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The cerebrum is composed of:

The diencephalon and the telencephalon


Anatomical borders of the diencephalon

Extends from the posterior commissure to the foramen of Monro.
Laterally it is bounded by the internal capsule, the tail of the caudate and the stria terminalis.


What are the components of the diencephalon

1. Thalamus
2. Epithalamus - 4 subcomponents

3. Hypothalamus

4. Subthalamus

5. Metathalamus - medial and lateral geniculate bodies.


What are the 4 components of the epithalamus

1. Habenular Trigone
2. Pineal Gland

3. Stria Medullaris

4. Roof of the third ventricle.


What are the functions of the thalamus

1. Integrate, correlate, and relay motor, sensory, visual, limbic and conscious systems.
2. Interpretation and conscious perception of pain

3. Enhance cortical areas


What structures divide the thalamic nuclei?

Thalamic medullary laminae.

The internal medullary lamina - between the medial and ventrolateral thalamic nuclei

The external medullary lamina - between the lateral and reticular nuclei.


Which thalamic nuclei comprise the anterior nuclear group?

1. Anteroventral
2. Anterodorsal

3. Anteromedial


Features of the anterior thalamic nuclear group

They receive input from the mammillothalamic tract and fornix. Project fibers to the cingulate gyrus via the anterior limb of the IC.
These nuclei are involved in the regulation of visceral function.


Features of the mediodorsal group of thalamic nuclei

Lies between the IML and periventricular gray. Controls affective behavior and is disconnected in prefrontal lobotomies.
Receives input from the amygdala, orbitofrontal and temporal cortex. Projects to the frontal association cortex or prefrontal area and has reciprocal connections to the FEF.

Lesions here cause Korsakoff's psychosis.


What are the nuclei which comprise the intralaminar nuclear group?

1. Centromedial
2. Parafascicular

3. Rostral intralaminar


General features of the intralaminal group of thalamic nuclei 

They receive input from the reticular activating system and output to the cortex diffusely.

It functions as a thalamic pacemaker for controlling electrical activities and wakefulness.


Input and output of the centromedial nuclei

Input: Area 4 - primary motor cortex
Output: Putamen


Input and output of the parafascicular nucleus

Input: area 6
Output: Caudate


Input and output of the rostral intralaminar nucleus

Input: Reticular formation
Output: Diffuse cortical areas


What are the midline thalamic nuclei and what structures do they output to?

The periventricular gray and the massa intermedia. They both output to the amygdala and the cingulate gyrus. 


Output of the lateral dorsal thalamic nuclei

Cingulum and the supralimbic parietal lobe


Input and output of the lateral posterior thalamic nuclei

Input: Parietal lobe
Output: Areas 5 and 7


Pulvinar nucleus: Input and role.  

1. Gets input from the superior colliculus, reciprocal connections with the occipital, temporal and parietal cortex.

It is involved with extrageniculate visual pathways to secondary visual areas.


Three key visuotopic thalamocortical pathways

1. LGB --> area 17
2. Inferior pulvinar --> area 18

3. Lateral pulvinar --> area 19


What are the three nuclei that comprise the dorsal tier of the lateral nuclear group?

1. LD
2. LP

3. Pulvinar


What are the nuclei which comprise the ventral tier of the lateral nuclear group

1. VA
2. VL

3. VP - VPLo, VPLc, VPM, VPI

They are all relay nuclei


Role of the VA nucleus

It recruits cortical response, programming of movements from the BG.
The mammillothalamic tracts also pass through the VA


What is the metathalamus, its inputs and outputs

Metathalamus = medial and lateral geniculate bodies.
Receives input from the GP, SN, areas 6 and 8.

Sends output to the frontal cortex and intralaminar nuclei.


VLo - input and output

Input: GP
Output - premotor and supplementary motor cortex.


VLc: Input and output.

Input: Contralateral deep cerebellar nuclei and the red nuclei.

It also has reciprocal connections with area 4.


VPLo: Input and output.

Input: Contralateral deep cerebellar nuclei

Output: Motor cortex


VPLc: Input and output.

Input: Medial Lemniscus
Output: Sensory cortex


VPM: Input and output.

Input: Contralateral spinal cord, principal sensory nucleus of CN5 and ipsilateral dorsal trigeminal tract.

Output: Sensory cortex to face - bilateral VPM representation.

Taste fibers from the nucleus solitarius--> central tegmental tract uncrossed to the VPMc --> parietal operculum area 43.


VPI output

Ipsilateral S2. 


Features of the medial geniculate body

It is an auditory relay nucleus which is located in the caudal ventral thalamus.
Input: inferior colliculus via the inferior brachium

Also has reciprocal connections with the primary auditory cortex, spatial representation of tonal frequency. Tonotopic, high frequency sounds lie medially.