Diencephalon & Basal Nuclei
Where does efferent information project to?
- Primary somaotsensory cortex (SI, area 3, 1, 2) of the post central gyrus of the parietal lobe
Where does the dorsal thalamus project to?
- Projects to nearly all areas of the cerebral cortex?
Activation of the direct pathway ____ movement.
- Promotes
How does cholinergic signaling affect firing in the indirect pathway?
- Promotes firing
Which is the largest nucleus in the thalamus?
- Pulvinar
The ____ and the caudate form the ____.
- Putamen - Striatum
What is the dorsal thalamus involved in?
- Receives & passes sensory information and involved in regulating complex cycles
What type of information does the habenular nuclei receive? Which structure receives this info first?
- Receives afferents from the ventral and medial forebrain that arrive though the stria modulars thalami
Most of the fibers in the internal capsule are ___ connections between the thalamus and the ____ cortex.
- Reciprocal - Cerebral
How does the basal ganglia modulate function?
- Release from inhibition (disinhibition)
What shape is the ventral thalamus? Where is it located?
- Resembles biconvex lens - Rostral to the substantia nigra & ventral to the lenticular fasciculus
What do both DA and ACh neuron populations respond to?
- Reward related and novel stimuli, particularly reward-predictive cues
Between which 2 structures does the stria modulars thalami run?
- Runs posteriorly in the groove between the thalamus & caudate
What does the internal medullary lamina do?
- Segments the thalamus into its principle nuclear groups
Regarding the direct pathway, what is the "loop of control"
- Selective movement - Disinhibition of thalamocortical target regions
The principal structure for all ____ and ____ info destined for the ____ cerebral cortex.
- Sensory - Motor - Ipsilateral
What does strong inhibition allow the basal ganglia to do?
- Serve as a master regulatory center - arbitrating between multiple excitatory inputs
When the firing rate of the GPe is inhibited, how does the subthalamic nucleus react?
- Short term excitation
Where is the globus pallidus with respect to the caudate?
- Slightly lateral and ventral
What type of information does the pulvinar process?
- Spatial aspect of visual processing
What efferent fibers are used to get info to the substancia nigra?
- Striatonigrals
Which fibers project efferents to the globus pallidus?
- Striatopallidals
Where are TAN neurons found?
- Striatum
Which structure receives efferents? Via?
- Striatum - Nigrostriatals
From which structures does the globus pallidus receive input?
- Striatum - Subthalamic nucleus - Substancia nigra
To which structures does the SNr send efferent fibers?
- Striatum - Superior colliculus - Parabrachial pontine RF
What do the firing rates in the striatum depend on?
- Strong cortical excitation
Which type of inputs are facilitated thru D1 receptors in the direct pathway?
- Strong, phasic inputs
What is required by those with Parkinson's Disease in order to initiate movement?
- Stronger cortical drive
To which structures does the subthalamus project? (2)
- Substancia nigra - Globus pallidus internus
From which structure does dopamine arise?
- Substancia nigra pars compacta (SNc)
What are the 2 parts of the nigral complex?
- Substancia nigra pars compacta (SNc) - Substancia nigra pars reticulata (SNr)
The majority of the ventral thalamus is the ____ ____.
- Subthalamic nucleus
The majority of the subthalamus is the subthalamic ____, one of the ____ ____.
- Subthalamic nucleus - Basal ganglia
Which structure does the globus pallidus externes primarily project to? By way of?
- Subthalamic nucleus - Subthalamic fasciculus
The ____ is supplied by central (perforating) branches of the ____.
- Subthalamus - Circle of Willis
Which structure sends input to the pulvinar? Which part of the cortex does the pulvinar project to?
- Superior colliculus - Visual association cortex
Does cholinergic signaling suppress or promote movement in the direct pathway?
- Suppress
How does D2 affect the firing rate of the striatum to the indirect pathway?
- Suppress
How is striatal activity affected by D2 receptors in the indirect pathway?
- Suppress
How do D2 receptors affect the firing rates of indirect pathway neurons?
- Suppress firing
Activation of the indirect pathway ____ movement.
- Suppresses
Does cholinergic signaling suppress or promote movement in the indirect pathway?
- Suppresses
Which neurons give off acetylcholine?
- TAN (Tonically active neurons)
The caudate is part of the ____.
