23A Cerebral Cortex Flashcards
Cerebral cortex develops as outpocketings of
Prosencephalon
Up until 6 mos, the cerebral cortex is smooth or…
Lissencephalic
By birth at nine months, the cerebral cortex is said to be Gyrencephalic or…
coverd with gyri and sulci
Three types of cortex have been defined based on histology
1) Allocortex- 3 layers
2) Isocortex- 6 layered
3) Mesocortex- 3-5 layers
Archicortex formed from which pallium
medial
Paleocortex formed from which pallium
lateral
Neocortex formed from which pallium?
Dorsal {Pallium
How many cortical layers are there?
6
Layer 1 is called
molecular layer
Layers 2,3 called
superficual pyramidal layer
Layer 4 called?
Granular layer
Layer 5 called?
Deep pyramidal cell layer
Layer 6 called
polymorphic layer
Supragranular layer
layers 1-3, because 4 = granular,
This makes 5-6 subgranular
Pyramidal vs non-pyramidal
pyramidal- pear shaped soma and a single dominant apical dendrite. Send axons deep to the white matter and are projection neurons. Project locally and to other areas. Excitatory. Glutamate as transmitter
non-pyramidal- mostly GABAergic neurone which are local only,,,only project into a local area of cortex. Typically multipolar or bipolar
Spiny vs Aspiny
pyramidal = spiny
non-pyramidal- sparsely spiny
What is a spiny stellate cell
found in layer 4 of primary sensory cortex. Mostly subtypes of pyramidal cells but only project locally. Called non-yramidal
Main input to most cortical neurons is from
other cortical neurons
What is the main extrinsic input to cortex?
Thalamus
What are the two types of Thalamic input?
Specific- from thalamic nuclei that project into a single cortical area and concerns a single modality such as VL (motor cortex neuron), VPL (somatosensory cortex neuron)
Non-specific- comes from thalamic nuclei that integrate information from many sources. This input is important for general brain states and arousal.
Specific thalamic nuclei generally project to what layer of the cortex?
Layer 4
Non-specific thalamic afferents generally project to what cortical layer
Layer 1
Pyramidal cells in what layers are the main source or cortico-cortical connections>
II and III… Association fibers and callosal projections….some also project to the striatum which surprisingly is still a part of the telencephalon
Association Fibers?
Pyramidal cells which project ipsilaterally (local and long distance)
Callosal projections
pyramidal cells which project contralaterally, via the corpus callosum
Layer V pyramidal neurons are what
The main output neurons of the cortex
Layer VI pyramidal neurons are what
They project primarily to the Thalamus
The Thalamocortical feedback loop is the basis for several thalamocortical thythms observed in EEG….important in regulation of sleep-wake cycle, consciousness, and several pathologic conditions
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Since most inputs to pyramidal cells come from other pyramidal cells, this system of mutual excitation wold lead to an unstable network if not for less numerous non-pyramidal inhibitory neurons. (80% pyramidal and excitatory, 20% non pyramidal)
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A central belief regarding cortical function is that the cortex is composed of repeated modules called cortical columns.
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Macrocolumn=
all of the cells allied together for a particular function. The idea is that a macrocolumn is the basic functional unit.
The basic idea is that all of the pyramidal cell members of a developmental mini-column are ancestors of a single precursor cell in the ventricular zone of the embryonic cerebral vesicles
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What is association cortex
Cortex that is not primary motor or sensory…all 6 layers very obvious…called homotypic
Non-asssocaition areas where cortex layers are less obvious are called
heterotypic
Which layer of cortex is virtually absent from Primary Motor cortex?
Granular layer…thus motor cortex is referred to as agranular
Which layer is very large?
Layer V is very large in motor cortex because it has large pyramidal cells to project to spinal cord and subcortical motor centers
Primary Sensory cortex
Large granular layer
Primary Motor Cortex = what Brodmans areas
4
Primary somatosensory cortex is brodmann’s area number what?
3, 1, 2
Primary visual cortex is brodman number
17
Primary auditory complex brodmann area
41,42
Brodmans area 6?
Premotor cortex- unimodal association area
Brodman area 5,7
unimodal association areas for somatesthesias
General layout of a somatosensory and motor homunculus?
Medial –> Lateral
Lower limb, trunk, shoulder, arm, hand, neck, head, mouth, throat
Basically, lower limb in the mid-sagital area and upper limb on the lateral surface of the pre- or post-central gyri. Can be used to localize strokes since the middle cerebral artery supplies the putside of the cortex while the anterior cerebral artery supplies the mid-sagital area
Parietal association cortex is important for
attention to the physical world
Temporal association complex is important for
naming things
Prefrontal cortex acts as the overall executive for behavior
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Occipital association cortex is concerned with?
Visual system
If the parietal cortex is damaged in the dominant hemisphere (left side for right handers and usually left handers as well) what occurs?
Patients suffer from language disorders (aphasias)
What occurs with non-dominant parietal damage?
sensory neglect…pts ignore sensory experiences on the half of the body contralateral to the injury. this the non-dominant parietal association cortex is necessary for attention to the internal and external environment
Temporal association cortex important for
recognizing and naming objects
Pre-frontal association cortex
Largest component of the cortex. Important for determining personality and our sense of self
What are teh two components of the Pre-frontal cortex?
Dorsolateral- working memory and planning behaviors
orbitofrontal- aggression and emotions
PFC allows us to choose between actions. Mnemonic RIO stands for what
Restraint
Initiative
Order
