Basal Ganglia and Cerebellum Flashcards
T/F The basal ganglia and cerebellum directly influence lower motor neurons.
FALSE The basal ganglia and cerebellum do NOT directly influence lower motor neurons. They influence movement by regulating activity in upper motor neuron circuits.
Basal Ganglia
-most known for
Not ganglia
Definitely basal
*Most known for role in movement but functions not limited to movement
Parts of the Basal Ganglia
Striatum (aka corpus striatum): caudate and putamen
Pallidum: globus pallidus and substantia nigra (pars reticulata)
Pallidum:
-made up of ?
globus pallidus and substantia nigra (pars reticulata)
Main source of output from basal ganglia to other parts of brain
Where the medium spiny neurons send their axons
Striatum (aka corpus striatum):
-neurons
- caudate and putamen
- Main area of input
- Contains medium spiny neurons with large dendritic trees***
caudate and putamen make up
make up the Striatum (part of the basal ganglia)
Caudate:
-where sends projects?
sends projections to the substantia nigra pars reticulata (and internal portion of globus pallidus)
Putamen:
-where sends projections
Putamen: sends projections to the external and internal globus pallidus
what areas of the basal ganglia are defs true basal ganglia structure
- caudate, putamen, and globus pallidus ARE FOR SURE
Note: Not everyone agrees on which structures are a part of the basal ganglia or not. however they argree on the above
Input to Basal Ganglia
-mostly from cortex
- Nearly all regions of the cortex send direct projections to the striatum
- Therefore, the cortex is the largest source of input
- Mostly from association areas and the temporal, insular, and cingulate cortices
- Collectively refer to these pathways as the CORTICOSTRIATAL PATHWAY
*The cortical input to the caudate and putamen are NOT equal
*The cortical input to the caudate and putamen are NOT equal, explain
- Caudate receives projections mostly from multimodal association cortices and motor areas in the frontal lobe that control eye movement
- Putamen receives projections from the primary and secondary somatosensory cortices, extrastriate visual cortex, premotor and primary motor cortices, and auditory association areas
Multiple Parallel Pathways
- to the caudate and the putamen
*The caudate and putamen receive different streams of information from different regions of the cortex
*This suggest that the corticostriatal pathway is composed of multiple parallel pathways and that the caudate and putamen have different functional roles
The output from the caudate and putamen is also segregated, which reinforces this idea
*Some of the projections to the basal ganglia are topographically mapped (visual and somatosensory) and some are overlapped (those from more interconnected or association regions)
There are rostrocaudal bands of cells that seem to be concerned with different parts of the body and the movement of that part
Striatum: Patch and Matrix
*If you look for acetylcholinesterase (inactivator of acetylcholine), you see that there is compartmental organization of the striatum
*Patch: lightly stained
Makes up less of the striatum
Receives most of input from the prefrontal cortex
Caudate patches project mostly to the substantia nigra pars compacta (dopaminergic cells)
*Matrix: densely stained
-Makes up the bulk of the striatum
-Receives input from most of the regions of the cortex
-Projects mostly to globus pallidus and substantia nigra pars reticulata
see slide 11
Substantia Nigra
-the parts
*Pars compacta- most of DA neurons are from here; projects to basal ganglia and cortex
These are the cells containing neuromelanin that you see when looking at the brain specimens
*Pars reticulata- where the dendrites go to get info; GABAergic interneurons; projects to basal ganglia
Pars reticulata
-projects to:
- of the Substantia Nigra
* where the dendrites go to get info; GABAergic interneurons; projects to basal ganglia
Inputs to Striatum
information from the cortex:
or
From other inputs: from medium spiny neurons via axon collaterals, Local circuit interneurons in the striatum, Multiple brainstem nuclei, Midline and intralaminar nuclei of thalamus
explain how each medium spiny neuron can integrate the information from thousands of cortical cells
-inputs to striatum from the cortex
the other inputs, besides from the cortex to the striatum:
Local circuit interneurons in the striatum
Multiple brainstem nuclei (using biogenic amine neurotransmitters like histamine and serotonin)
Including the substantia nigra pars compacta (dopamine)
Midline and intralaminar nuclei of thalamus
Cortical and substantia nigra inputs synapse on the dendritic spines. Thalamic and local circuit synapses happen on the dendritic shaft or near the soma.
