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Chika- SF2 > Thalamus- Burke > Flashcards

Thalamus- Burke Flashcards

1
Q

The thalamus is an important processing station in the brain as nearly all pathways that project to the cerebral cortex does so via relays in the thalamus. What is the exception?

A

(the exception is olfaction)

All sensory projections are first processed through the thalamus with the except of olfaction.

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2
Q

Thalamus function

A
  • a major integrator of information
  • relay system
  • convert chemical signals to consciousness
  • is the gateway to the cerebral cortex

without thalamus we would not have consciousness

Lesions of the thalamus can produce disturbances in sensation, motor function, cognitive function, memory, emotional behavior, and levels of arousal. Damage to the thalamus can lead to permanent coma.

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3
Q

Lateral geniculate nucleus

A

thalamic nucleus for VISION

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4
Q

Thalamic nuclei typically receive dense reciprocal feedback connections from the cortical areas to which they project. Vast minority come back from the primary cortex.

A

In fact, corticothalamic projections outnumber thalamocortical projections by about 40:1.

brainstem–> thalamus–> cortex

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5
Q

Thalamus is the size of a cashew but has around 50 distinct regions (nuclei).

A

There are over 50 defined subnuclei of the thalamus based on cytoarchetecture, connections and function.

  • part of the diencephalon
  • has specific nuclei like LGN
  • not all 50 nuclei are specific but are nonspecific

-All thalamic nuclei have reciprocal connections with specific cortical layers

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6
Q

Charles S. Sherrington (1906)

T. Graham Brown (1915)

Rodolfo Llinás 1990’s

A

external factors drives

brain is driving how our brain works

intrinsic connectivity along with external signals influence functioning of brain

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7
Q

Thalamic cortical AKA corticopetal projections

A

projections from thalamus to cortex which are excitatory (glutamate)

  • they help form the pattern of what the cortex will look like (embryonically)
  • uses GLUTAMATE which is EXCITATORY
  • Conveys sensory, motor, and autonomic information from the brainstem and spinal cord
  • Estimated that for every 1 thalamocortical projection there are 40 corticothalamic projections

Thalamocortical (corticopetal-towards cortex) projects to layer IV and are glutamatergic-excitatory
All thalamic nuclei have reciprocal connections with specific cortical layers

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8
Q

Corticothalamic AKA corticofugal projections

A

projections from cortex down to thalamus which are excitatory

(corticofugal-away from cortex) originates from layer VI excitatory glutamate

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9
Q

Layer IV

A

Thalamocortical (corticopetal-towards cortex) projects to layer IV and are glutamatergic-excitatory

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10
Q

Layer VI

A

project back to the thalamus

Corticothalamic (corticofugal-away from cortex) originates from layer VI excitatory glutamate.

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11
Q

Specific nuclei in the thalamus: Lateral geniculate nucleus of the thalamus

A
  • is a specific thalamic nucleus AKA has a specific modality: it is driven by (vision)
  • main driving force is the eye
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12
Q

Nonspecific Thalamic Nuclei

A
  • get return of Layer VI projections as they are modulated
  • driven by primarily Layer V input from the cortex

again these are all excitatory

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13
Q

Neurons of the thalamus (embryology)

A
  • formed really early in embryonic development
  • formed before the cortex is formulated

We go from an outside in formation of the cortex; when the cortex is being populated by neurons layer VI gets populated first the 5, 4, 3, 2, 1; so these neurons have to go through the different layers to get to the top but they have to be guided somehow

  • we will have radial glial cells and thalamocortical projections that will help guide these thalamic neurons up the cortex
  • since the neurons are formed before the cortex, the axons of these neurons have nowhere to go so there is a waiting period what we call the subplate zone

so we have these thalamus neurons that are already formed and want to get to the cortex because they are getting signals to go up the cortex; so they start to be placed in the cortex that is when the thalamocortical projections can finally go to their resting place; but interestingly these thalamocortical projections, since they have no where to go they will help form the cortex through signaling pathways

  • when the thalamic nuclei are since they don’t have a place to go they will help form the cortex and this is done by signaling pathways projections from the thalamus along with radial glia
  • they help form the pattern of what the cortex will look like
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14
Q

Thalamocortical migration/projection during development

A

???

