Lec 15 Thalamus Flashcards
What is the order of diencephalon structures from dorsal to ventral?
- epithalamus [including pineal, pretectal nuclei, habenula]
- dorsal thalamus [nuclei that communicated wiht cerebral cortex mostly]
- ventral thalamus [mostly TRN]
- hypothalalmus [underneath and adjacent to ventricle 3]
What does dorsal thalamus do?
- processes ascending sensory, motor, and limbic/cognitive info
- sharpens and refines receptive fields and other aspects of coding
- relays info to cortical areas [somatosensory, visual, auditory, motor, etc]
What structure is epithalamus most directly connected to?
hypothalamus
What is corticothalamic input?
- info the thalamus receives from cortical areas
- feedback inhibition from TRN
- feedfoward inhibition from descending cortical fibers
What type of transmitters do thalamocortical and corticothalamic projections use? contralateral or ipsilateral?
- both excitatory
- use glutamate
- strictly ipsilateral
What is the TRN?
- ventral hypothalamus
- composed entirely of GABAergic inhibitory interneurons
- send axons ONLY to dorsal hypothalamus [not to cerebral cortex]
What two types of neurons exist in dorsal thalamus nuclei?
- excitatory relay neurons –> project via internal capsule to middle layers [4] of cortex
- local GABAergic inhibitory interneurons –> axons remain local
What are the 3 nuclear groups of the dorsal thalamus? What divides them?
- medial [MD]
- lateral [VA, VL, LD, LP, VPL, pulvinar, LGN, MGN]
- anterior [anterior nuclei]
- divided by internal medullary lamina
What is function of nuclei within internal medullary lamina?
- receive ongoing info from all cortical areas
- project to striatum and layer 1 of cortex
- integrate info across modalities
What 3 input/output tracks via VPL? function?
function = sensory
input –> output
DC-ML AB, group 1, 2 –> S1/S2
spinothalamic Ad, C, 3, 4 –> S1/S2
vestibular nuclei –> posterior parietal cortex
What 3 input/output tracks via VPM? function?
function = sensory
input –> output
principal CN V nucleus = AB, 1, 2 –> S1, S2
spinal nucleus of V –> S1, S2
spinothalamic Ad, C, 3, 4 –> S1, S2
What 2 input/output tracks via VM? function?
function = sensory
input –> output
solitary nucleus [taste] –> gustatory cortex
spinothalamic –> insula
What 1 input/output track via LGN? function?
function = sensory
input –> output
optic nerve/tract –> V1 [primary visual cortex in occipital]
LGN = Light
What 1 input/output track via MGN? function?
function = sensory
input –> output
inferior colliculus –> A1 [primary auditory cortex in lateral fissure/heschl’s]
MGN = Music
What 2 input/output tracks via VA? function?
function = motor
input –> output
substantia nigra –> frontal cortex
globus pallidus –> frontal cortex
What 1 input/output track via VLa? function?
function = motor
input –> output
globus pallidus –> premotor cortex [PM], primary motor cortex [M1], supplementary motor cortex [SMC]
What 1 input/output track via VLp? function?
function = motor
input –> output
cerebellum –> M1
What 1 input/output track via anterior nuclei? function?
function = limbic/cognitive
input –> output
hypothalamus [mamillothalamic tract] –> cingulate cortex[gyrus]
What 2 input/output tracks via MD? function?
function = limbic/cognitive
input –> output
amygdala –> prefrontal cortex
hippocampus via subiculum –> prefrontal cortex
What 1 input/output track via LD? function?
function = limbic/cognitive
input –> output
hippocampus [via subiculum] –> prefrontal cortex, retrosplenial cortex, parahippocampal gyrus
What input/output to intra-laminar nuclei? function?
function = widespread activation of cortex/striatum, arousal integraiton
input: globus pallidus, spinothalamic, cerebellum, substantia nigra, multiple cortical areas
output: striatum [caudate and putamen], multiple cortical areas [layer 1]
What 1 input/output track via LP/pulvinar? function?
function = sensory
superior colliculus –> temporal cortex and parietal cortex
What type of neurons in the relay nuclei do ascending input neurons synapse onto?
both relay neurons and local GABA interneurons
What kind of collateral do thalamocotical axons give off en route from thalamus to layer 4 of cortex?
- give off collateral to TRN GABA cells that in turn project back into dorsal thalamus = feedback inhibition
What neurons are responsible for feedforward inhibition of dorsal thalamus relay neurons?
- collateral branches of corticothalamic axons [axons from cortex to thalamus] give off collateral to TRN which synapse onto GABAergic that target dorsal thalamus
When do you get tonic firing of thalamus? what is it?
- see it in awake/alert states
- high frequency, desynchronized activity
- thalamus fires single, high-freq APs –> favorable for information transfer through to cortex
- resting membrane potential relatively depolarized relatively depolarized
When do you get burst firing? what it it?
- see it when drowsy or in deep sleep
- slow, rhythmic oscillations, delta and spindle waves with bursts of APs
- not favorable for information flow
- resting membrane potential hyperpolarized, blocking flow of info to cortex
- maintained by functional loop between TRN and dorsal thalamus
What are the steps by which TRN-dorsal thalamus functional loop maintains burst firing?
- TRN AP causes release of GABA –> generates ISPs [hyperpolarization] in dorsal thalamus relay nuclei
- ISPSs trigger hyperpolarization sensitive channels –> increase conductance of Na –> triggers AP in neurons –> triggers AP in TRN via feedback
–> cycle repeats
How do you transition burst to tonic?
When you sleep, 5HT [serotonin] hyperpolarized membrane
causes burst firing mode and prevents info going to cortex
How do you transition tonic to burst?
ACh, histamine, and NE depolarize membrane of dorsal thalamic nuclei
–> kick relay neurons into tonic firing mode
What is the name for the set of systems of cells/nuclei that produce modulatory NTs?
reticular activating system
What kind of waves when you are awake?
low voltage, high frequency > 30 Hz, random, fast
What kind of waves when you are drowsy?
alpha waves
8-12 cps
What kind of waves when you are in REM sleep?
low voltage, random fast
sawtooth waves
What kind of waves when you are in stage 1 sleep?
3-7 cps
theta waves
What kind of waves when you are in stage 2 sleep?
12-14 cps
sleep spindles and k complexes
synchronized oscillations
6-15 Hz
What kind of waves when you are in delta sleep?
- 1/2 - 2 cps
delta waves [0.5-4 Hz]
deep sleep
synchronized oscillations
What is thalamic syndrome?
damage to posterior thalamus [eg VPL/VPM]
- causes contralateral hemianesthesia with excruciating “central” pain
- usually due to some vascular damage [thrombosis of one of arteries off of posterior cerebral artery]
What happens in tremor states due to thalamic lesion?
- rhythmic bursts in VA/VLa due to frequency abnormalities in GP-thalamus circuits
- ex parkinsons
What are 4 types of lesions that can happen from thalamus?
- thalamic syndrome
- tremor state
- amnesia
- absence seizres
What happens in amnesia due to thalamic lesion?
- vascular lesion of anterior or medial [MD] group nuclei
- disrupts amygdala/hippocampus circuitry
What happens in absence seizure due to thalamic lesion?
- form of epilepsy
- characterized by sudden arrest of movement, blank stare, fluttering eyelid, loss of ability to interact
- related to abnormal spindle wave generation caused by sustained periods of TRN GABA-ergic neuron activity
What are corticothalamic vs thalamocortical neurons?
corticothalamic: from cortex to thalamus
thalamocortical: from thalamus to cortex
