Cerebral Cortex (23 A) Flashcards
What are the three layers of cortex based on histology?
Allocortex, isocortex, mesocortex
The cortical surface is lissencephalic, or smooth, until ____ months gestation.
6 months
Is gyrencephalic by birth
What type of cortex based on evolutionary origin is the same as isocortex?
Neocortex
How many layers does isocortex (neocortex) have?
Six layers
What is layer I of neocortex called?
Molecular layer - poorly cellular and only has GABAergic neurons
What are layers II and III of the cortex collectively known as?
Superficial pyramidal cell layer
What is layer IV called?
Granular layer
What is layer V of cortex called?
Deep pyramidal cell layer
What is layer VI, the deepest layer of cells in cortex known as?
Polymorphic layer
Layers I-III are collectively known as? Layers V and VI?
Supragranular layer
Subgranular layer
Cortical cells are pyramidal or non pyramidal… Which are projection neurons and which are interneurons?
Pyramidal –> are projection neurons and usually glutaminergic
Nonpyramidal–> interneurons, most are usually GABAergic
Where does most of the do infant input to the cortex come from?
From other cortical neurons
From what two sources does most of the extrinsic input to the cortex come from?
Thalamus
Widely-projecting brainstem nuclei
What Re four widely projecting brainstem nuclei?
- Locus ceruleus (NE)
- Raphe nuclei (serotonin)
- Ventral tegmental area (DE)
- Basal forebrain nuclei (Ach)
What is specific input? To which layer in the cortex is it projected?
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
What structures in General does non-specific input to cortex come from? To what layer of cortex is this info projected to?
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)
Which two layers are responsible mainly for cortico-cortical projections?
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
Pyramidal cells in which layer are the main output neurons of the cortex?
Layer V (deep pyramidal cell layer)
Where do layer VI pyramidal cells (polymorphic layer) cells generally project?
To the thalamus
What neuronal feedback loop is the basis for the oscillation seen on an EEG
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
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?
Superficial layer of V (deep pyramidal layer)
Where do cells in the deep layer of V tend to project in general?
Beyond telencephalon–> Spinal cord, tectum, pons, brain stem
Why are inhibitory neurons within the cortex very important?
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
Where do chandelier cells (interneurons) connect to the pyramidal cells?
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
What is the significance of basket cells’ synapses on the soma of pyramidal cells?
Allows inhibitory control at the final summation point for synaptic input from the whole dendritic tree (in the soma)
Where do bipolar (double bouquet) cells synapse onto pyramidal cells?
On the dendrites, so allows for fine-tuned control on local signals in the dendrites
What is the basic functional unit for the cortex?
Macrocolumn–> ~10,000 cells, arranged in vertical columns all allied together for a similar function
What is the path of information through the cortex(in a column) in terms of layers?
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
What three ways can cortical areas be defined?
- Histologically
- Via connection with other structures
- By function
What is a heterotypic cortex? Example?
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)
What is homotypic cortex? Example?
6 layers are normal and easy to tell apart –> association cortex
What Brodmann area is the primary visual cortex?
Area 17
What two Brodmanns areas contain the primary auditory cortex
Areas 41 and 42
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?
Initial processing of the modality; loss leads to loss of perception of that modality
What happens in unimodal association areas?
Different aspects and sub modalities of a stimulus are added
What occurs in hereromodal association areas?
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
What is most of the cortex involved with?
Association– few areas are primary motor or primary sensory
