Cerebral Cortex (23 A)

Question 0

What are the three layers of cortex based on histology?

Answer 0

Allocortex, isocortex, mesocortex

Question 1

The cortical surface is lissencephalic, or smooth, until ____ months gestation.

Answer 1

6 months

Is gyrencephalic by birth

Question 2

What type of cortex based on evolutionary origin is the same as isocortex?

Answer 2

Neocortex

Question 3

How many layers does isocortex (neocortex) have?

Answer 3

Six layers

Question 4

What is layer I of neocortex called?

Answer 4

Molecular layer - poorly cellular and only has GABAergic neurons

Question 5

What are layers II and III of the cortex collectively known as?

Answer 5

Superficial pyramidal cell layer

Question 6

What is layer IV called?

Answer 6

Granular layer

Question 7

What is layer V of cortex called?

Answer 7

Deep pyramidal cell layer

Question 8

What is layer VI, the deepest layer of cells in cortex known as?

Answer 8

Polymorphic layer

Question 9

Layers I-III are collectively known as? Layers V and VI?

Answer 9

Supragranular layer

Subgranular layer

Question 10

Cortical cells are pyramidal or non pyramidal… Which are projection neurons and which are interneurons?

Answer 10

Pyramidal –> are projection neurons and usually glutaminergic

Nonpyramidal–> interneurons, most are usually GABAergic

Question 11

Where does most of the do infant input to the cortex come from?

Answer 11

From other cortical neurons

Question 12

From what two sources does most of the extrinsic input to the cortex come from?

Answer 12

Thalamus

Widely-projecting brainstem nuclei

Question 13

What Re four widely projecting brainstem nuclei?

Answer 13

1. Locus ceruleus (NE)
2. Raphe nuclei (serotonin)
3. Ventral tegmental area (DE)
4. Basal forebrain nuclei (Ach)

Question 14

What is specific input? To which layer in the cortex is it projected?

Answer 14

From thalamic nuclei that project to a single cortical area and usually concerns a single modality
*to layer IV (granular layer)
Examples: VL to motor cortex, VPL to somatosensory cortex, lateral geniculate for visual cortex, medial geniculate to auditory cortex

Question 15

What structures in General does non-specific input to cortex come from? To what layer of cortex is this info projected to?

Answer 15

Specific thalamic nuclei that integrate info from a variety of sources (ex. Intralaminar and midline thalamic nuclei)
* goes to layer I (local interneurons and apical tuft of pyramidal cells apical dendrites)

Question 16

Which two layers are responsible mainly for cortico-cortical projections?

Answer 16

II and II (collectively the superficial pyramidal cell layer)
Include association fibers that project ipsilaterally and Callosal projections that cross to equivalent layers in contralateral cortex

Question 17

Pyramidal cells in which layer are the main output neurons of the cortex?

Answer 17

Layer V (deep pyramidal cell layer)

Question 18

Where do layer VI pyramidal cells (polymorphic layer) cells generally project?

Answer 18

To the thalamus

Question 19

What neuronal feedback loop is the basis for the oscillation seen on an EEG

Answer 19

Tracts going from cortex to thalamus and back–> thalamocortical rhythms

• important in regulation of the sleep-wake cycle, consciousness, and also altered in several pathological conditions

Question 20

Cells from which part of layer V tend to be thinner, with a less robust apical dendrite and project to contralateral cortex and subcortical telencephalon targets like the striatum?

Answer 20

Superficial layer of V (deep pyramidal layer)

Question 21

Where do cells in the deep layer of V tend to project in general?

Answer 21

Beyond telencephalon–> Spinal cord, tectum, pons, brain stem

Question 22

Why are inhibitory neurons within the cortex very important?

Answer 22

Most input to cortical cells is from other cortical cells, 80% of which are pyramidal, excitatory cells. Inhibitory interneurons keep it from being an unstable network

Question 23

Where do chandelier cells (interneurons) connect to the pyramidal cells?

Answer 23

At the axon initial segment–> allows for powerful inhibition and thus control over the output to the local circuit; local circuits are numerous in the cortex

Question 24

What is the significance of basket cells’ synapses on the soma of pyramidal cells?

Answer 24

Allows inhibitory control at the final summation point for synaptic input from the whole dendritic tree (in the soma)

Question 25

Where do bipolar (double bouquet) cells synapse onto pyramidal cells?

Answer 25

On the dendrites, so allows for fine-tuned control on local signals in the dendrites

Question 26

What is the basic functional unit for the cortex?

Answer 26

Macrocolumn–> ~10,000 cells, arranged in vertical columns all allied together for a similar function

Question 27

What is the path of information through the cortex(in a column) in terms of layers?

Answer 27

Excitatory input to IV (via thalamus, etc)–> II/III (excitatory)–> V/VI (excitatory)–> layer V projects to other columns, to other areas of cortex, or subcortically

• anatomical layout along with lateral inhibition by interneurons keep the excitatory input within the confines of the vertical column

Question 28

What three ways can cortical areas be defined?

Answer 28

1. Histologically
2. Via connection with other structures
3. By function

Question 29

What is a heterotypic cortex? Example?

Answer 29

Areas in which the 6 layers of the brain are not so obvious, due to individual differences in the layers in that part of cortex

• primary motor cortex–> has almost no granular layer, known as agranular cortex; has a large layer V, befitting its role in sending lots of output to control movement
• primary sensory cortex–> well defined granular layer, known as granular cortex (lots of input here from thalamus, so this layer, which relieves this output is larger)

Question 30

What is homotypic cortex? Example?

Answer 30

6 layers are normal and easy to tell apart –> association cortex

Question 31

What Brodmann area is the primary visual cortex?

Answer 31

Area 17

Question 32

What two Brodmanns areas contain the primary auditory cortex

Answer 32

Areas 41 and 42

Question 33

What goes on in the primary cortical area for a given sensory modality ( like lateral geniculate nucleus for vision)? What happens of these are damaged?

Answer 33

Initial processing of the modality; loss leads to loss of perception of that modality

Question 34

What happens in unimodal association areas?

Answer 34

Different aspects and sub modalities of a stimulus are added

Question 35

What occurs in hereromodal association areas?

Answer 35

Modalities of a stimulus are combined

• in the uni- and hetermodal association areas the individual types of inputs from the periphery are combined into a total picture

Question 36

What is most of the cortex involved with?

Answer 36

Association– few areas are primary motor or primary sensory