23.1 Cortex Flashcards
What are the different types of cortex?
Neocortex
Allocortex
What is the neocortex?
Found only in mammals and is the newest part of the brain to evolve
Largest part of the cerebral cortex containig six horizontal layers of grey matter
What is the neocortex derived from?
Dorsal telencephalon (rostral part of the forebrain)
What is found in the allocortex?
Three layered structure containing the olfactory system and hippocampus
How many layers are found in the neocortex?
6
How many layers makes up the hippocampus?
3
How is the cerebral cortex different from the cerebrum?
Cerebral cortex is the outer layer of the cerebrum made up of grey matter
What is layer I known as?
Molecular layer
What is found in layer I?
Occupied by dendrites of cells in deeper layers
What is layer II known as?
External granule layer
What is found in the external granule layer?
(layer II)
Contains small spherical (stellate) neurons
What is layer III known as?
External pyramidal cell layer
What is found in layer III?
External pyramidal layer
Contains pyramidal cells
What is layer IV known as?
Internal granule layer
What is found in layer IV? What is its main function?
Contains a large number of small spherical (stellate/granular) neurons and a smaller portion of pyramidal cells
Receives the largest sensory input (e.g. primary somatosensory cortex has prominent IV layer)
What are areas with a prominent layer IV known as?
Granular cortex
What is layer V known as?
Internal pyramidal
What is contained in layer V?
Medium and large pyramidal cells
SOURCE OF OUTPUT
What is layer VI known as?
Multiform (fusiform) layer
What is contained within layer VI?
Fusiform cells with dendrites projecting to superficial cortical regions and axons projecting to thalamus and commissural fibres
Some pyramidal cells and interneurons
Where do thalamic afferents end in the cortex?
Thalamic afferents end on layer 4/ granular cells.
Where are output pyramidal cells from in the cortex?
Layer 3,5 and 6
What are the three types of efferent fibres within the cortex?
Comissural
Association
Projection
What are commissural fibres?
Axons of pyramidal cells from layers III and IV which cross the midline to terminate in the corresponding cortical area of the contralateral hemisphere
Where in the brain do commissural fibres travel?
Travel in and form the corpus callosum which connects the two hemispheres
What are associative fibres?
Axons from cells in layers II and III which project to ipsilateral association cortical areas (other regions in the cortex)
What are projection fibres?
Fibres which leave the cortex and project to different regions of the CNS (thalamus, spinal cord)
Where are the cell bodies of projection fibres?
Layers V and VI
Generally these fibres are arranged into tracts
Which tyep of efferent fibres originate in layer IV?
Commissural from pyramidal cells
Stellate synapse locally
What is highlighted?
Internal capsule
What is the internal capsule?
White matter fibres that link the cerebral cortex to subcortical structures such as the corpus striatum, thalamus and brain stem
Carries both ascending and descending fibres
What structure is highlighted below?
Fornix
What is the function of the fornix?
Commissural fibre that connects the hippocampus to the hypothalamus (part of limbic system)
Give examples of tracts that pass through the internal capsule?
corticospinal tracts
the posterior limb has corticobulbar, corticospinal and thalamocortical fibers.
The retrolenticular segment carries fibers of the auditory and visual pathways
PROJECTION FIBRES
What is the supragranular part of the cerebral cortex?
Layers I to III
Projects to other columns
Where do the majority of afferent connections come from?
Thalamus
Brainstem
Hypothalamus
Which types of neurons terminate in layers III and IV of the cerebral cortex?
Second neurons of the sensory tracts that arise from the thalamus (thalamocortical)
Which neurotransmitter dominates layer IV?
Spiny stellate cells found here which release glutamate = excitatory neurons
What are secondary areas?
Located around every primary sensory area which get afferent projections from corresponding primary areas and the thalamus
What is the function of the area shown?
Primary somatosensory
Post central gyrus
integrates incoming sensory information regrading mechanical and noxious stimulation
What is the function of the region highlighted?
Precentral gyrus = primary motor cortex
Generation of movement patterns
What is the function of the area that lies either side of this sulcus
Calcarine sulcus
Primary visual cortex involved in the integration of retinal information
What is the function of the region highlighted?
Anterior transverse temporal gyrus containing primary auditory area (A1)
involved with the understanding and interpretation of detected sounds, allowing for analysis of what is heard and isolation into a range of streams to enable comprehension of speech, etc.
What are the main tracts innervating this region?
Parietal lobe
Dorsal column medial lemniscus pathway (fine touch and proprioception)
Spinothalamic (pain and temperature)
trigeminothalamic tract
What is the function of the region highlighted?
Orbitofrontal cortex on the inferior surface of the frontal cortex at the roof of the orbit
Involved in decision making
Percieves smell
What is the region shown?
Olfactory tract
What makes up the olfactory cortex?
-Piriform cortex
-Amygdala
-Entorhinal cortex
What is the function of the region shown?
Limbic lobe
Regulates emotional and behavioural expression
What is the result of a lesion in the posterior parietal cortex?
Sensorimotor deficits - spatial relationships and memory, inaccurate reaching and grasping, eye movement and inattention (part of corticohippocampal circuit)
Visual cortex - Brodmann’s Area 71
Pre-motor cortex + Brodmann’s Area 6
What are the major cortico-thalamic and thalamo-cortical connections?
Where do stellate cells in layer IV of the primary visual cortex receive fibres from?
LGN
Where do stellate cells in layer IV of the auditory cortex receive fibres from?
Medial geniculate nucleus
Which cell type dominates layer IV?
Stellate cells (granular) which receive INPUT
Some pyramidal
Where do stellate cells in layer IV of the primary sensory cortex receive fibres from?
Ventral posterolateral and ventral posteromedial nuclei of the thalamus
What is the columnar organisation of the cortex?
A cortical column is a group of neurons that form a cylindrical structure through the cerebral cortex, perpendicular to the cortical surface. These columns are thought to be the basic functional units of the cortex.
What can cause a physical lesion?
Gunshot, stroke
What is the result of a lesion in the posterior parietal cortex?
Sensorimotor deficits - spatial relationships and memory, inaccurate reaching and grasping, eye movement and inattention (part of corticohippocampal circuit)
Where do the fibres in the corpus callosum originate from?
Rostrum + Genu - frontal lobe
Body/ trunk of corpus callosum - parietal/ frontal lobes. Pass through corona radiata to reach hemisphere surface.
Splenium - fibres from temporal + occipital lobe
Forceps minor (genu) and major (splenium)
