Thalamus | Anatomy2Medicine
thalamus

Thalamus

Thalamus

    • is the largest division of the diencephalon.

 

  • receives precortical input from all sensory systems except the olfactory system.

 

    • receives its largest input from the cerebral cortex.

 

  • projects primarily to the cerebral cortex and to a lesser degree to the basal ganglia and hypothalamus.

 

    • plays an important role in sensory and motor systems integration.

 

  • Primary Thalamic Nuclei and Their Major Connections

 

      • Anterior nucleus

 

  • receives hypothalamic input from the mamillary nucleus via the mamillothalamic tract

 

        • receives hippocampal input via the fornix.
        • projects to the cingulate gyrus.
        • is part of the Papez circuit of emotion (the limbic system).
      • Mediodorsal nucleus (dorsomedial nucleus)
        • is reciprocally connected to the prefrontal cortex.
        • has abundant connections with the intralaminar nuclei.

 

  • receives input from the amygdaloid nucleus, the temporal neocortex, and the substantia nigra.

 

        • is part of the limbic system and striatal system.
        • when destroyed, causes memory loss (Wernicke-Korsakoff syndrome).

 

  • plays a role in the expression of affect, emotion, and behavior (limbic function).

 

      • Intralaminar nuclei

 

  • receive input from the brainstem reticular formation, the ascending reticular system, and other thalamic nuclei.

 

        • receive spinothalamic and trigeminothalamic input.
        • project diffusely to the entire neocortex.
        • projects to the mediodorsal nucleus.

 

  • Centromedian nucleus

 

            • is the largest of the intralaminar nuclei.

 

  • is reciprocally connected to the motor cortex (area 4).

 

            • receives input from the globus pallidus.

 

  • projects to the striatum (caudate nucleus and putamen)

 

            • projects diffusely to the entire neocortex.

 

  • Parafascicular nucleus
  • projects to the striatum and the supplementary motor cortex (area 6).

 

      • Dorsal tier nuclei

 

  • Lateral dorsal nucleus

 

          • is a posterior extension of the anterior nuclear complex
          • receives mamillothalamic input.
          • projects to the cingulate gyrus.
          • is a part of the limbic system.

 

  • Lateral posterior nucleus

 

          • is located between the lateral dorsal nucleus and the pulvinar.

 

  • has reciprocal connections with the superior parietal cortex (areas 5 and 7).
  • Pulvinar

 

          • is the largest thalamic nucleus.

 

  • has reciprocal connections with the association cortex of the occipital, parietal, and posterior temporal lobes.
  • receives input from the lateral and medial geniculate bodies and the superior colliculus.

 

          • is concerned with the integration of visual, auditory, and somesthetic input.
          • Lesions of the dominant side may result in sensory aphasia.
      • Ventral tier nuclei

 

  • Ventral anterior nucleus

 

          • receives input from the globus pallidus (via the thalamic and lenticular fasciculi, H1 and H2) and the substantia nigra (motor function).
          • projects diffusely to the prefrontal and orbital cortices.
          • projects to the premotor cortex (area 6).

 

  • Ventral lateral nucleus

 

          • receives input from the globus pallidus (via the thalamic and lenticular fasciculi, H1 and H2), substantia nigra, and the cerebellum (dentate nucleus).

 

  • projects to the motor cortex (area 4) and to the supplementary motor area (area 6).
  • influences somatic motor mechanisms via the striatal motor system and the cerebellum.

 

          • Stereotactic destruction reduces parkinsonian tremor.

 

  • Ventral posterior nucleus

 

          • is the nucleus of termination of general somatic afferent (GSA; pain and temperature) and special visceral afferent (SVA; taste) pathways.
          • contains three subnuclei:

 

  • Ventral posterolateral (VPL) nucleus
  • receives the spinothalamic tracts and the medial lemniscus.

 

            • projects to the somesthetic (sensory) cortex (areas 3, 1, and 2).
            • Lesion results in
              • contralateral loss of pain and temperature sensation

 

  • loss of tactile discrimination in the trunk and extremities.
  • Ventral posteromedial (VPM) nucleus

 

            • receives the trigeminothalamic tracts.

 

  • receives the taste pathway via the solitary nucleus and the parabrachial nucleus.

 

            • projects to the somesthetic cortex (areas 3, 1, and 2).
            • Lesion results in
              • contralateral loss of pain and temperature sensation
              • loss of tactile discrimination in the head
              • results in ipsilateral loss of taste.

 

  • Ventral posteroinferior (VPI) nucleus

 

            • receives vestibulothalamic fibers from the vestibular nuclei
            • projects to the vestibular area of the somesthetic cortex.
      • Lateral geniculate body (LGB)
        • is a visual relay nucleus.

 

  • receives retinal input via the optic tract.

 

        • projects to the primary visual cortex (area 17, the lingual gyrus and the cuneus) via the optic radiation.
      • Medial geniculate body (MGB)
        • is an auditory relay nucleus.

 

  • receives auditory input via the brachium of the inferior colliculus.

 

        • projects to the primary auditory cortex (areas 41 and 42) via the auditory radiation.

 

  • Blood Supply of the Thalamus

 

    • Posterior communicating artery
      • gives rise to the anterior thalamoperforating arteries.
    • Posterior cerebral artery
      • gives rise to the posterior choroidal arteries.
      • gives rise to the posterior thalamoperforating arteries.
    • Anterior choroidal artery (LGB)

 

Internal Capsule

  • is a layer of white matter (myelinated axons)
  • separates the caudate nucleus and thalamus medially from the lentiform nucleus laterally.
  • consists of three divisions:
    • Anterior limb
      • is located between the caudate nucleus and the lentiform nucleus (the globus pallidus and the putamen).
    • Genu – contains corticobulbar fibers.
    • Posterior limb
      • is located between the thalamus and the lentiform nucleus.
      • contains the sensory radiations (pain, temperature, and touch).
      • contains the corticospinal fibers.
      • contains the visual and auditory radiations.

 

  • Blood Supply of the Internal Capsule

 

      • Anterior limb is irrigated by the
        • medial striate branches of the anterior cerebral artery
        • lateral striate branches (lenticulostriate) of the middle cerebral artery.
      • Genu is perfused either by
        • direct branches from the internal carotid artery

 

  • pallidal branches of the anterior choroidal artery.

 

      • Posterior limb is supplied by
        • branches of the anterior choroidal artery
        • branches of the lenticulostriate branches of the middle cerebral arteries.
      • Ligation of the anterior choroidal artery (in a parkinsonian patient results in
        • infarction of the corticospinal tract

 

  • destruction of the inner segment of the globus pallidus
  • The patient will have contralateral hemiparesis and contralateral reduction of the rigidity.

 

    • Infarction of the internal capsule
      • most frequently results from occlusion of the lenticulostriate branches of the middle cere- bral artery
      • results in:
        • Contralateral tactile hypesthesia
        • Contralateral anesthesia
        • Contralateral hemiparesis (with the Babinski sign)
        • Contralateral lower facial weakness
        • Contralateral homonymous hemianopia
    • Thalamic syndrome (Dejerine and Roussy)
      • is usually caused by occlusion of a posterior thalamoperforating artery.
      • classic signs
        • contralateral hemiparesis

 

  • contralateral hemianesthesia

 

      • elevated pain threshold
      • spontaneous, agonizing, burning pain (hyperpathia)
      • athetotic posturing of ´┐╝the hand (thalamic hand).