23 - Cerebral Cortex Flashcards
The gray matter of the cerebral cortex has three components. What are they?
1 - Allocortex
2 - Mesocortex
3 - Neocortex
How may layers is gray matter predominantly organized into?
3-6 layers
The allocortex of the gray matter has two components. What are they?
1 - Archicortex
2 - Paleocortex
What is the archicortex?
- Responsible for memory and emotions
- Contains 3 layers of gray matter
- Contains the hippocampal formation
What is the paleocortex
- Contains 3-5 layers of gray matter
- Contains the parahippocampal gyrus, uncus and the lateral olfactory gyrus (olfactory system)
What does the mesocortex of the white matter contain?
- The cingulate gyrus and the insula
- 3-6 layers of gray matter
Describe the neocortex of the gray matter
- It is also called the isocortex
- There are 6 layers of gray matter present with regional variations
- There are two different cortexes present
- The neocortex makes up 90% of the cerebral cortex!!!
What two components are present in the neocortex?
- Homotypical cortex
- Heterotypical cortex
Describe the homotypical cortex of the gray matter
- The homotypical cortex contains the ASSOCIATION areas of the cerebral cortex
- All six layers of gray matter are present here
Describe the heterotypical cortex of the gray matter
- The heterotypical cortex contains the PRIMARY areas of the cerebral cortex
- Granular and agranular areas are present
What is meant by an “agranular” area?
This is based on the gross appearance - they have a smooth, agranular appearance
An example of an agranular area of the heterotypical cortex is the PRIMARY MOTOR CORTEX
What is meant by a “granular” area?
Based on appearance - these areas have a sandy, bumpy, granular appearance
An example of a granular area of the heterotypical cortex is the PRIMARY SENSORY CORTEX
What cell types are present in the cerebral cortex?
1 - Pyramidal cells
2 - Fusiform cells
3 - Stellate (granule) cells
4 - Other cell types
What are pyramidal cells?
- The most abundant of all cell types in the cerebral cortex
- Make up 75% of the cells present
What types of axons do we find with pyramidal cells?
Long axons that form white matter tracts
What are fusiform cells?
- The cells that are located the deepest in the cortical layers
What types of axons do we find with fusiform cells?
Axons that project to the thalamus
What are stellate (granule) cells?
Interneurons of two different forms
- Aspiny, INHIBITORY interneurons
- Spiny, EXCITATORY interneurons that are located in Layer IV of the gray matter
There are two other cell types found in the cerebral cortex. What are they?
- Horizontal cells of Cajal
- Cells of Martinotti
What are horizontal cells of Cajal?
- Cells of the cerebral cortex that are located in the superficial-most layer of gray matter
- Horizontal cells of Cajal are seldom seen or completely lacking in the adult brain
- We don’t know what they do, but it is likely that it has something to do with development
What are cells of Martinotti?
- Interneurons that are located deep in the layers of gray matter
White matter is formed primarily by which cell type?
Pyramidal cell axons
How do the pyramidal cell axons of white matter form connections within the cortex (i.e. cortical connections)?
There are three ways…
1 - Association fibers
2 - Commisural fibers
3 - Projection fibers
Describe the association fibers that exist to connect the pyramidal cell axons of white matter
Association fibers
- These are intracortical fibers, meaning within the SAME hemisphere
- This means there is no crossing of these fibers, so they are IPSILATERAL
Describe the commissural fibers that exist to connect the pyramidal cell axons of white matter
Commissural fibers
- These fibers are located in the corpus callosum and the anterior and posterior commisures
- They go to and from the OPPOSITE hemisphere
- This means they are crossing fibers, so they are CONTRALATERAL
Describe the projection fibers that exist to connect the pyramidal cell axons of white matter
Projection fibers
- These fibers run UP & DOWN
- The first set of projection fibers run to/from the cortex and spinal cord
- They exist in three different divisions - corticobulbar, corticothalamic, corticopontine
- The second set of projection fibers are found within the internal capsule
- They exist in three different divisions - Genu, anterior limb, posterior limb
What are some examples of association fibers?
Association fibers are bundles of axons within the brain that unite different parts of the same cerebral hemisphere
- Uncinate fasciculus
- Occipitofrontal fasciculus
- Superior longitudinal fasciculus
Remember these are INTRA-cortical fibers
Fasciculus just means a small, slender bundle of nerves
What is the neocortex again?
The largest part of the cerebral cortex (90%), which covers the two cerebral hemispheres, with the allocortex and mesocortex making up the rest.
The neocortex is made up of six layers, labelled from the outer in, I to VI.
In humans, the neocortex is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning, conscious thought and language.
What are the six gray matter layers of the neocortex?
