Tuesday, April 11, 2017

Thalamus.

Helloooo everybody!
 let's quickly learn a few basics and beyond in today's post on Thalamus.
So thalamus is nothing but a collection of neurons which are organized well-defined nuclear masses.
The nuclei have confusing names and are difficult to remember too.

But from a functional point of view they are divisible into four groups to keep our lives simple.

1) Specific Sensory Nuclei
2) Association Nuclei
3) Nonspecific Nuclei
4) Motor Nuclei.

Specific Sensory Nuclei :These receive all sensory afferents. The arrangement of fibres is topographic and so is their projection to the somatosensory cortex. 
Corresponding to the thalamocortical projection fibres, there are also corticothalamic fibres which provide feedback information to the relay nuclei.
Let us now see how the sensory relay nuclei work.
A specific sensory stimulus activates neurons in the sensory relay nucleus.
                           
The thalamic nuclei activate some thalamic interneurons as well as an area in the sensory cortex. Activated sensory cortex also sends impulses back to the thalamic relay nucleus, thereby modulating the thalamic output.
In short, the sensory relay nuclei really do not act as simple relays.  They process the sensory signal by local intrathalamic circuits and descending corticothalamic  fibres before sending it to the sensory cortex.

Association Nuclei :
These help achieve integration of different types of sensory information.

Nonspecific​ Nuclei:
These also receive sensory information but project to the cortex in a diffuse manner.  Therefore they seem to be involved in the arousal induced by sensory stimuli.
They also project to the limbic system, thereby suggesting their involvement in the emotional impact of sensory stimuli.

Motor Nuclei :
They relay and process messages from the basal ganglia and cerebellum to the motor and premotor cortex.


All nuclear groups have to and fro connections with the cerebral cortex. Thus the thalamus and cortex function as one functional entity, the thalamocorticalsystem.

Possibly the thalamus prepares a crude blue pint of the  final product achieved by the cortex.

The global involvement of the thalamus in central nervous function is revealed when its function is impaired, as in the thalamic syndrome.


Let's now quickly learn about Thalamic Syndrome.

Level of lesion : Posteroventral thalamus.

Etiology: Thrombosis of  Posterolateral branch of the posterior cerebral artery.

Manifestations :
1) Impairment of discrimination in sensory perception,
2) Hypotonia, muscular weakness and incoordination,
3) Volatile emotions, pleasant or unpleasant. 
After a few weeks to months, partial recovery may occur.

The sensations, regardless of the nature of the stimulus, may be very painful
The symptoms are thought to arise partly because the medial nuclei of the thalamus are spared by the lesion. 
 The medial nuclei are the nonspecific nuclei which receive major projections from pain  fibres.Hence the dominance of pain among the sensations. 

Well that's all on Thalamus,Hope it was helpful!

Let's learn Together!
-Medha.

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