Thalamus Flashcards
Convergence
Neuron in brainstem is receiving sensory input from e.g skin, the neuron is getting input from many sensory neurons, they are all converging on this neuron
Neuron is getting complex input
Divergence
One sensory neuron is sending an axon that splits and communicates with multiple neurons. Multiple 2nd order neurons are innervated by one sensory neuron
Seems like we are losing precision
Retina example of divergence
Millions of pixels coming up from retina, as we move up through visual pathway info gets combined
Lines make shapes, shapes make more complex shapes
Explain Lateral Inhibition
Strong central signal passes through and filters out weak surrounding signals
Inhibits neurons that are lateral to middle neuron
Inhibitory interneurons release GABA on side neurons so they are inhibited so center neuron fires a lot of AP but lateral neurons don’t fire
Lateral inhibition is found everywhere in sensory systems
2 types of neurons in the brain
Excitatory - Glutamate
Inhibitory - GABA
GABA vs Glutamate axon length
Glutamate - long
GABA - short, localized
Gateway to cerebral cortex almost always…
Thalamus
3 planes of cutting brain
Coronal
Horizontal
Sagittal
Thalamus
Organized as numerous discrete nuclei
3 functional distinct groups of thalamic nuclei
specific relay
association
intralaminar
Specific relay nuclei
Converge in VPL and VPM (ventral posterior lateral/medial)
VPL
SomatoSensory from body
VPM
Somatoensory info from head
Where in thalamus do specific relay nuclei convey visual information?
Lateral Geniculate Nucleus
Where in thalamus do specific relay nuclei convey auditory information?
Medial Geniculate Nucleus
Regions that control movement
Cerebellum
Basal ganglia
Ventral anterior and ventral lateral nuclei
Specific relay nuclei that connect the cerebellum and basal ganglia with the motor cortex
2 main association nuclei
Medial Dorsal Nucleus
Pulvinar Nucleus
How do we ignore everything that we see except what we focus on?
Blocking some stuff
What might association nuclei be doing?
Gatin info flow between different regions of the cerebral cortex (thalamus can act as a gate)
POSSIBLE NOT FOR SURE
Medial Dorsal Nucleus (MD)
Inputs: Prefrontal cortex, olfactory and limbic structures
Cortical outputs: Prefrontal cortex
Pulvinar Nucleus
Inputs: Parietal, Occipital and temporal lobes
Outputs: Parietal, occipital and temporal lobes, superior colliculus
Intralaminar Nuclei
Internal medullary lamina has clusters of neurons embedded in it, probably part of the arousal system but this is hypothesized
Project diffusely to many region so cortex as well as subcortical structures such as basal ganglia
What’s up with that stray neural synapse in the brainstem on the anterolateral pathway?
Activates the arousal system. That’s why pain causes arousal.
MEMORIZE SPCIFIC RELAY NUCLEI OF THALAMUS TABLE
GO TO SLIDE NAMED SPECIFIC RELAY NUCLEI OF THE THALAMUS
Pulvinar
Posterior/Caudal (Back parts of brain)
Medial Dorsal
Medial Dorsal
Every single thalamic nucleus is getting input from the cerebral cortex
Feedforward projections
Projections going UP the pathway
E.g brainstem to VPL nucleus
Feedback projections
Projections going down to thalamus
Feedforward and feedback vision example
Retina -> LGN -> Cerebral cortex = feedforward
Cerebral cortex -> LGN = feedback
Cerebral Cortex
Thin sheet of tissue 2-4mm
Divided into 6 layers
1 - outermost
6 - deepest
Where do feedforward projections from the relay nuclei project?
Layer 4
Example of C.C layer projections
Optic tract, Brainstem and Thalamic reticular Nucleus (GABA) feedforwarding to the Lateral Geniculate which then feedforwards to Layer 4 which then shows a feedback signal going back to the Lateral Geniculate from LAYER 6
Driver inputs
Come from retina
Modulator inputs
Feedback inputs coming from Layer 6 of cortex going back to Lateral Geniculate
Come from brainstem (NE neurons) - tweak and modulate basic physiologic properties of the thalamic neurons
Neuromodulators modulate behavioral of thalamus
Thalamic reticular nucleus (GABA) projects into thalamus and modulate
For Association nuclei…
Driver inputs are coming from the cerebral cortex AND modulator inputs are coming from the cerebral cortex
Driver inputs come from layer 5
Modulator come from layer 6
Feedback projections to the thalamus come from which Layer of CC?
Layer 6
Hypothesis for what thalamus is doing - gatekeeper regulating info flow to the cortex
Modulatory inputs could be playing a role in altering the physiological properties with specific thalamic neurons so that the different neurons are either relaying the info to the cortex in different ways or maybe some of the neurons are relaying the info up and other neurons the info is getting filtered out
Maybe helps you pay attention
AP firing methods for thalamic neurons
Transmission mode
Bursting Mode
Transmission Mode
Output mirrors input
If sensory inputs increase their firing rates then thalamic neurons will increase their firing rates
Bursting Mode
Fire bursts of 3-8 action potentials separated by quiet periods lasting 100s of milliseconds
Sleep wave cycles
2 diff firing modes of thalamic neurons
Bursting
Transmission
Bursting mode and Sleep wave cycles
Neurons in cerebral cortex start firing in rhythmic bursts similarly to thalamic neurons
Complicated interaction between C.Cortex and thalamus
How are thalamic neurons shifted from burst firing mode to tonic (transmission) firing mode?
Neuromodulators (Acetylcholine, NE and Histamine) which are released during wakefulness depolarize thalamic neurons
Reading 3
Association Nuclei of the Thalamus
Internal Capsule
Axons follow the internal capsule which is a massive fiber tract to get to and from the cerebral cortex
Where is the internal capsule?
Thin sheet of white matter surrounding the thalamus
Horizontal view of internal capsule vs Coronal view
Look at slides