  • do NOT use glutamate as the primary signal
  • use serotonin as trophic factor or signaling pathway to help make sure these thalamic neurons are getting to proper areas in the cortex; not glutamate which is later used

-also uses signaling pathways that guide development of cortex like:
Ephrin: spasticity; remodeling, and migration

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15
Q

Subplate zone in developmental aspects of thalamus

A

subplate zone is the waiting area for the cortical projection and the subplate zone after birth eventually becomes white matter

subplate zone is the future white matter; is involved in the development of the cortical circuitry and is relevant for the pathogenesis of migration disorders and cortical dysplasia

-like schizophrenia

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16
Q

Serotonin in developmental aspects of cerebral cortex

A
  • is a modulator of developing thalamocortical axons (TCAs)
  • TCA transiently express serotonin transporters that actively takes up serotonin and then uses this as a “borrowed transmitter” for development
  • if serotonin transporters are block you alter signaling which will alter the baby’s cortical development

elevate serotonin you alter the cortical development permanently (can contribute to autism)

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17
Q

NEED to KNOW

A
  • Thalamus plays a major role in development
  • TCP are sitting in the subplate zone (resting area) helping the migration of newly generated neurons to reach the cortical plate
  • TCP borrows serotonin as the NT not for neurotransmitter activity but s a trophic factor; if you alter that amount of serotonin available, you alter migration thus altering cortical development through these TCP
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18
Q

What happens when you add too much interstitial interneurons? How does it affect neural circuitry?

A

Note that subplate neurons are key neuronal elements in the fetal cortex and important interneurons for thalamic input.

TCP get messed up

  • schizophrenia
  • hyperactivity of dopamine neurons
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19
Q

Thalamus location

A
  • Thalamus proper: Dorsal thalamus
  • superior thalamus is grooved by the fornix, lateral to which the thalamus forms part of the lateral ventricle

-Anterior-Posterior
Interventricular foramen to posterior commissure

-Transversely
From internal capsule to third ventricle

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20
Q

Basic anatomy of thalamus

A

-landmark: internal medullary lamina divides the thalamus with a medial, anterior, and lateral cell groups

21
Q 
Lateral dorsal (LD)
Medial dorsal (MD)
thalamic nuclei
A

autonomic and limbic related

22
Q 
Ventral Intermedial (VI)
Ventral Anterior (VA)
Ventral Lateral (VL)
thalamic nuclei
A

motor related

-so will have a lot of basal ganglia and cerebellar connections

23
Q

Ventral posterolateral (VPL) thalamic nucleus

A

sensory info from all of our entire body related except for head and neck coming into VPL

24
Q

Ventral Posteromedial (VPM) thalamic nucleus

A

sensory info from head and neck

Which cranial nerve would provide the majority of sensory info for the head and neck?

trigeminal nerve provides:

  • chief mesencephalic -trigeminal spinal ganglion
  • all go to the VPM
25
Q

Different Pathways to get to the brain

hippocampus????
2 other things mentioned 35 minutes

A

Medial group helps connect the cortex to to her cortical regions???