Better at modulating the activity that is induced or not by the cortical synapses
inputs to striatum from the cortex
Lots of glutamatergic input from corticocortical, corticothalamic, and corticospinal collaterals
Few contacts between each axon and each medium spiny neuron
One axon, however, makes contact with lots of medium spiny neurons and each medium spiny neuron receives input from lots of different axons
****Therefore, each medium spiny neuron can integrate the information from thousands of cortical cells
Nonspecific Nuclei
-probs involved in:
Many of the intralaminar nuclei and midline nuclei have diffuse projections to the cortex and have been termed “nonspecific”.
Project broadly to the cortex
Also project to more ‘nonspecific’ regions of the cortex
These nuclei are probably mostly involved in arousal and alertness.
Medium Spiny Neuron Activity
*Due to various Cell Neuro things (inward-rectifier potassium conductances), they rarely display spontaneous activity
*Almost always only activity right before and during movement
*Increase firing rate before movement (even by several seconds)
Putamen- discharge in anticipation of limb and trunk movements
Caudate- discharge in anticipation of eye movement
Some vary based on destination of movement
Overall, suggests that these cells encode the decision to move
Also fire again after a movement is complete
Usually another motor program will follow (reinstitution of stable posture)
_____ Neuron encode the decision to move
Medium Spiny Neuron
Due to various Cell Neuro things (inward-rectifier potassium conductances), they rarely display spontaneous activity
Almost always only activity right before and during movement
Involved in the planning process
Increase firing rate before movement (even by several seconds)
Putamen- discharge in anticipation of limb and trunk movements
Caudate- discharge in anticipation of eye movement
Some vary based on destination of movement
Overall, suggests that these cells encode the decision to move
Also fire again after a movement is complete
Usually another motor program will follow (reinstitution of stable posture)
Outflow of the basal ganglia
- Caudate –> substantia nigra pars reticulata –> superior colliculus (head and eye movements)
- Putamen –> external globus pallidus –> subthalamic nucleus –> internal globus pallidus (and substantia nigra)
- Putamen –> internal globus pallidus –> ventral anterior and ventral lateral nuclei of dorsal thalamus –> frontal cortex (premotor and primary motor)
Subthalamic nucleus:
receives input from motor areas of the cerebral cortex, projects to the substantia nigra, and is reciprocally connected with the globus pallidus.
Ventral Anterior Nucleus
*Receives most of input from the basal ganglia
Especially the medial globus pallidus and substantia nigra, parts reticulata.
Projects to premotor cortex including the supplementary motor area of the frontal lobes
**Involved in planning and initiating movements.
Ventral Lateral Nucleus
*Receives input from the CEREBELLUM
Small input from the basal ganglia to the rostral part of the VL, as well.
Projects to the primary motor area, area 4, of the precentral gyrus and also has a smaller projection to premotor areas.
*Thus involved in MOTOR FEEDBACK from the cerebellum and basal ganglia to the cerebral cortex
-Along with ventral anterior nucleus
**Coordination, planning, learning of movement
motor nucleus of the thalamus
Ventral Anterior Nucleus, Ventral Lateral Nucleus …. idk some other stuff?
