Unit 2 Flashcards
Cerebral Cortex
What does the cerebral cortex consist of?
the outer layer of cells on the surface of the cerebral hemispheres
What is the cerebral cortex vital for?
conscious awareness, thought, memory and intellect
-> part of the brain to wich all sensory information is eventually sent, and where it is consciously perceived
What is initiated in the cortex?
motor actions
What are the outer cells of the cerebral cortex called?
grey matter - made up of neuronal cell bodies
-> represents sites of neural processing
-> neural processing only occurs where neurones synapse on the cell bodies and dendrites of other neurones
What is the role of white matter in the cerebral hemispheres? How is it formed?
The axons of neurones in the cortex extend inward, forming white matter.
-> axons CARRY signals to other parts of brain and the spinal cord
What does white matter consist of?
consists of axonal pathways that connect different brain regions, allowing for communication between various parts of the nervous system
How thick is the cortex?
~3-5 mm
-> extensive folding increases the area of cortex, allowing more neurones to be packed into a smaller space
What do the folds of the brain produce? What is it?
gyri: bulges of the folds
sulci: valleys
fissures: valley that are considerably deeper than sulci
How does the size of the cerebral cortex and the degree of folding differ between humans and other mammals?
differs considerably
-> in terms of evolution: more advanced brains tend to have more folds in cerebral cortex - therefore more neurones
How is communication between areas of the cortex possible?
via white matter pathways
What are the 2 main white matter pathways that connect the hemispheres?
- the corpus callous (lies within the great longitudinal fissure)
- anterior commissure (relatively smaller)
What is a commissure and are there other ones?
Commissure: an axon tract that connects the hemispheres
-> there are several other ones, such as hippocampal commissure (communication between subcortical structures in each hemisphere)
How do most sensory and motor functions work?
contralaterally: left hemisphere receives sensory information from the right side of the body and controls movement in right side of body (and vice versa)
What would happen without the corpus callosum?
your left brain hemisphere would only be able to react to information on the right side of your body and vice versa for right side
-> allows hemispheres to communicate with each other
What are the cells in the cerebral cortex organized into?
laminae and columns
What are laminae and columns?
laminae: six different layers of cell bodies that run parallel to the surface of the cortex
columns: groups of cells that run perpendicular to the surface of the cortex
How does the laminae vary across different areas of the cortex and what does it depend on?
varies in thickness, sometimes may even be absent in some parts
-> depends on function of each lamina: each one sends and receives different types of information - communicates with different parts of CNS
What is structurally similar within each lamina?
the cell bodies, axons and dendrites
What do Laminae I, II and IV receive?
sensory information detected from around the body
What do Laminae III and V contain?
neurones that communicate with other parts of the brain, and play an important role in communicating messages for producing movements
What does the Lamina VI also contain?
Neurones that send message to other parts of the brain (e.g.: thalamus, other areas of the cerebral cortex)
How do the columns of cells in the cortex run compared to the laminae?
perpendicular (at 90 degrees to another)
What characterizes a column of cells in the cortex?
consists of a narrow chain of cells that share similar properties and functions.
-> cells can communicate with neighboring columns and may group together with similar columns to enhance processing power
What is the advantage of grouping cells with the same function in well-connected columns within the brain?
allows the brain to operate quickly and efficiently, enhancing overall processing capabilities.
How does the structure of columns in the cortex contribute to processing power?
Each column contains many cells, providing greater processing power than a single neuron
-> allowing for more complex functions and information handling.
What can columns be seen as?
single processing units of the cerebral cortex
How do cells within a column of the cortex communicate across different laminae?
vertically with other cells in the same column that belong to different laminae, facilitating integrated processing across the layers of the cerebral cortex
What did Brodmann produce in the early 20th century?
a numbered cytoarchitectural map of the cerebral cortex based upon how each region differs from each other in terms of cellular structure
What is Cytoarchitecture? Is it still used in modern research?
how neurones are arranged in the CNS
-> yes, but less and less areas are now labelled according to the function they are associated with
What remains regarding to the Brodmann’s area?
a significant correspondence between these areas and functionally defined regions of the cortex
-> suggests that the functionality of cortical regions is closely related to their cellular structure
What are the three main types of axon fibers in the brain?
