Thalamus Full Game BEST Download
Adeline Haverstock
The thalamus is a mostly gray matter structure of the diencephalon that has many essential roles in human physiology. The thalamus is composed of different nuclei that each serve a unique role, ranging from relaying sensory and motor signals, as well as regulation of consciousness and alertness. Clinically, there are only a few conditions related to thalamic damage and dysfunction. Most of these conditions are rare, but some of the more common conditions have significant anatomical changes that are visible with neuroimaging. Surgical interventions of the thalamus in the past have had limitations, but currently, this field is evolving due to increased accessibility through the advancement of microsurgical techniques and improved neuroimaging.
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.[1]
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.[2] The connection of limbic system structures to the anterior nuclei of the thalamus allows the thalamus to be involved in learning and episodic memory.[3] The thalamus is also involved in the regulation of sleep and wakefulness.[4]
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.
During the third week of embryogenesis, the neural tube forms from the ectoderm. The neural tube forms the prosencephalon, the mesencephalon, and rhombencephalon. The prosencephalon is the most rostral of these structures and further divides into the telencephalon and diencephalon. The thalamus develops from the embryonic diencephalon.[7]
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[6][8][6]:
Due to the deep location of the thalamus, thalamic tumors have historically been challenging to manage. Recently contemporary microsurgical techniques and advances in neuroimaging have resulted in some improvement in outcomes of resections involving the thalamus.[9]
After a thalamic stroke, a rare condition called Dejerine-Roussy syndrome or thalamic pain syndrome may occur; this usually presents initially with the absence of sensation and tingling of the body contralateral to the affected thalamus. Months later, numbness occurs, eventually developing to severe chronic pain.[12] It is due to the involvement of the thalamogeniculate branch, thereby leading to excruciating pain owing to the absence of central cortical inhibition.[13]
A hereditary prion disease called fatal familial insomnia exists in which the gene PRNP located on chromosome 20 at p13 deposits in the thalamus, causing degeneration over time. Patients develop worsening insomnia that can have associated psychiatric symptoms such as panic attacks, paranoia, and phobias. They then develop hallucinations and the complete inability to sleep. Rapid weight loss follows with dementia and mutism until death occurs.[17][18]
Concerning anatomical changes, the interthalamic adhesions appear enlarged in patients with Arnold-Chiari malformation type II.[21] Additionally, the ventral intermediate nucleus of the thalamus has been the target for deep brain stimulation for the treatment of medically refractory essential tremors and tremor-dominant Parkinson disease with some success.[5]
The thalamus (pl.: thalami; from Greek θάλαμος, "chamber")[1] is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, allowing hub-like exchanges of information. It has several functions, such as the relaying of sensory signals, including motor signals to the cerebral cortex[2][3] and the regulation of consciousness, sleep, and alertness.[4]
The thalamus is a paired structure of gray matter located in the forebrain which is superior to the midbrain, near the center of the brain with nerve fibers projecting out to the cerebral cortex in all directions. The medial surface of the thalamus constitutes the upper part of the lateral wall of the third ventricle, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the interthalamic adhesion. The lateral part of the thalamus is the phylogenetically newest part of the thalamus (neothalamus), and includes the lateral nuclei, the pulvinar and the medial and lateral geniculate nuclei.[6][7] There are areas of white matter in the thalamus including the stratum zonale that covers the dorsal surface and the external and internal medullary laminae. The external lamina covers the lateral surface and the internal lamina divides the nuclei into anterior, medial, and lateral groups.[8]
The thalamus derives its blood supply from a number of arteries: the polar artery (posterior communicating artery), paramedian thalamic-subthalamic arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries.[9] These are all branches of the posterior cerebral artery.[10]
Derivatives of the diencephalon include the dorsally-located epithalamus (essentially the habenula and annexes) and the perithalamus (prethalamus) containing the zona incerta and the thalamic reticular nucleus. Due to their different ontogenetic origins, the epithalamus and the perithalamus are formally distinguished from the thalamus proper. The metathalamus is made up of the lateral geniculate and medial geniculate nuclei.
The thalamus comprises a system of lamellae (made up of myelinated fibers) separating different thalamic subparts. Other areas are defined by distinct clusters of neurons, such as the periventricular nucleus, the intralaminar elements, the "nucleus limitans", and others.[11] These latter structures, different in structure from the major part of the thalamus, have been grouped together into the allothalamus as opposed to the isothalamus.[12] This distinction simplifies the global description of the thalamus.
The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch. There are two main parts: the lateral spinothalamic tract, which transmits pain and temperature, and the anterior (or ventral) spinothalamic tract, which transmits crude touch and pressure.
The thalamus also plays an important role in regulating states of sleep and wakefulness.[18] Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness.[19] The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma.[20]
The role of the thalamus in the more anterior pallidal and nigral territories in the basal ganglia system disturbances is recognized but still poorly understood. The contribution of the thalamus to vestibular or to tectal functions is almost ignored. The thalamus has been thought of as a "relay" that simply forwards signals to the cerebral cortex. Newer research suggests that thalamic function is more selective.[21] Many different functions are linked to various regions of the thalamus. This is the case for many of the sensory systems (except for the olfactory system), such as the auditory, somatic, visceral, gustatory and visual systems where localized lesions provoke specific sensory deficits. A major role of the thalamus is support of motor and language systems, and much of the circuitry implicated for these systems is shared. The thalamus is functionally connected to the hippocampus[22] as part of the extended hippocampal system at the thalamic anterior nuclei[23] with respect to spatial memory and spatial sensory datum they are crucial for human episodic event memory.[24][25] The thalamic region's connection to the mesio-temporal lobe provide differentiation of the functioning of recollective and familiarity memory.[13]
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