The thalamus is a structure located in the middle of the brain between the cerebral cortex and midbrain. It is the largest component of the diencephalon. The thalamus acts as a relay station for sensory information (except smell) sending signals to the appropriate areas of the cerebral cortex. It is divided into nuclei that each have distinct functions and connections related to motor control, sensory processing and integration, arousal, memory and cognition. Damage to different thalamic nuclei can disrupt various functions and result in sensory deficits, movement problems or changes to consciousness.

1. KURSK STATE MEDICAL UNIVERSITY
DEPARTMENT OF NORMAL PHYSIOLOGY
Professor AV Zavyalov
THE THALAMUS

2. Thalamus localization
 Thalamus (Greek) means “inner chamber” or “meeting place”
 The thalamus is a structure in the middle of the brain. It is located
between the cerebral cortex
and the midbrain.
 Part of the forebrain, below
the corpus
callosum.

3. Division of Brain – Thalamus localization
Thalamus

4. Localization of Thalamus at
Diencephalon
 Dorsal-posterior structures
• Epithalamus
• Thalamus (Largest component of the diencephalon)
• Metathalamus
• Medial geniculate body – auditory relay
• Lateral geniculate body – visual relay
 Ventral-anterior structure
• Hypothalamus

5. Thalamus localization
 The thalamus is sitting at
the top of the brain stem
 Composed of two parts,
often referred to as lobes,
that are symetrical

6. Thalamus localization
 The thalamus surrounds the third ventricle.
 It is a subdivision of part of the brain called the
diencephalon
 One of the largest
structures derived
from the diencephalon
during embryonic
development.

7. Thalamus localization
 The thalamus lies at the top of the brain stem near the centre
of the brain from where nerve fibres project out towards the
cerebral cortex.
 The thalamus is divided
into two prominent bulb
shaped masses of around
5.7 cm in length and
positioned symmetrically
on each side of the
third ventricle.

8. Thalamus localization

9. Thalamus localization
Thalamus

10. Thalamus blood supply
 The thalamus is supplied with blood by four branches
of the posterior cerebral artery, namely the polar
artery,
paramedian
thalamic-subthalamic
arteries,
thalamogeniculate
arteries and the posterior
choroidal arteries.

11. Thalamus Physiology
 Primarily a relay station that modulates and coordinates the
function of various systems
 Locus for integration, modulation, and intercommunication
between various systems
 Has important motor, sensory, arousal, memory, behavioral,
limbic, and cognitive functions

12. Thalamus Physiology
 The largest source of afferent fibers to thalamus is cerebral
cortex and cortex is the primary destination for projection fibres
from the Thalamus
 Characteristically, thalamic connections are reciprocal, that is,
the target of the axonal projection of any given thalamic
nucleus sends back fibers to that nucleus. Nevertheless,
thalamocortical projections are often larger than their
corticothalamic counterparts

13. Summary functions of thalamus
 Relay of sensation (Except olfactory system)
 Spatial sense
 Regulation of consciousness
 Regulation of sleep
 and alertness
 Main largest product of embryonic diencephalon
 Great sensory gateway to cerebral cortex
 Damage to thalamus can lead to permanent coma

14. Summary functions of thalamus
 Sensory integration relay station for all sensory pathway (Except olfaction)
 Capable of recognition of pain, thermal & tactile sensations
 Influences voluntary movements through basal ganglia & cerebellum – cerebral
cortex – cortico-nuclear / cortico-spinal pathways
 Through ascending activating system – maintains state of wakefulness and alertness
 Impulses received from hypothalamus projected o prefrontal & cingulate gyrus –
Determination of mood
 Recent memory and emotions
 Influences electrical activity of cerebral cortex (EEG)

15. Thalamus

16. Nuclei of Thalamus
 It is subdivided into the following major nuclear groups
on the basis of their rostrocaudal and mediolateral
location within the thalamus:
 Anterior
 Medial
 Lateral
 Intralaminar
and reticular
 Midline
 Posterior

17. Nuclei of Thalamus – Anterior group
 Internal medullary lamina divides the thalamus into medial and lateral groups
of nuclei
 Anterior nuclear group consists
of two nuclei: principal anterior
and anterodorsal.

18. Nuclei of Thalamus – Anterior group
 The anterior group of thalamic
nuclei has reciprocal connections
with the hypothalamus (mamillary
bodies) and the cerebral cortex
(cingulate gyrus).
 The anterior group also receives
significant input from the hippocampal
formation of the cerebral cortex

19. Nuclei of Thalamus
Medial nuclear group
 The dorsomedial nucleus is reciprocally connected with the prefrontal
cortex via the anterior thalamic peduncle, and with the frontal eye fields
 Receives inputs from
• the temporal neocortex
(via the inferior thalamic peduncle)
• amygdaloid nucleus and substantia
nigra pars reticulata
• adjacent thalamic nuclei (lateral
and intralaminar groups)
 Concerned with affective behavior, decision making and judgment,
memory, and the integration of somatic and visceral activity.

