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Thalamus Relay Station and Role in Sensory Processing
- 1. THALAMUS a report by Avee Diana
- 2. The thalamus is situated at the rostral end of the brainstem and functions as an important relay and integrative station for information passing to all areas of the cerebral cortex, the basal ganglia, the hypothalamus, and the brainstem. SNELL’S CLINICAL NEUROANATOMY
- 3. The thalamus is a paired gray matter structure of the diencephalon located near the center of the brain. It is above the midbrain or mesencephalon, allowing for nerve fiber connections to the cerebral cortex in all directions — each thalamus connects to the other via the interthalamic adhesion. It forms the upper and lateral walls of the third ventricle while the dorsal surface is part of the floor of the body of the lateral ventricle. Laterally, it limits with the posterior arm of the internal capsule. Anterolaterally, it limits with the head of the caudate and ventral nucleus with the subthalamus and hypothalamus.
- 5. Medial to the thalamus, there’s the lateral wall of the third ventricle. Anterior to the thalamus, there’s the interventricular foramen, or foramen of Monro, through which the cerebrospinal fluid, or CSF, flows from the lateral ventricles to the third ventricle. Lateral to the thalamus, there’s the posterior limb of the internal capsule, while the posterior part of the thalamus, called the pulvinar, is not covered by other structures and can be seen superior to the posterior aspect of the midbrain.
- 8. STRATUM ZONALE- a thin layer of white matter covers the thalamus on its superior surface. EXTERNAL MEDULLARY LAMINA- another layer that covers the lateral surface of the thalamus. INTERNAL MEDULLARY LAMINA- a vertical sheet of white matter that divides the gray matter of the thalamus into medial and lateral halves.
- 10. The ventral postero-lateral (VPL) nucleus receives input from the medial lemniscus and the spinothalamic tract and projects to the primary somatosensory cortex. In order to easily remember sensations that this nucleus transmits you can remember that for VPL: V in ventral stands for the vibration; P in posterior for pain, pressure and proprioception; L in lateral for the light touch; then just add the temperature.
- 11. The ventral postero-medial (VPM) nucleus receives input from the trigeminal and gustatory pathways and projects to the primary somatosensory cortex as well. To remember the sensations that this nucleus transmits, you can use the mnemonic: Makeup goes on the face. The M in makeup refers to the ventral postero-medial nucleus while the face refers to somatosensations from the face as well as taste.
- 12. The ventral lateral nucleus receives input from the cerebellum and the basal ganglia, and it projects to the motor and premotor regions of the cerebral cortex. This nucleus relays motor information and can influence movements.
- 13. The medial geniculate body is a small bulge under the posterior end of the pulvinar. It receives input from the inferior colliculus via the inferior brachium and from the superior olivary complex, and then projects to the auditory cortex of the temporal lobe.
- 14. Lateral to the medial geniculate body is another small bulge called the lateral geniculate body. It receives input from the retina, via the optic nerve, optic chiasm and optic tract, and then projects to the primary visual cortex of the occipital lobe via the optic radiation.
- 15. Functionally, the thalamus divides into five major functional components as: 1. Reticular and intralaminar nuclei dealing with arousal and pain regulation 2. Sensory nuclei regulating all sensory domains except olfaction 3. Effector nuclei governing motor language function 4. Associative nuclei connoting cognitive functions 5. Limbic nuclei encompassing mood and motivation
- 16. BLOOD SUPPLY AND LYMPHATICS The basilar communicating artery, posterior cerebral artery, and posterior communicating artery are the major blood supply for the thalamus. The major vascular pedicles supplying the thalamus divide into: 1. Tuberothalamic artery (polar artery) 2. Paramedian artery 3. Thalamogeniculate artery and 4. Medial and lateral posterior choroidal artery
- 17. CLINICAL SIGNIFICANCE ● Cerebrovascular accident (stroke) can lead to the Thalamic Syndrome which involves a one-sided burning or aching sensation often accompanied by mood swings. ● Damage to the thalamus can result in coma. ● Fatal Familial Insomnia is a hereditary prion disease in which degeneration of the thalamus occurs, causing the patient to gradually lose his ability to sleep and progressing to a state of total insomnia, which invariably leads to death. ● Korsakoff's Syndrome occurs from damage to the medial thalamus & mammillary body due to Thiamine deficiency
Notas del editor
- There are actually two thalami, one on each side, flanking the lateral aspect of the space created by the third ventricle. Between the left and right thalami there’s a bridge of gray matter that connects them, called the interthalamic adhesion, or connection. Between the thalamus and the hypothalamus there’s the hypothalamic sulcus, which separates them. The diencephalon contains two endocrine glands as well: the posterior lobe of the pituitary gland, below the hypothalamus, and the pineal gland, near the caudal end of the thalamus.