Outflow- Disinhibition
- substantia nigra pars reticulata –> superior colliculus (head and eye movements)
- external globus pallidus –> subthalamic nucleus –> internal globus pallidus
- internal globus pallidus –> ventral anterior and ventral lateral nuclei of dorsal thalamus –> frontal cortex (premotor and primary motor)
The medium spiny neurons of the caudate and putamen release GABA onto their targets when they are excited by inputs
Inhibiting the inhibitors = disinhibition
Caudate –> substantia nigra pars reticulata –> superior colliculus (head and eye movements)
Putamen –> external globus pallidus –> subthalamic nucleus –> internal globus pallidus
Putamen –> internal globus pallidus –> ventral anterior and ventral lateral nuclei of dorsal thalamus –> frontal cortex (premotor and primary motor)
slide 23! look at the colors of the arrows
T/F Globus pallidus and substantia nigra pars reticulata lack spontaneous activity
FALSE
Globus pallidus and substantia nigra pars reticulata have lots of spontaneous activity
Are constantly and tonically inhibiting their target structures because they release GABA
(-caudate and putamen are NOT spontaneously active, have to wait to be activated)
explain the double GABA thing slide 24
Remember, in the absence of movement intention, the medium spiny neurons are silent
If you are not intending to move, you do not want to be moving
So the baseline state is inhibition of upper motor neuron circuitry
When you want to move, the medium spiny neurons get all firey and tell the inhibitory cells to stop it –> disinhibition of motor thalamus, superior colliculus, other things –> disinhibition of upper motor neurons movement permitted to occur
Also probably why the medium spiny neurons start getting active BEFORE you execute a movement
summarize the globus pallidus and movement
At Baseline:
Globus pallidus –> prevents movement by inhibiting the motor thalamus (which is fundamentally good)
Time to Move:
Cortex- “I like to move it, move it”
Striatum- “You like to move it, move it”
Globus pallidus- “If you insist… I will just be quiet.”
Motor thalamus- “I like to move it, move it”
Upper motor neurons: “I like to move it, move it”
Lower motor neurons: “I like to MOVE IT”
Globus pallidus at baseline
Globus pallidus –> holding back the movement party by inhibiting the motor thalamus (which is fundamentally good)
Globus pallidus at Time to Move:
Cortex- “I like to move it, move it”
Striatum- “You like to move it, move it”
Globus pallidus- “If you insist… I will just be quiet.”
Motor thalamus- “I like to move it, move it”
Upper motor neurons: “I like to move it, move it”
Lower motor neurons: “I like to MOVE IT”
summary of ouflow
*Superior colliculus- influence head and eye movements
Secondary influence on eye movement comes from substantia nigra pars reticulata connections to relay neurons in the mediodorsal and ventral anterior thalamic nuclei, which project to the frontal eye field regions of the premotor cortex
This connection through the thalamus is a mechanism to facilitate or suppress inputs to circuits of upper motor neurons
Circuits Within the Basal Ganglia - names
Direct Pathway and indirect pathway
Direct Pathway
- medium spiny neurons of striatum –> internal globus pallidus
JOB: release tonic inhibition of the thalamic neurons connected to upper motor neurons
Way for basal ganglia to initiate intentional movement
Indirect Pathway:
Indirect Pathway: select group of medium spiny neurons of striatum –> lateral division of globus pallidus (external segment)
External segment –> internal segment and subthalamic nucleus
Subthalamic nucleus also gets excitatory projections from cortex
Subthalamic nucleus –> internal segment of globus pallidus and substantia nigra pars reticulata
Indirect Pathway of the Basal ganglia
-job
Job: ANTAGONIZE the activity of the direct pathway to help open and shut the gates that start and stop movements
the direct and indirect pathways of the basal ganglia
- Subthalamic neurons use GLUTAMATE in their synapses with the globus pallidus and substantia nigra
- Activate indirect pathway –> excitation of globus pallidus and substantia nigra cells –> release GABA in response –> INCREASES INHIBITION WITHIN THE BASAL GANGLIA
Helps to:
Suppress competing motor programs
Select proper motor program
Still do not fully understand how this all works together
Direct and Indirect Pathways
Remember:
The caudate and putamen receive different streams of information from different regions of the cortex
The output from the caudate and putamen is segregated
Some of the projections to the basal ganglia are topographically mapped (visual and somatosensory) and some are overlapped (those from more interconnected or association regions)
There are rostrocaudal bands of cells that seem to be concerned with different parts of the body and the movement of that part
dopamine
-released by :
*Substantia nigra pars compacta cells release dopamine
Receive direct inputs from medium spiny neurons of striatum
Sends dopaminergic projections back to the medium spiny neurons
End result? Complex and depends on type of dopamine receptor expressed
*D1: increase cAMP and increases excitability (basically excitatory)
*D2: work with inhibitory G-proteins to decrease cAMP (basically inhibitory)
Receptors are on the shafts of the dendritic spines, which is a good place to modulate responses to cortical input
Dopamine to spiny cells that project to internal globus pallidus as part of the direct pathway is excitatory through D1
Dopamine to spiny cells that project to the external globus pallidus as part of the indirect pathway is inhibitory through D2
Substantia nigra pars compacta cells release ?
