Thalamus and Cortex I Flashcards
What is the structure of most of the cerebral cortex? What about the rest of the cortex?
6 layered neo-cortex
rest: 3 layers- olfactory cortex and hippocampus only.
What are the shapes of the somata in the 6 layers of neocortex?
layers I, II, IV are granular
layers III and V are pyramidal
layer VI is fusiform
Where do axonal proejctions go in the first 3 layers of neocortex?
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
Where do axons project in layer IV, V, and VI of the neocortex?
IV recieves the bulk of input from thalamus
V: project to subcortical centers
VI: other areas of cortex and subcortical centers
What are the structural charachteristics of the koniocortex? Where is if found?
thick layer IV, little layer V (lots of thalamic input)
primary somatosensory, visual, and auditory area
What are the structural characteristics of the agranular/dysgranular cortex? Where is it found?
lots of layer V, little 4. found in primary motor cortex and other motor areas (lots of subcortical output
What are the characteristics of of the isocortex?
moderate layers IV and V- association cortex
What is the basis of other variation in the cortex?
cytoarchetectonics (neuron shape) and myeloarchitecture (patterns of myelinated fibers)
What is the Brodman area for the primary motor cortex?
Area 4
What are the Brodman areas for the primary somatosensory cortex?
3,1,2
What is the Brodman area for the primary visual cortex?
17
What is the Brodman area for the primary auditory area?
41, 42
Where does spacial thinking localize? What is the syndrome of loss
right parietal lobe. syndrome of loss is neglect.
Where does visual recognition localize and what is the syndrome of loss?
temporal lobe. prospagnosia
ventro postero medial:b nucleus, input, output, system
trigeminal sensory nuclei
Where are corticospinal axons found within the cerebral peduncle? What happens to these axons in the pons?
middle third of the cerebral peduncle. in the ponse, axons of the peduncle become intermixed with pontine nuclear neurons
What happens in terms of synapses in the spinal cord for most corticospinal tracts?
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
What are the important non-corticospinal tracts that influence movement?
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
What does somatotopic mean?
organization of the primary motor cortex according to major body parts.
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)
distal is more caudal (anterior bank of central sulcus). also caudal is lips and tongue
proximal is more rostral
Why isn’t there an exact correlation between location of lesion and exact deficits? 4 reasons
- Outputs from a wide cortical region converge onto the motorneuron pool for a single muscle
- Outputs from a single neuron diverge to influence many other neurons.
- Collaterals of neurons in layers II, III, and V extend horizontally in the cortex, which connects much of the body part representation
- motor cortical activity during movement of even a single small body part is widely distributed
What should I know about cortex reorganization?
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
Why do lesions of the cortex or corticospinal tract produce weakness?
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
What are some pre-motor regions? How are they different/what do they control? Include evidence from experiments.
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)
What is one interesting thing that PMv neurons do?
“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.
