Flashcards in (incomplete) 2: Intro to the Anat. Org./Cerebral Cortex Deck (12)
Describe the anatomical layout of the cerebral cortex and its laminar structure.
Each lamina has a distinct structure of cell types that participate in distinct ways in the workings of the cortex
Three main types of cells, layers they're in, how they're connected together, how info flows, how info is integrated
Identify the main neuron types present in the granular layer, the supragranular layers, and the infragranular layers of cortex.
Describe at least three biochemical, physiological, and/or morphological features that differentiate pyramidal neurons from non-pyramidal neurons.
Soma shaped like a PYRAMID
--Long APICAL dendrite extending vertically toward layer 1, ending in APICAL TUFT (TOP DOWN, from CORTEX, EXPECTANCY)
--Shorter BASAL dendrites extending from soma (BOTTOM UP, from thalamic nuclei/cortex, PERCEPTION)
--OBLIQUE dendrites extend from the proximal apical shaft (collaterals??? FINISH)
Excitatory inputs (NT = GLUTAMATE) occur on dendritic spines
Cell bodies are the main excitatory cell type in layers...
---2/3: corticocortical or callosal [synapse on other hemisphere] corticocortical
---5: deep subcortical projections to spinal cord, brainstem, some thalamus
---6: projects to thalamus; also have lots of dendrites in layer 4
Draw a simple schematic of the 'cortical circuit', including spiny stellate neurons in layer 4, pyramidal neurons in supragranular layers, and pyramidal neurons in infra granular layers.
(he puts up a complicated diagram; skip this diagram, know the simplified stuff)
1. Thalamic input to layer 4 spiny stellate (SS) cells
2. SS project to pyramidal (P) cells in layer 2/3
3. P cells in layer ⅔ are highly interconnected and synapse with layer 5
4. Layer 5 (and layer 6) P cells provide the majority of cortical output
5. Feedback and feedforward inhibition shape the flow of excitatory activity
Identify the main targets for cortical input, and the neurons that provide the bulk of cortical output.
Compare and contrast the functional role of “feedforward” and “feedback” inhibition in cortical circuits.
Main role: quiet things down to prevent over-excitement
--Excitatory flow of information synapses onto pyramidal and GABA-ergic neurons
GABA-ergic neurons then provide feed-forward inhibition to pyramidal cells
--Pyramidal cell -> AP, which also synapses on GABA-ergic neuron
--GABA-ergic neuron feeds back on pyramidal cell in proportion to how excited it is
Describe how pyramidal neurons allow the cortex to integrate "top-down" and "bottom-up" information.
Compares brain's predictions of what is about to happen with what happens
--Pyramidal neurons: distinct input at tuft and basal dendritic locations
Top-down: predictive information
--Info from non-specific thalamic nuclei arrives near layer 1
--What the brain EXPECTS to happen
Bottom-up: perceptive information
--Info from specific (sensory) thalamic nuclei and cortical inputs arrive near basal dendrites of layer 5
--What the brain PERCEIVES is happening
Act as COINCIDENCE DETECTORS for top-down and bottom-up input
--Events happening at tuft only (internal/predictions) can be invisible at soma; while events happening at soma alone (external/data) generate a single AP
--Stimulation at soma AND tuft at the same time -> burst of APs
---->This is when EXPECTATIONS match PERCEPTIONS
Present in ALL neocortical layers (1-6)
Make up about 20% of cortical neurons
Inhibitory neurons: use GABA as NT
Most cell types LACK SPINES on their dendrites
Diverse populations, very SPECIALIZED SUBTYPES (don't need to get into these)
--Classified based on morphology, connectivity patterns, and cellular physiology
Discuss the cost, benefit, and vulnerabilities (6) of having a cortex that consists of a rich substrate of excitatory synapses.
Benefit: extensive excitatory connectivity provides a rich substrate for learning, memory, and cognition
Cost: too much excitation can injure/kill neurons (excitotoxicity)
How does our cortex protect against excitotoxicity? (3)
--Enhance inhibition: feedforward and feedback
--Limit action potentials
What does cortical dysplasia tell us about the importance of the laminar structure of the cortex?
Cortical dysplasia -> cognitive deficits, epileptogenic
Laminar structure -> connectivity of the cortical circuit -> important for FINISH!?!!????