lecture 17 Flashcards
what is the cerebral cortex?
thin sheet of neurons and their interconnections
the cerebral cortex is organized into ____ and ____ to ____________?
gyri, sulci, increase the surface area
evoluntionarily, the cerebral cortex has increased in both ____ and ____ due to ____________?
size of hemispheres, area of cerebral cortex, its role in language and abstract thinking
what are the areas of the cerebral cortex?
- paleocortex (old)
- archicortex (begining)
- neocortex (new)
what is encompased by the paleocortex?
some of the base of the telencephalon
what is encompased by the archicortex?
hippocampus
what is encompased by the neocortex?
what can be seen on the outside of the brain - 95% of total cortical area in primates
what are the 2 cell types of the neocortex?
pyramidal cells and non-pyramidal cells
describe pyramidal cells
- most numerous cell type and principal output neuron of neocortex
- named after shape
- have long axons to reach other cortical areas/subcortical areas where they synapse
what are Betz cells?
- giant pyramidal cells in neocortex
- axons can project several feet to the spinal cord
where can Betz cells be found?
corticospinal, corticobulbar and corticothalamic tracts
describe non-pyramidal cells
- granule (stellate) cells
- principle interneurons
- varied shapes
- multipolar
- short axons that remain in the cortex
the neocortex is subdivided into a ___ layered structure?
6
what are the 6 layers?
(1) molecular layer
(2) external granular layer
(3) external pyramidal layer
(4) internal granular layer
(5) internal pyramidal layer
(6) multiform layer
describe the molecular layer
- cell poor layer
- contains axons and dendrites of neurons from deeper layers
describe the external granular layer
projects to other areas of the cortex and is thought to participate in higher cognitive function
describe the external pyramidal layer
projects to other areas of the cortex and is though to participate in higher cognitive function
describe the internal granular layer
receives input from the thalamus
describe the internal pyramidal layer
output layer that sends information from the cortex to the brainstem, spinal cord, and basal ganglia
describe the multiform layer
- made of fusiform shaped, modified pyramidal cells
- projects to the thalamus
what are minicolumns?
cells in the layers of the neocortex line up in columns perpendicular to the sheets of cells
describe how the neurons within minicolums will synapse
what is the result?
they synapse with those in layers above and below, forming a functional unit
are the layers equally prominent throughout the neocortex?
no
describe the distribution of layers throughout the granular neocortex
layers 2-5 are dominated by small granule and pyramidal cells
the lack of what makes the granular cortex look like on continuous layer? provide an example
large pyramidal cells
-e.g. primary sensory areas
describe the distribution of layers throughout the agranular neocortex
- layers 2-5 are dominated by large pyramidal cells
- smaller granule cells appear minor in comparison
provide an example of agranular neocortex
primary motor area
what is the result of the differing size and types of cells across cortical areas?
can see a difference in thickness of the neocortex (1.5-4.5 mm)
what is the thickest cortical area?
precentral gyrus (primary motor area)
what Is the thinnest cortical area?
postcentral gyrus (primary somatosensory area)
what are Brodmann’s areas?
- 52 functionally and organizationally distinct regions of the cortex
- developed by Korbinian Broadman in 1909
what is BA4?
primary motor cortex
where is BA4 located?
anterior wall of central sulcus, tapering the strip of the precentral gyrus
BA4 is the _____ cortex of the brain
thickest
describe the cells of BA4
what do they give rise to?
- contains Betz cells
- these extend to the spinal cord where they synpase on motor neurons
- gives rise to much of the corticospinal tract
what is unique about BA4 cells?
85% of fibers cross to the opposite side of the body
decussation of the pyramids
how are BA4 cells organized?
somatotopically
-anatomical map of the body is based on the areas of the cortex that process those motor functions - areas with more intricate motor functions have a larger representation in the cortex
what is the function of BA4?
generate impulses that control the execution of movement for the opposite side of the body (inititation of movement)
what would be the result of a lesion to BA4?
hemiparesis of the opposite side
what is BA6?
premotor and supplementary motor area
where is the premotor area located?
anterior to the primary motor cortex (BA4) on lateral surface of hemisphere
what is the function of the premotor area?
externally (sensory) guided movement (e.g. catching a ball)
where is the supplementary motor area located?
anterior to the primary motor cortex, dorsal to the premotor area, and extends medially to the surface of the hemisphere
what are the functions of the supplementary motor area?
- internally guided movement
- sequence of learned actions
(e. g. playing piano)
what would be the result of a lesion to BA6?
problems preforming purposeful, coordinated movement (apraxia)
what is BA8?
frontal eye field
where is BA8 located?
medial surface of hemisphere, anterior to the motor cortex
what are the functions of BA8?
