Flashcards in Cortex Deck (93):
-embryonic structure of cortex
Gross Structure of Cortex?
-dominated by convoluted gyri and sulci
-laminar structure with many diff. cell types
Cerebral Cortex Prenatal Development
-outpocketing of Prosencephalon (most anterior part of neural tube)
-its a telencephalic structure (2 cerebral hem. form laterally on either side of the telencephalon)
~100 days, grows over most of brain
-smoothness of cortex until 6 months gestation
-cortex surface with ridges & valleys to package it
Brain to Body Weight Ratio
helps normalize brain size differences b/w species
Weight of human brain
Is there a correlation b/w brain size & intelligence within humans?
Lobes of the Cerebral Cortex?
-Frontal Lobe (frontal pole to central sulcus)
-Parietal Lobe (central sulcus to imaginary line connecting the preoccipital notch to the parietooccipital sulcus)
-Occipital lobe (line to occipital pole)
3 Types of Cortex (histology)?
-6 layered, I to VI starting from pia surface, layer I is cell poor
-less regular, 3-5 layers
3 Types of Cortex (origin)?
-Paleocortex (oldest, olfactory) - formed from lateral pallium
-Archiocortex (next, hippocampal formation) - formed from medial pallium
-Neocortex (new, isocortex) - formed from dorsal pallium
I - molecular layer, poor in cells (GABAergic interneurons)
II & III - continuous & hard to tell apart from one another, superficial pyramidal cell layer
IV - contains many small cells (granular layer)
V - deep pyramidal cell layer (largest pyramidal cells)
VI - multiple cell types (polymorphic layer)
V & VI - subgranular layers, I-III supragranular
-pear-shaped soma & a single dominant apical dendrite
-send axons to deep white matter & are projection neurons of cortex, local collaterals
-variable density of spines
-project locally & to other cortical/subcortical areas
-excitatory (glutamate or aspartate)
-Apical Dendrite, Basal Rosette of Dendrites, Axon
-GABAergic interneurons (local circuit neurons that only project locally within a given area of cortex)
-multipolar or bipolar
-in layer IV of primary sensory cortex, glutamate is used as neurotransmitter (spiny stellate cell) - local
-aspiny or very sparsely spiny
Nonpyramidal cell types?
-layers II/III and V
-vary in size
-multipolar and axons have basket-shaped terminations that surround somas of pyramidal cells
-axonal terminations, cassettes of which contact the initial segments of pyramidal neurons & collectively make the cell look like a chandelier
Bipolar & Bi-tufted cells
-cells have long dendrites & axons that are organized vertically as opposed to the more horizontal organization of basket & chandelier cells
-tend to innervate more distal dendrites of pyramidal neurons (compared to chandelier or basket cells)
Dominant Input to most cortical neurons?
-comes from other cortical neurons
-excitatory pyramidal neurons are highly interconnected
Main extrinsic input to the cortex comes from?
others are: widely-projecting brainstem nuclei which serve modulatory functions (locus ceruleus, raphe nuclei, ventral tegmental area, & basal forebrain nuclei
2 Types of Thalamic Input to Cortex?
1. Specific - from thalamic nuclei that project to a single cortical areas & typically concerns a single modality (VL to motor cortex, VPL for somatosensory cortex, lateral geniculate for visual cortex, or medial geniculate to auditory cortex
2. Non-specific - comes from thalamic nuclei that integrate info from many sources & this input is thought important for general brain states & arousal (intralaminar & midline thalamic nuclei)
Path of all extrinsic inputs to enter the cortex?