Layer I - Molecular layer Layer II - External granular layer Layer III - External pyramidal layer Layer IV - Internal granular layer Layer V - Internal pyramidal layer Layer VI - Polymorphic (multiform) layer
Describe the molecular layer of the neocortex
Layer I
- This is a synaptic area that contains the meeting point for axons and dendrites
- We will see neuroglia and cells of Cajal in the molecular layer
Neuroglia - non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons
Cells of Cajal - developmental (?) cells that are completely lacking in the adult brain
Describe the external granular layer of the neocortex
Layer II
- Contains axons and dendrites from deeper layers
- We will see small pyramidal cells and stellate cells in the external granular layer
Pyramidal cells - neurons with long axons that form white matter tracts
Stellate cells - interneurons that can either be inhibitory (“aspiny”) or excitatory (excitatory or “spiny” stellate interneurons are only found in layer IV)
Describe the external pyramidal layer of the neocortex
Layer III
- Contains moderate sized pyramidal cells (long axons - white matter tracts)
- It is an EFFERENT layer, meaning the fibers are carrying information away from the brain - it is an OUTPUT layer
- This layer contains corticocortical fibers, meaning fibers that travel from one side of the cerebral hemisphere to the other side or stay within the same side - These are commissural fibers and association fibers
Describe the internal granular layer of the neocortex
Layer IV
- This layer is densely packed with STELLATE cells (inhibitory/excitatory interneurons)
- The most important aspect of this layer is that it is the CHIEF INPUT LAYER - it is the dominant afferent layer
- There are afferents from the thalamus present (ventral posterolateral nucleus = VPL, ventral posteromedial nucleus = VPM) which are “thalamocortical fibers” running from thalamus to cortex
- The outer band of Baillarger is present and can be stained with myelin-stain
Describe the internal pyramidal layer of the neocortex
Layer V
- Giant pyramidal cells of Betz, a smaller number of stellate cells, and cells of Martinotti are present (deep gray interneurons)
- The inner band of Baillarger is present and can be seen with a myelin stain
- This an efferent or OUTPUT layer of the brain
- There are projection fibers (which makes sense) including corticofugal (striate) fibers, corticobulbar fibers and corticospinal fibers
Describe the polymorphic (multiform) layer of the neocortex
Layer VI
- Small pyramidal cells, stellate cells, cells of Martinotti (deep gray interneurons) and fusiform cells (axons to thalamus) are present
- This is also an efferent or OUTPUT layer of the brain
- Fibers here are corticothalamic fibers, meaning they run from the cortex to the thalamus
Now it’s time to memorize anatomical maps of Brodmann’s areas
YAYYYYYY!
Frontal lobe first…
What is found in the precentral gyrus? What BA is this?
Primary motor cortex - BA 4
M1 for primary motor
What will happen if there is a lesion in the precentral gyrus?
- Contralateral weakness
- Spastic paralysis (UMN)
- Hyperreflexia (UMN)
What is found in the superior and middle frontal gyri? What BA?
Premotor and supplementary motor areas - BA 6
M2 for secondary motor
What is the function of BA 6?
Responsible for the programming that is necessary for movements
What happens with a lesion in BA 6?
Apraxia
Individual will have difficulty with the motor planning required to perform a task
Unsteady, uncoordinated movements
What is found in the superior and middle frontal gyri of the pre-frontal cortex?
Frontal eye field - BA 8
What happens with a lesion to BA 8?
Disruption of some of the most complex aspects of behavior
This is NOT vision-related, but is named according to location. Think of the story about Phinaeus Gage.
Phinaeus Gage
Had a lesion in BA 8 - frontal eye field
Went from being a mellow, responsible, well-liked, hard working to being a smoker/drinker who used profanity, was late for work or didn’t show up, and was angry and violent.
What is found in the opercular and triangular parts of the inferior frontal gyrus?
Broca’s area - BA 44
What is Broca’s area (BA 44) responsible for?
Motor programs necessary for the generation of language
It is located in the DOMINANT hemisphere
What happens with a lesion to BA 44?
Broca’s aphasia
- Non-fluent speech
- Motor issue moving mouth to talk
- Can’t express what they want to say
- Fully comprehend language, just have difficulty producing language
- Affects both written and spoken words
Those were the four frontal lobe BA to know… Now we’re onto the parietal lobe
FIRST REVIEW…
Precentral gyrus = primary motor cortex = BA 4
Superior and middle frontal gyri = BA 6 = Premotor and supplementary motor area
Superior and middle frotal gyri of pre-frontal cortex = BA 8 = Frontal eye field
Opercular and triangular part of inferior frontal gyrus = BA 44 = Broca’s area
What are the two areas of the parietal lobe you need to learn?
1 - Postcentral gyrus
2 - Superior parietal lobe
What is found in the postcentral gyrus?
Primary somatosensory area = BA 3, 1, 2
S1 for primary sensory
What occurs with a lesion to BA 3, 2, 1?
Loss of tactile discriminatory and proprioception to the CONTRALATERAL side
Pain is not elicited, abolished or relieved
What is found in the superior parietal lobe?
Somatosensory association area = BA 5, 7
What is BA 5, 7 responsible for?
