cerebral cortex (I) Flashcards
T or F: Every human has the same cerebral cortex structure.
False!
The cerebral cortex can show substantial structural variability in different individuals, but all anatomical landmarks should be present.
T or F: Approximately 80% of the human brain is comprised of cerebral cortex.
True!
Gyri
Folds of the cerebral cortex which enable the large cortical surface area to fit inside the skull.
→particular characteristic in human brains!
Sulci/Fissures
Grooves between the folds.
Two prominent landmarks of the cortex
- Central sulcus (Rolandic fissure)
- Lateral sulcus (Sylvian fissure)
Central sulcus
Prominent sulcus that runs down the middle of the lateral surface of the brain, separating the frontal lobe from the parietal lobe.
Lateral sulcus
Very deep fold seen on the lateral surface of the hemisphere running in an anterior to posterior direction and serves to separate the temporal lobe from the frontal and parietal lobes.
The lateral surface of the cerebral cortex is divided into _____ lobes.
Four.
Cerebral cortex lobes
- Frontal
- Temporal
- Parietal
- Occipital
Limbic lobe
Comprises a wide portion of cortex on the inner side of each hemisphere including parts of the frontal and temporal lobes.
→surround the core of the brain
→usually hidden within the longitudinal fissure
Cingulate sulcus
Binds the limbic lobe to other lobes of the cortex.
Longitudinal fissure
Deep groove that separates the two cerebral hemispheres of the vertebrate brain.
a mid-sagittal section would be done right down the longitudinal fissure
Corpus callossum
Large bundle of more than 200 million myelinated nerve fibers that connect the two brain hemispheres, permitting communication between the right and left sides of the brain
According to Korbinian Brodmann, in how many sections can the cortex be divided?
52 numbered areas
Name two relevant numbered areas
- 4 = primary motor cortex
- 17 = primary visual cortex
Cortex characteristics
- thin sheet of tissue
- 2-4 mm thick
- its basic architecture is nearly identical over a broad range of species
- it is the “outer coating”
- consists of cell bodies
The cortex comprises _____ layers.
Six
Layers of the cortex
- Molecular layer
- External granule layer
- External pyramidal layer
- Internal granule layer
- Internal pyramidal layer
- Multiform layer
Types of stains used to visualize cortex layers
- Golgi stain
- Nissl stain
- Weigert stain
Golgi stain
Stains the whole neuron (cell body, dendrite, axon), but it does so randomly.
→since neurons are densely packed, this allows you to actually see the neuron rather than one black spot
Nissl stain
Stains ribosomes, and thus cell bodies (not axons, not dendrites).
→it will do this in all neurons,
→allows you to see well how neurons are organized in space
Weigert stain
Stains myelinated axons.
in VI you start entering white matter, explaining why it is all black
Pyramidal cells
Pyramidal neurons are responsible for output.
→smaller ones won’t project too far (more nearby regions), but the larger ones will project further
(I) Molecular layer
- generic term referring to a region that does not have many cell bodies.
- mostly dendrites, synapses, and axons
(II) External granule layer
SUPERFICIAL LAYER
- generic term referring to little cells (pyramidal) close to the outside of the brain
- filled with very very small pyramidal cells
- pyramidal neurons make feedforward projections to other regions of cortex
→Golgi stain: neurons have a pyramidal shapes
(III) External pyramidal layer
SUPERFICIAL LAYER
- filled with slightly bigger pyramidal cells
- pyramidal neurons make feedforward projections to other regions of cortex
(IV) Internal granule layer
THE INPUT LAYER
- the main recipient of afferent inputs from the thalamus
- filled with densely packed small cells
- input layer of the cerebral cortex for feedforward projections (going up the pathway)
→Golgi stain: cells are not pyramidal
(V) Internal pyramidal layer
DEEP LAYER
- filled with bigger pyramidal cells
- neurons project to subcortical targets
- large pyramidal neurons in layer project to the basal ganglia, thalamus, brainstem and spinal cord
- feedforward output layer
→Golgi stain: the pyramidal neuron is very big and its dendrites are covering many layers of the cerebral cortex
(VI) Multiform layer
DEEP LAYER
- many different types of cells that then segue into white matter
- neurons project to subcortical targets
- feedback projections to the thalamus come from layer VI
T or F: The thickness of the various layers varies in different regions of cortex.
True.
Primary motor cortex layers
The primary motor cortex is a major output cortex.
→ large layers III & V
→ barely any layer IV
Primary visual cortex layers
A primary sensory area which receive its input from the thalamus.
→ large layer IV
→ barely any layer III & V
Excitatory neurons in the cortex have highly complex _____ and _____ projections.
Axonal & dendritic
Excitatory neurons of primary visual cortex: layers & projections
☆chill time, go read slide 119☆
Cortical columns
The cortex is organized into vertical columns.
-100 – 500 μM in diameter
- neurons in a column are highly interconnected and show similar response properties
- the column is the fundamental functional module of the cortex
T or F: All the neurons in a column have
different response properties.
False! All the neurons in a column (which spans all 6 layers) will have the same response properties.
→they are all in tune/hooked together in a way that all the layers respond to the same stimulus
→but the next column over will respond to a different unique property
Example: Columns in the primary visual cortex
☆chill time, go read slide 121☆
Organization of layers within a single column
- Thalamocortical projections
→thalamus to layer IV - Neurons in layer IV project to layers II & III
- Neurons in layers II & III project to layers V & VI
(OR feedforward cortical projections from layers II & III to other cortical areas) - Subcortical and cortical feedback projections
T or F: Different regions of the cortex are specialized for different functions
True!