dopamine
Hypokinetic Movement Disorders
Parkinson’s disease:
Parkinson’s disease **
degeneration of the dopaminergic neurons in the substantia nigra pars compacta
- Symptoms: bradykinesia (slowness of movement), rigidity of neck and extremities, minimal facial expression. Hypokinetic = decreased voluntary movement
- Lose the effects of dopamine on movement (which was enhancing direct pathway and decreasing responsiveness of indirect pathway
- Direct pathway results in disinhibition of motor thalamus
- Indirect pathway reinforces inhibition of motor thalamus
- Results in abnormally high inhibitory outflow to the motor thalamus
Hyperkinetic Movement Disorders
Huntington’s disease is what type of movement disorder
Insufficient tonic output from pallidum –> unwanted movement
Huntington’s disease
- gradual onset of defects in behavior, cognition, and movement; genetic, progressive, and results in death
While it is a movement disorder, the first symptoms are usually an increase in irritability, suspiciousness, and/or impulsive behavior
Movement symptoms: rapid, jerky (“dancelike”) motions with no purpose; no weakness or ataxia
Selective atrophy of the caudate and putamen (medium spiny neurons), with some additional degeneration in the frontal and temporal cortices
External globus pallidus loses inhibitory input reduces subthalamic nucleus excitatory input to internal globus pallidus –> reduced inhibitory outflow
nickname for the cerebellum and why
The Little Brain:
-it is pretty big
*Approximately 10% of the brain’s volume
Contains over 50% of the total number of neurons in the brain
Is the cerebellum considered a motor structure
Yes, but she is confusing me
-Considered a motor structure
Motor Functions of the Cerebellum
- Maintenance of Balance and Posture
- Coordination of Voluntary Movements
Majority of the cerebellum’s outputs are to parts of the motor system.
Motor commands are not initiated in the cerebellum
The cerebellum MODIFIES the motor commands of the descending pathways to make movements more adaptive and accurate.
Motor Functions- Maintenance of Balance and Posture
Important for making postural adjustments in order to maintain balance.
Input from vestibular receptors and proprioceptors
Modulates commands to motor neurons to compensate for shifts in body position or changes in load upon muscles.
damage to cerebellum:
Cerebellar damage leads to impairments in motor control and posture
Patients with cerebellar damage suffer from balance disorders, and they often develop stereotyped postural strategies to compensate for this problem (e.g., a wide-based stance).
Motor Functions- Coordination of Voluntary Movements
Most movements are composed of a number of different muscle groups acting together in a temporally coordinated fashion.
Coordinate the timing and force of these different muscle groups to produce fluid limb or body movements.
-example: doing a cartwheel
Motor Functions of the cerebellum: name them
give some examples
- Coordination of Voluntary Movements
- Maintenance of Balance and Posture- a cartwheel
- Motor Learning- hitting a baseball
Cerebellum: Motor Functions- Motor Learning
Plays a major role in adapting and fine-tuning motor programs to make accurate movements through a trial-and-error process (e.g., learning to hit a baseball).
Anatomy of the Cerebellum
Two major parts:
slide 43
Cerebellar deep nuclei and cerebellar cortex
Two major parts of the Cerebellum
Two major parts: Cerebellar deep nuclei and cerebellar cortex
Cerebellar Deep Nuclei
-of the Cerebellum
the deep nuclei are the main way info gets OUT of the cerebellum
*Sole output structures of the cerebellum, as a whole
Axons leave the cerebellum
Almost all of the output of the cerebellum is through the deep nuclei
T/F a lesion to the Cerebellar Deep Nuclei is better than an entire cerebellum lesion
FALSE
*Lesions of cerebellar deep nuclei are the same as complete lesion of the entire cerebellum
Output from the fastigial nucleus of the cerebellar cortex influence:
- orienting
- vigilance
- positional-autonomic
- oromotor
- posturomotor
slide 46
Interposed nuclei:
-of the Deep Cerebellar Nuclei
*input from the intermediate zone and from cerebellar afferents that carry spinal, proximal somatosensory, auditory, and visual information.
