Download - Getting to and from the cerebral cortex
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Oval, nuclear mass Forms 80% 0f diencephalon Anterior extent- interventricular foramen Superiorly- transverse cerebral fissure, floor
of 3rd ventricle Inferiorly- hypothalamic sulcus Posteriorly- overlaps midbrain
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All sensory pathways relay in thalamus. Many circuits used by cerebellum, basal
nuclei and limbic system involve thalamus. These utilize more or less separate portions
of thalamus, which has been subdivided into a series of nuclei.
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Nuclei can be distinguished from each other by topographical locations within thalamus and by input/output patterns.
Thalamus is divided into medial and lateral nuclear groups by a thin curved sheet of myelinated fibres called internal medullary lamina..
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It splits anteriorly to enclose a group of nuclei, collectively called anterior nucleus, which is close to interventricular foramen
Medial group contains one large nucleus called dosomedial nucleus
Lateral group is subdivided into a dorsal and ventral tier
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All thalamic nuclei are a mixture of projection neurons, whose axons provide the output of thalamus, and small inhibitory interneurons that use GABA as a neurotransmitter
Projection neurons account for 75% or more of the neurons of the most thalamic nuclei, though the relative proportions of projection neurons and interneurons vary in different nuclei
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Dorsal tier consists of lateral dorsal, lateral posterior nuclei and pulvinar.
Lateral posterior nucleus and pulvinar have almost similar connections
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Ventral anterior, ventral lateral- concerned with motor control; are connected to basal nuclei and cerebellum
Ventral posterior is subdivided into ventral posterolateral[ smatosensory input from body] and ventral posteromedial [somatosensory input from head]
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Lateral and medial geniculate nuclei / bodies are considered as posterior extensions of ventral tier
Intralaminar nuclei Embedded in internal medullary lamina Largest of this group are centromedian and
parafascicular nuclei
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• Lies between lateral thalamic surface and external medullary lamina
• Reticular nucleus is developmentally not a part of thalamus.
• It has distinct anatomical and physiological properties.
• Considered a part of thalamus because of location and extensive involvement in thalamic function.
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Rostral continuation of periaqueductal gray matter
Form interthalamic adhesion [when present]
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Pipelines for flow of information to cerebral cortex
Site where decisions are implemented about which information should reach cerebral cortex for processing
Any particular type of information affected by any thalamic nucleus is a function of its input and output connections
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Specific - Regulatory Specific inputs convey information that a
given nucleus may pass to cerebral cortex [and for some nuclei to additional sites].
Examples; Medial lemniscus specifically to VPL. Optic tract to LGB
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Regulatory inputs contribute to decisions about whether or in what form information leaves a thalamic nucleus
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cortical area to which the nucleus projects thalamic reticular nucleus diffuse cholinergic, noradrenergic,
serotonergic endings from brainstem reticular formation
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Relay nuclei• receive well defined specific input fibres
and project to specific functional areas of cerebral cortex
• deliver information from specific functional systems to appropriate cortical areas
Intralaminar and midline nuclei seem to have special role in function of basal nuclei and limbic system
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project to association areas of cerebral cortex
receive major inputs from cerebral cortex and subcortical structures
probably important in distribution and gating of information between cortical areas
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Every nucleus of the thalamus except the reticular nucleus sends axons to the cerebral cortex, either to a sharply defined area or diffusely to a large area.
Every part of the cortex receives afferent fibers from the thalamus, probably from at least two nuclei.
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• Every thalamocortical projection is faithfully copied by a reciprocal corticothalamic connection.
• Thalamic nuclei receive other afferent fibers from subcortical regions.
• Probably only one noncortical structure, the striatum , receives afferent fibers from the thalamus.
• .
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The thalamocortical and corticothalamic axons give collateral branches to neurons in the reticular nucleus, whose neurons project to and inhibit the other nuclei of the thalamus
No connections exist between the various nuclei of the main mass of the thalamus, although each individual nucleus contains interneurons
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The synapses of the interneurons are inhibitory, and most are dendrodendritic.
