QS Study

The thalamus is a structure in the middle of the brain. It is a large ovoid mass of gray matter situated at the top of midbrain and forms the major part of the diencephalon. It is located between the cerebral cortex and the midbrain.

The pons is anterior to the cerebellum and connects the medulla oblongata to the midbrain. The nuclear masses and tracts of the thalamus. It works to associate numerous vital processes, including consciousness, sleep, and sensory interpretation.

Connections of thalamus –

Afferent impulses front a large number of subcortical centers converge on the thalamus. Exteroceptive and proprioceptive impulses ascend to it through the medial lemniscus, the spinothalamic tracts, and trigeminothalamic tract.

  • Visual and auditory impulses reach the geniculate body,
  • Taste sensation is conveyed to it through solitariothalamic fibers,
  • Visceral information passes to it from hypothalamus via reticular formation.

In addition to these, it receives profuse connections from all parts of the cerebral cortex.

Functions –                                                

  • All the sensory impulses convey to the thalamus, so, It is regarded as a great integrating center.
  • Through its profuse thalamocortical projections, it projects all the information to the whole of the cerebral cortex.
  • Besides its integrating function, the thalamus is believed to have the ability to perceive exteroceptive sensations, especially pain.
  • It also helps hypothalamus in the regulation of temperature.
  • It’s capable of recognition, though badly, of pain, thermal and some tactile sensations at its own level.
  • It contains many nuclei.

Nuclear Masses of Thalamus 1

Fig: Nuclear Masses of Thalamus

Thalamic nucleus: Anterior, Dorsomedial, Lateral dorsal, lateral posterior, pulvinar; Ventral anterior; Ventral posteromedial; Ventral posterolateral.

Anterior

  • Function: Emotional tone, mechanism of recent memory.
  • Afferent: Mamillothalamic tract, cingulate gyms, hypothalamus.
  • Efferent neuronal loop: Cingulate gyms, hypothalamus.

Dorsomedial:

  • Function: Integration of somatic, visceral & of factory information.
  • Afferent: Prefrontal cortex, hypothalamus other thalamic nuclei.
  • Efferent neuronal loop: Prefrontal cortex, hypothalamus, other thalamic.

Lateral dorsal, lateral posterior, pulvinar:

  • Function: Unknwon.
  • Afferent: Cerebral cortex, other thalamic nuclei.
  • Efferent neuronal loop: Cerebral cortex, other thalamic nuclei

Ventral anterior Ventral lateral:

  • Function: Influences the activity of motor cortex
  • Afferent: Reticular formation, premotor cortex, other thalamic nuclei substantia nigra, corpus striatum.
  • Efferent neuronal loop: Cerebral cortex, other thalamic nuclei.

Ventral posteromedial:

  • Function: Relays common sensations of consciousness
  • Afferent: Trigeminal lemniscus, gustatory fibers
  • Efferent neuronal loop: Primary somatic sensory cortex.

Ventral posterolateral:

  • Function: Relays common sensations of consciousness
  • Afferent: Medial and spinal lemnisci
  • Efferent neuronal loop: Primary somatic sensory cortex.
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