Dorsal thalamus and corticothalamic projections Flashcards
What is the dorsal thalamus?
One of the 4 parts of the diencephalon (epithalamus, subthalamus, hypothalamus)
paired organ
ovoid
What is the location of the thalamus?
deep in cerebral hemispheres, close to midline, joined by interthalamic adhesions (no functional properties, at level of lateral wall of 3rd ventricle (forms superior 2 3rds), extends above hypothalamic sulcus
lat: thalamus
inf: hypothalamus, just below hypothalamic sulcus –> forms floor of 3rd ventricle , close to central cavity represented by 3rd ventricle, close anatomical relations with internal capsule.
What are the functions of the dorsal thalamus?
relay of sensory information
assistance in regulation of motor function
relays information from extrathalamic sources towards other parts of CNS
essentially by cerebral cortex
Gate modulating flow of information from periphery to cerebral cortex to achieve conscious perception.
Also selects most adequate flow of information reaching cerebral cortex –> organize best response
What are the 4 general principles of thalamic organisation?
All thalamic nuclei receive input from extrathalamic regions
All thalamic nuclei send output to cerebral cortex (with exception of reticular thalamic nucleus).
Each portion of thalamus receives a reciprocal connection from the same portions of the cerebral cortex, whereby the cortex can modify thalamic functions.
Thalamic nuclei not inter-connected (with exeption of intralaminar nuclei)
Explain the following principle: “All thalamic nuclei receive input from extrathalamic regions”
o Afferents
Specific (sensory – motor –limbic): strictly focused on specific relay nuclei
Non specific (e.g. cholinergic afferents from brain stem): may diffuse
Explain the following principle: “All thalamic nuclei send output to cerebral cortex (with exception of reticular thalamic nucleus)”
o Thalamo-cortical efferents include:
Specific projections
Diffuse projections
Projection from thalamus to cortex uses __________
internal capsule, both anterior + posterior limbs.
This portion of internal capsule is known as thalamic radiation.
What are the 2 types of thalamic nuclei?
Specific and non-specific nuclei
What are the 2 types of specific nuclei?
Relay nuclei
Association nuclei:
What are relay nuclei?
Relay nuclei receive well-defined inputs + project this signal to functionally distinct areas of the cerebral cortex
What are association nuclei?
receive most of input from cerebral cortex + project back to cerebral cortex in association areas where they appear to regulate activity.
Describe the fundamental thalamic circuitery
different players, most relevant cells
Thalamus.
Although nucelei have different functions –> share same circuitery
What is a thalamic relay neuron?
o glutamatrgic cell (red)
o receives afferent (yellow extrathalamic imput, synapses with thalamic relay neuron (yelloy and red)synaptic contact surrounded by buttons in green coming from interneuron –> THALAMIC TRIAD, surrounded by podocyted of astrocytes )
o sends projections to cerebral cortex
What is a thalamic interneuron?
o Green o intrinsic cells o only involved in local circuitery o gabaergic cells o contact synaptic contact between exothalamic input and relay cell of thalamusmodulating transmission of information from afferent + relay cellmodulating activity of relay cell
What is a corticothalamic neuron?
o Cortex sends feedbak to thalamus after receiving projections from thalamus –> reciprocal
Two Classes of Cortico-thalamic Neurons: cerebral cortex provides feedback to thalamus via projections of 2 distinct classes of pyramidal cells with somata located in different layers
What are the 2 classes of corticothalamic neurons?
• Neuron located in layer 6 of same cortical column which receive projections from that specific thalamic nucleux
axon of neuron will contact reticular nucleus of thalamus
• smaller number of cortico-thalamic neurons found in layer V of same area
o project mainly to different, although functionally related, thalamic nuclei.
o axon of a layer V cell does not give off collaterals to reticular nucleus.
What are reticular nucleus cells?
o only thalamic nucleus that does not project to cerebral cortex.
o modulates information from other nuclei in thalamus
o modulates signals going through thalamus (and + reticular nucleus)
o active during drowsiness + sleep + inactive during wakefulness –> relay cells may convey information to cerebral cortex
o Gabaergic nuceus
o Separated from thalamus by external medullary lamina
o Around thalamus
What are the 3 types of Relay nuclei –>(specific thalamic nuclei)?
sensory relay nuclei
motor relay nuclei
limbic relay nuclei
What are the 3 sensory relay nuclei and what do they do?
- VENTRAL POSTERIOR NUCLEUS: relay nucleus for somatosensory pathway
- LATERAL GENICULATE NUCLEUS: thalamic relay nucelus for visual pathway
- MEDIAL GENICULATE NUCLEUS : relay nucelus for auditory pathway
What are the 2 motor nuceli and what do they do?
- VENTRAL ANTERIOR NUCLEUSreceive info from cerebellum and basal ganglia and send projections to motor cotexes
- VENTRAL LATERAL NUCLEUS
What are the 2 limbic relay nuceli and what do they do ?
- DORSOMEDIAN NUCLEUS: connect amygdala and frontal cortex
* ANTERIOR NUCLEUS: connecting manillary bodies and hypocampus with sin
What is an example of a NON SPECIFIC THALAMIC NUCLEUS?
INTRALAMINAR NUCLEI
Describe intralaminal nuclei.
o Afferents: (Cerebellum, Globus pallidus, Reticular formation, Substantia nigra, Superior colliculus, Spino-thalamic tract (pain)–> diffuse projections to cerebral cortex + striatum –> involved in sensory motor integration
