Cerebral Cortex and Thalamocortical Relationships (Week 4--Houser) Flashcards Preview

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Flashcards in Cerebral Cortex and Thalamocortical Relationships (Week 4--Houser) Deck (41):
1


Diencephalon


1) Thalamus: one on each side of 3rd ventricle

2) Subthalamus (subthalamic nuclei mentioned in basal ganglia)

3) Hypothalamus: immediately ventral to the thalamus

4) Epithalamus: habenular nucleus and pineal

2


Divisions of the thalamus


Anterior: relay nucleus (thalamus to cortex and back)

Medial: relay nucleus; goes to reticular activating system; mediodorsal (MD) nucleus

Lateral: relay nucleus; VA, VL, LD, LP, VPL, VPM

Internal medullary lamina: thin band of myelinated fibers separating divisions

Intralaminar nuclei: small nuclei located within internal medullary lamina

3


Which regions and pathways have "relays" in the thalamus?


Almost all!

Sensory pathways

Connections from cerebellum

Connections from basal ganglia

Connections from cerebral cortex

4


What determines which regions of the cortex are specialized for which functions?

Connections with the thalamus are important in determining function of each cortical area

Specific types of sensory and motor information are relayed to specific regions of the thalamus then neurons of thalamus project to specific regions of the cortex

5


Major functional areas of the cerebral cortex and Brodmann's areas and lobes


Primary motor = area 4 = frontal lobe

Primary somatosensory = areas 3, 1, 2 = parietal lobe

Primary visual = area 17 = occipital lobe

Primary auditory = area 41 = temporal lobe

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Additional motor areas of the cortex


Supplementary motor area (SMA) = area 6 = frontal lobe = programming/planning complex set of movements and may be activated by "mental rehearsal" (more medial/midline on cortex)

Premotor cortex = area 6 = frontal lobe = involved in preparing for a movement, ready set go, and movements guided by external stimuli such as reaching for a visible object (more lateral on cortex)

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"Association cortex"


The remainder of the brain

Determined by types of info integrated (associated) in the region

Prefrontal cortex, language areas?

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Prefrontal cortex


"Executive functions"

"Association area" because receives inputs from many other regions of the cortex (as well as thalamus and limbic areas)

Rostral to motor areas and much of the frontal lobe

Dorsal and lateral prefrontal cortex: planning, problem solving, working memory, maintaining attention

Orbital and medial prefrontal cortex: self-control, suppressing inappropriate responses

9


Language areas (Perisylvian language zone)


Broca's area: motor or expressive speech area; posterior part of inferior frontal gyrus, opercular and triangular parts (areas 44, 45)

Wernicke's area: sensory or receptive spech area; posterior part of superior temporal gurys and parietal-occipital-temporal junction

Connected through arcuate (superior longitudinal) fasciculus

10

Which hemisphere are language areas located in?

Left hemisphere in nearly all right handed people and half of left handed people

Called dominant hemisphere if that's where language is controlled

 

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Aphasia


Disturbance of formulation or comprehension of language, not a disorder of hearing, vision or motor control

Broca's aphasia

Wernicke's aphasia

Global aphasia

Conduction aphasia

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Broca's aphasia


"Broken Boca"

Nonfluent, motor or expressive aphasia (with intact comprehension)

13


Wernicke's aphasia

"Wernicke's is wordy but makes no sense--what?"

Fluent, sensory or receptive aphasia (with impaired comprehension)

14


Global aphasia


Wernicke's and Broca's areas are damaged

Nonfluent aphasia with impaired comprehension

Severe loss of all language skills

15


What happens if you have damage to the non-dominant (right) hemisphere?


Lesion to right parietal association cortex can produce contralateral neglect syndrome

Neglect the left side of body or space

Note: lesion on left (dominant) hemisphere does not produce severe neglect on right side

16


What sorts of functional deficits occur if there is damage to the parietal-occipital-temporal association cortex?


Agnosia: inability to recognize object with a particular sense even though that sense is intact (no loss in vision but can't recognize an object by sight)

Apraxia: inability to perform a learned motor skill on command even though no primary motor deficits (can perform same motor activity in different context); occur most commonly when lesion in dominant hemisphere

17


Basic pathway for visual information

Pathway referred to as geniculocalcarine tract or optic radiations

1) Ganglion cells in retina of each eye terminate in different layers of lateral geniculate nucleus (6 layers total)

2) Neurons of LGN project to primary visual area (striate cortex) on medial surface of cortex and surrounding the calcarine fissure (sulcus)

18


Superior colliculus


Not in the direct visual path from retina to cortex

Associated with visual function because part of reflex center for orienting the eyes and head in response to visual stimulation (so must receive visual stimuli)

Some retinal fibers and collaterals from retinogeniculate axons and info from primary visual cortex and other, nonprimary, regions of visual cortex send stimuli to superior colliculus

19


Contralateral or ipsilateral relationship between visual field and visual cortex?


Contralateral

Crossing of axons from nasal retina in optic chiasm so left visual field represented in right visual cortex

20

Cortical afferents

Info comes into the cortex from thalamus, other cortical areas and chemically defined nuclei in brainstem (NE, serotonin, dopamine) and basal forebrain (cholinergic)

21


Basal nucleus of Meynert


Cholinergic neurons here (in forebrain) project to virtually all areas of cerebral cortex

Neurons here also are lost in patients with Alzheimer's disease

22


Septal nuclei and nucleus of diagonal band


Cholinergic neurons here project to hippocampal formation

Neurons in these brain regions degenerate in patients with Alzheimer's disease, and loss is accompanied by marked reductions in choline acetyltransferase (enzyme that synthesizes ACh, marker for cholinergic neurons)

23


Cortical efferents


Projections from the cortex go to numerous subcortical regions such as the thalamus, striatum, brainstem and spinal cord

Also project to other cortical areas: same region of the opposite hemisphere (callosal fibers) and to other regions of the same hemisphere (association fibers)

24


Posterior limb of internal capsule


Both motor and somatosensory areas are grouped together here so damage will produce both motor and sensory problems

25


What will damage to motor areas of cerebral cortex or descending axons from these areas cause?