- Association fibers
- Commissural fibers
- Projection fibers
What are white matter tracts and fibers responsible for?
carrying information between different parts of the cortex, and between the cortex and other parts of the CNS
What is the function of association fibres?
interconnect different parts of the cortex within one cerebral hemisphere
What is the function of Commissural fibres?
run from one cerebral hemisphere to the other, connecting functionally related structures
What is the function of projection fibres?
connect the cortex with subcortical structures such as the thalamus, striatum, brainstem and spinal cord
What are the cells of the cerebral cortex organized into?
4 lobes: frontal, temporal, parietal and occipital lobes
-> boundaries are marked out by prominent sulci and fissures in the cerebral cortex
What are the functions of lateral tissue and central sulcus?
- lateral fissue: separates the temporal lobe below from the frontal and parietal lobes above
- central sulcus: runs from great longitudinal fissure to lateral fissure, which marks boundary between the frontal and parietal lobes
What is the boundary between the parietal and occipital lobe marked by?
parieto-occipital sulcus on the medial surface
How do cells in different lobes of the brain relate to common functions, and what complicates the assignment of specific functions to particular regions?
Cells in each lobe of the brain, such as those in the occipital lobe, share common functions, like processing visual information.
-> assigning a specific function to a region is complex because all cortical areas communicate with one another, contributing to various psychological functions
What is the main site of visual processes?
the occipital lobe
What is the most posterior part of the occipital lobe?
the primary visual area/cortex
-> receives visual information from the eyes
What is the pathway of visual information from the retina to the primary visual cortex?
- detected by the retina
- travels through the optic nerves, where half of the optic nerve fibers cross at the optic chiasm
- Most of information then reaches the lateral geniculate nucleus (LGN) in the thalamus
- there it is processed before being sent to the primary visual cortex for further analysis
What can damage to the primary visual cortex cause?
cortical blindness in the contra-lateral visual hemifield
What happens in cortical blindness, and how does it affect mental imagery and visual dreams?
visual cortex responsible for producing mental images and perceptions is damaged, not the eyes
-> result: individuals with cortical blindness cannot perceive stimuli but may still experience mental imagery and visual dreams because the primary visual cortex remains intact
What does the primary visual area (V1) process?
visual information in one small part of the visual field
-> passes it onto neighboring areas, for more complex processing of entire visual scenes
How does the brain process different types of visual information?
brain processes visual information through two pathways that communicate between neighboring areas.
-> ventral stream and dorsal stream
-> pathways involve different brain areas and are responsible for processing distinct types of visual information
What does the term “Association area” refer to?
cortical areas that perform more complex processing than primary sensory areas (such as combining information)
What is the role of the visual association cortex (V2, V3, V4, V5) in visual processing?
integrates various aspects of visual information, allowing for the perception and understanding of complex visual scenes
-> located around the primary visual area in the occipital lobe
What does the ventral stream (the “what” pathway) process in visual perception?
processes visual information related to colour, brightness, and shape, helping to recognise and identify what the visual stimulus is
-> connects the primary and secondary visual areas with regions in the occipital and temporal lobes
What happens if the ventral steam is damaged?
results in difficulty describing visual stimuli and causes deficits in visual imagery and memory, such as trouble remembering features like whether someone has a beard
What is the dorsal stream (the “where” pathway) responsible for in visual processing?
processes visual information related to guiding body movements and spatial awareness
-> connects the primary and secondary visual areas with regions in the temporal lobe (e.g., V5/MT) and parietal lobe, helping the brain determine “where” objects are in space
What are the effects of damage to the dorsal stream pathway?
results in difficulty with reaching for and grasping objects, even though the individual can describe the visual stimulus
-> can also lead to problems locating unseen body parts, such as describing the position of a hand beneath a table
How do the ventral and dorsal streams interact in visual processing?
Though the ventral (“what”) and dorsal (“where”) streams are distinct, they are highly interconnected.
-> Activities like reaching for a pen require both streams—identifying the pen (ventral stream) and orienting your body to grasp it (dorsal stream)