20. Nuclei of Thalamus
 Dorsomedial Nucleus
 Bilateral lesions of the dorsomedial nucleus result in a syndrome of
lost physical self-activation, manifested by apathy, indifference, and
poor motivation.
 The reciprocal connections between the prefrontal cortex and the
dorsomedial nucleus can be interrupted surgically to relieve severe
anxiety states and other psychiatric disorders.
 This operation, known as prefrontal lobotomy is rarely practiced
nowadays, having been replaced largely by medical treatment

21. Nuclei of Thalamus
 Lateral nuclear group
is subdivided into two groups: dorsal and ventral
 The pulvinar is a relay station between subcortical visual centers and their
respective association cortices in the temporal, parietal, and occipital lobes.
 Has a role in selective visual attention.
 Plays a role in speech mechanisms.
 Stimulation of pulvinar of dominant hemisphere has produced nominal
aphasia
 Has role in pain mechanisms.

22. Nuclei of Thalamus
 Ventral Subgroup
 Share the following characteristics:
 They receive a direct input from the long ascending tracts.
 They have reciprocal relationships with specific cortical areas.
 They degenerate on ablation of the specific cortical area to which they project

23. Nuclei of Thalamus
 Ventrolateral group
 Ventral anterior and ventral lateral nuclei together comprise MOTOR THALAMUS.
 AFFERENT FIBERS TO THE VENTRAL LATERAL NUCLEUS:
• Deep cerebellar nuclei
• Globus pallidus (internal segment)
• Primary motor cortex (area 4)

24. Nuclei of Thalamus
 Ventrolateral group
 Ventral anterior and ventral lateral nuclei together comprise MOTOR THALAMUS
 EFFERENT FIBERS
• mainly go to primary motor cortex
• nonprimary somatosensory areas in the
parietal cortex (areas 5 and 7)
• premotor and supplementary motor cortices

25. Nuclei of Thalamus
 Ventroposterior group
 Receives the long ascending tracts conveying sensory modalities (including taste) from
the contralateral half of the body and face.
 The ventral posterior nucleus is made up of two parts:
• ventral posterior medial (VPM) nucleus
receives the trigeminal lemniscus and taste fibers
• ventral posterior lateral (VPL) nucleus
receives the medial lemniscus and spinothalamic tracts.
• Both nuclei also receive input from the primary somatosensory cortex
 The output from both is to primary somatosensory cortex (area 1, 2, and 3).
 The VPL and VPM nuclei collectively comprise - ventrobasal complex

26. Nuclei of Thalamus
Intralaminar group
 The Intralaminar nuclei- divided into caudal and rostral groups.
• The Caudal group includes the centromedian and parafascicular nuclei
• The Rostral group includes the paracentral, centrolateral, and centromedial nuclei

27. Nuclei of Thalamus
 Intralaminar group
 Afferent connections
• Reticular formation of the brain stem (major input)
• Cerebellum : The dentatorubrothalamic system
• Spinothalamic and trigeminal lemniscus
• Globus pallidus
• Cerebral cortex
 Efferent Connections
• Other thalamic nuclei (influences cortical activity via other thalamic nuclei)
• The striatum (caudate and putamen)

28. Nuclei of Thalamus
Reticular group
 Is a continuation of the reticular formation of the brainstem into the diencephalon.
 Afferents from the cerebral cortex and other thalamic nuclei.
 The former are collaterals of corticothalamic projections, and the latter are collaterals of
thalamocortical projections.
 Efferent projections to other thalamic nuclei. The inhibitory neurotransmitter in this
projection is GABA.
 It plays a role in integrating and gating activities of thalamic nuclei

29. Nuclei of Thalamus
Metathalamus
 Medial Geniculate Nucleus
• This is a relay nucleus in the auditory system.
• It receives fibers from the lateral lemniscus directly or, more frequently,
after a synapse in the inferior colliculus.
• efferent outflow from the MG nucleus forms the auditory radiation of
the internal capsule (sublenticular part) to the primary auditory cortex in
temporal lobe (areas 41 and 42)

30. Nuclei of Thalamus
Metathalamus
 Lateral Geniculate Nucleus
• This is a relay thalamic nucleus in the visual system.
• It receives fibers from the optic tract conveying impulses from both
retinae
• The efferent outflow from the lateral geniculate nucleus forms the optic
radiation of the internal capsule (retrolenticular part) to the primary
visual cortex in the occipital lobe

31. Nuclei of Thalamus
 The motor group receives motor inputs from the basal ganglia (ventral
anterior, ventral lateral) or the cerebellum (ventral lateral) and projects to
the premotor and
primary motor cortices.
 The sensory group receives inputs
from ascending somatosensory
(ventral posterior lateral and medial),
auditory (medial geniculate), and
visual (lateral geniculate) systems.
 The limbic group is related to limbic structures (mamillary bodies,
hippocampus, cingulate gyrus).

32. Nuclei of Thalamus
Functional Specific Group:

33. Nuclei of Thalamus
Functional Non-Specific Group:

34. Nuclei of Thalamus
Reticular Group:

35. Damage of Thalamus
 Damage to the thalamus may result in a number of problems
related to sensory perception.
 Thalamic syndrome is condition that causes an individual to
experience excessive pain or a loss of sensation in limbs.
 Damage to areas of the thalamus that are associated with
visual sensory processing can cause visual field problems.
 Damage to the thalamus can also result in sleep disorders,
memory problems, and auditory issues.

36. Referências
 http://brainmadesimple.com/thalamus.html
 http://www.news-medical.net/health/What-is-the-Thalamus.aspx
 http://study.com/academy/lesson/thalamus-definition-functions-
location.html
 http://www.neuroanatomy.wisc.edu/coursebook/thalamus.pdf
 http://biology.about.com/od/anatomy/p/thalamus.htm
 http://biology.about.com/od/anatomy/p/thalamus.htm