Upper motor neuron signs: paralysis, paresis, spasticity

Depends on location and extent of lesion

Not usually paralysis of limbs, but voluntary movements cannot be "fractionated" into normal patterns

26

Explanation for spasticity


Not completely understood

In general, loss of proper balance of facilitation and inhibition at both alpha and gamma motor neurons

Inhibitory control of motor neurons by descending pathways is decreased

Not damage of corticospinal tract alone but damage to multiple descending pathways that could include projections from cortex to brainstem motor centers (red nucleus, reticular formation, etc) or pathways within the brainstem itself

27


Two cell types of cerebral cortex


1) Pyramidal cells: apical dendrites coming out the top of cell body toward pial surface of cortex and basilar dendrites from base of cell body horizontally; project to thalamus, brainstem, spinal cord, other cortical areas; primary projection/output of cerebral cortex; excitatory actions on targets

2) Non-pyramidal cells (stellate or granule cells): small, axons of most remain within cerebral cortex so they're interneurons or local circuit neurons; most use GABA and are inhibitory but not all; basket cells contact cell bodies and proximal dendrites of pyramidal neurons to control excitability of output neurons (remember, this is an influential place to be!); cnahdelier cells form axo-axonic contacts with axon initial segments of pyramidal neurons (one neuron can have wide effect on function!)

28


Layers of the cerebral cortex


Neocortex has 6 layers

Each of the 6 layers has combination of pyramidal and nonpyramidal neurons (but different predominance in each layer)

Olfactory region and hippocampus have only 3 layers

29


6 layers of the cerebral cortex


Molecular layer: not many cell bodies (Layer I)

External granular layer (Layer II)

External pyramidal layer: project to cerebral cortex of opposite hemisphere (Layer III)

Internal granular layer: receive information (Layer IV)

Internal pyramidal layer: project information; project to subcortical regions (striatum or spinal cord) (Layer V)

Multiform layer: wide variety of cell types (Layer VI)

30


Layers in primary motor vs. sensory areas of cortex


In primary motor area, have poorly developed layer IV; "agranular"

In sensory areas, have poorly developed layer V; "granular cortex"

31


Laminar organization in the cerebral cortex


There is specificity in the sites to which neurons in the different layers project

32


Columnar organization in the cerebral cortex


Axons and apical dendrites have vertical organization and there is synaptic interaction between different layers

Info comes in from afferent cell, goes to interneuron in layer IV which sends projections to spines of a pyramidal cell --> pyramidal cell sends projections down/out but also sends collaterals to GABAergic neurons that can inhibit pyramidal cells on either side of this functional column --> more specificity

Vertical columns (functional columns) from cortical surface to white matter

Neurons in given column respond to same stimulus (Ex: some columns activated by touch and others by position of joint)

Prominent feature of visual cortex

"Sharpened" by inhibitory neurons that influence other neurons at edges of columns (basket cells)

This is how we get functional specifications within the areas we've been talking about

33


Conduction aphasia


Lack of communication between Broca's and Wernicke's areas

34


Blood supply territories of the brain


Middle cerebral artery: lateral hemisphere surfaces, temporal and frontal lobes, striatum and globus pallidus (specifically deep branches of MCA/lenticulostriate arteries); affects Broca's, Wernicke's, primary motor and primary somatosensory, auditory

Anterior cerebral artery: front and center; oflactory bulbs, primary motor and primary somatosensory, corpus callosum

Posterior cerebral artery: back, part of temporal lobe and occipital lobe, visual, thalamus

35


Thalamocortical relationships


Basal ganglia and cerebellum --> VA and VL of thalamus --> motor cortex of cerebral cortex

Spinothalamic tract and medial lemniscus and trigeminal lemniscus --> VPL and VPM of thalamus --> somatosensory cortex of cerebral cortex

Substantia nigra, ventral pallidum, olfactory cortex, amygdala --> MD of thalamus --> prefrontal cortex of cerebral cortex

Optic tract --> LG --> primary visual cortex of cerebral cortex

Inferior colliculus and lateral lemniscus --> MG --> primary auditory cortex

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Optic radiations and Meyer's Loop


From LGN, upper fibers take care of lower visual field and lower fibers take care of upper visual field

37


Terminology for visual field defects


Side of field: right vs. left visual field

Region of field: homonymous (same field for each eye) vs. temporal (bitemporal) vs. nasal (binasal)

Amount of field: hemianopia (half) vs. quadratanopia (superior or inferior)

38


What are fibers that eventually make up internal capsule called higher up?


Centrum semiovale --> corona radiata --> internal capsule

39


3 parts of internal capsule


Anterior limb: frontopontine fibers, anterior thalamic radiation (sensory??)

Genu: corticobulbar fibers?

Posterior limb: corticopontine fibers, superior thalamic radiation, corticofungal fibers, corticospinal fibers (motor??)

40


Pyramidal vs. granular cell


Pyramidal cells are projecting (layer V)

Granular cells are receiving (layer IV)

41


Basket cells


GABAergic interneurons in the cerebral cortex, but also in the cerebellum, hippocampus

Project to pyramidal cells right near the body of the pyramidal cell, which is an influential place to be!

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