  • paraventricular: limbic related
  • rhomboids and reuniens: interface btw medial prefrontal cortex which is the cortical region for our executive functions making us different from other mammals
  • reuniens nuclei in the midline group
  • hippocampus: can project to the cortex but the cortex cannot project to it; is for short and long term memory in which you have to go to the thalamus through the midline neurons

these are major cognitive areas

26
Q

Higher order thalamic nuclei

A

pulvinar and lateral posterior thalamic nuclei

-pulvinar nucleus the one that has expanded the most

27
Q

interthalamic adhesion/massa intermedia

A
  • Right and left thalamus are connected by this (but it doesn’t really connect it???)
  • we do not see many axons or neuron present in the massa intermedia
  • has glia
  • function is unsure
  • in the internal medullary lamina
28
Q

external medullary lamina

A

separates thalamus with reticular nucleus

29
Q

reticular nucleus

A
  • reticular nucleus of the thalamus helps to regulate the excitability of the thalamic projection nuclei
  • is a little covering on the outside of the thalamus; it is a regulator of the thalamus; all the projections coming from the thalamus to the cortex are glutamate (Excitatory); the cortex is also sending its modulatory projections back to the thalamus and typically back to the same nuclei it got projections from
  • visual system: LGN sends projections the primary visual cortex and vice versa; but in order to reach each other they both have to pass through this reticular nucleus
  • all GABAergic (inhibitory)
  • has no projections to the cortex -will give feedback to thalamus and attenuate info through GABA projections from the thalamus that will eventually go to the cortex
  • and the reticular projection to the dorsal thalamus is part of an inhibitory feedforward connection
  • receives bi-directional input
  • projects to domain-specific areas of the thalamus
30
Q

Thalamic relay neurons may receive around 5000-8000 synapses.

A

Driving form of LGN is the retina but is modulated by so many other things

  • 44% derived from corticothalamic fibers
  • Around 40% are GABAergic mostly derived from the reticular nucleus
  • The cortex has the potential to exert disynaptic, inhibitory effect on the thalamus
31
Q

Thalamic Projecting Neurons Have what Two Physiological States?

A

Tonic vs Burst Mode

32
Q

Tonic Mode

A
  • real representation of the outside world

- Allows transmission of info to cortex

33
Q

Burst Mode

A
  • using threshold spike to give a wake up call

- disconnects cortex from incoming info, but allows signal detection

34
Q

tonic vs. Burst

A
  • Tonic reflects better linear summation
  • Spontaneous activity is higher during tonic firing which helps to maintain linerarity
  • Lower signal-to-noise ration, therefore higher detectability than during burst
  • Tonic firing minimizes nonlinear distortions in the relay thereby supporting a more faithful reconstruction of the world
35
Q

What supplies the thalamus?

A

posterior cerebral artery

The thalamus derives its blood supply from a number of arteries including polar and paramedian arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries. These are all branches of the posterior cerebral artery. Infarcts of these branches can lead to different clinical manifestations. A cautionary note however, discrete lesions of the thalamus are not common as most infarcts will include other connections or areas.

36
Q

How do we go from thalamus to cortex?

A

through peduncles:

-Anterior thalamic peduncle
Passes through the anterior limb of the internal capsule to reach the prefrontal cortex and cingulate cortex

-Superior thalamic peduncle
Passes through the posterior limb of the internal capsule to reach the premotor, motor, and somatic sensory cortices

-Posterior thalamic peduncle
Passes through the retrolentiform part of the internal capsule to reach the occipital lobe and posterior parts of the parietal and temporal lobes

-Inferior thalamic peduncle
Passes below the lentiform nucleus to reach the anterior temporal and orbital cortices

37
Q

What are the nuclear divisions of the thalamus?

A

specific (relay) nuclei:

  • Reciprocally connected to specific motor or sensory areas of the cerebral cortex
  • Ventral tier nuclei
  • Medial and lateral geniculate

association nuclei:

  • Reciprocally connected to the association areas of the cortex
  • Lateral dorsal nucleus
  • Mediodorsal nucleus
  • Lateral poster nucleus
  • Pulvinar

non-specific nuclei:

  • Not specific to any one sensory modality
  • Reticular
  • Intralaminar nuclei
  • CM
  • Parafascicular
  • Medial VA

The thalamus is divided into a medial nuclear group, lateral nuclear group, and anterior nuclear group by a Y-shaped white matter structure called the internal medullary lamina. Nuclei located within the internal medullary lamina itself are called the intralaminar nuclei. The midline thalamic nuclei are an additional thin collection of nuclei lying adjacent to the third ventricle, several of which are continuous with and functionally very similar to the intralaminar nuclei. Finally, the thalamic reticular nucleus (to be distinguished from the reticular nuclei of the brainstem) forms an extensive but thin sheet enveloping the lateral aspect of the thalamus.