- Telencephalon
The putamen is part of the ____.
- Telencephalon
What structure is formed when the ansa lenticularis and the lenticular fasciculus merge?
- Thalamic fasciculus
Disinhibition of which connection will result in movement?
- Thalamocortical
Caudal thalamus, MGB, LGB, and the pulvinar are supplied by the ____ artery, a branch off of the ____ PCA (posterior cerebral artery)
- Thalamogeniculate - P2
Which arteries supply rostral areas of the thalamus? Which part of PCA do they branch from?
- Thalamoperforating arteries - P1 of PCA near the basilar bifurcation
What structures make up the diencephalon?
- Thalamus - Hypothalamus - Epithalamus - Subthalamus
Which structure does the globus pallidus internus primarily project to? By way of? (2)
- Thalamus - Lenticularis & Lenticular fasciculus
What is the physical structure of the thalamus? Which ventricle does it surround?
- Thalamus consists of 2 symmetrical, ovoid masses of tissue - Surrounds the 3rd ventricle
Which structures does the internal capsule separate?
- Thalamus from the globus pallidus and putamen (lentiform nucleus) - Caudate from the putamen
Where do efferents from the globus pallidus project to, eventually making their way to the premotor and supplementary motor areas? Via?
- Thalmus (VA, VL) - Thalamocorticals
What does "ansa lenticularis" mean?
- The handle of the lenticular nucleus
Do the nuclei groups communicate?
- There is NO interconnection fibers among different nuclei groups within the thalamus
What increases with rising task complexity?
- Time delays - Cognitive loading
What type of neuronal firing takes place resulting in the absence of movement?
- Tonic neural firing
What are the 2 types of intrinsic interneurons?
- Tonically active neurons (TAN) - Medium spiny neurons
How does a brief decrease in firing rate affect target regions?
- Transiently release target regions from this inhibition
What is the pineal gland really?
- Underdeveloped third eye
Where does the thalamic fasciculus go to?
- VA thalamus - VL thalamus
What is another name for the subthalamus?
- Ventral thalamus
What 2 divisions is the ventral posterior nucleus separated into? 1 for ____ info and 1 for ____ info.
- Ventro posteromedial (VPM): head related information - Ventral posterolateral (VPL): for body related information
Where is the ventral segmental area located?
- Ventromedial to SNr, unpaired region of the midbrain
Are striatal neurons typically hypo- or hyper-polarized?
- Very hyperpolarized
Are medium spiny neurons active?
- Very little spontaneous activity
Fibers from ____ ____ complex (position sense) and from ____ nucleus (taste)
- Vestibular nuclear complex - Gustatory
What is affected as a result of the anterior choroidal artery syndrome (blockage or stroke)?
- Visual and motor deficits that reflect damage to the optic tract and the inferior portion of the posterior limb of the internal capsule
Which type of inputs are suppressed thru D1 receptors in the direct pathway?
- Weak inputs
What are pinealocytes?
- Weakly light sensitive and receive information concurring light levels though a multi-synaptic neural circuit
What is the extra medullary lamina? Where is it found? What 2 parts of the thalamus does it separate?
- White matter sheath; over covering of the lateral aspect of the dorsal thalamus (medial aspect borders 3rd ventricle) - Blends with projection pathways to separate dorsal & ventral thalamus
Indirect pathways are ____ and ____.
- Widespread - Diffuse
What neurotransmitter do TAN's use?
- Cholinergic
The caudate is involved more so with ____ functions than with ____.
- Cognitive - Movement
What is required to move the striatum into an up state? What is this called?
- Concerted cortical activation to move striatum to up state - Selection mechanism
What type of information is the ventral posterior nucleus a pathway for?
- Conscious awareness of somatic sensation, pain, temperature, touch, proprioception
What does the temporal cortex perceive?
- Conscious awareness of sound
What is the relationship between cortical and striatal activity?
- Constantly oscillating with spontaneous low-frequency membrane oscillations
What does the dorsal thalamus control?
- Control the flow of information from the periphery to the cortex
Where does the habenulointerpeduncular tract send output?
- Conveys output to descend to paramedian midbrain reticular nuclei
Which structure fans out above the internal capsule?
- Corona radiata
Almost all nuclei send fibers to the ____ and receive ____.
