2 - Cerebral Hemispheres Flashcards
Organization of the Cortex
- Neocortex - 6-layered (90% mass)
- Allocortex - 3-layered (10% mass)
- Paleocortex (Olfactory)
- Archicortex (Hippocampal)
Clinical: Columnopathies & Autism
Disorder or modular arangement of Cortical Columns
Autism Spectrum Disorder - too many column and subcortical white matter
False Locatization
Focal lesions cause specific defects, but there is overlap–exam may yield incorrect findings
Disconnection Syndromes
Impairments in signaling fibers between regions
Cortical Signs
Aphasia
Alexia
Agraphia
Acalculia
Neglext
Visual Spatial Disorientation - early alzheimers
Memory Impairment
Behavior/Personality Change
Hemianopsia
Eye Deviation (destructive: toward side of lesion)
*Apraxia - can also be subcortical
Clinical: Observe infant reflex (Palmar Grasp, Glabellar, Sucking, Snout, Babinski)
Possible cause?
Prefrontal Cortex lesion
Agnosia
Deficits in sensory information processing, with no damage to sensory organs or memory circuits
Normal perception + stripped meaning
Damage to ventral stream of sensory perception
Visual Agnosia
Apperceptive vs Associative
Inability to recognize visual obects
Associated with Left Occipital/Temporal Lobe lesions
May be either:
Appereceptive - unilateral failure of perception
Associative - bilateral failure of recognition despire accurate perception
Clinical: Audtory Agnosia
Semantic-Associative vs Discriminative
Inability to recognize sounds; associated with Auditory Cortex/Temporal Lobe lesion
- - -
May be either:
Semantic-Associative - linguisitic left hemisphere
Discriminative - environmental sounds, music, right hemisphere
Clinical: Contralateral Neglect
Sign?
Non dominant hemisphere
Constriction Apraxia
“Clock w/all the numbers on 1/2 the face”
Major Association Pathways
Arcuate Fasciculus (think clinical)
Cingulate Gyrus
Within hemispheres ONLY
Arcuuate Fasciculus - Part of the superior longitudinal fasciculus, connects Broca’s and Wernicks’s — DISCONNECTION SYNDROME = Conduction Aphasia, can’t repeat
Cingulate Gyrus - Cells give rise to cingulum fibers, connecting emotion centers and the default mode network w/memory structures such as hippocampus and pary of limbic system
Commissural Pathways:
Anterior Commissure
Connects temporal lobes, olfactory cortices, and olfactory bulbs
Commissural Pathways:
Posterior Commissure
Connects pretectal structures (rostral midbrain)
Commissural Pathways:
Corpus Callosum
When would you medically alter this structure?
Connects homotypical regions on both sides of brain
Can alter this structure (bisect) as a treatment option for extreme seizures; however may result in some sort of change for the patient
Projection Pathways:
Corona Radiata
Passage of axons as they bundle and pass through capsules, once expanded they become the corona radiata that transverse the whole cortex
Internal Capsule
Limbs: Anterior, Genu, Posterior
“The Big One”
Nearly all ascending/descending axons pass through here
Anterior - Frontal cortex
Genu - Corticobulbar
Posterior - Corticospinal, Sensory, Temporopontine, Visual/Auditory
Medial / Lateral Geniculate
Medial sends information to Auditory Cortex (Brodman 41/42)
Lateral sends information to Optical Cortext (Brodman 17)
What blood vessel supplies the Internal Capsule and what does this result in?
Middle Cerebral Artery
Vulnerable for damage during strokes
Neostriatum
Lentiform Nucleus
Corpus Striatum
Neostriatum (C+P) - embryonically linked
Lentiform Nucleus (P+GP) - physically connected
Corpus Striatum (C+P+GP) - principle component of extrapyramidal motor system
C = Caudate
P = Putamen
GP = Globus Pallidus
Lateral Ventricles
Separation of Anterior Horns?
Clinical impact?
Septum Pallucidum separates anterior horns
Lie beneat cortical/subcortical system; any deficits (hydrocephalus, lesions, etc) can have impact on cortical/subcortical systems
What does presence of third ventricle on a cornonal cross section indicate?
you’re looking at the posterior limb of the internal capsule
Thalamus
Origin?
Major Function?
Origin: Diencephalon
Function: Receives precortical input, relays to higher areas = sensory and motor integration
*Does NOT receive Olfactory input
Thalamic Nuclei and Projections
IML
Reticular Nucleus
Internal Medullary Lamina (IML) - White Matter Tracts that divides thalamus into three primary regions (medial/lateral/anterior nuclear groups)
Reticular Nucleus - Does not project to cortex; inhibitory circuits that project back to thalamus
Functional Divisions of the Thalamus:
Sensory
VPL
VPM
LGN
MGN
Functional DIvisions of the Thalamus:
Motor
VA
VL
Clinical: Abnormalities of Thalamus
Paresthesia
and
Dejerin-Roussy Syndrom (Thalamic Pain Syndrome)
Paresthesia - Aberrant positive sensations; contralateral tingling or numbness; may be innocuous or painful
Thalamic Pain Syndrom (Dejerine) - Contrallateral lack of sensation and tingling that prigresses to severe pain; follow Thalamic Stroke
Clinical: Abnormalities of Thalamus
Dysesthesia
Allodynia
Hyperalgesia
Hemianesthesia
Homonymous Hemianopsia
Dysesthesia - Abnormal, unpleasant sense of touch (can be painful)
Allodynia - Painful stimulus induced by innocuous stimuli
Hyperalgesia - Enhance pain to hamful stimuli
Hemianesthesia - Contrallateral loss of sensation (damage to VPL/VPM)
Homonymous Hemianopsia - Loss of same half of each visual field (damage to LGN)`
VPL - Ventral Posterolateral
VPM - Ventral Posteromedial
LGN - Lateral Geniculate Nucleus
MGN - Medial Geniculate Nucleus
VPL - Ventral Posterolateral: Sensory Relay - Body
VPM - Ventral Posteromedial: Sensory Relay - Face
BOTH: Vibration, Pain, Pressure, Proprioception, Light Tough
- - -
LGN - Lateral Geniculate Nucleus: Sensory Relay - Retinal Axons to Optic Radiations (VISION)
MGN - Medial Geniculate Nucleus: Sensory Relay - Auditory Axons to Auditory Radiations (HEARING)
Brodman:
Motor
Sensory
Visual
Auditory
Motor - 4
Sensory - 3/1/2
Visual - 17
Auditory - 41/42
MCA Stroke:
Dominant Hemisphere
Non-Dominant Hemisphere
Dom - Global Aphasia
Non-Dom - Hemispatial Neglect
PCA Stroke?
Pure Alexia (Loss of reading ability)
Changes in hypersexuality/hyperaggression?
Damage to Amygdala
Two causes for homonymous hemianopia?
- Internal capsule damage
- Lateral Geniculate nucleus
Where vs What streams?
Where - Dorsal Stream
What - Ventral Stream
Akinetopsia
Motion blindness, Lateral Occipital Lob damage
Fusiform Gyrus damage
Prosopagnosia (inability to recognize faces)
Associational Fibers
Arcuate Fibers
Major arcuate fiber?
Intrahemisphere connections
Connect adjacent gyri
Superior Longitudinal Fasciculus–connects Frontal to Occipital lob
Clinical: Lesion of Arcuate Fasciculus
Conduction Aphasia (Broca/ Wernicke connection)
Limbic System Functions
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Homeostasis
Olfaction
Memory
Emotion
