Thalamus I Flashcards
Charles S. Sherrington’s theory
–The nervous system is organized as a set of complex neuronal connectivity pathways triggered into action by the outside world
–Behavior is the result of sensory input
T. Graham Brown’s theory
–Function is mostly organized as intrinsically generated activity
–Sensory inputs are mostly modifiers of intrinsic activity
NOTE: Brown believed that behavior is not dictating sensory input but in fact it simply modifies it.
Rodolfo Llinás’s theory
–Proposes consciousness is a case of intrinsic activity modulated by the senses
–Functional significance of the electrophysiological properties of thalamic neurons and their connectivity with the cortex
The thalamus is an important processing station in the brain in all pathways, except __________.
olfaction
We have _________ that connect one cortical area to the next through the gyri.
U-fibers
*The thalamus is also used
The thalamus is apart of what part of the brain?
Diencephalon
There are 4 components to the thalamus. Which component is related to the basal ganglia and has limbic, motor and association areas?
Subthalamus (Ventral Thalamus)
*The ventral medial striatum (part of the basal ganglia) is limbic related; it’s involved in the reward pathway
This is the the visceral/autonomic portion of the diencephalon.
Hypothalamus
Which part of the thalamus receives limbic and amygdala input and projects to insula and ventral striatum and plays a regulatory role in autonomic functions especially responses to stress.
Epithalamus
____________ produces melatonin and is associated with biological rhythms based on light/dark cycles.
Pineal gland
What is the habenular complex?
Involved in sleep, nocioception, sensitization to drugs, motor exploration, hoarding behaviour.
- Lateral habenula is involved with stress responses, maternal behaviour, male social behaviour, reward, and estrogen dependent reproductive behaviour in females.
–All sensory projections are first processed through the thalamus except the ___________.
olfaction
Thalamocortical fibers projects to layer _______ and are ___________ (excitatory/inhibitory).
IV; Excitatory
*Thalamocortical fibers are glutamatergic
Corticothalamic fibers originates from layer _______ and are ___________ (excitatory/inhibitory).
VI; Excitatory
Visual input from the optic tract is processed by the __________ nucleus of the thalamus, auditory input in the __________nucleus, and somatosensory input in the _________ nucleus of the thalamus.
lateral geniculate; medial geniculate; ventral posterior
What role does the thalamus play in neurodevelopment?
- During development these neurons that help drive cortical development-they’re glutaminergic neurons that express a different neurotransmitter: serotonin, which is used as a trophic factor that will guide the thalamocortical projections during development, which are going up to the cortex, which hasn’t been generated yet.
- Cortical neurons are generated in the sub-ventricular zone and are guided up to the cortex to their final resting spot through the radioglial cells. Before they get to their final resting spot, these cortical neurons are going to the go into an area right below the cortex called the sub-plate zone. The subplate zone is also where the thalamocortical projects are hanging out, waiting for the cortical neurons to reach their final destination.
The __________ and _________ zones are the earliest sites of synaptogenesis in the developing cortex.
marginal; subplate
–These synapses are transient and disappear when afferents move to the cortex
–The ECM contains permissive, attractive or repellent guidance cues for growing axons
–Mediates cellular interactions required for cortical development
The superior thalamus is grooved by the ___________, lateral to which the thalamus forms part of the lateral ventricle.
fornix
____________divides the thalamus into the medial dorsal, anterior, and lateral cell groups
Internal medullary lamina
*The lateral group comprises both and anterior and posterior tiers
Right and left thalamus are connected by the __________.
Interthalamic adhesion/massa intermedia
–Transverses the 3rd ventricle
–Not considered a commisure since there is a lack of decussating fibers
–Function is currently unknown
______________separates the thalamus from the reticular nucleus
External medullary lamina
This is the only thamalic nucleus that does not project to the cortex.
Reticular nucleus
GABAergic cells of the thalamic reticular nucleus are innervated by collateral branches of_____________ and ____________ as they transverse.
thalamocortical relay cells (TCR); corticothalmic fibers
*The reticular nucleus receives bi-directional input
The reticular nucleus is over 90% made up of _____________ neurons, which are inhibitory.
GABAergnic
Does the reticular nucleus project to the cortex?
The reticular nuclei does not project to the cortex, but it will modify/ attenuate signals going to and from the thalamus to the cortex. They won’t cut off the signals completely, they’ll just tone it down. It will also send direct projections to the thalamus, but NOT THE CORTEX.
Reticular neurons project back to the relay neuron to form an ____________connection to the relay cells.
inhibitory feedback
Inputs from the periphery or intrinsic brain structures excite relay neurons, which as it transverses to the cortex excites ____________.
reticular neurons
Fibers returning to the thalamus from the cortex (to which the particular dorsal thalamus just excited) excite reticular neurons in the same sector and the reticular projection to the dorsal thalamus is part of an ____________ connection.
inhibitory feedforward
So all the fibers that go through the reticular fibers that go through the reticular fibers will activate a GABAergic component. It can be either ________ or ___________, coming down from the cortex
feedback or feedforward
Reticular Neuron Synapses
- 70% arise from corticothalamic projections
- 20-25% arise from thalamocortical collateral synapses
- The rest seem to be GABAergic possibly from other reticular neurons
The cortex has the potential to exert _________, __________ effect on the thalamus
disynaptic, inhibitory
Thalamic projecting neurons have two physiological states: ___________ and __________.