Other synapses in the thalamus are excitatory, with glutamate as the transmitter, and so are thalamocortical projections
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Input Output Functions
Collateral branches of thalamocortical and corticothalamic axons
To each thalamic nucleus that sends afferents to reticular nucleus
Inhibitory modulation of thalamocortical transmission
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Input Output Functions
Cholinergic and central nuclei of reticular formation,locus coeruleus, collateral branches from spinothalamictracts, cerebellar nuclei, pallidum
Extensive cortical projections, especially to frontal and parietal lobes; striatum
Stimulation of cerebral cortex in waking state and arousal from sleep;somatic sensation, especially pain [from contralateral head and body]; control of movement
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Input Output Functions
Inferior colliculus
Primary auditory cortex
Auditory pathway [from both ears]
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Input Output Functions
Ipsilateral halves of both retinas
Primary visual cortex
Visual pathway [from contralateral visual fields]
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Input Output Functions
Contralateral gracile and cuneate nuclei; contralateral dorsal horn of spinal cord
Primary somatosensory area
Somatic sensation [principal pathway, from contralateral body below head]
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Input Output Functions
Contralateral trigeminal sensory nuclei
Primary somatosensory area
Somatic sensation [principal pathway, from contralateral side of head: face, mouth, larynx, pharynx, dura mater]
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Input Output Functions
Contralateral cerebellar nuclei
Primary motor area
Cerebellar modulation of commands sent to motor neurons
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Input Output Functions
Pallidum Premotor and supplementary motor areas
Planning commands to be sent to motor neutons
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Input Output Functions
Pallidum Frontal lobe, including premotor and supplementary motor areas
Motor planning and more complex behavior
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Input Output Functions
Spinothalamic and trigeminothalamic tracts
Insula and nearby temporal and parietal cortex, including second somatosensory srea
Visceral and other responses to somatic sensory stimuli
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Input Output Functions
Hippocampal formation; pretectal area, superior colliculus
Cingulate gyrus; visual association cortex [occipital,posterior parietal and temporal lobes]
Memory ; interpretation of visual stimuli
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Input Output Functions
Superior colliculus
Parietal, temporal, and association cortex
Interpretation of visual and other sensory stimuli; formation of complex behavioral responses
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Input Output Functions
Pretectal area; primary and all association cortex for vision;retinas
Parietal lobe, anterior frontal cortex, cingulate gyrus, amygdala
Interpretation of visual and other sensory stimuli, formation of complex behavioral responses
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Input Output Functions
Etorhinal cortex, amygdala ,collaterals from spinothalamic tract, pallidum, substantia nigra
Prefrontal cortex Behavioral responses that involve decisions based on prediction and incentives
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Input Output Funtions
Amygdala, hypothalamus
Hippocampal formation and parahippocampal gyrus
Behaviorr;including visceral and emotional responses
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Input Output Funtions
Mamillary body Cingulate gyrus Memory
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Vascular accidents Can involve adjacent structures Small lesion can lead to large collection of
deficits
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Paroxysms of intense pain triggered by somatosensory stimuli
Pain may spread to involve entire one- half of the body- analgesic resistant
Abnormal perception of stimuli that do not cause pain
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Intensity and modality may be distorted May seem unusually uncomfortable or
unpleaseant Similar syndrome can develop in some
patients after damage in almost any part of Anterolateral pathway
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This type of pain is called Thalamic pain/central pain
Cause not understood Lesions causing this pain always involve
VPL/VPM nuclei with sparing of spinothalamic and spinoreticulothalamic fibres that end in other thalamic nuclei
May result in imbalanced thalamic activity
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Total/nearly total loss of somatic sensation in contralateral head and body
Gradually – return of some appreciation of painful, thermal and gross tactile stimuli
Functions associated with Medial lemniscus tend to more severely and oermanently impaired
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Discriminative touch may be abolished Position sense may be greatly impaired Sensory ataxia [due to loss of
proprioception] may be present
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Tahalamic pain+ hemianaesthesia+sensory ataxia contralateral to a posterior thalamic lesion= thalamic syndrome
It is often accompanied by mild and transient paralysis [damage to corticospinal fibres in Internal capsule] and various types of residual involuntary movements [damage to adjacent basal nuclei]
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It is often accompanied by mild and transient paralysis [damage
to corticospinal fibres in Internal capsule]
various types of residual involuntary movements [damage to adjacent basal nuclei]