They project to the contralateralred nucleus(rubrospinal tract).
Dentate nucleus:
-projects to:
-of the Deep Cerebellar Nuclei
largest of the cerebellar nuclei; input from the lateral hemisphere and from cerebellar afferents that carry information from the cerebral cortex (via the pontine nuclei).
It projects to the contralateralred nucleusand theventrolateral (VL) thalamic nucleus.
Vestibular nuclei:
location
outside the cerebellum in the medulla; functionally equivalent to the cerebellar nuclei because their connectivity patterns are identical to the cerebellar nuclei.
which of these nuclei is not found in the cerebellum?
Vestibular nuclei
Cerebellar Cortex
Highly convoluted sheet of tissue that encases the cerebellar deep nuclei
Contains almost all the neurons in the cerebellum.
Intricate pattern of folds and fissures that characterize the cerebellar cortex
the part of the cerebellum that see from the outside
Cerebellar Cortex
Functional Subdivisions of the cerebellum : name them
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
Vestibulocerebellum(flocculonodular lobeand its connections with thelateral vestibular nuclei):
-a Functional Subdivision of the cerebellum
the oldest part of the cerebellum
Involved in vestibular reflexes (such as the vestibuloocular reflex) and in postural maintenance.
Spinocerebellum
-a Functional Subdivision of the cerebellum
(VERMISand theintermediate zones, as well as thefastigialandinterposednuclei):
major inputs from the spinocerebellar tract.
Its output projects to rubrospinal, vestibulospinal, and reticulospinal tracts
Involved in the integration of sensory input with motor commands to produce adaptive motor coordination.
Only part to get direct input from spinal cord
Vermis
-falls under the Spinocerebellum
Most medial portion
Concerned with movements of proximal muscles
Regulates certain types of eye movements
Cerebrocerebellum
(lateral hemispheresand thedentatenuclei): largest subdivision
*Extensive connections with the cerebral cortex, via the pontine nuclei (afferents) and the VL thalamus (efferents)
Cerebellar Peduncles (Tracts)
Three fiber bundles carry the input and output of the cerebellum.
Cerebellar Peduncles (Tracts)- name them
Three fiber bundles carry the input and output of the cerebellum.
Theinferior cerebellar peduncle
Theinferior cerebellar peduncle(also called therestiform body) primarily contains afferent fibers from the medulla, as well as efferents to the vestibular nuclei.
Most complex
Themiddle cerebellar peduncle
(also called thebrachium pontis) primarily contains afferents from the pontine nuclei.
One of the largest pathways in the brain (>20 million axons on each side)
Thesuperior cerebellar peduncle
(also called thebrachium conjunctivum) primarily contains efferent fibers from the cerebellar nuclei, as well as some afferents from the spinocerebellar tract.
Axons coming mostly from the deep cerebellar nuclei and go to motor thalamus and upper motor neurons in the superior colliculus
Cerebellar Peduncles: Inputs
Inputs to the cerebellum are conveyed primarily through the inferior and middle cerebellar peduncles
Arise ipsilaterally
Cerebellar Peduncles: Outputs
Outputs are conveyed primarily through the superior cerebellar peduncle.
