Class Notes (806,748)
Canada (492,424)
Neuroscience (296)
NROC69H3 (37)
Lecture 4

Lecture 4.docx

12 Pages
Unlock Document

University of Toronto Scarborough
Rutsuko Ito

Lecture 4  synaptic organization of the thalamus Midterm  calculator  40 MCQ  5 SAQ  Lante et al  Okubo et al Position and size of thalamus  human  monkey  cat  rat Thalamus anatomy  largest structure of diencephalon  collection of anatomically and functionally discrete nuclei  diagram o slide 5 Function  relay station o primary site for relay for all  sensory (except olfaction)  cerebellum  basal ganglia (motor)  limbic (motivational)  information, en route to the cortex o all systems (except olfactory system) send projections from the periphery to the thalamus o modulator of information throughout o regulation of sleep and wakefulness Table  different nuclei in thalamus o inputs o outputs o functions  different functions attributed to different nuclei o specific functions / nuclei are studied in this course Groups of thalamic nuclei  first order relays o relay thalamic nuclei  anterior thalamic nuclei  ventral anterior thalamic nuclei  ventral lateral thalamic nuclei  lateral geniculate nucleus  retina  LGN  cortex o receive well defined inputs from lower brain centers  and project to functionally distinct areas in cerebral cortex  higher order relays o association thalamic nuclei  largest part of thalamus  pulvinar region  medial dorsal nucleus  laterodorsal nucleus o receive inputs predominantly from the cerebral cortex  and project back to cerebral cortex  (associated areas)  non-specific o intralaminar nuclei o midline nuclei  receive mixed inputs from cortex and sub-cortical regions  has a wide projection pattern to the cerebral cortex and striatum Focus on LGN  parallel pathways o there is little or no interaction between the separate streams of information processing in the thalamus  midget (parvocellular) o details o facial patterns  parasol (magnocellular) o involved in movement  laminar organization o retinotopic maps exist in the LGN  monkey  functionally and anatomically segregated pathways  cat  anatomically segregated but functionally integrated? o Review! Afferents to thalamus  driver input o <10%  much less numerous  retina input is example of driver input  carries primary information to be relayed to cortex  dominates receptive field properties of target cells (for sensory relays) o removing retinal input eliminates LGN receptive fields  whereas removal of cortical or brainstem input does not  e.g LGN cells have center surround receptive fields just like theretinal ganglion cells o it appears that there is little or no information processing beyond that done in the retina in LGN  modulator input o <90% of input  comprised of local GABAergic inputs  cortical inputs and brainstem inputs (~30% each) o as well as NA, serotonergic, histaminergic inputs (<5%)  providing means by which information flow from sensory organs to the cortex can be modulated  e.g. thalamus is more of a modulator input o Review! Varied types of terminals  electron micrograph of a glomerulus (small cluster of nerve fibers) from the A layer of the cat LGN o round vesicles  large profile terminals  (5-10% of synaptic contacts) o  glutamatergic driver cell o dendrite of a relay cell o flattened terminals  f2: dendrite of GABA interneuron  associated with type 2 asymmetric synaptic terminals o irregularly sized vesicles (non-round) o lots of synaptic contacts between many types of neurons More types of terminals  round vesicles o small profile terminals  (~50% of all contacts)  glutamatergic OR modulator NA/5HT afferent from brain stem  GABA terminal of axons of local reticular cells, interneurons or nucleus of optic tract  only makes one synaptic contact o a lot of synaptic contact occurs within a very small space Triadic 'driver' junction in a glomerulus  only X cells form triadic junctions o a relay cell dendrite receives multiple synaptic transmission  there is very little astrocytic cytoplasm between synaptic profiles  Review! o what is the importance of astrocytic cytoplasm? Drivers vs Modulators  table o slide 14  modulators play a big role in thalamic function  (~90% of relay cells involved with modulation)  driver input  determines relay cell receptive field properties  excitatory (glutamatergic)  ionotropic receptors  large EPSPs  large terminals on proximal dendrites  each terminal (RL) makes multiple contacts  little convergence onto target  thick axons o faster conduction  modulator input  does not determine relay cell receptive field  excitatory and inhibitory  metabotropic receptors  small EPSPs  small terminals on dendrites o distal and proximal  each termina (RS) forms one contact  much convergence onto target  thin axons  although fewer in number, drivers are powerful activators of relay cells Cortical afferents  all 'modulator' cortical afferts to relay cells are excitatory and originate in layer 6 o each cortical modulator axon shows rich divergence and convergence  higher order thalamic nuclei receive excitatory cortical 'driver' inputs originating in layer 5 o driver input for higher order nuclei is actually a cortical one  thalamocortical neurons exhibit reciprocity of connectivity o cortical input for each thalamic nucleus generally receives inputs from the same nucleus  retonitopic map is preserved in visual cortex that receives LGN input o however, retinotopic map in the pulvinar region is less precise Corticothalamic circuitries in first and higher order nuclei  diagram o slide 16  first order nucleus (LGN)  layer 5 cell becomes driver input for cortical area of a higher order nucleus (pulvinar)  driver inputs are different according to which nucleus we are looking at  higher order nucleus (pulvinar)  Review! Other afferents  diagram o slide 17  relay cells receive  GABAergic ...  Review! Differential synaptic organization of X and Y cells in LGN  given what we know of the differential functions of X and Y cells o how is this reflected in the synaptic organization of X and Y cells? Location of afferent inputs to relay cells  retinal and parabrachial inputs are limited to proximal dendrites (ca. 100-150 m from the cell body)  cortical inputs are located at distal sites  inputs from interneurons (both from axons and dendrites) are more concentrated in the proximal zone o amonst retinal and parabrachial inputs  reticular inputs are concentrated in the distal zone, amongst cortical inputs  reticular and cortical inputs are more distal  modulator inputs are more proximal X and Y pathways through the LGN  X pathway o glomerulus triadic junction o interneuronal dendritic and axonal innervation  more complicated in terms of synaptic junctions and contacts  Y pathway o simpler in terms of synaptic junctions and contacts  how is it functionally relevant?  importance in conveying temporal information (as opposed to spatial information) o since it only few synaptic contacts o simple sunaptic contact on proximal dendritic shaft o axonal interneurons target proximal sites  X and Y cells of the cat are equivalent to the P and M cells of the rat Dendritic properties  based on assumption of passive cable properties o synaptic activity at distal dendritic sites are functionally isolated from soma and axon  diagram o slide 21  interneurons have elaborate dendritic trees  with long and thin dendrites  X and Y relay cells have compact dendritic structures  very little attenuation of PSP  inputs at distal sites seem to influence soma potential ? o Review!  it is not known if dendrites of interneurons have active electrogenesis  how is this functionally relevant? o dendritic inputs distally do not influence soma  why then are these dendrites important? Intrinsic electrophysiological properties of thalamic relay neurons  diagram o slide 22  thalamic relay neurons display diffe
More Less

Related notes for NROC69H3

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.