export_diencephalon Flashcards
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
- Thalamus
- Epithalamus - 4 subcomponents
- Hypothalamus
- Subthalamus
- Metathalamus - medial and lateral geniculate bodies.
What are the 4 components of the epithalamus
- Habenular Trigone
- Pineal Gland
- Stria Medullaris
- Roof of the third ventricle.
What are the functions of the thalamus
- Integrate, correlate, and relay motor, sensory, visual, limbic and conscious systems.
- Interpretation and conscious perception of pain
- 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?
- Anteroventral
- Anterodorsal
- 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?
- Centromedial
- Parafascicular
- 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.
- 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
- LGB –> area 17
- Inferior pulvinar –> area 18
- Lateral pulvinar –> area 19
What are the three nuclei that comprise the dorsal tier of the lateral nuclear group?
- LD
- LP
- Pulvinar
What are the nuclei which comprise the ventral tier of the lateral nuclear group
- VA
- VL
- 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.
Features of the lateral geniculate body
Visual relay nucleus, located rostral and lateral to the MGB and ventral to the pulvinar. It has 6 layers: 1+2=magnocellular. 3-6: parvicellular.
Input: retinal ganglion cells
Retina sends crossed fibers from the contralateral eye to layers 1,4,6. Uncrossed fibers go to layers - 2,3,5. Lower retina –> lateral geniculate –> lower calcarine cortex.
It has reciprocal connections with the calcarine cortex and the pulvinar.
Input and output of the posterior thalamic nuclear complex
Input: Spinothalamic tract, ML and S1
Output: Retroinsular cortex and posterior auditory cortex.
Features of the thalamic reticular nuclei
It is located between the IC and the external medullary lamina. It forms a shell over the dorsal thalamus.
It samples passing fibers and gates the activity of the thalamus but does not have any cortical projections.
What are the neurotransmitters involved in thalamic signaling
Input - aspartate and glutamate (excitatory) from the cortex and the deep cerebellar nuclei.
Output - GABA
What are the thalamic radiations?
Portions of the IC with reciprocal connections between the thalamus and the cortex.
What are the four thalamic peduncles
- Anterior - fibers from the medial and anterior thalamic nuclei to the frontal lobe
- Superior - connections –> to the precentral and postcentral gyri
- Posterior - Connections –> visual to calcarine cortex.
- Inferior - Connections –> auditory to Heschl’s gyri.
What is the habenulum
A part of the epithalamus involved in smell and emotional pathways.
Where does the habenulum receive its input from:
- GP –> lateral habenulum
- Septal nuclei, lateral pre-optic region and anterior thalamic nuclei to the medial habenulum via the stria medullaris.
- Lateral hypothalamus, substantia innominata, midbrain raphe nucleus and superior cervical ganglia also send inputs to the habenulum
Output of the habenulum
Via the fasciculus retroflexus to the interpedunculular nuclei and midbrain raphe nuclei —> to the reticular, hypothalamic and preganglionic nuclei.
Borders of the pineal gland
It is attached to the pineal gland by the posterior commissure ventrally and the habenular commissure dorsally.
Basic functions of the pineal gland
- Secretion of 5HT from pinealocytes.
- Secretion of norepi from terminating sympathetic neurons.
- Secretes melatonin - levels fluctuate with light, maximal in the dark. Oversecretion leads to delayed puberty. Hyposecretion causes precocious puberty.
Sympathetic innervation to the pineal gland
Sympathetic innervation inhibits the pineal gland.
Light hits the retina –> suprachiasmatic nucleus of the hypothalamus–> dorsal longitudinal fasciculus –> upper intermediolateral cell column of superior colliculi –> pineal inhibition.
Which nucleus relays light/retinal input to the pineal gland
Hypothalamic suprachiasmatic nuclei.
Bilateral lesions to this region abolishes circadian rhythms of eating and drinking.
Fibers and blood supply of the anterior limb of the internal capsule
Fibers: Anterior thalamic radiation, prefrontal corticopontine tract.
Blood Supply: RAH (ACA), Lenticulostriates (MCA)
Fibers and blood supply of the genu of the internal capsule
- Corticobulbar tract
- Corticoreticular tract
Perforators off of the ICA.
Lenticulostriates (MCA)
Fibers and blood supply of the posterior limb of the internal capsule
Fibers:
Superior thalamic radiation, frontopontine tract, corticospinal/tectal/rubral and reticular tracts.
Motor fibers lie anterior to the sensory fibers.
Supplied by the lenticulostriate arteries, Anterior ChA, and the PcommA.
Fibers and blood supply of the retrolenticular limb of the internal capsule
Posterior thalamic radiations - visual.
Parietal and occipital corticopontine fibers.
AChA
Fibers and blood supply of the sublenticular limb of the internal capsule
Inferior thalamic radiations - auditory.
Temporal and parietooccipital corticopontine fibers.
AChA