Tonic and burst mode
What are the major characteristics of tonic mode?
- Tonic reflects what goes in and comes out, linearly
- Because tonic neurons are always firing, this allows us to maintain the linearity
- Will have a lower signal: noise ratio. This is what will allow for more detectability during tonic firing than during burst firing
- Tonic firing will minimize non-linear distortions. This works to make a more accurate representation of the world
Tonic= ______ state
Burst=_____ state
Alert
Sleep
During tonic firing action potentials in the relay are linked ___________ (directly/indirect) to an EPSP.
Directly
Link between EPSP and burst firing is ________ via the all or none low-threshold spike.
indirect
What is required for activation of the burst mode?
Burst mode is a true intrinsic activation mode that can only be evoked by a period of sustained hyperpolarization that results in a well-defined cyclical activation pattern that are maintained for as long as the cells remain hyperpolarized.
Burst will maximize the _________ stimulus detection. It functions as sort of a “wake up call”.
initial
Oscillations in the 40Hz range are synchronized between a cortical area and its thalamic relay by ___________
corticothalamic projections
How do you synchronize specific thalamic relay with widespread cortical activation?
Rodalfo’s thought behind this is that the interlaminar nuclei groups- since they are widespread, they bind to different parts of the cortex together. There’s a 40 Hz oscillation through the cortex that match up with these non-specific nuclei. When two parts of the cortex are oscillating at the same time, they are bound together through the thalamus
Ted Jones’ theory
•Ted Jones- his thought is we have these input/outputs, we have the thalamus projecting to layer 4, and the cortex in layer 6 projecting back to the thalamus. What about layer 5 projections. In Jones’ model, he looks at 2 separate corticothalamicocortical pathways.
- One is: Layer 6 to the thalamus, back up to layer 4 (specific)
- The other is higher functioning thalamus- which is layer 5 cortical to thalamus (which could be associative, or to other thalamic nuclei), then back up to the cortex
- So we have two different pathways that could account for binding cortical regions together.
- Both models help bind together different cortical regions in the layer 5 cortical pathway, which allows for cortical-cortical communication, not just through the association fibers from one gyrus to the next, but from cortex to thalamus, to different parts of the cortex. That’s layer 5 connection pattern.
Neurotransmitters in the thalamus
- Glutamate (AMPA receptor)
- GABA (y-aminobutyric acid) GABA (A or B receptor)
- Acetylcholine (nicotine or muscarinic receptor)
- Noradreneline
- Serotonin
- Histamine
The ___________ supplies blood to the thalamus
Posterior Cerebral artery
What are the branches of the posterior cerebral artery?
–Polar artery
–Paramedian artery
–Inferolateral (thalamogeniculate)
–Posterior (medial and lateral) choroidal artery
What are the basic functions of the thalamus?
- Sensory integration and relay
- Motor integration and relay
- Awareness of nociceptive stimuli
- Emotional and subjective response to sensation
- Memory and instinctive behaviour
- Activation and arousal
What are the four thalamic peduncles and what the final destinations for each?
Anterior thalamic peduncle
- Destination: prefrontal cortex and cingulate cortex
Superior thalamic peduncle
- Destination: premotor, motor, and somatic sensory cortices
Posterior thalamic peduncle
- Destination: occipital lobe and posterior parts of the parietal and temporal lobes
Inferior thalamic peduncle
- Destination: anterior temporal and orbital cortices
Anterior thalamic peduncle pathway
Anterior limb (of internal capsule)-> Prefrontal cortex and cingulate cortex
Superior thalamic peduncle pathway
Posterior limb (of the internal capsule)-> premotor, motor, and somatic sensory cortices
Posterior thalamic peduncle pathway
Retrolentiform (of internal capsule)-> occipital lobe and posterior parts of the parietal and temporal lobes
Inferior thalamic peduncle pathway
Lentiform nucleus-> anterior temporal and orbital cortices
What are the three nuclear divisions of the thalamus?
- Specific or Relay nuclei
–Reciprocally connected to specific motor or sensory areas of the cerebral cortex
- Association nuclei
–Reciprocally connected to the association areas of the cortex
- Non-specific nuclei
Not specific to any one sensory modality
What are the specific nuclei of thalamus?
Motor-Related Nuclei
Ventral lateral (VL)- anterior
Ventral lateral (VL)- posterior
Ventral Intermedial (VI)
Ventral Anterior (VA)
Autonomic- & Limbic-Related Nuclei
Lateral nuclei
- Lateral dorsal
- Lateral posterior
Mediodorsal
Anterior nuclei
- Anterodorsal
- Anterventral
- Anteromedial
What are the afferent and efferents of the Ventral lateral (VL)- anterior nuclei of the thalamus?