Outputs go ipsilaterally
Projections to the Cerebellum
*indirect: from one side of the cortex to the other side of the cerebellum
*Also gets lots of sensory information
Axons from vestibular portion of CN8, and axons from vestibular nuclei in the pons and medulla
Go to vestibulocerebellum
Somatosensory relay neurons in the dorsal nucleus of Clarke in the spinal cord and external cuneate nucleus in medulla
Relay neurons carrying proprioceptive info from the body
Go to spinocerebellum
Face proprioceptive info sent via the mesencephalic trigeminal nucleus
Helps cerebellum figure out where your body and body parts are in space
Visual and auditory signals also relayed to cerebellum to supplement the proprioceptive information
*Somatosensory input is somewhat topographically mapped in the spinocerebellum
Maps are fractured, in that, each small area of the body is represented multiple times by spatially separated clusters of cells rather than on a single, continuous map
*Vestibular and spinal inputs remain ipsilateral
-Right cerebellum concerned about the right…
Cerebellum is generally concerned about same side things
*Receives modulatory inputs from the inferior olivary nucleus (inferior olive)
Largest source of input to the cerebellum
cerebral cortex
*Major destination of the projections to the cerebullum:
*Major destination: cerebrocerebellum
Projections from the Cerebellum
-outputs
*the deep nuclei are the main way info gets OUT of the cerebellum
*Cerebellar cortex projects to deep cerebellar nuclei
Deep nuclei also get input from different part of the cerebellar cortex
Basically, outputs are to the cerebral cortex, upper motor neurons, and sometimes lower motor neurons
Dentate nuclei Fastigial Nuclei Interposed Nuclei Vestibular nuclei:(outside the cerebellum in the medulla) (MIGHT HAVE MISSED SOME)
Dentate nuclei
-a projections from the cerebellum
*Input: Mostly info from cerebrocerebellum
Output: premotor and association cortices involved in planning and initiating movement
Output exits through the superior cerebellar peduncle, crosses the midline, and relays first in VL thalamus
*On the way to the thalamus, sends axons to eye-movement-related upper motor neurons in superior colliculus and to the red nucleus
Red nucleus –> inferior olive
Serves as feedback onto cerebellar inputs
Important for adaptive functions of motor learning
Fastigial Nuclei
- input:
- output:
-a projection from the cerebellum
Fastigial Nuclei
Input: spinocerebellum
Output: nuclei of the reticular formation and vestibular complex
Outputs sent through the inferior cerebellar peduncle
*Influence pathways controlling axial and proximal limb musculature
Interposed Nuclei
- input:
- output:
-a projection from the cerebellum
Interposed Nuclei
Input: spinocerebellum
Output: thalamic circuits that project to motor regions concerned with volitional movement of the limbs
Outputs sent through the superior cerebellar peduncle
In non-human primates, also send axon collaterals to the rubrospinal tract
Also output to superior colliculus to modulate eye movement (crosses midline)
Vestibular nucleus
-a projection from the cerebellum
Vestibular nucleus
Input: vestibulocerebellum
Output: vestibular nuclei in the brainstem, which govern movement of eyes, head, and neck in response to changes in head placement
Outputs sent through the inferior cerebellar peduncle
Vestibulocerebellum also sends out direct projections to the vestibular nuclei
-NOT technically in the cerebullum
(I THINK!)
Projections from the Cerebellum: closed loops
Also have closed loops where outputs are sent through the thalamus to non-motor areas of the cortex that provided initial inputs
These closed loops permit the cerebellum to regulate its own input
May influence coordination of non-motor programs (ex- problem solving)
Circuits within the Cerebellum
Inputs to the cerebellar cortex synapse on the _____
Inputs to the cerebellar cortex synapse on the Purkinje cells… eventually
Largest of these pathways: cerebral cortex –> pontine nuclei –> contralateral cerebellum
*MOSSY FIBERS
- Axons of granule cells = parallel fibers
- Parallel fibers form excitatory synapses on the dendritic spines of Purkinje cells
- The granule cells send axons up toward the cortical surface and each axon bifurcates in the molecular layer, sending a collateral in opposite directions.
- Parallelfibers, run parallel to the folds of the cerebellar cortex, where they make excitatory synapses withPurkinjecellsalong the way.
Mossy fibers
(Circuits within the Cerebellum)
- Originate in thepontinenuclei, the spinal cord, the brainstem reticular formation, and the vestibular nuclei
- Collateral branches that form excitatory connections on neurons in the deep nuclei AND on the granule cells of the cerebellar cortex
- Each mossy fiber innervates hundreds of GRANULE CELLS.
parallel fibers*
Axons of granule cells =
Purkinje Cells
-structure
*Big cells with massive dendritic trees
*Essentially the only output from the cerebellar cortex
GABAergic
Each Purkinje cell has dendrites positioned to receive input from ~200,000 parallel fibers
Each parallel fiber can contact tens of thousands of Purkinje cells
*Purkinje cells also receive direct input onto their dendrites (not dendritic spines) from climbing fibers
Climbing Fibers
Called climbing fibers because their axons climb and wrap around the dendrites of the Purkinje cell like a climbing vine and make multiple synapses
**Each Purkinje cell receives a single, extremely powerful input from a single climbing fiber. ****
*Each climbing fiber contacts only 10 Purkinje cells on average, making ~300 synapses with each Purkinje cell.