- controls eye movements
- generates saccades in contralateral direction via connection to contralateral paramedian pontine reticular formation
what would be the result of a lesion to BA8?
impaired eye movement in contralateral direction
what is BA 44&45?
Broca’s area
where are BA 44&45 located?
inferior to frontal gyrus, on the left side in most individuals
what is the function of Broca’s area?
production of written and spoken language
what would be the result of a lesion to BA44/45?
broca’s aphasia
- nonfluent aphasia
- trouble producing language
- no issues with comprehension of language
what is BA 1,2&3?
primaey somatosensory area
what is a unique feature of BA 1,2&3?
somatotopically organized
where is BA 1,2&3?
three parallel strips in the parietal lobe
BA1: postcentral gyrus
BA2: on anterior wall of postcentral gyrus
BA3: on posterior wall of the central sulcus
what is the function of BA 1,2,&3?
initial processing of touch, pain, temperature sense ans proprioception for opposite site of the body
what is the pathway for BA 1,2&3?
medial lemniscus and spinothalamic tracts –>
relay in ventral posterolateral nucleus –>
projects through posterior limb of internal capsule to BA 3, then 1, then 2
what is BA 5&7?
somatosensory association area
where is BA 5&7?
ventral to the primary somatosensory cortex
what are the functions of BA 5&7?
- orientation of objects to self and other objects by touch
- oject recognition by touch
what would be the result of a lesion to BA 5&7?
inability to recognize objects based on touch (called asterognosis, or tactile agnosia if one sided)
what is BA 17?
primary visual cortex
where is BA 17?
medial surface of hemispheres, surrounding the calcarine sulcus, extends slightly to occipital lobe
what is the function of BA 17?
communicated informatoin about contralateral visual field
what is the primary visual pathway?
optic nerve –> optic chiasm –> lateral geniculate nucleus (in the thalamus) –> banks of calcarine sulcus
what is a unique feature of BA 17?
retinotopic organization
explain retinotopic organization
how does this impact the way information from the visual field is projected onto the calcarine sulcus?
- image from visual field is flipped vertically and horizontally onyl the retina and projected to the primary cortex
- information from upper part of visual field is projected to lower banks of calcarine sulcus
- information from lower part of visual field is projected to upper banks of calcarine sulcus
what would be the result of a lesion to BA 17?
cortical blindness
- total or near loss of conscious awarness of visual stimuli
- information cannot be turned into meaningful input
what is BA 18&19?
visual association cortex
where is BA 18&19?
surrounds BA 17, occupies the remainder of the occipital lobe, and extends into temporal lobe
what is the function of BA 18/19?
higher order processing of information from primary visual cortex to recognize features as objects or people
what is BA 41?
primary auditory cortex
where is BA 41?
superior surface of the temporal lobe and transverse temporal gyri
what is the function of BA41?
perception of sound (frequency)
what is unique to BA41?
tonotropic organization
explain tonotropic organization
auditory information is projected to the primary auditory cortex tonotopically - layout of neurons in based on the frequency of sound
where is auditory information from BA 41 relayed?
medial geniculate nucleus
what would be the result of a lesion to BA 41?
unilateral lesions do not affect hearing bc of bilateral representation
what are BA 42 & 22?
auditory association areas
where are BA 42 & 22 located?
inferior to BA 41, forms most of superior temporal gyrus
what is the function of BA 42/22?
aids in the perception of auditory inputs (necessary to recognize sounds)
what would be the result of a lesion to BA 42/22?
can still hear sounds but unable to tell the difference btwn them
what is part of BA 22?
Wernicke’s area
where is Wernicke’s area located?
posterior aspect of superior temporal gyrus
on left side in most people
what is teh function of Wernicke’s area?
required for understanding written and spoken language
what would be the result of a lesion to Wernicke’s area?
- fluent aphasia
- ability to produce written and spoken word
- words/sequences have little to no meaning
- trouble comprehending language (written and spoken)
describe hemispheric specialization
-left side of cerebral cortex is the dominant hemisphere in 95% of right handed people and 60-70% of all ppl
-left handed people who are not left brain dominant can be either right brain or bilateral
^these people will recover faster from damage to lesions of language centers
what functions are associated with the left brain?
- language (broca’s and wernicke’s)
- skilled complex motor tasks
- detailed analytical abilities
- logic and problem solving
what functions are associated with the right brain?
- complex visual-spatial skills
- music perception
- imparting emotional significance to events and language
- creativity and imagination
describe structural asymmetries using planum temporale as an example
planum temporale is the heart of wernicke’s area - leftward asymmetry is seen in 60-70% of people, atypical (rightward) asymmetry has been correlated to familial risk of dyslexia