-enter from deep white matter & travel vertically
-Cortico-cortico connections - layers II & II (pyramidal)
-include association fibers that project ipsilaterally (local & long distance) & callosal projections (cortralateral cortex via the corpus callosum)
Layer V Pyramidal Neurons
-pyramidal neurons are the main output of cortex in general
-project to various subcortical regions, including the spinal cord (corticospinal tract), pons (corticopontine), tectum (corticotectal), & basal ganglia (corticostraiatal)
Layer VI Pyramidal Cells
-primarily project to thalamus
-thalamus projects to cortex & cortex projects back to the same areas of thalamus (feed-back loop)
-basis for several thalamocortical rhythms in EEG (sleep-wake cycle, consciousness)
Cortical White Matter
-axons of cortical projection neurons have different targets
Layers II & III - primarily project to the contralateral cortex (commissural) or other cortical areas on the same side of the brain (associational)
-may project to striatum
Layer V - (superficial) cells are thinner with less robust apical dendrite, project to contralateral cortex & to subcortical telencephalic targets like the striatum (deep) robust in form & tend to project beyond the telencephalon
Basis of Neural Diseases
-subtle changes in balance of excitation to inhibition in local cortical circuits `
-all cells encode similar features
Microcolumn or Hyper column
-encompass all of the cells allied together for a particular function
What are cortical columns?
10000 macrocolumns act as a basic functional unit and are made up of 200 cells minicolumns (vertical arrangement of cells in local circuits that encode similar features). Layer 4 spiny stellates get thalamus input, then excite 5 and 6 pyramidal cells (5 gives output locally, to other cortex, and subcortically); interneurons exist laterally in columns for regulation.
How does the cortex work?
-functions can be localized within the cortex
How can cortical areas be classified?
1. Histology (Brodmann's, for example prefrontal cortex is homotypic because all 6 layers are obvious but primary sensory is heterotypic granular (large 4, small 5) while primary motor is heterotypic agranular (small 4, large 5)), connections (each part gets input from thalamus, i.e. VPL/VPM for somatosensory, VL for motor), or function.
(sensory modalities first go to their respective cortex, then are processed first at unimodal association areas and then combined with other senses at heteromodal ones; motor functions also have association processing, hence why most of the cortex is association and not simple motor or sensory).
Unimodal Association Areas
-concerned with a single modality
Heteromodal Association Areas
-concerned with more than one (combo)
What area is the primary motor cortex?
precentral gyrus (4)
Area of primary somatosensory cortex?
3, 1, 2 anterior to posterior, posterior to central sulcus
Area of primary visual cortex?
banks of calcarine fissure 17
Area of primary auditory cortex?
Heschl's gyrus (transverse gyri: 41, 42)
Unimodal Association Areas?
-somatosensory association 5, 7
-shows how much cortex is devoted to specific parts of body (more for face, fingers, less for back or legs)
Cerebral Blood Supply
-mid-sagittal surface is supplied by the anterior cerebral artery
-lateral surface is supplied by the middle cerebral artery
Describe sensory processing
VPM/VPL sends info to 3,1,2 (3a and 1 for muscle/deep tissue, 3b and 2 for cutaneous) in homunculus formation, then they send info to 5 and 7 (S2, combines different sensation submodalities), then they send info to heteromodal areas in parietal/frontal/temporal cortex that provide perception of reality (maybe bound via gamma 30-50 Hz rhythm of EEG). Learning, memory, and especially altered use that change organization of cortex (i.e. phantom limb where cortical cells take over areas that there is no more input, like face taking over arm area so that touching face = referred sensation of arm).
Evoked Electrical Potentials
-useful clinical tool for assessing somatosensory pathways
-map receptive fields on primary somatosensory cortex
-cortex can change in response to altered use pattern (physical, learning, memory)
-perceive missing limb, adjacent cells in the cortical map take over the area that was originally concerned with the lost area
-not primary motor or sensory
-6 layered cortex in adult
-frontal, parietal, temporal, occipital
-relatively larger proportion of cortex as ascend phylogenic tree
Parietal Association Cortex
-attention to the physical world
-if damaged, language disorders in dominant hemisphere
-in non-dominant "sensory neglect" ignore sensory experience on half of body contralateral to the injury
Temporal Association Cortex
-lesion: deficits in recognition of objects & people
-executive for behavior
-frontal eye fields, dorsolateral, orbitofrontal, working memory, planning, aggression, emotions, restraint, initiative, order, "personality"
-1/3 of cortical volume, last part of brain to develop
1. Orbitofrontal: limbic, aggression & emotion
2. Dorsolateral: working memory
Occipital Association Cortex
-lobe surrounds borders the lateral ventricles on a mid-sagittal view
Areas of brain involved in emotional experience?