- Afferents: globus pallidus ( of the basal ganglia)
- Efferents: supplementary motor area
What are the afferents and efferents of the ventral lateral (VL)- posterior nuclei of the thalamus?
- Afferents: cerebellum
- Efferents: motor cortex
What are the afferents and efferents of the Ventral Intermedial (VI) nuclei of the thalamus?
- Afferents: cerebellum
- Efferents: motor cortex
What are the afferents and efferent of the ventral anterior nuclei of the thalamus?
- Afferents: globus pallidus
- Efferents: prefrontal cortex
The lateral posterior nuclei of the thalamus has reciprocal connections with the____________
cingulate cortex
What are the functions of the mediodorsal nuclei of the thalamus?
- 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 (prefrontal cortex)
The anteromedial nuclei of the thalamus has reciprocal connections with the __________ and ___________.
mammillary bodies and cingulate gyrus.
What is the major function of the anterior nuclei of the thalamus?
Encoding memory and sustained attention (limbic)
What are the association nuclei of the thalamus?
Pulvinar and lateral posterior (LP)
•Lateral Posterior nucleus continuous with the pulvinar: both nuclei have some what similar connections, so the two together are sometimes referred to as the pulvinar-LP complex
- Largest thalamic nucleus
- Majority of the pulvinar is involved in vision
- The pulvinar is extensively and reciprocally connected with much of the cerebral cortex, especially visual and oculomotor areas
- Role in attention
*The pulvinar nucleus is association but has specific function as well.
The pulvinar is extensively and reciprocally connected with much of the ______________, especially visual and oculomotor areas
cerebral cortex
*The pulvinar is sometimes classified as nonspecific thalamic relay nuclei because of its diffuse projections to the parietal, temporal, and occipital association cortex. It is involved in behavioural orientation toward relevant stimuli. We will see in the next lecture that the pulvinar is probably best described as higher-order.
____________ nuclei send diffuse connections to widespread regions of the cerebral cortex and to other thalamic nuclei. These take center stage in Llinas’ theory of consciousness.
Nonspecific thalamic
Nonspecific Thalamic Nuclei
Intralaminar nuclei
- Central lateral
- Paracentral
- Central medial
- Centre median
(centromedian)
- Parafascicular
Midline nuclei
- Paratenial
- Paraventricular
- Rhomboid
- Reunions
What are the causes of damage to VPL or VPM?
–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 hemiaopia which would suggest the involvement of the internal capsule, LGN or optic radiations
–Affected individuals may become hypersensitive to painful stimuli
•Medial superior olive (MSO)
–Computes the___________of sound by interaural time differences
•Lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB)
–Computes ___________ of a sound source through interaural intensity differences
•Nuclei of the lateral lemniscus
–Contralateral side responds to sound arriving at one ear only-monaural
–Signal _________of sound regardless of intensity or frequency
–Process aspects of sound such as ________
location
position
onset ;duration
What is the midbrain auditory center?
Inferior Colliculus
–receives ascending auditory pathways via the olivary and lemniscal complexes and others that arise directly from cochlear nucleus
–Processes sounds with complex temporal patterns
____________ is the obligatory relay for all ascending auditory information destined for the cortex.
Medial geniculate
Retinogeniculostriate pathway
LGN sends axons to the cortex via the optic radiation of the internal capsule
____________ information (of the optic nerve) decussates at the optic chiasm
Nasal
The lateral geniculate nucleus has 6 layers. Which cells make up each layer?
- Magnocellular-motion and spatial analysis (layers 1 & 2)
- Parvocellular-detailed form and color (layers 3-6)
- Koniocellular- in between each of magnocellular and parvocellular layers
What are the characteristics of each layer of the LGN?
- Layer 1 and 2= big neurons
- Layer one receives visual input from contralateral eye
- Layer two receives visual input from ipsilateral eye
- Magnocellular
- Layer 3-6= small neurons
- Layers 3 and 5 are the ipsilateral eye
- Layers 4 and 6 is from the contralateral eye
- Parvocellular
Of the LGN, __________ will project to the dorsal stream of the visual system that will tell you your motion; what’s happening, where the object is moving to and from. ___________ is associated with projecting to the ventral stream, which is what’s the object, how big is, what’s the shape.
Magnocellular; Parvocellular
What would happen if you have a disorder where your magnocellular neurons are smaller? What kind of deficit would you have?
•A deficit in motion
- This is seen in fetal alcohol syndrome. When a mom drinks during pregnancy, the magnocellular becomes smaller. The ability for that child to process motion is going to be decreased
What are the characterstics of the magnocellular pathway?
–Layers 1 and 2
–Terminates 4Cα
–Larger receptive fields than Parvocellular
–Respond transiently to the presentation of stimuli
–motion
What are the characteristics of the parvocellular pathway?
–Layers 3-6
–Terminates in 4Cβ
–Respond to sustained fashion, transmit information about color
–Detailed analysis of shape, size and color-high spatial resolution
What are the characteristics of the koniocellular pathway?
- Interlaminar zones
- Terminates in patchy pattern in layers 2 and 3
- Some aspects of color vision
