cerebral cortex - jullet Flashcards
What is the difference between primary cortices and association cortices?
PRIMARY = receive specific sensory input and provide limb/eye movements. ASSOCIATION = combine input from multiple primary cortical areas and participate in complex cortical functions
What is the difference between the neocortex and the allocortex?
NEOCORTEX: outer layer of the cerebral cortex, with 6 layers. ALLOCORTEX: regions of the cerebral cortex that has fewer celll layers than the neocortex
What is the allocortex subdivided into:
paleocortex (olfactory cortex) and archicortex (hippocampus)
What is layer I of the neocortex called?
molecular layer
What is layer II of the neocortex called?
external granular layer
What is layer III of the neocortex called?
external pyramidal layer
What is layer IV of the neocortex called?
internal granular layer
What is layer V of the neocortex called?
internal pyramidal layer
What is layer VI of the neocortex called?
multi-form/fusiform layer
Which layer(s) of the neocortex project out of the cortex?
layers V, VI
What is the supragranular layer?
layers I-III of the cerebral cortex; primary origin and termination of INTRAcortical connections (associational or commissural)
The intracortical connections of the supragranular layers of the cortex can either be associational or commissural. What does this mean?
ASSOCIATIONAL: connections with areas of the SAME hemisphere. COMMISSURAL: connections with the contralateral hemisphere (ie corpus callosum, anterior commissure)
What are association fibers? Where do they arise and terminate?
white matter fibers that connect one part of the cortex to another in the same hemisphere. ARISE: pyramidal neurons in layers 3 and 5 and terminates in layers 1, 2, 3
What are commissural fibers? Where do they arise and terminate?
connect one hemisphere to another (ie corpus callosum, anterior commissure)
What is the internal granular layer?
layer IV of the cerebral cortex, receives thalamocortical input, especially from thalamic nuclei. Most prominent in primary sensory areas. Least prominent in motor areas (= agranular cortex)
Where is the internal granular layer most prominent? Least?
layers IV, most prominent in primary sensory areas. Least prominent in motor areas (= agranular cortex)
What is the infragranular layer?
layers V-VI; connect cerebral cortex with subcortical regions; most prominent in motor areas.
Where is the infragranular layer most prominent?
layers V-VI; most prominent in motor areas.
Where does layer 5 of the infragranular layer project to?
basal ganglia, brainstem, spinal cord
Where does layer 6 of the infragranular layer project to?
thalamus
What are the 3 neuronal cell types in the neocortex?
1) spiny stellate, 2) pyramidal, 3) non-pyramidal/interneurons.
What type of neurotransmitters do the neuronal cell types in the neocortex release? (remember there are 3 major cell types, but 2 major neurotransmitters)
GLUTAMATE = spiny stellate and pyramidal. GABA = non-pyramidal/interneurons
What type of cells are present in layer I of the neocortex?
mostly inhibitory (GABAergic) neurons and axons/dendrites of excitatory neurons from the deep cortical layers
What type of cells are present in layer IV of the neocortex?
spiny stellate cells - receive thalamocortical input as well as input from other cortical cells. Output results from the integration of these two inputs
What type of cells are present in layers V, VI of the neocortex?
excitatory (glutamatergic) and inhibitory (GABAergic) neurons
Where are spiny stellate neurons primarily found?
layer IV
Where are pyramidal neurons primarily found?
layers 2, 3, 5, 6
What is the basic structure of pyramidal neurons? What is the functional purpose of these 3 structures?
1) prominent apical dendrite that extends into layer I, 2) numerous basal dendrites that branch laterally from the base of the cell body, and 3) axon from base of cell body. FUNCTIONAL PURPOSE: allows pyramidal neurons to receive and integrate information arriving simultaneously from multiple input pathways as well as connect to other other neurons, cortical areas (contralateral hemisphere), and subcortical areas (brainstem/spinal cord)
What does it mean that the cerebral cortex and hippocampus have “reverberatory circuit”?
excitatory neurons here are capable of maintaining activity after the initiating impulse has died out (essentially + feedback within neuronal network, resulting in a vicious cycle that is limited by 1) availability of NT and its cognate receptor and 2) non-pyramidal inhibitory neurons)
What is the functional significance of non-pyramidal inhibitory neurons? (2)
1) limit activity of pyramidal excitatory neurons, 2) either feed-forward or feed-back inhibition
What are epileptic seizures? How does the brain prevent epileptic seizures from happening?
Excessive excitatory activity. Controlled by non-pyramidal inhibitory neurons
What’s the difference between feed-forward and feed-back inhibition? What is the functional significance of these two pathways/
Feed-FORWARD: inhibitory neurons are excited by direct thalamic input and then inhibit nearby neurons that also receive thalamic input. Feed-BACK: inhibitory neurons inhibit the excitatory neurons that they are reciprocally connected with. FUNCTION: to shape the flow of excitatory activity
How does the information flow in the cortex?
1) Thalamic projections to spiny stellate neurons of Layer IV of 1˚ sensory areas (V1, S1). 2) info relayed to pyramidal neurons of supragranular layers II, III. 3) info projected to other pyramidal neurons of II, III and to infragranular layers V, VI. 4) infragranular layers project to subcortical brain structures (brainstem/thalamus)
How is information processed within a primary sensory area?