-cortex needed for subjective emotional experience
-expression of emotions requires hypothalamus
-central emotive process initiated in the hippocampus
hypothalamus (mammillary bodies) to ant. N. thalamus, Cingulate Cyrus to ERC to Hippocampus (fornix) back
-olfactory bulb, tract, cortex
-Control of Emotions
-in temporal lobe, just anterior to the hippocampal formation (level of the anterior termination of the inferior horn of the lateral ventricle)
-several nuclei: not all functionally related
-olfaction, emotions, autonimic, learning & memory
-located in anterior part of temporal lobe
3 Main groups of Amygdaloid Nuclei
1. Corticomedial (olfactory) - anterior, medial, cortical nuclei
2. Central (output; autonomic; striatum-like) - high DNA content, close relationship to striatum (GABAergic medium spiny cells)
3. Basolateral (input; sensory; associated with cortex, thalamus) - largest, best differentiated, pyramidal cells basal; lateral; accessory basal N.
Corticomedial Nuclei Connections
In: olf bulb, parabrachial N., septal, MD & VM thalamus
Out: hypothalamus, olf bulb, Stria terminalis
Central Nuclei Connections
In: Basolateral N, hypothalamus
out: brain stem, hypothalamus, striatum, midline thalamus
Basolateral Nuclei Connections
In: pyriform cortex, inf. temporal cortex, association cortex, thalamus
Out: central nucleus, hypothalalmus, cortex, thalamus, frontal cortex, ERC, subiculum
-link to emotions (fear, anxiety, anger)
Bilateral Lesions of the Amygdala
-tend not to eat central, or if basolateral eat all the time
-oral (put things in mouth)
-bilateral loss of the anterior temporal lobe
-hypersexual, oral examination, tame, hyperphagia, hyperactive, psychic blindness (emotional content of facial expressions)
-calcification of neural tissue (bilaterally in anterior temporal lobes)
-worse at recognizing faces expressing fear
-amygdala (basolateral), executor of emotions, fear
-placed b/w cortical and sensory inputs & outputs to hypothalamus & central nucleus to integrate emotional behavior and sensory experience
-learning & memories
-a telencephalic structure located within the temporal lobe
-anteriorly it relates to the amygdaloid nuclei
-collected axons of hippocampal pyramidal cells
-fibers from hippocampal pyramidal cells, becomes the fornix
-main white matter to and from hippocampal formation
-gray matter in the parahippocampal, with characteristic deep white mater and superfical grey matter
Components of Hippocampal Fromation
-CA fields (CA1-4) - hippocampus proper
Principle Cells in entorhinal cortex, subiculum, & CA (Cornus Ammoni) fields?
-pyramidal cells (glutamatergic, excitatory)
Principle Cells of the dentate gyrus?
Cell Distributions of hippocampal formations?
-highly laminar & regular
-CA fields & subiculum are a 3 layered allocortex
-molecular layer (cell poor)
-pyramidal layer (cell bodies of principle, pyramidal neurons)
-polymorphic layer (interneurons)
Cells of Dentate Gyrus?
granular (principle cells)
Main input to dentate gyrus?
Main output to dentate gyrus?
Canonical Hippocampal Circuitry
-input: excitatory projection from entorhinal cortex to granule cells
-granule cells in dentate gyrus project to CA3 pyramidal cells
-CA3 pyramidal cells project to CA1 pyramidal cells
-loss of hipocampal neurons (pyramidal cells are sensitive)
-acquiring new info
-storage & retrieval of info
-stored info lost with time
-in hipo, orientation with environment
-material available to conscious mind (can be symbolically encoded as in language)
-Procedural: not available to the conscious mind
(ride bike, instrument, conditioning, motor actions, priming, muscle memory, emotionsl
-emotional content of memories
Time Course of Memory
-Short-term (sec to min, subset = working memory)
-Long term (days, weeks, life) neocortex
-hippocamups necessary for short-term declarative memory