Restricted, but extremely powerful, excitatory input onto Purkinje cells.
*Purkinje cells are primary output of cerebellar cortex, so climbing fibers have a lot of power on what comes out
*So, what do Climbing Fibers do?
-Error signals
-May serve to provide a “motor clock” function in the initiation and timing of movements
“Climbing fibers evoke complex spikes immediately, which fits perfectly the high temporal precision required for the cerebellum to initiate or coordinate muscles” (Zang and Schutter, 2019)
Drive cerebellar learning
Purkinje cells send ___ input to the _____
Purkinje cells send inhibitory input to the deep cerebellar nuclei
Deep cerebellar nuclei also get excitatory input from collaterals of mossy and climbing fibers
The inhibitory projections of Purkinje cells help to sculpt the discharge patterns of the deep nuclei
also have…
Inhibitory (GABAergic) interneurons which modulate the inhibitory activity of Purkinje cells
Inhibiting inhibition
Basket cells: most powerful of the inhibitory interneurons
Stellate cell: another local circuit neuron; receives input from parallel fibers and can also inhibit Purkinje cells
Golgi cells: receive input from parallel fibers and provide an inhibitory feedback to the granule cells that gave rise to the parallel fibers
Circuits within the Cerebellum
- Deep excitatory loop:
* Cortical inhibitory loop:
*Deep excitatory loop:
*Deep excitatory loop: mossy fiber and climbing fiber collaterals drive activation of neurons in the deep cerebellar nuclei
Input converging on the source of the final output
How do we use the cerebellum?
The modulation of the cerebellar cortex on the output of the cerebellum may be important for motor learning
Learned adjustments to movement amplitude and timing
Lots of evidence from eyeblink conditioning
Inactivate cerebellum no learning
Belief that procedural memories are formed in the cerebellum
Cerebellum and Coordination of Ongoing Movement
Cerebellum: monitors and adjusts motor behavior
Activity changes constantly during the course of movement
Cells tonically active and rest, but firing frequency increases during movement
Responses influenced by relaxation/contraction of muscles, position of joints, direction of next movement
What if your cerebellum is dysfunctional? 2 things
Bottomline: always have problems making smooth, precisely directed movements*
Deficits can be quite specific.
Site specific damage:
Vestibulocerebellum: problems standing upright and controlling direction of gaze
Nystagmus: eyes drift from target and then jump back to it with a corrective saccade
Spinocerebellum: difficulty controlling walking movements, shuffling walk.
Dysdiadochokinesia: difficulty performing rapid alternating movements
Dysmetria: over- or under-reaching
Intention tremors: due to disruption of the mechanism for detecting and correcting movement errors
Cerebrocerebellum: impairments in highly skilled sequences of learned movements (speech, playing music)
Cerebellar ataxia:
Appendicular ataxia
Cerebellar ataxia:
sort of a hallmark symptom that something is wrong with your cerebellum; movements are jerky and imprecise instead of smooth and well-coordinated
Why? Cerebellum is important for correcting errors to ongoing movements and adapt to changing circumstances.
Movement errors are on same side of the body as damage
Alcohol abuse degeneration of the anterior portion of the cerebellar cortex (which affects movement of lower limbs)
Results in staggering gait. No issues with arm or hand movement.
Bird versus Humans
Birds have a very different shaped cerebellum (round vs spherical)
Bird cerebellum greater in size and weight
Cerebellums in different places
Vermis is larger in birds
Larger in birds that can fly than not
Center of equilibrium while flying?
Differences in sulci
Cytoarchitecture very similar between the two
Beak control?
elephant Cerebellum
Largest cerebellum of all mammals relative to brain
Trunk-eye coordination
Cerebellums are overrated
Started walking late (at age 7) Walks unsteadily as an adult Slurred speech Mild intellectual impairment Has normal word comprehension and was “fully orientated”
Contains medium spiny neurons with large dendritic trees
Striatum (aka corpus striatum): caudate and putamen
corticostriatal pathway
- Nearly all regions of the cortex send direct projections to the striatum
- Therefore, the cortex is the largest source of input
- Mostly from association areas and the temporal, insular, and cingulate cortices
- Collectively refer to these pathways as the CORTICOSTRIATAL PATHWAY
basal ganglia is most known for what function?