- Cortex - Reciprocal connections
Regarding the motor loop, what structures make up the motor loop?
- Cortical input (Primary motor cortex, Premotor, Supplementary cortex) - Striatum (Putamen) - Pallidum (Lateral globus pallidus, internal segment) - Thalamus (Ventral lateral and ventral anterior nuclei)
What are the 2 tracts going thru the internal capsule?
- Corticothalamics - Thalamocorticals
Which layers are crossed?
- Crossed fibers to layers 1, 4, 6; Nasal hemiretinas
Which population of dopamine receptors are associated with the direct pathway?
- D1
Which population of dopamine receptors are associated with the indirect pathway?
- D2
Where do efferent fibers project to preferentially? What other areas?
- D2 neurons of the striatum - Ventral striatum, limbic, and neocortical areas
What affect does the D2 have on Ca++ currents? Less positive charge ____ the neuron.
- Decreasing Ca++ currents - Enters
Which other structures observe patch boundaries?
- Dendritic arbors
Where do medium spiny neurons receive input from to be active? With which disease are the lost?
- Depend on excitatory input for discharge (from corticostriates mainly) - Huntington's disease
Effect of indirect pathway output on GPi/SNr?
- Diffuse, widespread excitatory contact
What promotes movement? Which circuit discharge?
- Disinhibited thalamocortical circuit discharges promoting movement
Movement modulation (section) occurs through ____.
- Disinhibition
What has to happen in order for movement to take place?
- Disinhibition of thalamocoritcal target regions
What results from damage to or disorders of the basal nuclei?
- Disruption of movements
VAT is ____.
- Dopamenergic
SNc are ____ neuromodulators. These are lost with ____ disease.
- Dopaminergic - Parkinsonism
What is the largest division of the thalamus?
- Dorsal thalamus
Which layer is more dorsal? Ventral?
- Dorsal: Substancia nigra pars compacta (SNc) - Ventral: Substancia nigra pars reticulata (SNr)
How many nuclei make up each half of the thalamus?
- Each half can be divided into numerous nuclei (~26)
In the direct pathway, narrowly focused GPi/SNr inhibition leads to thalamic ____.
- Excitation
What affect does inhibition of GPi/SNr firing have on the thalamus?
- Excitation of thalamus
Is the subthalamic nucleus inhibitory or excitatory?
- Excitatory
Does D2 activity on the indirect pathway facilitate or inhibit movement?
- Facilitate
How are strong cortical inputs affected by D1 activity in the striatum?
- Facilitated
How does D1 presence/activity affect the direct pathway?
- Facilitates movement
What is the ultimate net effect? For?
- Facilitation of movement in response to reward predictive cues, selection action to get reward
What is another name for the habenulointerpeduncular tract?
- Fasciculus retroflexus
What is the habenula functionally implicated with? Via?
- Fear & "reward negative" responses via caudally directed limbic projections
From where does the LGB receive afferent information?
- Fibers from retina/optic nerve (crossed fibers to layers 1, 4, 6)
Effect of direct pathway output on GPi/SNr?
- Focal inhibitory contact
Direct pathway inputs are ____ and ____.
- Focused - Dense
The diencephalon is the caudal most subdivision of the embryonic _____?
- Forebrain (prosencephalon)
The substancia nigra pars reticular is ____ but interconnected with ____.
- GABAergic - SNc
Where does the SNc receive afferents from?
- GPe - Parabrachial pontine RF
Which structure is this similar to?
- GPi
The SNr is a major output of basal ganglia (with ____) for the ____ selection loop.
- GPi - Motor
What do the basal ganglia do?
- Generation and selection of goal-oriented voluntary movements
Which structures does the anterior choroidal artery go into?
- Genu - Posterior limb of internal capsule
What dose the pineal gland help with?
- Give the brain information to adjust circadian rhythm functions: sleep, body temp, appetite, etc.
To which structures does the striatum project efferent fibers?
- Globus pallidus - Substancia nigra
Which part of the globus pallidus is part of the indirect pathway? Direct pathway?
- Globus pallidus externus (lateral, GPe) - Globus pallidus internus (medial, GPi)
Unlike any of the basal ganglia, the subthalamus is ____?
- Glutamatergic (excitatory); most of the basal ganglia are inhibitory
What is a result of a vascular lesion on the subthalamus?
