3.12.14 27 Telencephalon Flashcards
Name the layers of the telencephalon
- Molecular
- External Granular
- External Pyramidal
- Internal Granular
- Internal Pyramidal
- Multiform
Which layer is the molecular layer? What is it’s primary function?
Layer 1
Horizontal cells and fibers (pyramidal and granule cell dendrites)
Interconnections between adjacent cortical columns
Which layer is the external granular layer? What is it’s primary function?
Layer 2
Small pyramidal cells and closely packed granule cells
Dendrites to Layer 1, axons to deeper layers: receives info from ipsilateral (association) or contralateral (commissural) hemispheres
What is the difference between association and commissural axons?
Association: ipsilateral (same hemisphere)
Commissural: contralateral (opposite hemisphere)
Which layer is the external pyramidal layer? What is it’s primary function?
Layer 3
Small pyramidal cells
Send axons to other cortical areas (ipsilateral/association or contralateral/commissural)
Which layer is the internal granular layer? What is it’s primary function?
Layer 4
Many closely-packed granule cells
Receives the preponderance of afferent input to the cortex (corticopetal axons)
Mostly from thalamus (ventral tier and geniculate bodies especially)
What are corticopetal axons?
The preponderance of afferent input to the cortex, specifically to layer 4 (internal granular layer)
Which layer is the internal pyramidal layer? What is it’s primary function?
Layer 5
Medium and large pyramidal cells
Axons project to the striatum, brainstem, and spinal cord
Corticofugal fibers (axons that leave the cerebral cortex and do not communicate to other regions of cortex) extend from here
What are corticofugal fibers?
Fibers extending from the cortex to other regions (e.g. striatum, brainstem, and spinal cord)
Which layer is the multiform layer? What is it’s primary function?
Layer 6
Axons which project toward the pial surface; association and projection axons
Major cortical feedback to the thalamus
Brodmann area 1,2,3
Granular
Primary sensory cortex
Postcentral gyrus
Input from VPL and VPM
Brodmann area 17
Granular
Primary visual cortex
Occipital lobe in the calcarine fissure
Input from lateral geniculate bodies
Brodmann area 41, 42
Granular
Primary auditory complex
Dorsal temporal lobe
Receive input from medial geniculate bodies
Brodmann area 5, 7
Less granular
Secondary somatosensory
Input from non-specific thalamic sensory nuclei
Brodmann area 18, 19
Less granular
Secondary visual/visual association
Occipital lobe
Brodmann area 4
Agranular
Primary motor cortex
Precentral gyrus
Brodmann area 8
Agranular
Frontal eye fields (movement of eyes)
Brodmann area 44, 45
Agranular
Motor speech areas
Brodmann area 6
Less agranular
Premotor cortex
Frontal lobe
Brodmann area 22
Less agranular
Wernicke’s area (comprehension of speech)
Temporal lobe
What does the anterior commissure connect?
Middle and inferior temporal gyri of both hemispheres
What does the corpus callosum connect?
Everything but middle and inferior temporal gyri of both hemispheres (which would be the anterior commissure)
What are the 5 main intracortical connections (association cortical projections)
Uncinate Arcuate Superior longitudinal Inferior longitudinal Cingulum
What does the uncinate projection connect?
Temporal
and
Orbital gyri of frontal lobe
What does the arcuate projection connect?
Superior temporal
and
Middle and inferior frontal
What does the superior longitudinal fasciculus/projection connect?
Frontal
and
Parietal/Occipital
What does the inferior longitudinal fasciculus/projection connect?
Temporal
and
Parietal/Occipital
What does the cingulum projection connect?
Frontal and parietal
and
Parahippocampal (and adjacent temporal)
Which side is typically the dominant hemisphere? What is the dominant hemisphere in control of?
Left --- Speech (verbal memory) Writing Calculation Ideomotor and ideational praxis
Which side is typically the non-dominant hemisphere? What is the non-dominant hemisphere in control of?
Right --- Non-verbal ideation Artistic side Spatial recognition (map reading) Arousal, awareness, orientation Construction/dressing praxis
Suppose you present something to a patient’s left visual field; they are unable to tell you what they saw, but when instructed, their left hand can pick up the item out of a line-up
What is wrong with the patient?
Why can the left hand pick up the object?
Why can’t he tell you what he has seen?
Corpus callosum has been sectioned
The patient perceives the item with the right occipital lobe, instructs left hand to pick up
Can’t relay information to the associative centers or speech centers of the left hemisphere, so cannot verbally ID the object
What is alexia?
Inability to read
What is agraphia?
Inability to write
What causes alexia without agraphia?
Infarct of the branches of the left posterior cerebral artery, blood supply to the splenium (posterior aspect) of the corpus callosum and left primary visual cortex
What is associated with infarcts of branches of the left posterior cerebral artery?
Alexia without agraphia
Right homonymous hemianopsia (no right visual field)
Inability to read (even what they themselves have written)
Left hemisphere is not receiving visual information
What is apraxia? What causes it?
Inability to perform programmed, purposeful movements
Premotor areas (6, 8) are lesioned
Areas 6,8 are found where the occipital, temporal, and parietal lobes meet
What is agnosia? What causes it?
Inability to recognize objects visually
Lesion occurs in the association cortex (18,19)
18,19 found where the occipital, temporal, and parietal lobes meet
- Lesion usually occurs bilaterally
- Primary visual cortex (17) is intact
What is astereognosis? What causes it?
Inability to ID an object by touch alone
Lesion occurs in parietal association cortex (5,7)
Inability to ID object in the hand contralateral to the lesion
What is contralateral neglect syndrome? What causes it?
Neglect of the left side of the body; right side neglect is very rare
Lesion of the right parietal lobe (39,40)
If the lesion occurred in the LEFT hemisphere, the right would compensate; if it occurs in the RIGHT hemisphere, the left can control the right side of the body, but is unable to also take over responsibility for the left side
What is the blood supply for the frontal lobe?
Lateral - MCA
Medial - ACA
Inferior - ACA, MCA
What is the blood supply for the parietal lobe?
Lateral - MCA
Medial - ACA
What is the blood supply for the occipital lobe?
Lateral - MCA
Medial/inferior - PCA
What is the blood supply for the temporal lobe?
Lateral - MCA
Medial/inferior - PCA
Temporal pole - MCA
What is the blood supply for the limbic system?
Cingulate - ACA
Parahippocampal - PCA
What is a penumbra?
The area surrounding an infarct that is temporarily rendered dysfunctional; may become more active after recovery
