Cortex and Connections Flashcards
number of cortical layers
6
exceptions to typical number of cortical layers and how many
hippocampus and parahippocampus which thin to 5 and then 3
cortical layers from superficial to deep
- molecular
- external granular
- external pyramidal
- internal granula
- internal pyramidal (ganglion)
- multiform
example of different areas of cortex with different characteristics
primary motor cortex has larger “layer 5” where there are more outgoing pyramidal cells (called Betz cells in the motor cortex)
5 lobes
frontal, parietal, temporal, occipital, and limbic
frontal lobe bounds
central sulcus and lateral fissure
parietal lobe bounds
central sulcus, lateral fissure, and parieto-occipital fissure
temporal lobe bounds
sylvian fissure and preoccipital notch
occipital lobe bounds
parieto-occipital sulcus and preoccipital notch
limbic lobe bounds
consists of parahippocampal, cingulate, and subcallosal gyri
major gyri of frontal lobe
precentral - primary motor strip
superior frontal - supplementary motor area (SMA)
middle frontal - frontal eye fields
inferior frontal - pars orbitalis, pars triangularis, and pars opercularis
precentral gyrus
primary motor strip with motor homunculus
superior frontal gyrus
supplemental motor area (SMA)
middle frontal gyrus
contains frontal eye fields
necessary for voluntary saccadic eye movements
inferior frontal gyrus
pars orbitalis and pars triangularis - associated with Broca’s area
pars opercularis - role in thought, cognition and planning behavior
parietal lobe parts
post-central gyrus - primary sensory cortex with sensory homunculus
superior parietal lobule - somatosensory association area
inferior parietal lobule - sensory association cortex
precuneus - broad functions including visuospatial processing, memory, and first-person perspective
posterior portion of the paracentral lobule - tertiary somatosensory cortex involved in stereognosis
postcentral gyrus
contains primary sensory cortex
superior parietal lobule
somatosensory association area
inferior parietal lobule
two components: angular and supramarginal gyri
sensory association cortex and has a role in perception, vision, reading, and speech
lesion to this region can lead to Gerstmann’s syndrome
precuneus
area of cortex just anterior to the occipital lobe on the medial surface
broad functions including visuospatial processing, memory, and first-person perspective
early region of atrophy in Alzheimer’s dementia
posterior portion of the paracentral lobule
tertiary somatosensory cortex involved in stereognosis
stereognosis
perception, understanding, recognition, and identification of an object by touch
tested by having a patient feel an object and identify it, such as a paperclip or a set of keys
often accompanied by other deficits like agraphesthesia
occipital lobe parts
divided into the cuneus and lingual gyri by the calcarine fissure
primary visual cortex
straite cortex
within the banks of the calcarine fissure
lesions to bilateral primary visual cortices lead to Anton’s syndrome
secondary visual cortex
visual association necessary for visual processing and depth
lies dorsal and ventral to the primary visual cortex
tertiary visual cortex
where color, motion, and depth are processed
located anterior to the secondary visual cortex
limbic system responsible
emotion, behavior, and long-term memory formation
limbic system structures
limbic lobe (parahippocampal, cingulate, and subcallosal gyri), amygdala, hippocampus, mammillary bodies, and anterior thalamus
Papez circuit
collection of structures of the limbic system that connect the limbic lobe and the hypothalamus
Parts of Papez Circuit
cingulate gyrus
parahippocampal gyrus
hippocampus
fornix
mammillary bodies
anterior nucleus of the thalamus
cingulate gyrus location
immediately above the corpus callosum
cingulate gyrus
receives input from the thalamus and surrounding cortex
projects fibers via the cingulum to the parahippocampal gyrus
damage to cingulate gyrus
unilateral damage can lead to apathy or cognitive dysfunction
bilateral damage can cause akinesis and mutism
parahippocampal gyrus
represents the cortex that surrounds the hippocampus
anterior region is entorhinal cortex, which is where the fibers from cingulate terminate
axons from parahippocampal gyrus project to the hippocampus
hippocampus location
inferomedial temporal lobe
