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Chapter 33
The Cerebral Cortex: Intrinsic Organization & Connections
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Undergraduate 3
12/06/2015

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Term
intracortical synaptic organization
Definition
information processing in a small volume of cortex
Term
interareal synaptic organization
Definition
the interconnection of functionally different cortical units with long association & commissural fibers
Term
laminae
Definition
the six layers in which neurons are arranged & are oriented parallel to the surface of the cortex
Term
columns
Definition
how neurons are organized oriented perpendicular to the cortical surface
Term
About how many neurons are cortical pyramidal cells?
Definition
2/3
Term
What is the typical anatomy of a typical pyramidal cell?
Definition
a long axon arising from the base of the pyramid & a long apical dendrite that extends toward the cortical surface; it extends through several layers superficial to the layer in which the cell body is located
Term
Do pyramidal cells have a large or small number of dendritic spines?
Definition
large number
Term
What is characteristic of the most superficial cortical layer (layer 1) (the molecular layer)?
Definition
rich in fibers but has few neurons
Term
What is characteristic of layer 2 (the external granular layer)?
Definition
contains densely packed small cell bodies
Term
What layer is layer 4 (the internal granular layer) similar to in terms of anatomy?
Definition
layer 2 (the external granular layer)
Term
What is the difference in anatomy between layer 3 (the external pyramidal layer) & layer 5 (the internal pyramidal layer)?
Definition
layer 3 = medium-sized pyramidal cells

layer 5 = large pyramidal cells
Term
What is characteristic of layer 6 (the multiform layer)?
Definition
many cells wit spindle-shaped bodies
Term
What is the difference in the role of layers 2 & 4 and the role of layers 3 & 5?
Definition
2 & 4 = mainly receiving (most developed in the primary sensory areas)

3 & 5 = mainly efferent (send their axons out of the part of the cortex in which they are located)
Term
Where do the pyramidal cells of layer 5 send their axons?
Definition
primarily to subcortical nuclei (particularly well developed in the motor cortex)
Term
Where does layer 6 send many axons?
Definition
to the thalamus
Term
Where do pathways that convey precise sensory information primarily end?
Definition
layer 4
Term
What 2 layers do association fibers preferentially end?
Definition
2 & 4
Term
Where do subcortical afferents with modulatory effects especially end?
Definition
layer 1
Term
Where do pyramidal cells send their axon?
Definition
toward the white matter to reach other parts of the cortex or subcortical cell groups
Term
What is the significance in that projection neurons send recurrent collaterals before the axon leaves the cortex?
Definition
it can influence the level of activity among the cortical neurons in their vicinity
Term
How many types of interneurons are there?
Definition
3
Term
What do vertically oriented axons ensure?
Definition
the communication among neurons within a narrow cortical cylinder (column)
Term
What do horizontal axonal branches mediate?
Definition
communication among neurons in different columns
Term
What do horizontal intracortical connections do in sensory cortical areas?
Definition
they mediate lateral inhibition which increases the spatial resolution of the sensory information
Term
How do horizontal intracortical connections contribute to cortical plasticity?
Definition
they modulate the size of the receptive fields of cortical neurons
Term
What is the main neurotransmitter for projection neurons (those sending their axons to subcortical nuclei & those forming association or commissural connections)?
Definition
glutamate
Term
What is involved with glutamate released from pyramidal-cell collaterals that binds to N-methyl-D-aspartate (NMDA) receptors?
Definition
they are involved in plastic changes related to learning & restitution after brain damage
Term
Are spiny stellate cells excitatory or inhibitory?
Definition
excitatory
Term
aspiny interneurons
Definition
interneurons that have few spines
Term
Do most of the GABAergic interneurons also contain one or several neuropeptides?
Definition
yes!
Term
What contributes to epilepsy?
Definition
selective loss of GABAergic cortical interneurons
Term
What is the main job of inhibitory interneurons?
Definition
to focus the excitatory signals & to limit the activity of the projection neurons
Term
disinhibition
Definition
when an inhibitory interneurons inhibit other inhibitory interneurons
Term
Do glutamate thalamocortical fibers act through AMPA receptors or NMDA receptors?
Definition
AMPA
Term
What type of receptors do pyramidal cell collaterals act on?
Definition
NMDA
Term
What results from simultaneous activation of a cortical neuron from the thalamus & from other cortical neurons?
Definition
LTP
Term
What does the response of so many cortical neurons depend on?
Definition
the context of a stimulus
Term
How do horizontal connections affect receptive fields of cortical neurons?
Definition
they ensure that the receptive fields are not static but subject to modification by inputs from their neighbors
Term
What causes cortical plasticity?
Definition
changes in the synaptic efficacy of horizontal connections
Term
4 types of afferent connections of the cerebral cortex
Definition
1. precise, topographically organized connections from the "specific" thalamic nuclei
2. diffusely organized connections from the intralaminar thalamic nuclei & several other subcortical nuclei
3. association fibers
4. commissural fibers
Term
2 types of efferent connections of the cerebral cortex
Definition
1. subcortical
2. corticocortical
Term
What does it mean that the corticocortical connections are "reciprocal"?
Definition
an area receives fibers from the same areas to which it sends fibers
Term
What is the difference in the role of the ventral posterolateral nucleus, the lateral geniculate body, & the medial geniculate body?
Definition
ventral posterolateral nucleus = receives afferents from somatosensory pathways & projects to the SI

lateral geniculate body = receives afferents from the retina & projects to the striate area

medial geniculate body = the last station in the auditory pathways & sends efferents to the AI
Term
What pathway depends on the ventrolateral nucleus & the ventral anterior nucleus?
Definition
they are the relay stations to the pathways from the cerebellum & the basal ganglia to the motor & premotor cortical areas
Term
How are the anterior thalamic nucleus VS the mediodorsal nucleus involved in limbic stuff?
Definition
anterior = receives afferents from the mammillary nucleus & projects to the cingulate gyrus

mediodorsal = relays signals from the amygdala to the frontal lobes
Term
Where does the contralateral nucleus send fibers?
Definition
the parietal cortex
Term
How do intralaminar nuclei affect cortical neurons?
Definition
they exert effects on the excitability of cortical neurons
Term
What is the difference in where dopamine fibers from the VTA end & where noradrenergic fibers from the locus coeruleus end?
Definition
dopamine = prefrontal & temporal neocortex

noradrenergic = the central region
Term
Do the thalamic nuclei receive a lot or a few back-projections from the cerebral cortex?
Definition
a lot
Term
What do the longest association fibers interconnect?
Definition
functionally related areas in different lobes
Term
Where do fibers going outward (feedforward connections) mainly arise & end?
Definition
arise = layer 3

end = layer 4
Term
Where do fibers going backward (feedback connections) arise & end?
Definition
arise = deep layers

end = the most superficial layers
Term
What are the outward connections from the sensory areas concerned with?
Definition
segregation & specific convergence of sensory information
Term
What are backward sensory connections concerned with?
Definition
context-dependent modifications of sensory processing
Term
Where do most commissural fibers pass through?
Definition
the corpus callosum
Term
What do commissural fibers interconnect?
Definition
corresponding areas in the two hemispheres
Term
3 places that are basically devoid of commissural fibers
Definition
1. striate area
2. MI representing distal parts of the extremities
3. SI representing distal parts of the extremities
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