For instance, there are regions are dedicated to one specific sensory modality (i.e. primary somatic sensory cortex, primary auditory cortex, etc.)
read slide 123 for more context:)
Name 4 important primary cortices
- Primary motor cortex
- Primary somatic sensory cortex (SI)
- Primary auditory cortex
- Primary visual cortex
Primary somatic sensory cortex location
Postcentral gyrus
T or F: Somatotopic organization is preserved up to the level of primary somatic sensory cortex
True!
How is somatotopic organization represented in the primary sensory cortex?
Areas of greater importance for somatic sensation will have large representation; it is a highly distorted map.
→barely any representation for the back and legs
→huge representation for the hands and face
What can explain the distortion of the somatotopic map in the primary sensory cortex?
- Resources are being allocated where they are needed
(i.e. somatic sensation is very important in the hands and face) - Differences in number is preserved up into the primary somatic sensory cortex
(i.e. the receptive fields in the hands are smaller than in your back, such that there are more neurons innervating)
Somatic sensory association cortex
-higher order processing areas in the cortex
-includes Area 5 & SII
-neurons in SI project to these areas
-specialized for more complex somatic sensory processing
info comes up from the thalamus and is then processed by S1, it will then be sent up to a higher level for more complex processing, where it can then go to a higher level
sensory information is being processed at the lowest level, then it goes up to a higher level where the little pieces get combined into more complex pieces, which can then be combined as well, gradually building up sensory perception
SII
Involved in the conscious perception of somatic sensation
Area 5
Involved in your need for somatic sensory information to guide movement
Primary & association cortex feedforward projections
Feedforward projections originate in superficial layers and project to layer IV.
→pyramidal cells from layers II and III will send their axons to the region with which they want to communicate, these axons will get projected to layer IV of the higher order area
Primary & association cortex feedback projections
Feedback projections originate in deep layers and avoid layer 4.
→these feedback projections (originating in layer V/VI, and avoiding layer 4, going only to layers II, III, V…)
→go back down the pathway and enable higher levels to regulate what’s going on at lower levels
→EX: feedback projections that go back to the thalamus from the primary cortical areas
Unimodal association regions
Unimodal association regions are involved in higher order processing of individual sensory modalities.
these higher order regions process sensory information in a more complex way, but they are still dedicated to only one specific sensory modality, but they will be combined to give us our actual perception of the world (the combination of these different modalities will occur in an even higher order area)
Name important unimodal association regions
- Somatic sensory association cortex
- Visual association cortex
- Auditory association cortex
- Premotor cortex
- Supplementary motor area
Visual association cortex
Higher order visual processing
→EX: neurons in the primary visual cortex will basically only respond to very simple bars / stimulus of light, whereas neurons in the visual association cortex (higher order) will only respond to a human face (very specialized!)
Which system tends to see reverse hierarchal processing?
The motor systems.
-you start with an abstract idea and it gets translated into the specific commands for action
-you are not taking details and combining them to make
something whole, instead, you are starting with something abstract and then in a series of steps, translating that down into the specific actions
Receptive fields in somatic sensory association cortex are _____ than in primary somatic sensory cortex.
Larger
→due to integration of information
→convergence of small receptive fields to form a bigger one
Receptive fields: Name three examples in the somatic sensory association cortex
- Receptive field getting larger (not just one spot on the hand, but the whole upper half of the hand)
- A neuron responding to sensory stimulation of either hand
- A neuron that is most sensitive to a sitmulus moving in a specific direction
What are the two main streams by which the primary areas leave and then go to the higher order areas?
- Dorsal sensory association areas
- Ventral sensory association areas
Dorsal sensory association areas
Dorsal sensory association areas enable sensory information to be used to direct action
-feeds forward to motor areas of the cortex
Ventral sensory association areas
Ventral sensory association areas are involved in object recognition, memory, and conscious perception
Multimodal association cortex
Multimodal association cortex puts together the different sensory modalities into unified perceptions and mediates the most complex aspects of human cognition.
take up a majority of the cortex in humans
What are the main areas of the multimodal association cortex?
- Frontal multimodal association cortex
- Posterior multimodal association cortex
Frontal multimodal association cortex
-receives its input from the medial dorsal nucleus
-involved in executive function
Posterior multimodal association cortex
-involved in integrating the different sensory modalities together to form a single unified whole
-involved in language
T or F: The two hemispheres of the brain are the same
False!
The functions of the two hemispheres of the brain are _____
Lateralized
In most people, language is mainly lateralized to the _____ hemisphere
Left
Aphasia
Loss of language function.
→this can result from a lesion to the left hemisphere posterior association cortex
Wernicke’s area
Region of the brain that contains motor neurons involved in the comprehension of speech
What happens if the Wernicke’s area is damaged?
Damage to Wernicke’s area of the brain can cause a unique type of language disorder known as fluent aphasia. With this disorder, a person can speak phrases that sound fluent (have a lot of words) but lack meaning.
Broca’s area
-also known as the motor speech area
-near the motor cortex and
-utilized in speech production
-located in the inferior frontal gyrus
Broca’s aphasia
-results from left-side lesions to more rostral regions of the cortex
-non-fluent aphasia in which the output of spontaneous speech is markedly diminished and there is a loss of normal grammatical structure
Split-brain patients
The right and left cerebral hemispheres act independently of each other
☆Refresh by reading slides 139-141☆
Common features of the different sensory modalities
- Transduction
- Labeled lines
- Combinatorial processing
- Sensory information destined for the cortex passes first through the thalamus
- Hierarchal levels & complexity of receptive fields at higher levels
- Initial cortical processing occurs in primary sensory areas, followed by unimodal and multimodal association cortex areas
- Sensory perceptions are constructed by the brain. They are abstractions not replications of the real world.
☆FULL explanation on slide 142☆
