Dorsal thalamus and corticothalamic projections

Question 1

What is the dorsal thalamus?

Answer 1

One of the 4 parts of the diencephalon (epithalamus, subthalamus, hypothalamus)
paired organ
ovoid

Question 2

What is the location of the thalamus?

Answer 2

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.

Question 3

What are the functions of the dorsal thalamus?

Answer 3

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

Question 4

What are the 4 general principles of thalamic organisation?

Answer 4

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)

Question 5

Explain the following principle: “All thalamic nuclei receive input from extrathalamic regions”

Answer 5

o Afferents

Specific (sensory – motor –limbic): strictly focused on specific relay nuclei

Non specific (e.g. cholinergic afferents from brain stem): may diffuse

Question 6

Explain the following principle: “All thalamic nuclei send output to cerebral cortex (with exception of reticular thalamic nucleus)”

Answer 6

o Thalamo-cortical efferents include:
Specific projections
Diffuse projections

Question 7

Projection from thalamus to cortex uses __________

Answer 7

internal capsule, both anterior + posterior limbs.

This portion of internal capsule is known as thalamic radiation.

Question 8

What are the 2 types of thalamic nuclei?

Answer 8

Specific and non-specific nuclei

Question 9

What are the 2 types of specific nuclei?

Answer 9

Relay nuclei

Association nuclei:

Question 10

What are relay nuclei?

Answer 10

Relay nuclei receive well-defined inputs + project this signal to functionally distinct areas of the cerebral cortex

Question 11

What are association nuclei?

Answer 11

receive most of input from cerebral cortex + project back to cerebral cortex in association areas where they appear to regulate activity.

Question 12

Describe the fundamental thalamic circuitery

Answer 12

different players, most relevant cells
Thalamus.
Although nucelei have different functions –> share same circuitery

Question 13

What is a thalamic relay neuron?

Answer 13

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

Question 14

What is a thalamic interneuron?

Answer 14

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 thalamusmodulating transmission of information from afferent + relay cellmodulating activity of relay cell

Question 15

What is a corticothalamic neuron?

Answer 15

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

Question 16

What are the 2 classes of corticothalamic neurons?

Answer 16

• 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.

Question 17

What are reticular nucleus cells?

Answer 17

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

Question 18

What are the 3 types of Relay nuclei –>(specific thalamic nuclei)?

Answer 18

sensory relay nuclei
motor relay nuclei
limbic relay nuclei

Question 19

What are the 3 sensory relay nuclei and what do they do?

Answer 19

• 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

Question 20

What are the 2 motor nuceli and what do they do?

Answer 20

• VENTRAL ANTERIOR NUCLEUSreceive info from cerebellum and basal ganglia and send projections to motor cotexes
• VENTRAL LATERAL NUCLEUS

Question 21

What are the 2 limbic relay nuceli and what do they do ?

Answer 21

• DORSOMEDIAN NUCLEUS: connect amygdala and frontal cortex

* ANTERIOR NUCLEUS: connecting manillary bodies and hypocampus with sin

Question 22

What is an example of a NON SPECIFIC THALAMIC NUCLEUS?

Answer 22

INTRALAMINAR NUCLEI

Question 23

Describe intralaminal nuclei.

Answer 23

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