hippocampus projections
to the mammillary bodies via the fornix, which is its major efferent pathway
associated syndromes with abnormal hippocampus
gliosis and neuronal loss of hippocampal CA1 pyramidal cell layer can lead to mesial temporal sclerosis (MTS) and focal seizures
area CA1 particularly sensitive to ischemic damage
Area CA2 is relatively spared whileCA3 and CA4 are less involved
lesions to bilateral hippocampi
profound anterograde amnesia
fornix
major outflow white fiber tract from the hippocampus synapse at the mammillary bodies
located below splenium of the corpus callosum
mammillary bodies location
round, paired structures located on the inferior surface of the hypothalamus
mammillary bodies connection
mammillothalamic tract connects the mammillary nucleus to the anterior nucleus of the thalamus
mammillary body dysfunction
occurs in the setting of Wernicke’s encephalopathy
anterior nucleus of the thalamus
the anterior thalamic nucleus projects to the cingulate cortex through the thalamocingulate fibers, completing the Papez’s circuit
Papez circuit pathway
cingulate gyrus -> cingulum -> parahippocampal region -> hippocampus (subiculum) -> fornix -> mammillary bodies -> mammillothalamic tract -> anterior thalamic nucleus -> thalamocingulate fibers -> cingulate gyrus
temporal lobe gyri
three gyri: superior, middle, inferior separated by superior, middle, and inferior sulci
superior temporal gyrus
associated with language comprehension
damage to dominant superior temporal gyrus
leads to Wernicke’s aphasia
posterior region of the superior temporal gyrus
transverse temporal gyrus of Heschl = primary auditory cortex
- receives bilateral auditory input so unilateral lesions to this area do not lead to auditory disturbances
middle and inferior temporal gyri
role in formed vision and processing
fusiform gyrus
occipitotemporal gyrus
necessary for facial recognition
lesion to fusiform gyrus
prosopagnosia/visual agnosia and Capgras delusion
prosopagnosia
failure to visually identify objects and faces
Capgras delusion
variant of prosopagnosia and psychosis where the patient has the belief that close friends and family are replaced by an imposter
major white matter tracts
U fibers
Long association fibers
Commissural fibers
Projection fibers
U-fibers
aka arcuate fibers linking one gyrus to another
most leukodystrophies will characteristically “spare the U-fibers” as opposed to a demyelinating process that will not
U-fibers are some of the last (slowest) fibers to myelinate in development
Long association fibers
connect to different ipsilateral regions of the brain
include: arcuate fasciculus, superior and inferior longitudinal fasciculi, uncinate fasciculus, cingulum
arcuate fasciculus
links Wernicke’s and Broca’s areas
if damaged, pateitns will develop conduction aphasia
superior and inferior longitudinal fasciculi
like the arcuate fasciculus, the superior longitudinal fasciculus connects Wernicke’s and Broca’s areas
inferior longitudinal fasciculi connect occipital and temporal lobes
uncinate fasciculus
connects the inferior temporal lobe to the orbital surface of the frontal lobe
cingulum
part of the Papez’s circuit that connects the cingulate gyrus to the entorhinal cortex
commissural fibers
connect contralateral cerebral hemispheres
includes: corpus callosum, anterior commissure, posterior commissure, hippocampal commissure
corpus callosum
organized into four segments; rostrum, genu, gody, and splenium
alexia without agraphia occurs secondary to infarction of the splenium of the corpus callosum and left occipital lobe
agenesis of the corpus callosum: a midline patterning defect that can be seen with other developmental abnormalities
anterior commissure
connects the olfactory bulbs, amygdala, and basal forebrain
posterior commissure
connects language processing centers from both hemispheres
hippocampal commissure
aides in memory function
projection fibers
link the brain and spinal cord
can be either afferent or efferent
internal capsule most important
internal capsule
divided into three regions:
- anterior limb: has multiple different radiations but includes many thalamocortical fibers
- genu: contains the corticobulbar tract (cortex to the brainstem)
- posterior limb: contains corticospinal (axons from the primary motor cortex), somatosensory, and corticopontine fibers
