR NUCLEUS
Input Output Functions
Collateral branches To each thalamic Inhibitory
of thalamocortical nucleus that sends modulation of
and corticothalamic afferents to thalamocortical
axons reticular nucleus transmission

37. Intralaminar nuclei
Input Output Functions
Cholinergic and Extensive cortical Stimulation of
central nuclei of projections, cerebral cortex in
reticular especially to frontal waking state and
formation,locus and parietal lobes; arousal from
coeruleus, collateral striatum sleep;somatic
branches from sensation, especially
spinothalamictracts, pain [from
cerebellar nuclei, contralateral head
pallidum and body]; control
of movement

38. VENTRAL GROUP OF NUCLEI

39. Medial geniculate body
Input Output Functions
Inferior colliculus Primary auditory Auditory pathway
cortex [from both ears]

40. Lateral geniculate body
Input Output Functions
Ipsilateral halves of Primary visual Visual pathway
both retinas cortex [from contralateral
visual fields]

41. Ventral posterolateral
Input Output Functions
Contralateral gracile Primary Somatic sensation
and cuneate nuclei; somatosensory area [principal pathway,
contralateral dorsal from contralateral
horn of spinal cord body below head]

42. Ventral posteromedial
Input Output Functions
Contralateral Primary Somatic sensation
trigeminal sensory somatosensory area [principal pathway,
nuclei from contralateral
side of head: face,
mouth, larynx,
pharynx, dura
mater]

43. Ventral lateral [posterior division]
Input Output Functions
Contralateral Primary motor area Cerebellar
cerebellar nuclei modulation of
commands sent to
motor neurons

44. Ventral lateral [anterior division]
Input Output Functions
Pallidum Premotor and Planning commands
supplementary to be sent to motor
motor areas neutons

45. Ventral anterior
Input Output Functions
Pallidum Frontal lobe, Motor planning and
including premotor more complex
and supplementary behavior
motor areas

46. Posterior group
Input Output Functions
Spinothalamic and Insula and nearby Visceral and other
trigeminothalamic temporal and responses to
tracts parietal cortex, somatic sensory
including second stimuli
somatosensory srea

47. LATERAL GROUP OF NUCLEI

48. Lateral dorsal
Input Output Functions
Hippocampal Cingulate gyrus; Memory ;
formation; pretectal visual association interpretation of
area, superior cortex visual stimuli
colliculus [occipital,posterior
parietal and
temporal lobes]

49. Lateral posterior
Input Output Functions
Superior colliculus Parietal, temporal, Interpretation of
and association visual and other
cortex sensory stimuli;
formation of
complex behavioral
responses

50. Pulvinar
Input Output Functions
Pretectal area; Parietal lobe, Interpretation of
primary and all anterior frontal visual and other
association cortex cortex, cingulate sensory stimuli,
for vision;retinas gyrus, amygdala formation of
complex behavioral
responses

51. MEDIAL GROUP OF NUCLEI

52. Mediodorsal/dorsomedial
Input Output Functions
Etorhinal cortex, Prefrontal cortex Behavioral
amygdala responses that
,collaterals from involve decisions
spinothalamic tract, based on prediction
pallidum, substantia and incentives
nigra

53. ‘Midline’ nuclei
Input Output Funtions
Amygdala, Hippocampal Behaviorr;including
hypothalamus formation and visceral and
parahippocampal emotional
gyrus responses

54. Anterior
Input Output Funtions
Mamillary body Cingulate gyrus Memory

56. Thalamic damage
• Vascular accidents
• Can involve adjacent structures
• Small lesion can lead to large collection of
deficits

57. Damage restricted to posterior
thalamus
• Paroxysms of intense pain triggered by
somatosensory stimuli
• Pain may spread to involve entire one- half of
the body- analgesic resistant
• Abnormal perception of stimuli that do not
cause pain

58. • Intensity and modality may be distorted
• May seem unusually uncomfortable or
unpleaseant
• Similar syndrome can develop in some
patients after damage in almost any part of
Anterolateral pathway

59. • This type of pain is called Thalamic
pain/central pain
• Cause not understood
• Lesions causing this pain always involve
VPL/VPM nuclei with sparing of spinothalamic
and spinoreticulothalamic fibres that end in
other thalamic nuclei
• May result in imbalanced thalamic activity

60. Extensive thalamic damage to
posterior thalamus
• Total/nearly total loss of somatic sensation in
contralateral head and body
• Gradually – return of some appreciation of
painful, thermal and gross tactile stimuli
• Functions associated with Medial lemniscus
tend to more severely and oermanently
impaired

61. • Discriminative touch may be abolished
• Position sense may be greatly impaired
• Sensory ataxia [due to loss of proprioception]
may be present

62. • Tahalamic pain+ hemianaesthesia+sensory
ataxia contralateral to a posterior thalamic
lesion= thalamic syndrome
• It is often accompanied by mild and transient
paralysis [damage to corticospinal fibres in
Internal capsule] and various types of
residual involuntary movements [damage to
adjacent basal nuclei]

63. It is often accompanied by
• mild and transient paralysis [damage to
corticospinal fibres in Internal capsule]
• various types of residual involuntary
movements [damage to adjacent basal
nuclei]