What Is Thalamus and How It Looks Like?
- Who was the first to use the word ‘thalamus’ in the anatomical context?
- How many thalami are there in your brain?
- Which body system does thalamus belong to?
- How does the thalamus create partial awareness of the stimuli?
- What are the main thalamic divisions?
Wondering what is thalamus and where its miraculous powers come from? Here is a precise yet comprehensive account of thalamus structure and function with thalamus diagram and facts.
The first use of the word ‘thalamus’ in anatomical context is found in the writings of Galen, a 2nd century AD scholar who wrote in Greek. However, he used the word in a derivative sense and applied it to something other than a large mass in diencephalon that you call the ‘thalamus’ today.
By the term ‘thalamus’, he meant a region at the back of diencephalon and adjacent to the lateral geniculate bodies where the lateral ventricles come together. According to him, the optic tracts arose from this region of the brain.
The thalamus can be defined as a group of nuclei which act in a unified way as a final relay station for messages going to the cerebral cortex.
Thalamus makes one of the two parts of diencephalon – the part of the brain located just below the cerebral cortex and above the mesencephalon – with the other being the hypothalamus.
How many thalami are there in your brain? There is a pair of thalami, one per hemisphere. They lie deep within the brain close to the midline third ventricle. An inter-thalamic adhesion, called the massa intermedia, connects them with each other.
The location of the thalamus helps it perform its primary function, that is relaying information from below.
According to Edward G. Jones (2012), the author of ‘The Thalamus’, the thalamus has traditionally been divided into three parts, namely, the epithalamus, the dorsal thalamus, and the ventral thalamus. He based these divisions on the derivatives of three types of cellular masses observed in the wall of developing diencephalon. This tripartite division provides an increasingly strong connectional basis.
The epithalamus is made up of the anterior and posterior paraventricular nuclei and the habenular nuclei. This part of the thalamus neither receives nor sends fibres to the cerebral cortex. However, there are closer affinities between the epithalamus and the hypothalamus.
Comprising several types of nuclei, the dorsal thalamus both sends to and receives fibres from the cerebral cortex and the striatum. Here the striatum is a crucial part of the motor and reward systems. The nuclei lying in the dorsal region of the thalamus can be distinguished into the principal nuclei and the nuclei of the internal medullary lamina.
The ventral division or the ventral thalamus is made up of the ventral lateral geniculate nucleus, reticular nucleus, and zona incerta. Some researchers, however, also claim the nucleus of the fields of Forel to be found in the ventral segment of the thalamus.
In the thalamus diagram, you will find that the ventral division does not send axons to the cerebral cortex and the striatum even though it may receive fibres from both these sites.
What Does It Do?
The thalamus is traditionally known for its job as a sensory relay in the systems like hearing, vision, taste, and perception of sensory stimuli from the skin and internal organs. The latest research has pointed out some more jobs performed by this part of the brain, which include motor activity, memory, emotions, and arousal, etc. Richard Stevko (2014) enlists and describes various functions performed by the thalamus in the book “Neurophysiology”.
When you drive in traffic, run through the woods, dream, or suffer a bellyache, you are surrounded with masses of internal and external data coming to you through the sensory system. It needs to be sorted, which is done by the thalamus. The thalamus serves the functions of correlation and making a perception out of sensation.
Another important function of the thalamus is that it helps you to create a partial awareness of the sensory stimuli received from the peripheral organs. On receiving a sensation, you use the thalamus to focus on, become aware of, and initiate the formulation of thought.
With this part of the brain, you can also focus on or maintain attention. During this process, the thalamus temporarily makes certain areas in the cerebral cortex more receptive and sensitive to the coming data.
Thalamus Facts in Brief:
- The thalamus is a dual lobed mass of grey matter located beneath the cortical region.
- It is the component of the limbic system, which is a set of brain structures located beneath the cortex and on top of the brainstem.
- Diencephalon is a part of the forebrain, which further comprises two components, that is, the thalamus and hypothalamus.
- While the job of the thalamus is to facilitate sensory perception and regulate motor functions, the hypothalamus is concerned with the regulation of hormonal secretions, the pituitary and adrenal glands, and the body temperature, etc.
- As a relay station, the thalamus connects the cerebral cortex with other parts of the brain and the spinal cord which have a role in sensory perception and movement.
- Your thalamus is responsible for regulating sleep, alertness, and consciousness.