Lecture 14: Thalamus/Cortex 1

Question 1

What does thalamus mean?

Answer 1

It is Greek for “inner chamber”

Question 2

Where is the thalamus located?

Answer 2

Below lateral ventricle
Lateral to the third ventricle
Medial to the internal capsule

Question 3

What is a thalamus?

Answer 3

It is a conglomerate of nuclei

So it is GRAY MATTER

Question 4

What is the internal medullary lamina?

Answer 4

Anatomic marker that divides thalamus from medial and lateral and separates the anterior group of nuclei
A thin, curved sheet of myelinated fibers

Question 5

What are the four types of nuclei anatomically?

Answer 5

i. lateral
ii. medial
iii. anterior
iv. intralaminar

Question 6

Reticular nucleus (nucleus reticularis

Answer 6

special nucleus of thalamus that consists of a thing sheet of elongated cells covering the lateral and dorsal aspects of thalamus

Question 7

What are the three types of input-outputs?

Answer 7

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

Question 8

What are the sensory relays of the thalamus?

Answer 8

a. auditory  medial geniculate nucleus (MGN)  auditory cortex
b. visual  lateral geniculate (LG)  visual cortex
c. Somatosensory  Ventrobasal (VPM and VPL)  somatosensory cortex

Question 9

What are the motor relays of the thalamus?

Answer 9

Basal ganglia and cerebellum  ventral anterior and ventral lateral  M1

Question 10

What are the limbic relays of the thalamus?

Answer 10

Mamillary bodies  anterior nucleus  cingulate gyrus (part of Papez circuit)

Question 11

What are the two association nuclei?

Answer 11

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

Question 12

Where are the non-specific nuclei located?

Answer 12

In the internal medullary lamina…so intralaminar nuclei

Question 13

What is function of intralaminar nuclei?

Answer 13

Receive inputs from basal ganglia and project BACK to the basal ganglia
-all areas receive non-specific input from intralaminar nuclei

Question 14

What are the two main cell types in the thalamus and how are they interconnected

Answer 14

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

Question 15

What is the concept of reciprocal excitation in the thalamus?

Answer 15

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

Question 16

The loop from TC cell to cortex and cortex back to TC and RE (and RE to TC) is the loop responsible for what?

Answer 16

Circuit for consciousness = loop between cortex and thalamus

Question 17

What is the significance of reticular nucleus?

Answer 17

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

Question 18

Do thalamocortical cells connect with other thalamocortical cells?

Answer 18

No

Question 19

What are the six layers of cortex?

Answer 19

i. Molecular layer
ii. External granular layer
iii. external pyramidal layer
iv. internal granular layer
v. internal pyramidal layer
vi. multiform layer

Question 20

What do the cortical layers of the motor cortex look like?

Answer 20

Large pyramidal cells and lack of stellate (granule) cells

Known as Agranular

Question 21

What do cortical layers of the sensory areas look like?

Answer 21

Few pyramidal cells, dominated by small 9cranular) cells

Known as granular cortex

Question 22

Is the cortex vertically or horizontally organized?

Answer 22

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

Question 23

What are the two types of excitatory cells in the cortex?

Answer 23

i. granular cells

ii. pyramidal cells

Question 24

Granular cells characteristics

Answer 24

• excitatory
• in layer 4
• receive input from thalamus and send output to layers 2 and 3
• most prominent in sensory areas
• spiny stellate

Question 25

Pyramidal cells:

Answer 25

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

Question 26

What is the local circuit in the cerebral cortex?

Answer 26

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

Question 27

What types of cells send shit out of cortex?

Answer 27

Pyramidal cells