1˚ sensory»_space; 2˚/3˚ sensory»_space; associational areas process inf from multiple sensory systems»_space; 2˚ motor areas»_space; 1˚ motor areas to generate behavioral output. Note that information also flows back to the 1˚ sensory cortex, which integrates the old input with the newly arriving sensory input
What is the primary excitatory neuron in the cortex?
pyramidal neuron
How does synergy in the cortex work?
pyramidal neurons have their apical dendrite extending into layer I, which receives top-down input from higher cortical areas and non-specific thalamic nuclei, and peri-somatic dendrites, which receives input from lower cortical areas and the sensory nuclei of the thalamus. Both kinds of input allows the pyramidal neuron to compare what is expected to what is actually happening. SYNERGY is when the pyramidal neuron gets simultaneous input from both dendritic fieldsand generates a burst of action potentials that convey meaning
What areas make up the primary somatosensory cortex? Where is it located?
SI, areas 3 (a,b), 1, 2. In post-central gyrus
The primary somatosensory cortex receives somatotopic input from: (2)
VPL and VPM
What areas make up the secondary somatosensory cortex? Where is it located?
SII, area 40. In lower parietal lobe
The secondary somatosensory cortex receives input from: (2)
primary sensory cortex and less-specfiic thalamic nuclei
What areas make up the somatosensory association cortex? Where is it located?
areas 5 and 7. located directly posterior to the sensory cortex in the superior parietal lobes.
The somatosensory association cortex receives input from: (2)
primary and secondary sensory cortices
What areas make up the primary visual cortex? Where is it located?
VI, area 17 aka striate cortex. Surrounds the calcarine sulcus of the occipital lobe.
The primary visual cortex receives input from:
Eye»_space; lateral geniculate
What areas make up the visual association areas of the cortex? Where is it located?
V2, V3; areas 18 and 19. Surrounds the primary visual cortex of the occpital lobe
The visual association cortex receives input from: (2)
primary visual cortex (areas 17) and directly from lateral geniculate.
What areas make up the primary auditory cortex? Where is it located?
AI, area 41. located on the transverse temporal gyri and extends into the lateral fissures.
What areas make up the auditory association cortex? Where is it located?
AII, area 42. Surrounds the primary auditory cortex.
What is Wernicke’s area? What is this area important for?
area 22. important for understanding langugage and decoding context from sound features.
What areas make up the primary motor cortex? Where is it located?
M1, area 4. Precentral gyrus
Where does layer 5 of the primary motor cortex project to? (5)
1) corticospinal tract, 2) corticobulbar fibers (control motor cranial nerves), 3) thalamus, 4) basal ganglia, 5) sensory cortical areas
Where does the primary motor cortex receive input from? (3)
1) VL of thalamus, 2) sensory cortical areas, 3) premotor cortex (area 6)
What areas make up the premotor cortex area? Where is it located?
area 6. located immediately anterior to the motor cortex and has many of the same connections as the motor cortex
Where does the premotor cortex project to?
motor cortex (mostly), brain stem, spinal cord
Where does the premotor cortex receive input from?
1) sensory association nuclei, 2) basal ganglia via VA/VL, 3) nuclei of thalamus
What areas make up the supplementary motor areas (MIII)? Where is it located?
also area 6. part of the premotor cortex that extends into the medial side of the hemisphere.
Where does the supplementary motor areas project to:
1) primary motor cortex, 2) basal ganglia, 3) thalamus, 4) brainstem, 5) contralateral supplementary motor areas.
What is the functional significance of the supplementary motor areas?
it is most active before movement and is thought to be involved in the INITIATION of movements.
What is abulia? What is this caused by?
inability to initiate movements; caused by lesions to the supplementary motor areas (area 6)
When does cortical remapping occur?
1) amputated body region/loss of input, or 2) increased use of a body part relative to other parts around it
What happens when there is damage to the primary somatosensory cortex?
decreased sensory thresholds, inability to discriminate the properties of tactile stimuli, or to identify objects by touch
What happens if there are lesions to the secondary somatosensory cortex?
some elements of sensory discrimination may be impaired
What happens when there is damage to the occpital lobe?
cortical blindness and difficulty tracking objects
What happens if there are lesions to the visual association areas?
inability to recognize objects when they may be seen (visual agnosia)
What happens if there are lesions to the transverse temporal gyri?
nothing. This is the primary auditory cortex, but because there is bilateral sound representation in AI, unilateral cortical lesions do not affect hearing.
What happens if there are lesions to the auditory association areas?
inability to interpret sounds
What happens if there is damage to Wernicke’s area?
inability to understand language, including written language
What happens if there is a lesion in area 4?
(primary motor cortex, M1) contralateral weakness, most prominent in distal extremities
What happens if there is a lesion in area 6?
(premotor cortex) less severe weakness but greater spasticity than M1 lesions
What happens if there is a lesion to the supplementary motor area (area 6)?
inability to initiate movements (abulia)
What happens if there are lesions to comissural fibers (ie corpus callosum)?
split brain, where an individually has two independent minds