- While the thalamus is mostly gray matter (cell bodies of neurons), there are some areas of white matter (axons). The external and internal medullary laminae are white matter structures of the thalamus. The external medullary laminae cover the lateral surface of the thalamus, and the internal medullary laminae divide the thalamic nuclei into anterior, medial, and lateral groups.
- Now, to better understand its relation to adjacent structures, let’s make a transverse section of the brain. Medial to the thalamus, there’s the lateral wall of the third ventricle. Anterior to the thalamus, there’s the interventricular foramen, or foramen of Monro, through which the cerebrospinal fluid, or CSF, flows from the lateral ventricles to the third ventricle. Lateral to the thalamus, there’s the posterior limb of the internal capsule, while the posterior part of the thalamus, called the pulvinar, is not covered by other structures and can be seen superior to the posterior aspect of the midbrain.
- Now let’s switch to a coronal section of the brain. Here we can see that the dorsal surface of the thalamus is free, sitting under the lateral ventricle and the fornix, while ventrally there’s the tegmentum of the midbrain. Like on the transverse plane, the third ventricle lies medially and the internal capsule lies laterally.
- Switching to the sagittal plane, once again, inside the third ventricle, we can see the medial surface of the thalamus and the interthalamic adhesion arising from it.
- The thalamus is an egg-shaped structure made of gray matter that contains neuronal cell bodies. The thalamus is connected with almost all parts of the central nervous system, like the brainstem and the cerebral cortex, enabling it to influence many different processes in the brain. It serves as a major relay station that gathers, combines and processes afferent information before forwarding it to the cerebral cortex. The thalamus is made up of a series of nuclei which are responsible for the relay of the different sensory signals. These nuclei are formed mainly by neurons of excitatory and inhibitory nature. The thalamocortical neurons receive sensory or motor information from the rest of the body and present selected information via nerve fibers (thalamocortical radiations) to the cerebral cortex. The thalamus also has connections with the hippocampus, mammillary bodies, and fornix via the mammillothalamic tract.The connection of limbic system structures to the anterior nuclei of the thalamus allows the thalamus to be involved in learning and episodic memory.The thalamus is also involved in the regulation of sleep and wakefulness.
- Generally, the thalamus acts as a relay station filtering information between the brain and body. Except for olfaction, every sensory system has a thalamic nucleus that receives, processes, and sends information to an associated cortical area. The lateral geniculate nucleus of the thalamus receives visual sensory information from the retina to route to the visual cortex of the occipital lobe. The medial geniculate nucleus receives auditory sensory information from inferior colliculus and projects it to the primary auditory cortex in the temporal lobe. The ventral posterior nucleus of the thalamus is subdivided further by three. The spinothalamic tract is the sensory pathway for pain, temperature and crude touch that originates in the spinal cord and feeds into the ventral posterolateral nucleus of the thalamus for further processing, while the ventral posteromedial nucleus receives sensory information from the trigeminal nerve about the face. Lastly, the ventral intermediate nucleus has correlations with pathological tremors.[5] The reticular nucleus is in the ventral portion of the thalamus and forms a capsule around the thalamus laterally. Interestingly, this nucleus does not project to the cerebral cortex; rather, its function is to process and modulate information it receives from other thalamic nuclei. The reticular nucleus also receives disinhibitory input from the globus pallidus allowing for the initiation of voluntary movement.
- This way the thalamus can recognize that there is a hot object in our hands, but without the cortex, it cannot process more detailed information, like the shape and weight of the object or compare it to previous experiences. The only sensory pathway that doesn’t relay through the thalamus is the olfactory system, which enables us to smell. The thalamus plays a role in modulating movement through its connections with the basal ganglia, cerebellum and frontal lobe. It can also influence motivated behaviors via connections between the hypothalamus and the frontal lobe. The thalamus can even alter levels of consciousness by communicating with the reticular formation of the brainstem.