intro to anatomical organization of cerebral cortex objectives - michael

Question 1

1) Describe the anatomical layout of the cerebral cortex and it’s laminar structure

Answer 1

a) Sulci: inward folds seen on the surface of the human cortex
b) Gyri: exposed surfaces between sulci
c) Primary cortices: receive specific input of a given modality or produce limb or eye movements
d) Association cortices: integrate inputs from multiple primary cortical areas
e) Neocortex: most of the cerebral cortex; 6 layers
f) Allocortex: some phylogenetically older areas of cortex; 3 layers
i) Piriform lobe: specialized for olfaction
ii) Archicortex: includes the hippocampus, involved in encoding declarative memory and spatial functions
2) Name and characterize the major neuron types in each cortical layer

Question 2

a) Sulci:

Answer 2

inward folds seen on the surface of the human cortex

Question 3

b) Gyri:

Answer 3

exposed surfaces between sulci

Question 4

c) Primary cortices:

Answer 4

receive specific input of a given modality or produce limb or eye movements

Question 5

d) Association cortices:

Answer 5

integrate inputs from multiple primary cortical areas

Question 6

e) Neocortex:

Answer 6

a) most of the cerebral cortex; 6 layers

Question 7

f) Allocortex:

Answer 7

some phylogenetically older areas of cortex; 3 layers

i) Piriform lobe: specialized for olfaction
ii) Archicortex: includes the hippocampus, involved in encoding declarative memory and spatial functions

Question 8

i) Piriform lobe:

Answer 8

part of allocortex

: specialized for olfaction

Question 9

ii) Archicortex:

Answer 9

part of allocortex

includes the hippocampus, involved in encoding declarative memory and spatial functions

Question 10

2) Name and characterize the major neuron types in each cortical layer

Answer 10

a) Neocortex layers numbered superficial to deep
b) Supragranular layers (1 to 3): origin and termination of intracortical connections, either associational (with other areas of the same hemisphere) or commissural (connections to the opposite hemisphere through the corpus callosum)
i) Layer 1 (molecular layer): contains few, mostly inhibitory (GABAergic) neurons
ii) Layer 2/3 (external granular layer/external pyramidal layer)
c) Internal granular layer (4): spiny stellate cells receive direct thalamocortical input; motor areas are sometimes to referred to as “agranular” layers (no layer 4)
d) Infragranular layers (5 and 6): connect cerebral cortex with subcortical regions, most developed in motor areas
i) Layer 5 (internal pyramidal layer): efferent projections to basal ganglia, brain stem, spinal cord, thalamus
ii) Layer 6 (multiform or fusiform layer): projects primarily to the thalamus
e) Spiny stellate cells (excitatory; glutamate): Prominent in layer 4, integrate thalamocortical input with ongoing cortical recurrent input; look like stars with dendrites radiation in all directions
f) Pyramidal neurons (excitatory; glutamate): Main excitatory cell type in layers 2/3, 5, 6. Have a prominent “apical” dendrite that often extends to layer 1 and shorter “basal” dendrites that branch laterally from the cell body. Has a thin axon that contacts nearby neurons as well as other cortical areas or the brain stem or the spinal cord
g) Nonpyramidal GABAergic interneurons (inhibitory; GABA): dampens excitatory activity through feed-forward inhibition (excitation of a neuron leads to inhibition of nearby neurons) and feedback inhibition (inhibitory cells reciprocally connected with excitatory cells)

Question 11

Supragranular layers (1 to 3):

Answer 11

origin and termination of intracortical connections, either associational (with other areas of the same hemisphere) or commissural (connections to the opposite hemisphere through the corpus callosum)

i) Layer 1 (molecular layer): contains few, mostly inhibitory (GABAergic) neurons
ii) Layer 2/3 (external granular layer/external pyramidal layer)

Question 12

i) Layer 1 (molecular layer):

Answer 12

contains few, mostly inhibitory (GABAergic) neurons

Question 13

c) Internal granular layer (4):

Answer 13

spiny stellate cells receive direct thalamocortical input; motor areas are sometimes to referred to as “agranular” layers (no layer 4)

Question 14

d) Infragranular layers (5 and 6):

Answer 14

connect cerebral cortex with subcortical regions, most developed in motor areas

i) Layer 5 (internal pyramidal layer): efferent projections to basal ganglia, brain stem, spinal cord, thalamus
ii) Layer 6 (multiform or fusiform layer): projects primarily to the thalamus

Question 15

Layer 5 (internal pyramidal layer):

Answer 15

efferent projections to basal ganglia, brain stem, spinal cord, thalamus

Question 16

ii) Layer 6 (multiform or fusiform layer):

Answer 16

projects primarily to the thalamus

Question 17

e) Spiny stellate cells (excitatory; glutamate):

Answer 17

Prominent in layer 4, integrate thalamocortical input with ongoing cortical recurrent input; look like stars with dendrites radiation in all directions

Question 18

f) Pyramidal neurons (excitatory; glutamate):

Answer 18

Main excitatory cell type in layers 2/3, 5, 6. Have a prominent “apical” dendrite that often extends to layer 1 and shorter “basal” dendrites that branch laterally from the cell body. Has a thin axon that contacts nearby neurons as well as other cortical areas or the brain stem or the spinal cord

Question 19

g) Nonpyramidal GABAergic interneurons (inhibitory; GABA):

Answer 19

dampens excitatory activity through feed-forward inhibition (excitation of a neuron leads to inhibition of nearby neurons) and feedback inhibition (inhibitory cells reciprocally connected with excitatory cells)

Question 20

3) Outline the basic connectivity of the “cortical circuit”

Answer 20

a) Thalamic projections to a primary sensory area arrive onto spiny stellate cells in layer 4
b) This excitation is relayed to pyramidal neurons in the supragranular layers (layers 2/3)
c) These pyramidal neurons project to each other as well as to pyramidal neurons in the infragranular layers (layers 5 and 6)
d) Infragranular layer pyramidal neurons project to subcortical areas like the brain stem and thalamus

Question 21

4) Describe how pyramidal neurons allow the cortex to integrate “top-down” and “bottom-up” information

Answer 21

a) The apical dendrite of pyramidal neurons in layer 1 receive “top-down” input from higher cortical areas and non-specific thalamic nuclei
b) The basal dendrites of pyramidal neurons receive “bottom-up” input from lower cortical areas and from sensory nuclei of the thalamus
c) Thus, the apical dendrites signal what is “expected to happen” and the basal dendrites signal what is “actually happening.”
d) Apical dendrites on their own rarely initiate action potentials on their own, and basal dendrites generate single action potentials, but when both sets of dendrites are activated simultaneously, a burst of activity is observed.
e) These bursts convey meaning (a “hit”)
f) Brief note on excitotoxicity: excessive excitation can injure or kill neurons; can result from hypoxia, ischemia, traumatic, hypoglycemia, seizures, genetic mutations