38
Q

VPL
VPM
LGN
MGN

A

VPL: body except head and neck (dorsal root ganglion)
VPM: head and neck (trigeminal nucleus)
LGN: visual
MGN: auditory

39
Q

Specific (relay) nuclei

A

Specific (relay) nuclei - relay stations in pathways conducting specific sensory or motor information to specific cortical areas. This group includes: VPL, VPM, LGN, MGN, VA and VL.

40
Q

Association Related Nuclei

A

Pulvinar and lateral posterior (LP)

41
Q

Nonspecific Thalamic Nuclei

A 
The main Nonspecific Thalamic Nuclei
-Intralaminar nuclei: 
Central lateral
Paracentral
Central medial
Centre median
(centromedian)
Parafascicular

The intralaminar nuclei may be involved with the so-called “reticular activating system” proposed regulating sleep and wakefulness.

Ascending connections from the brainstem reticular formation terminate in the intralaminar nuclei. These connections with the reticular formation are not reciprocated.

-Midline nuclei: 
Paratenial
Paraventricular
Rhomboid
Reunions
42
Q

Posterior Column-medial Leminiscal pathway

remember dorsal column?

A
  • The medial lemniscus axons terminate in the ventral posterior lateral nucleus (VPL) of the thalamus.
  • once it gets in to VPL it is completely segregated by body parts (will have a hand area, finger area, etc.)
43
Q

Anterolateral-Spinothalamic Tract pathway

A
  • Conveys discriminative aspects of pain and temperature sensation
  • Processed through VPL
44
Q

Trigeminal Sensory Pathway

A
  • Mesencephalic: proprioception from muscles of mastication, tongue and extraocular muscles
  • Chief: fine touch and dental pressure
  • Spinal trigeminal: crude touch, pain, and temperature
45
Q

Specific Relay Divisions: Motor-Related Nuclei

A

Ventral lateral (VL)- anterior

  • Afferents: globus pallidus
  • Efferents: supplementary motor area

Ventral lateral (VL)- posterior

  • Afferents: cerebellum
  • Efferents: motor cortex

Ventral Intermedial (VI)

  • Afferents: cerebellum
  • Efferents: motor cortex

Ventral Anterior (VA)

  • Afferents: globus pallidus
  • Efferents: prefrontal cortex
46
Q

Autonomic- and Limbic-Related Nuclei

A

Anterior nuclei:
-Anterodorsal

-Anterventral

-Anteromedial: Reciprocal connections with the mammillary bodies and cingulate gyrus.
Anterior nuclei: encoding memory and sustained attention (limbic)

Lateral nuclei

  • Lateral dorsal
  • Lateral posterior: Reciprocal connections with cingulate cortex

Mediodorsal

  • Amygdala via the stria terminalis and the olfactory cortex
  • Serves as the major thalamic relay for information traveling to the frontal association cortex
  • higher order thalamic relay of the PFC
47
Q

Thalamic Pain Syndrome/Dejerine-Roussy Syndrome

A

Any damage within the pathway to VPL or VPM will cause:

  • Cause numbness on the contralateral body and face
  • Deficit may be more noticeable in the face, hand, and foot than in the trunk or proximal extremities
  • Larger lesions may be accompanied by hemiparesis or hemianopia which would suggest the involvement of the internal capsule, LGN or optic radiations
  • Affected individuals may become hypersensitive to painful stimuli
48
Q

MGN: specific sensory thalamic nucleus

A

relays auditory info

Chika- SF2 (63 decks)

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