- Hemiballismus
Does the SNr have a high or low rate of discharge?
- High
Firing rates given off by the GPe neurons are very ____.
- High
What is maintained by the basal ganglia in order to maintain suppressed (inhibited) thalamic activity?
- High tonic level of discharge
What do the output nuclei of the basal ganglia maintain? What affect does this have on target regions?
- High tonic level of discharge - Suppress activity in tonic regions
What specifically?
- Homonymous - Hemianopsia - Contralateral hemiparesis - Hemianesthesia
Which arteries does the anterior choroidal artery come from?
- ICA (internal carotid artery)
Where does the diencephalon begin?
- Imaginary line between the posterior commissar & mammillary bodies
What does the subthalamic nucleus keep in check?
- Inappropriate motor commands
DA neurons ____ their firing. ACh neurons ____ their firing.
- Increase - Decrease
How does the disinhibited firing rate of the subthalamic nucleus affect the firing rate of the output nuclei (GPi/SNr)?
- Increase suppression of connected thalamus
With D1, what occurs in the up state? More positive charge ____ the neuron.
- Increases voltage-dependent Ca++ current - Enters
With D1, what occurs in the down state? More positive charge ____ this neuron.
- Increases voltage-dependent K+ current - Leaves
What is necessary for rising task complexity?
- Increasingly sophisticated neural loops for action selection
Which pathway does the subthalamus participate?
- Indirect pathway for action selection
Where does the ansa lenticularis emerge from?
- Inferior surface of the globus pallidus
How does cholinergic signaling affect firing in the direct pathway?
- Inhibit firing
Ultimately, what does the net effect of ACh want to do?
- Inhibit movement
High firing rates of the GPe keeps the subthalamic nucleus tonically ____.
- Inhibited
Indirect pathways lead to widespread GPi/SNr excitation which will become thalamic ____.
- Inhibition
What affect does the striatum have on GPi/SNr firing?
- Inhibition of GPi/SNr firing
Are output nuclei of the basal ganglia inhibitory or excitatory?
- Inhibitory
Output nuclei of the basal ganglia are ____ to the thalamus via ____ fibers.
- Inhibitory - Thalamocortical
The putamen and caudate (together) are thought to be the ____ layer of the basal ganglia.
- Input layer
Diencephalon literally means...?
- Interbrain
What are the 2 parts of the globus pallidus?
- Internal - External
What is the lateral boundary of the diencephalon?
- Internal capsule
Efferent fibers travel thru the ____ and project primarily to the ____ (area 4)
- Internal capsule - Primary motor area
Which structures are rostrally bound to the diencephalon?
- Interventricular foramen of Monroe - Lamina terminalis - Optic chiasm
What type of neurons are found in the striatum?
- Intrinsic interneurons
How do the thalamocortical pathways respond to the GPi/SNr excitation?
- Inverse result across thalamocortial pathways
What is the internal medullary lamina made of?
- Investment of the white matter
What is hemiballismus
- Involuntary disorder on the contralateral side - Produce rapid, forceful flailing
MGB projects efferent information to the ____ & temporal cortex.
- Ipsilateral insular
Where do the efferents project to? By way of?
- Ipsilateral side of the occipital cortex - Optic radiations (geniculocalcarine)
What other structures does the anterior choroidal artery supply?
- Optic tract - Inferior part of the lenticular nucleus - Choroid plexus of the lateral ventricle - Much of the amygdala - Retrolenticular limb of the internal capsule - Large parts of the hippocampal formation
Where do ~10% of the synapses in the thalamus come from?
- Outside afferents
Caudal hypothalamus, the ventral thalamus, and subthalamus are served by branches off ____ PCA.
- P1
What is another name for the globus pallidus?
- Paleostriatum
Which structures make up the epithalamus?
- Pineal gland - Habenulus - Stria medullaris
What is the ventral anterior nucleus involved with?
- Planning - Initiating movements
What is the ventral segmental area known as?
- Pleasure center of the brain
What do the posterior and medial posterior choroidal arteries supply? Which segment of the PCA do they branch from?
- Portion of the caudal and medial thalamus - P2
Where is the epithalamus located?
- Posteriocaudally, close to the posterior commissure
Which structure does the ansa lenticularis "hook around" in order to get to the thalamus?