- Tactile and visual information
- Cognition of the body itself and the objects surrounding it
What happens with a lesion to BA 5, 7?
Tactile agnosia, asterognosis, neglect syndrome
Tactile agnosia
The inability to process sensory information related to touch in ONE hand
Astereognosis
The inability to identify an object by active touch of the hands without other sensory input
When this occurs in only one hand, it is referred to as tactile agnosia
Neglect syndrome
An inability of a person to process and perceive stimuli on one side of the body or environment, where that inability is NOT due to a lack of sensation
Patients with neglect act as if portions of their world do not exist
Now onto the occipital lobe…
REVIEW FIRST…
PARIETAL LOBE
Postcentral gyrus = BA 3, 1, 2 = primary somatosensory area
Superior parietal lobe = BA 5, 7 = Somatosensory association area
What are the two areas of the occipital lobe you need to memorize?
1 - Banks of calcarine sulcus
2 - Cortex surrounding area 17
What is found in the banks of the calcarine sulcus?
Primary visual cortex - BA 17
(V1 for primary visual)
AKA striate cortex (but I’ve never heard it called that)
Describe the primary visual cortex
- This cortex forms on the walls of the calcarine fissure
- This is the site of initial processing from both eyes
- The signal then distributes to association areas
What is found in the cortex surrounding BA 17?
Visual association areas - BA 18, 19
What is the function of BA 18, 19?
Receives visual information from BA 17
What type of information is processed by the BA 18, 19?
Motion and color are analyzed here
What will occur with a lesion to BA 18, 19?
Visual agnosia, achromatopsia, akinetopsia
Visual agnosia
Visual agnosia is an impairment in recognition of visually presented objects that is not due to a deficit in vision or memory
Achromatopsia
The inability to perceive color and to achieve satisfactory visual acuity at high light levels (typically exterior daylight)
Akinetopsia
A neuropsychological disorder in which a patient cannot perceive motion in his or her visual field, despite being able to see stationary objects without issue
Okay, now we’re moving onto the temporal lobe…
REVIEW FIRST…
Banks of calcarine sulcus = BA 17 = primary visual cortex
Cortex surrounding BA 17 = BA 18, 19 = visual association areas
What are the three areas of the temporal lobe you need to memorize? What is the overarching function you should think of when you think temporal lobe?
Emotions, memory and speech
1 - Superior temporal gyrus BA 41
2 - Superior temporal gyrus BA 42
3 - Superior temporal gyrus BA 39, 22
What is found in the superior temporal gyrus BA 41 area?
Primary auditory cortex
(A1 for primary auditory)
This is a granular cortex
What is found in the superior temporal gyrus BA 42?
Auditory association area
(A2 for secondary auditory)
There is input from BA 41 (primary auditory cortex)
What is found in the superior temporal gyrus BA 39, 42?
Wernicke’s area - Auditory association cortex
What is the function of Wernicke’s area?
Found on the DOMINANT side
Wernicke’s area functions in the mechanisms for formulating language
What is Wernicke’s aphasia
“Word salad”
- Fluent speech
- Intact sensory
- Receptive aphasia
- The patient is able to produce written or spoken words, but they string together words and phrases in an order that conveys little or no meaning
Now onto the limbic lobe…. LAST ONE!!!
REVIEW FIRST…
Temporal lobe
Pretty much, you need to know that there are four BA’s in the superior temporal gyrus that you need to know
BA 41 = Primary auditory area
BA 42 = Auditory association area
BA 39, 22 = Wenicke’s area (or auditory association cortex)
Describe the limbic lobe
It is a horseshoe-shaped cortex surrounding the junction of the diencephalon and each cerebral cortex
What is the function of the limbic lobe?
Drive-related emotional behavior functions
What are the three areas of the limbic lobe you need to memorize?
1 - Cingulate gyrus
2 - Parahippocampal gyrus
3 - Hippocampal formation
What is the function and what BA is found in the cingulate gyrus?
Involved in motivation (combination of emotional processing, formation, learning and memory)
There are MANY BA’s in the cingulate gyrus, but you only need to remember BA 24
The rest are: 25, 33, 24, 23, 26, 29, 30
What is the function and what BA is found in the parahippocampal gyrus?
The parahippocampal gyrus is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. This region plays an important role in memory encoding and retrieval.
The parahippocampal gyrus terminates in the uncus.
BA 34
What are the three parts of the hippocampal formation?
1 - Dentate system
2 - Hippocampus
3 - Subiculum
What is the function of the hippocampal formation?
The hippocampal formation is a compound structure in the medial temporal lobe of the brain and is thought to play a role in memory, spatial navigation and control of attention
I guess you don’t need to know the BA because it isn’t in the handout
Why could that american idol contestant sing really well, but had great difficulty speaking?
There is a dominance in a particular hemisphere and can help predict function or clinical effects of lesion
American Idol example
Can’t talk –> L hemisphere
Able to sing very well –> R hemisphere
