Lecture 2: Cerebral cortex Flashcards
What is the purpose of the Willis Circle
To allow shunting to occur when there is slow blockages in the brain circulation
What are the 3 main cerebral arteries, where are they mostly supplying and can be found
- Middle Cerebral artery: From the internal carotid artery, sitting in the lateral fissure, its branches supply the lateral periphery of the brain. Most common to be blocked
- Anterior Cerebral artery: Comes from Middle cerebral artery. Branches supply the medial upper side and anterior of the brain like a mohawk
- Posterior Cerebral artery: Comes from the Basilar artery which is from the vertebral arteries. Branches to the occipital lobe.
Other branches off the Basilar artery supply the cerebellum and Pons. (Anterior/Posterior inferior cerebellar arteries, Pontine arteries.
What is the Cerebral cortex and is it always the same
Thin layer of grey matter that covers the cerebral hemisphere and houses the cell bodies of neurons that can communicate outside and within the brain. Depending on the cortical region, the cellular structure in the 6 neuronal layers can be different.
What is the difference between Neocortex, Allocortex and Archicortex
Neocortex: Majority of cortex (outermost layer). Most organised with 6 layers. Each Layer has a job.
Archicortex: Modest layer of organisation with some regions with some jobs. Eg. Hippocampus
Allocortex: Old cortex, no logical organisation or connections, non laminar. Eg. Amgydala
What are the two main cell types in cerebral cortex
Pyramidal cells: Projection neurons with large width and are efferents- output. Controlling motor functions- eg. UMN or LMN.
Granule cells: small round neuron cell bodies that are local interneurons, Also receiving a lot of input from sensory systems/ afferent neurons.
What are the 6 layers of the homotypical neocortex from most superficial to deep, and the main types of fibres found in each
- Molecular: holds the cortex together, formed from marginal layer
- External Granular: Local brain (eg. Wernickes) Association and commissural afferents are found in 1-3.
- External Pyramidal: has cell bodies of some association and commissural efferents which project locally to around neck.
- Internal Granular: Lots of dendrites receiving specific afferents from long distance sensory (filtered through thalamus).
- Internal Pyramidal: Contains Betz cells (big projection fibres) output to subcortical structures (eg striatum, thalamus, medulla, spinal cord).
- Multiform: Contains equal proportion of cell types that are dominant in the upper layers depending on any special function of the cortex- cortex looking after itself.
What layers are supragranular layers, afferent granular layer and infragranular layers and what fibres
Supgn. Layers 2-3. Association and commisural cortical fibres
AG: Layer 4: Long distance afferents
Infragn Layers 5-6. Efferent motor fibres
What are the main features of Homotypical, Granular and Agranular cerebral cortex.
Homotypical: Mostly associated with Association cortex (prefrontal, parietal, and temporal).
Granular: No Pyramidal cells, Granule cells predominate layer 2 and 4. Nothing in layer 6. For areas with a lot of sensory processing eg. 1’ Sensory, Visual or Auditory cortexes.
Agranular: Pyramidal cells dominant in layer 3 and 4, no granule cells. More pyramidal cells in layer 6. For areas with lots of output - eg. 1’ Motor cortex.
What is the marginal layer in development and what is its relationship to molecular layer
Originally when the cortex was forming there was ventricular zone which had stem cells. They migrated up a radial fibre from radial glial cells that attached to the upper layer called marginal layer. Neurons migrated and deposited themselves in layers in specific order. Radial glial cells then disappeared and the marginal layer remnant forms part of the molecular layer with just supporting cells.
