Thalamus and Cortex I

Question 1

What is the structure of most of the cerebral cortex? What about the rest of the cortex?

Answer 1

6 layered neo-cortex

rest: 3 layers- olfactory cortex and hippocampus only.

Question 2

What are the shapes of the somata in the 6 layers of neocortex?

Answer 2

layers I, II, IV are granular
layers III and V are pyramidal
layer VI is fusiform

Question 3

Where do axonal proejctions go in the first 3 layers of neocortex?

Answer 3

layer I: project horizontally
layer II: project to deeper layers in the same cortical area
layer III” to other cortical areas or to the same area in the opposite hemisphere

Question 4

Where do axons project in layer IV, V, and VI of the neocortex?

Answer 4

IV recieves the bulk of input from thalamus
V: project to subcortical centers
VI: other areas of cortex and subcortical centers

Question 5

What are the structural charachteristics of the koniocortex? Where is if found?

Answer 5

thick layer IV, little layer V (lots of thalamic input)

primary somatosensory, visual, and auditory area

Question 6

What are the structural characteristics of the agranular/dysgranular cortex? Where is it found?

Answer 6

lots of layer V, little 4. found in primary motor cortex and other motor areas (lots of subcortical output

Question 7

What are the characteristics of of the isocortex?

Answer 7

moderate layers IV and V- association cortex

Question 8

What is the basis of other variation in the cortex?

Answer 8

cytoarchetectonics (neuron shape)
and myeloarchitecture (patterns of myelinated fibers)

Question 9

What is the Brodman area for the primary motor cortex?

Answer 9

Area 4

Question 10

What are the Brodman areas for the primary somatosensory cortex?

Answer 10

3,1,2

Question 11

What is the Brodman area for the primary visual cortex?

Answer 11

17

Question 12

What is the Brodman area for the primary auditory area?

Answer 12

41, 42

Question 13

Where does spacial thinking localize? What is the syndrome of loss

Answer 13

right parietal lobe. syndrome of loss is neglect.

Question 14

Where does visual recognition localize and what is the syndrome of loss?

Answer 14

temporal lobe. prospagnosia

Question 15

ventro postero medial:b nucleus, input, output, system

Answer 15

trigeminal sensory nuclei

Question 16

Where are corticospinal axons found within the cerebral peduncle? What happens to these axons in the pons?

Answer 16

middle third of the cerebral peduncle. in the ponse, axons of the peduncle become intermixed with pontine nuclear neurons

Question 17

What happens in terms of synapses in the spinal cord for most corticospinal tracts?

Answer 17

most synapse on interneurons in intermediate zone and ventral horn
some synapse directly on motor neurons
this monosynaptic connection is most common in the anterior bank of the central sulcus in cortical hand and foot representations
more anterior parts of the corticospinal tract usually have interneurons and control movement of more proximal limbs and axial muscles.
some of these axons cross back (double decussation)- thus there is relative preservation of movement after unilateral damage to the cortex

Question 18

What are the important non-corticospinal tracts that influence movement?

Answer 18

rubrospinal tract: motor cortex neurons synapse on the red nucleus
medial reticular formation of pons and medulla. medial reticular formation gets info form cortical motor areas

Question 19

What does somatotopic mean?

Answer 19

organization of the primary motor cortex according to major body parts.

Question 20

How are distal vs proximal parts represented within the primary motor cortex? (example: legs is more medial than arms, which is more medial than face)

Answer 20

distal is more caudal (anterior bank of central sulcus). also caudal is lips and tongue
proximal is more rostral

Question 21

Why isn’t there an exact correlation between location of lesion and exact deficits? 4 reasons

Answer 21

1. Outputs from a wide cortical region converge onto the motorneuron pool for a single muscle
2. Outputs from a single neuron diverge to influence many other neurons.
3. Collaterals of neurons in layers II, III, and V extend horizontally in the cortex, which connects much of the body part representation
4. motor cortical activity during movement of even a single small body part is widely distributed

Question 22

What should I know about cortex reorganization?

Answer 22

It is possible! It is important for acquiring new skills (typing, dancing, piano), and also for regain of function after a lesion. Think of monkeys with a small lesion- new areas start to evoke digit movements if you force the monkey to practice using the hand

Question 23

Why do lesions of the cortex or corticospinal tract produce weakness?

Answer 23

frequency of M1 firing correlates with the force of movement, direction of movement, and position of the joint/body part. Most neurons discharge at different rates for different values of a given parameter. Actual motion is the result of the combined efforts of many neurons. If you destroy these neurons or cut off communication, voluntary movements of the desired direction and force can’t be generated

Question 24

What are some pre-motor regions? How are they different/what do they control? Include evidence from experiments.

Answer 24

supplementary motor cortex vs. ventral premotor cortex.
supplementary motor cortex helps you initiate internally remembered/initiated movements
ventral premotor cortex helps you make movements in response to external cues.
monkey experiments with buttons: monkeys hit buttons that light up (primary motor cortex and ventral premotor cortex/PMv). Then the monkeys do that sequence of buttons by memory (primary motor cortex and supplementary motor cortex)

Question 25

What is one interesting thing that PMv neurons do?

Answer 25

“mirror neurons”

discharge when the monkey watches another primate perform a specific motion, or when the monkey does that motion himself. not seen if human uses a tool to pick something up, or if the monkey picks up a large object.