Lecture 14: Thalamus/Cortex 1 Flashcards
What does thalamus mean?
It is Greek for “inner chamber”
Where is the thalamus located?
Below lateral ventricle
Lateral to the third ventricle
Medial to the internal capsule
What is a thalamus?
It is a conglomerate of nuclei
So it is GRAY MATTER
What is the internal medullary lamina?
Anatomic marker that divides thalamus from medial and lateral and separates the anterior group of nuclei
A thin, curved sheet of myelinated fibers
What are the four types of nuclei anatomically?
i. lateral
ii. medial
iii. anterior
iv. intralaminar
Reticular nucleus (nucleus reticularis
special nucleus of thalamus that consists of a thing sheet of elongated cells covering the lateral and dorsal aspects of thalamus
What are the three types of input-outputs?
i. Relay (sensory, motor and limbic): relays shit from outside of cortex to the cortex
ii. Association (a connecting hub)
iii. Non-specific
- send nonspecific projections to widespread areas of the cerebral cortex and produces general changes in cortical function and brain state
What are the sensory relays of the thalamus?
a. auditory medial geniculate nucleus (MGN) auditory cortex
b. visual lateral geniculate (LG) visual cortex
c. Somatosensory Ventrobasal (VPM and VPL) somatosensory cortex
What are the motor relays of the thalamus?
Basal ganglia and cerebellum ventral anterior and ventral lateral M1
What are the limbic relays of the thalamus?
Mamillary bodies anterior nucleus cingulate gyrus (part of Papez circuit)
What are the two association nuclei?
i. Pulvinar = gets input and sends output to the same territory (parietal-occipital-temporal or POT association cortex)
ii. mediodorsal nucleus (MD or dorsomedial) = sends shit to the prefrontal cortex
Where are the non-specific nuclei located?
In the internal medullary lamina…so intralaminar nuclei
What is function of intralaminar nuclei?
Receive inputs from basal ganglia and project BACK to the basal ganglia
-all areas receive non-specific input from intralaminar nuclei
What are the two main cell types in the thalamus and how are they interconnected
i. Thalamocortical cell: Glutamatergic excitatory neurons
- TC is excitatory because it releases glutamate
ii. nucleus reticularis (RE): release GABA and inhibit shit
- only neurons in thalamus that has no neurons that extends to the cortex
What is the concept of reciprocal excitation in the thalamus?
All relay nuclei have a RECIPROCAL excitatory from the cortex
Translation: TC cells excite the cortex and areas of the cortex come back and excite the thalamus
-no one knows what or why the cortex control in thalamic function
The loop from TC cell to cortex and cortex back to TC and RE (and RE to TC) is the loop responsible for what?
Circuit for consciousness = loop between cortex and thalamus
What is the significance of reticular nucleus?
It is the only nucleus of the thalamus that has no projections outside of the thalamus and will be studied as local circuits
-sends inhibition to TC cells
Do thalamocortical cells connect with other thalamocortical cells?
No
What are the six layers of cortex?
i. Molecular layer
ii. External granular layer
iii. external pyramidal layer
iv. internal granular layer
v. internal pyramidal layer
vi. multiform layer
What do the cortical layers of the motor cortex look like?
Large pyramidal cells and lack of stellate (granule) cells
Known as Agranular
What do cortical layers of the sensory areas look like?
Few pyramidal cells, dominated by small 9cranular) cells
Known as granular cortex
Is the cortex vertically or horizontally organized?
There is a vertical division in the cortex
- this was done by electrode penetration - all cells in one vertical tract have some same property - allows for massive parallel processing
What are the two types of excitatory cells in the cortex?
i. granular cells
ii. pyramidal cells
Granular cells characteristics
- excitatory
- in layer 4
- receive input from thalamus and send output to layers 2 and 3
- most prominent in sensory areas
- spiny stellate
Pyramidal cells:
Excitatory and located everywhere except for layer 1
- apical dendrite that runs towards the pia
- make up 80% of all the cells in the cerebral cortex
- heavily interconnected
What is the local circuit in the cerebral cortex?
a. thalamocortical cells sends signals from thalamus to both excitatory and/or inhibitory cells of Layer 4 of cortex
b. excitatory cells of Layer 4 sends signals to excitatory/inhibitory cells in Layers 2/3
c. Layers 2/3 can both send signals to other cells in the same layer or send signals to excitatory/inhibitory layers 5/6
d. Layers 5/6 can both send signals to other cells in same layer and also out of cortex to its effector function
What types of cells send shit out of cortex?
Pyramidal cells