- Posterior limb of the internal capsule
What causes a striatal neuron to transition from down state to up date? (_ mV)
- Potentials correlated among nearby striatal neurons - -50mV
What type of information do tonically active neurons carry?
- Predictive information about reward value of any target
What areas of the cortex is the caudate connected to?
- Prefrontal & other association areas
Where do the efferent fibers project to? (Name and area)
- Premotor cortex/ supplementary motor area (Area 6) of the frontal lobe
Medium spiny neurons are ____ ____ neurons. They are GABAergic and ____ neurons.
- Primary projection - Inhibitory
How are the direct and indirect pathways of the basal ganglia different?
Direct pathway - Facilitates the flow of information through the thalamus - Promotes movement Indirect pathway - Inhibits the flow of information through the thalamus - Inhibiting movement
Direct Pathway
Facilitates movement
Indirect Pathway
Suppresses movement
The basic circuit is divided into 2 pathways with ____ actions.
- Opposing
The diencephalon is the main processing center for information designed to reach what structure?
- Cerebral cortex
From w which 2 structures does the neostriatum receive afferent information?
- Cerebral cortex - Substancia nigra pars compacta
Where do the corona radiate fibers go below the internal capsule?
- Cerebral peduncle
Substancia nigra pars compacta by way of ____.
- Nigrostriatals
What is one exception?
- Olfactory information passes through the thalamus only indirectly
How are D1 and D2 receptor populations arranged? These areas are ____ separate areas.
- On different neuron clusters - Neurochemically separate
What is found in the ventral segmental area?
- Opioid receptors (pleasure center of the brain)
Which 2 structures form the striatum?
- Caudate - Putamen
From which 2 structures does the VL nucleus receive afferent input?
- Cerebellum (mainly from the dentate nucleus) - Basal ganglia (small input)
What does the pineal gland consist of?
- CT - Glia - Pinealocytes (endocrine function, not true neurons)
The (dorsal) thalamus is called the ____ to the cerebral cortex.
- "Gateway"
What is the down state of a striatal neuron?
- -80 mV
How long is the pineal gland? Where is it located?
- 1 cm long - Found caudal to the posterior margin of the corpus callosum and the cerebellum
How many parts or divisions make up the globus pallidus?
- 2, reciprocally connected
The diencephalon is symmetrically arranged around (and separated medially by) ___?
- 3rd ventricle
How many layers make up the lateral geniculate nucleus?
- 6
What % of the neurons in the striatum are these?
- 90%
What are habenular nuclei? Where are they found?
- A small mound of neurons on the dorsomedial surface of the posterior thalamus
From which segment of the ACA does it branch 10% of the time? 90%
- A1, 10% - A2, 90%
Where is each later of the internal capsule located and to what areas of the brain are they associated with?
- AL: links thalamus to frontal lobe - Genu: sends fibers from cortex to cranial nerve nuclei (corticobulbar) - PL: connection with parietal lobe - RL: behind lenticular nucleus; connection btw lateral geniculate body (LGB) and occipital lobe - SL: connection between MGB and temporal lobe
Which systems does the hypothalamus control?
- ANS/endocrine system
In those with Parkinson's, what happens with the indirect pathway?
- Action inhibition is effectively facilitated
Together the direct and indirect pathway create a center-surround mechanism for ____ ____.
- Action selection
In those with Parkinson's, what happens with the direct pathway?
- Action selection is effectively suppressed
Co-activation of direct and indirect pathways?
- Action selection through a center-surround mechanism - Winner take all choice of action
____ and ____ are distinct. How are loops organized to reflect this?
- Afferents - Efferents - Keeps processing loops separate
From which tracts does the ventral posterior nucleus receive afferents?
- All fibers of the medial lemniscus - Most of the spinothalmic - Most of the trigeminothalamic
Direct pathway activation ____ movement via thalamic ____ of ____ targets.
- Allows - Excitation - Cortical
Just prior to which structure does the tail of the caudate end?
- Amygdala
What are the 3 organizational principles within the basal ganglia for connectivity?
- Anatomicall parallel loops with distinct functions - Fine-grain topographic organization within distinct loops - Patch/matrix architecture
In what 2 ways are the basal ganglia segregated? Why?
