Cortex Flashcards
Forebrain
- encompasses diencephalon and telencephalon
o Diencephalon – thalamus, hypothalamus, subthalamus, epithalamus
o Telencephalon encompasses – basal ganglia, hippocampus, amygdala, cerebral cortex
Three Types of Cortex
o Neocortex (isocortex) – 6 layers; primary sensory and motor cortex; “association” cortex
o Allocortex (paleocortex) – 3-5 layers
Entorhinal cortex (parahippampal gyrus), piriform cortex (uncus)
o Archicortex – 3 layers; hippocampal formation
Neocortex
o Thickness: 2-4 mm thickness ; Area: 2,500 cm2
o Location: surrounds the cerebrum (like bark around a tree)
o Structure: laminar; 6 layers; columnar; distinct columns; different cerebral regions have distinct cytoarchitectonics and distinct connectivity
o Functions: large range including, sensory, motor, cognitive, social, & emotional; vary by region
Laminar Microscopic Organization: Layer I & II
o Layer I – Molecular – acellular – contains apical dendrites of pyramidal cells that have many afferent connections; near the meninges
o Layer II - External Granule Cell Layer - granule (stellate) cells - small cells w/ local connections
Laminar Microscopic Organization: Layer III & IV
o Layer III – External Pyramidal Cell Layer – variety of cells including small pyramidal – project to other cortical regions (either on same side or to other side through corpus collosum)
o Layer IV – Internal Granule Cell Layer – primarily granule (stellate) cells – termination zone of primary thalamic inputs (i.e. thalamus projects to this layer)
Laminar Microscopic Organization: Layer V & VI
o Layer V – Internal Pyramidal Cell Layer – mainly pyramidal cells (larger than layer III) – form corticofugal efferents to all regions of brain outside the neocortex, except the thalamus
o Layer VI – Polymorphic (Multiform or Fusiform) Cell Layer – variety of neurons – neurons form reciprocal projections back to the thalamic nuclei that project to same cortical column
Columns
– local, highly interconnected cortical neurons that are derived from radial migration
o During development, form layer 6 first then form layers outward to layer 2
o Topographically organized
o Function: role as elementary processing modules
Pyramidal Cells
– principal output neurons of cerebral cortex
Shape – pyramid
Size – medium-large (Betz cells) (10-100 µm)
Location – primarily layers III & V; some VI
Dendrites – apical dendrites ascend vertically; basal dendrites near base
Axons – typically long axons to other cortex or subcortical sites
Interneurons
– stellate cells and others
Shape – wide assortment
Size – typically small (< 10 micrometers)
Location – various layers; stellate cells mostly in layer IV
Axons – short axons which do NOT leave the cortex
Cytoarchitectonics
– organization of cortical regions according to cell type and distribution over cortical layers
Homotypic vs. Heterotypic Cortex
oHomotypic Cortex – 6 layers of similar thickness; areas not used for sensory OR motor
oHeterotypic Cortex – does NOT have 6 distinctive layers
Granule Cortex – thin and contains granule cells associated with sensory cortex
• Large (thicker) in layer IV – gets inputs from thalamus
• Reduced (thin) in layers III and V
Agranular Cortex – thick and associated with motor cortex
• Large (thicker) in layers III and V (many pyramidal cells)
• Reduced (thin) in layer IV
Brodmann’s Area: 1,2,3,4,6
1,2,3 – parietal lobe (touch/pain sensation)
4 – posterior aspect of frontal cortex (primary motor)
6 – premotor cortex (higher/secondary motor/level processing)
Brodmann’s Area: 17,18,22
17 – primary visual cortex
18 – secondary (higher order) visual cortex
22 – posterior portion (Weirneckie’s) -posterior part of super temporal gyrus (language)
Brodmann’s Area: 39,40,41
39 – angular gyrus
40 – supramarginal gyrus
41 – primary auditory cortex
Brodmann’s Area: 42,44,45
42 – secondary (higher order) auditory cortex
44,45 (Brocha’s area) – speech and grammer