The thalamus serves as the main relay station for the brain. Motor pathways, limbic pathways, and sensory pathways in addition to olfaction pass through this central structure. The thalamus can be divided into about 60 areas called nuclei.Each nucleus has unique pathways as inputs and various projections as outputs, most of which send information to the cerebral cortex.
Structure and Function
The thalamus is a paired structure located in the center of the brain. Each side can be divided into three groups of thalamic nuclei: a lateral nuclear group, a medial nuclear group, and an anterior nuclear group. These three groups are separated by the inner medullary lamina, a Y-shaped structure present on each side of the ventricle. There is also a region of thin, midline thalamic nuclei adjacent to the third ventricle and a surrounding thalamic reticular nucleus covering each lateral ventricle.
In addition to grouping by anatomical location, thalamic nuclei can also be categorized by function. There are three categories:
Relay nuclei (lateral nuclear group, medial nuclear group, anterior nuclear group)
Relay cores account for the majority of the chamber. Their cortical projections are located in more specific areas than the reticular and intramuscular nuclei. The relay nuclei are subdivided into the three groups, as mentioned above, of the lateral nucleus, the medial nucleus, and the anterior nucleus. The most clinically important nuclei all fall into the lateral nuclear group. These include the ventrolateral, ventromedial, lateral genu, medial genu, and ventrolateral nuclei. A discussion of their relevance appears in detail in the Clinical Significance section.
The reticular nucleus surrounds each lateral chamber. Laterally is the internal capsule. This nucleus is unique in that its projections do not go to the cortex. Its projections go back to the chamber itself, from which it received its inputs. Thus, the reticular nucleus serves to regulate the activity of the ventricle.
The interglial nuclei also send projections to the cortex. Their inputs, however, come from the basal ganglia.
Classification of thalamic nuclei:
Lateral nuclear group
Ventral Posterior Lateral Nucleus (VPL)
Ventral posteromedial nucleus (VPM)
Lateral geniculate nucleus (LGN)
Median genitourinary nucleus (MGN)
Ventral lateral nucleus (VL)(Video) 2-Minute Neuroscience: The Thalamus
ventral anterior nucleus (VA)
I'm a pillow
Dorsal lateral nucleus
Lateral posterior nucleus
Ventral medial nucleus
Intermediate nuclear group
Median Dorsal Nucleus (MD)
Anterior nuclear group
Midline thalamic nuclei
Rostral intramuscular nuclei
Central medial nucleus
Central lateral nucleus
Uroid intramuscular nuclei
Embryologically, the parts of the brain can be divided into three origins: forebrain, midbrain, and rhombencephalon. The forebrain becomes the forebrain, the midbrain becomes the midbrain, and the rhombus becomes the hindbrain. These three subdivisions can be further subdivided, such that the forebrain consists of the telencephalon and diencephalon, the midbrain is unsubdivided, and the rhombencephalon consists of the metabrain and medulla.
At week 3 of embryonic development, the ectoderm forms the neural tube. The cranial part of the neural tube then becomes the forebrain, midbrain and rhombencephalon. In the 5th week, the thalamus emerges from the diencephalon along the sides of the third ventricle. Other structures arising from the diencephalon include the pituitary gland, hypothalamus, epithalamus, optic vesicle, optic cup, which forms the retina, and optic stalk.
There is a developmental relationship between the thalamus and the cortex. Both parts of the brain influence each other by influencing the proliferation, axonal connections and maturation of interneurons.
Classification of the embryological origin of the brain:
Midbrain(Video) Diencephalon Anatomy (Thalamus, Epithalamus, Subthalamus, Metathalamus, Hypothalamus)
Blood supply and lymphatics
Several arteries supply the thalamus with blood, all of which are branches of the posterior cerebral artery. These include the salpingothalamic, inferior lateral, paramedian, and posterior choroidal arteries.
The Percheron's artery is an anatomical variation in the blood supply to the brain. This artery branches from the posterior cerebral artery to supply the thalamus. The prevalence of Percheron artery is estimated to be 4% to 12%.Occlusion of this artery can result in symmetrical infarction of both sides of the ventricle.
The most clinically important nuclei all fall into the lateral nuclear group. These include the ventrolateral, ventromedial, lateral genu, medial genu, and ventrolateral nuclei. The ventromedial posterolateral nucleus is supplied by the vertebral tracts and dorsal columns of the spinal cord. As a result, this nucleus handles temperature and pain sensations, along with vibration, pressure, fine touch, and proprioception. The signals then proceed to the primary somatosensory cortex within the metacentral gyrus.The ventromedial nucleus receives inputs from the trigeminal tract and the gustatory or gustatory tract. The sense of face and the sense of taste are relayed here. Similar to its lateral counterpart, the ventromedial posteromedial nucleus sends this information to the primary somatosensory cortex within the mesocentral gyrus. The third major thalamic nucleus is the lateral geniculate nucleus. Visual sensory information from the eyes is sent through the optic nerves, through the optic chiasm where some fibers cross and others remain ipsilateral, and finally through the optic tracts before entering this nucleus. From the lateral geniculate nucleus, visual information is sent to the primary visual cortex, which is located in the calcareous sulcus of the occipital lobe.The medial geniculate nucleus, on the other hand, relays auditory sensory information from the superior olive and inferior colliculus of the tectum. The auditory information then travels to the auditory cortex of the temporal lobe. Finally, the ventromedial lateral nucleus receives input from the cerebellum and basal ganglia. Thus, it handles motor information and sends it to the precentral (motor) cortex.
The reticular nucleus receives inputs from the other thalamic nuclei, but also the reticular activating system and the basal forebrain. As a result, the thalamus plays a role in controlling alertness and attention.
The central medial nucleus, one of the intermuscular nuclei, is another clinically relevant thalamic nucleus. It receives inputs from the globus pallidus internus, the deep cerebellar nucleus and the reticular activating system and mainly sends this information to the cerebral cortex and striatum. The central midbrain is located deep within the brain and handles alertness, motor information, consciousness, and awareness.
Thalamic projections. Image courtesy O.Chaigasame
Thalamic nuclei. Image courtesy of S Bhimji MD
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The thalamus - the brain's sensory switchboard. It directs messages to the sensory areas in the cortex and transmits replies to the cerebellum and medulla. Helpful mnemonic: Hal & Amos are traffic cops…. The Hippocampus is involved in memory.What are the 4 nuclei of thalamus? ›
These include the ventral posterolateral, ventral posteromedial, lateral geniculate, medial geniculate, and ventral lateral nuclei.Which thalamic nuclei are most important in relaying somatosensory information to the somatosensory cortices? ›
The ventral posterior nucleus is the main relay nucleus for the somatosensory pathways. It is subdivided into two parts: ventral posteromedial (or VPM) and ventral posterolateral (or VPL).