What is the Difference Between Thalamus and Hypothalamus

The main difference between thalamus and hypothalamus is that the thalamus coordinates sensory and motor functions and regulates consciousness, sleep, and alertness. Whereas, the hypothalamus works together with the pituitary gland to regulate the secretion of hormones. Furthermore, the thalamus is located in the middle portion of the brain, while the hypothalamus is located between the thalamus and the pituitary gland. Moreover, the thalamus is the dorsal part of the diencephalon, while the hypothalamus is the ventral part of the diencephalon. 

Thalamus and hypothalamus are two masses of the gray matter made up of small nuclei. Also, they are two components of the diencephalon, which is a division of the forebrain.  

Key Areas Covered 

1. What is Thalamus
     – Definition, Anatomy, Function
2. What is Hypothalamus
     – Definition, Anatomy, Function
3. What are the Similarities Between Thalamus and Hypothalamus
     – Outline of Common Features
4. What is the Difference Between Thalamus and Hypothalamus
     – Comparison of Key Differences

Key Terms 

Hypothalamus, Diencephalon, Hormones, Pituitary Gland, Thalamus

What is Thalamus 

Thalamus is a large mass of the gray matter. It forms the dorsal part of the diencephalon and is located between the cerebral cortex and the midbrain. Also, it is a midline symmetrical structure with two halves called lobules located in each brain hemisphere. Further, the medial surface of the thalamus forms the upper part of the lateral wall of the third ventricle. And, the lateral part of the thalamus is the neothalamus, including the lateral nuclei, the pulvinar, and the medial and lateral geniculate nuclei. 

Figure 1: Thalamus and Hypothalamus

Moreover,  the stratum zonale is the white matter of the thalamus, covering the dorsal surface, and the external and internal medullary laminae. Besides, the external lamina covers the lateral surface, and the internal lamina divides the nuclei into anterior, medial and lateral groups. Concerning the functions, the main function of the thalamus is to serve as a relay station, relaying information between different subcortical regions and the cerebral cortex. In addition to this, it also regulates consciousness, sleep, and alertness. 

What is Hypothalamus 

The hypothalamus is the region of the forebrain and is just below the thalamus. It connects to both lobes of the pituitary gland. Specifically, the hypothalamus connects the anterior pituitary gland by means of a portal blood system communicating through chemical signals, and thus, stimulating and inhibitory hormones. Meanwhile, it directly connects to the posterior pituitary through neurons. Thereby, the hypothalamus, basically, regulates the functions of the pituitary gland.

Figure 2: The Anterior Pituitary Complex

Especially, the posterior pituitary gland stores and releases hormones produced by the hypothalamus, including the antidiuretic hormone and oxytocin. However, dopamine, somatostatin, corticotrophin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), thyrotrophin-releasing hormone (TRH), and gonadotrophin-releasing hormone (GnRH) are the hormones produced by the hypothalamus. These are sent to the anterior pituitary gland for secretion. In the meanwhile, the hypothalamus is also responsible for regulating the blood pressure, the levels of circulating hormones, body temperature, hunger, thirst, sleep, and emotional activity. 

Similarities Between Thalamus and Hypothalamus  

• Thalamus and hypothalamus are two components of the forebrain.  
• Also,  they are two masses of gray matter made up of small nuclei.  
• Besides, they are two of the four components of diencephalon;  the other two components include epithalamus and perithalamus.  
• Moreover, the main function of them is to coordinate the functions of the body.  
• They also serve as bridges, which connect different parts of the brain. 

Difference Between Thalamus and Hypothalamus

Definition 

Thalamus refers to either of the two masses of gray matter. It lies between the cerebral hemispheres on either side of the third ventricle, relaying sensory information and acting as a centre for pain perception. Meanwhile, hypothalamus refers to a region of the forebrain below the thalamus, coordinating both autonomic nervous system and the activity of the pituitary, controlling body temperature, thirst hunger, other homeostatic systems, sleep, and emotional activity. 

Location 

Thalamus is located in the center of the brain, while the hypothalamus is located below the thalamus. 

Structure 

Thalamus has two bulbs; one for each hemisphere, while the hypothalamus contains a large number of small nuclei. 

Size 

Also, the diameter of the thalamus is around 6 cm, while the hypothalamus is comparatively small. 

Diencephalon 

Thalamus is the dorsal part of the diencephalon, while the hypothalamus is the ventral part of the diencephalon. 

Function 

Functionally, the thalamus relays information between different subcortical regions and the cerebral cortex, while the hypothalamus produces several neurohormones. 

Main Regulatory Functions 

Thalamus regulates sleep, alertness, and wakefulness, while the hypothalamus regulates body temperature, hunger, fatigue, and metabolic processes. 

Bridging 

Thalamus connects the cerebral cortex to the midbrain, while the hypothalamus connects the nervous system to the endocrine system. 

Significance 

Besides, the thalamus is a part of the nervous system, while the hypothalamus is a part of both nervous and endocrine systems. 

Conclusion 

In Brief, the thalamus is a component of the forebrain, consisting of two lobules for each of the two brain hemispheres. Also, its diameter is around 6 cm. Generally, the main function of the thalamus is to relay information between different subcortical regions of the brain. On the other hand, the hypothalamus is another component of the forebrain and it is made up of small nuclei. However, it is comparatively smaller. Functionally, the main function of the hypothalamus is to control body temperature, hunger, metabolic functions, etc. Moreover, it produces some neurohormones secreted by the pituitary. Therefore, the main difference between thalamus and hypothalamus is anatomy, location, and function. 

References:

1. Bengochea, Kim. “Thalamus.” Kenhub, Kenhub, 9 Dec. 2019, Available Here.
2. Bowen, Richard. “Functional Anatomy of the Hypothalamus and Pituitary Gland.” Vivo.colostate.edu, Available Here.

Image Courtesy:

1. “Figure 35 03 06” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “1808 The Anterior Pituitary Complex” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia