thalamus + cortex (dr maloney) Flashcards
how are cells organized/layered in lateral geniculate nucleus
by cell type + eye:
- magnocellular: contra
- magnocelular: ipsi
- parvocellular: ipsi
- parvocellular: contra
- parvocellular: ipsi
- parvocellular: contra
ex. if we are in the right LGN, layer 1 is input from magnocellular cells in the left eye
info from the nasal side of eyefields DOES/DOES NOT cross in optic chiasm
DOES
(fibers from left eye cross to right in optic chiasm and project to right LGN)
info from the temporal hemifeild DOES/DOES NOT cross in optic chiasm
does NOT
(fibers from left eye remain on left and project to left LGN)
BLANK cell layers seperate/sandwich between the parvocellular and magnocellular layers
KONIOcellular
thalamacortical cells (def)
project from thalamus to cortex
generally round and bushy, make up ~80-98% of neuron cell bodies in thalamus
intrinsic interneurons (def)
other major neuron type in thalamus (besides thalamacortical neurons)
form sparse dendrites over a large area, dont leave thalamus
what percentage of neuron cell bodies in thalamus do intrinsic interneurons take up
~2-20%
(other 80-98% made up of thalamacortical neurons)
the receptive fields in thalamus/lgn are largely THE SAME/NOT THE SAME as those in the retina/rgc
THE SAME
inputs to the thalamus/types of synapses occuring within the thalamus
drivers and modulators
drivers (thalamus) def.
primary excitatory inputs to thalamus
drive response of thalamocortical cells because these synapses are stronger than the others (which are mostly inhibitory)
what percentage of synapses in the thalamus are drivers
~5% of synapses
what percentage of synapses in the thalamus are modulators
~95% of synapses
modulators (thalamus) types
nonspecific and specific modulators
nonspecific modulators (thalamus) def
global,
mostly coming from brainstem (acetylcholine, seratonine, norepi)
largly serve function of global arousal (sleep/wake cycles for retic form.)
specific modulators (thalamus) def, where they project from, funciton
target localized part(s) of thalamic region
primarily from layer VI of cortex (thalamacortical neurons) and the thalamic reticular nucleus (TRN)
involved in attention + specifically gating information/selective control
firing modes of thalamicortical neurons
tonic firing + burst firing
burst firing (def)
all or nothing response (a lot of spikes or zero spikes)
burst firing thalamocortical neurons are “detectors,” quite useless unless something very important shows up
tonic firing (def)
tracks the amount of spikes in the input (not j a bunch of spikes all at once then none)
faithful relaying of info (constant)
rythems in thalamus (def + func)
thalamus (w/thalamic reticular nucleus) is responsible for brain rythyms
most prominent during sleep where one can see/measure “sleep spindles” – debated whether they have a function
the TRN (thalamic reticular nucleus) receives input from BLANK and gates what gets into the BLANK
the TRN (thalamic reticular nucleus) receives input from LAYER VI OF CORTEX and gates what gets into the THALAMUS
francis crick thought BLANK had a role in conciousness
TRN
primary nuclei of thalamus
- lateral geniculate nucleus (LGN)
- medial geniculate nucleus (MGN)
- VPL/VPM of thalamus
the primary nuclei of thalamus receive info from BLANK and send it onto BLANK
receive info from OUTSIDE OF CORTEX and sent it onto CORTEX
association nuclei of thalamus
pulvinar nucleus + mediodorsal nucleus
the association nuclei of thalamus receive info from BLANk and sent it onto BLANK
receive info from ONE PART OF CORTEX and send it onto ANOTHER PART OF CORTEX
motor thalamus (VA/VL) receive info from BLANK and send it onto BLANK
receive info from BASAL GANGLIA/CEREBELLUM and send it onto MOTOR CORTEX
what is the intralaminar nucleus (func)
receives info from reticular formation
part of the reticular activation pathway
projects directly onto cortex
name main 3 cell types in cortex
pyramidal cells (excitatory)
spiny stelate cells (excitatory)
inhibitory interneurons (inhibitory)
pyramidal cells
excitatory cells that project to cortical areas or thalamus (75% of cells)
largely define the activity/responses of cortex
spiny stelate cells
local excitatory cells, involved in computation within an area
inhibitory interneurons
non-spiny neurons in cortex (wide range of types)
help shape response of pyramidal cells, tend to have broader domains and broader tuning
how many layers are in neocortex
6
tuning (def)
the way neurons respond selectively to specific features or stimuli within their receptive field
generally speaking primary input goes into layer BLANK of cortex
IV/four
after entering layer IV of cortex, input goes BLANK
either to layers II and III (where it then goes to cortex) OR layers V and VI (where it then goes to thalamus/TRN/other subcortical structures)
ocular dominance columns (def)
columns of neurons in primary visual cortex that respond preferentially to one eye
these columns are consistant vertically and are one (of many) types of column in visual cortex
orientation comes from BLANK cells discovered by BLANK (won nobel prize)
SIMPLE cells discovered by HUBEL AND WEISEL
simple cells (function)
help with orientation.
thought to be generated by combining inputs from lateral geniculate nucleus specifically to make a bar
complex cells (function)
respond to oriented bars accross multiple locations in space making them “spacially invarient”
adapt quickely - therefore sensitive to motion
hypercomplex cells (function)
also known as “end stopped cells”
like complex cells EXEPT only respond to bars of short length rather than a moving edge (longer bar/complex cells)
true/false: excitatory neurons have SHARPER tuning than inhibitory ones
true!
cytochrome oxidase blobs (def)
specialized regions made up of kiniocellular cells found in layers 2 + 3 of visual cortex (blobs as opposed to columns like parvo and magnocellular cells)
have high concentration of cytochrome oxidase (enzyme) which is involved in mitochondrial respiration + energy production