Most known for role in movement but functions not limited to movement
what does the striatum look like?
Striped because thin strips of gray matter that pass through the internal capsule to connect the caudate and dorsal putamen
Subthalamic nucleus: *
Subthalamic nucleus: receives input from motor areas of the cerebral cortex, projects to the substantia nigra, and is reciprocally connected with the globus pallidus.
T/F Medium Spiny Neuron display spontaneous activity
FALSE
Due to various Cell Neuro things (inward-rectifier potassium conductances), they rarely display spontaneous activity
*Thalamus
*Thalamus- in general, talks back to regions of the cortex and serves as a modulator of cortical… decisions
Globus pallidus and substantia nigra pars reticulata release ____
GABA
Globus pallidus and substantia nigra pars reticulata have lots of spontaneous activity
Are constantly and tonically inhibiting their target structures because they release GABA
nonspecific nuclei are probs mostly involved in…
These nuclei are probably mostly involved in arousal and alertness.
Hypokinetic
Hypokinetic = decreased voluntary movement
anticipation of movement
-the specific parts of the basal ganglia:
Medium Spiny neurons increase firing rate before movement (even by several seconds)
Putamen- discharge in anticipation of limb and trunk movements
Caudate- discharge in anticipation of eye movement
Some vary based on destination of movement
Overall, suggests that Medium Spiny neurons encode the decision to move
release GABA
caudate and putamen, Globus pallidus, substantia nigra pars reticulata
explain the outflow of the basal ganglia that impacts head and eye movements
*Caudate –> substantia nigra pars reticulata –> superior colliculus (head and eye movements)
*Fastigial nucleus:
*Fastigial nucleus: medial; input from the vermis and from cerebellar afferents that carry vestibular, proximal somatosensory, auditory, and visual information
Projects to the vestibular nuclei, thalamus, and the reticular formation.
name the Deep Cerebellar Nuclei
Dentate nuclei
Fastigial Nuclei
Interposed Nuclei
Vestibular nuclei:(outside the cerebellum in the medulla)
vestibular nuclei
- inputs
- project
The vestibular nuclei receive input from the flocculonodular lobe (vestibulocerebellum) and from the vestibular labyrinth.
They project to various motor nuclei and originate the vestibulospinal tracts.
which Deep Cerebellar Nuclei carry spinal, proximal somatosensory, auditory, and visual information ?
Interposed nuclei
Cerebrocerebellum function
*Well developed in primates
*Involved in the PLANNING AND TIMING of movements.
Involved in the cognitive functions of the cerebellum.
Includes the flocculus and nodulus
indirect projections to the cerebellum
Projections are not direct
They synapse on ipsilateral pontine nuclei
Pontine nuclei receive input from a wide variety of sources, including most areas of cortex and the superior colliculus
Axons from the pontine nuclei (transverse pontine fibers or pontocerebellar fibers) cross the midline and enter contralateral cerebellum via the middle cerebellar peduncle
How we get info from one side of the cortex to the other side of the cerebellum
Which pair of cerebellar peduncles are the primary inflow pathways into the cerebellum?
middle and inferior
Climbing Fibers : originate
*Originate exclusively in the INFERIOR OLIVEand make EXCITATORY PROJECTIONS onto the cerebellar nuclei and onto thePurkinjecellsof the cerebellar cortex
modulatory inputs to the cerebellum
*Receives modulatory inputs from the inferior olivary nucleus (inferior olive)
Important for the learning and memory functions of the cerebellum
Inferior olive gets input from a wide variety of structures including: the cortex, red nucleus, reticular formation, and spinal cord
These olivo-cerebellar axons exit the inferior olive, cross the midline, and enter the contralateral cerebellum via the inferior cerebellar peduncle
The arrangement of Purkinje cells and parallel fibers
The arrangement of Purkinje cells and parallel fibers resembles telephone lines running between telephone poles.
Each parallel fiber makes contact with hundreds of Purkinje cells so the firing of each Purkinje cell can be influenced by thousands of mossy fibers.