- Anatomically & functionally segregated into parallel circuits that process different types of information
What are the 5 areas of the internal capsule?
- Anterior limb - Genu - Posterior limb - Retrolenticular portion - Sublenticular portion
What are the principal nuclear groups and what is associated with each?
- Anterior: related to limbic function & circuit of Papez (emotion) - Medial: may be related wit memory and the perception of pain - Lateral: dorsal & ventral tiers, sensory transmission - Intralaminar - receive afferent fibers from reticular formation, involved with consciousness & arousal
What results in motor learning? (Neurochemical alteration)
- Balance of inhibition and excitation
From which structures does the ventral anterior nucleus receive most of its afferent input?
- Basal ganglia, especially the globes pallidus internus (GPi) and substancia nigra, pars reticulata (SNr)
The MGB receives ____ auditory input.
- Bilateral
What does "substancia nigra" mean?
- Black substance
What are other names for the pineal gland?
- Body - Epiphysis cerebri
From where does the medial geniculate body receive afferent information?
- Brachium of the inferior colliculus - Fibers from internal capsule - Bilateral auditory input (majority contralateral)
TAN's have ____ cell bodies and are very active (> ____ Hz).
- Large - 100 Hz
Selection through surround inhibition occurs on ____ and ____ scales.
- Large - Small (i.e. not only reach left or right, but how far to reach)
Which nuclei makes up the lateral group, dorsal tier?
- Lateral dorsal - Lateral posterior - Pulvinar
What is formed by the joining of the globus pallidus and putamen?
- Lenticular/lentiform nucleus
Which arteries (off of M2 of MCA) supply the internal capsule, globus pallidus, and putamen?
- Lenticulostriate
What arteries serve most of the basal ganglia?
- Lenticulostriate arteries (most from M1 segment)
Direct pathway becomes ____ active, while indirect pathway becomes ____ active.
- Less - More
How does normal firing from the striatum affect Gpi/SNr discharge?
- Little impact
90% of the synapses in the thalamus originate from ___ and deciding outputs from ___.
- Local inhibitory neurons - Cerebral cortex
Tonic firing rates in the striatum are normally very ____.
- Low
Striatal neurons have ____ tonic firing rates; depending upon strong ____ inputs
- Low - Cortical
Off which segment of the MCA do the lenticulstriate arteries come off?
- M1
What is the function of the diencephalon?
- Main processing center for information destined to reach the cerebral cortex (relay structure)
What is made by pinealocytes?
- Makes and releases melanin, more strongly in the absence of light
With respect to the putamen, the globus pallidus is located immediately ____.
- Medial
What are other names for the recurrent artery of Heubner?
- Medial striate a. - Long central a.
Where does the lenticular fasciculus emerge from? What does it cross?
- Medially - Internal capsule
Aside from TAN's, what other type of intrinsic interneuron is located in the striatum?
- Medium spiny neurons
Where is the nigral complex found?
- Midbrain, just dorsal to the crus cerebri
Witch regard to the indirect pathway, what results with brief excitation of the striatum? (How is the firing rate from the GPe affected?)
- Momentary transient inhibition of GPe firing
The ventral lateral nucleus is involved in ____ feedback from the ____ and the ____ to the cerebral cortex
- Motor - Cerebellum - Basal ganglia
Cerebral cortex (primarily ____ and ____ areas) by way of ____.
- Motor - Somatosensory areas - Corticostriatals
From which structures does the subthalamus receive input? (3)
- Motor cortex - Globus pallius - Substancia nigra
What structures are involved in the indirect pathway?
- Motor cortex - Striatum - GPe - STN (subthalamic nucleus) - SPi/SNr - Thalamus
What structures are involved in the direct pathway?
- Motor cortex - Striatum - GPi/SNr - Thalamus
What functions is the putamen prominently involved with?
- Motor function of the basal ganglia
"Structured disinhibition" allows for ____.
- Motor pattern selection
Activation of the indirect pathway prevents ____ via increased thalamic ____.
- Movement - Inhibition
What are other names for the striatum?
- Neostriatum - Dorsal striatum - Caudate + Putamen
Diseases of the basal ganglia can be described as disruptions of ____ ____.
- Neurochemical interactions
What do the neurons of the substancia nigra contain?
- Neuromelanin