Download Function of Basal Ganglia (Summary)

Cerebellum and Basal Ganglia
The Cerebellum
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Located in the posterior cranial fossa
Bounded by the tentorium cerebella (cerebrum) and the 4th ventricle (brain stem)
Communicate with other structures via superior, middle and inferior peduncles
Traditionally divided into longitudinal and transverse subdivisions
o Longitudinal Subdivisions
 Vermis
 Paravermal region
 Cerebellar hemisphere
o Transverse subdivisions (3 lobes)
 Anterior Lobe
 Contains vermis and cerebellar hemispheres anterior to primary fissure
 Posterior Lobe
 Contains remaining parts of cerebellum posterior primary fissure
o includes cerebellar tonsils just above foramen magnum
 Bigger than the anterior lobe
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Flocculonodular Lobe
 Most caudal lobe of vernus, nodulus and flocculus (hence, the name)
 Oldest part of the cerebellum
 Smallest lobe of the cerebellum
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 Primary Fissure - demarcation between Anterior Lobe and Posterior Lobe
 Posterolateral Fissure- demarcation between Posterior Lobe and Flocculonodular Lobe
Other Information
o Cerebellar Peduncles- attachments of the cerebellar hemisphere into the brain stem
 Superior Cerebellar Peduncle- attached to the Midbrain
 Middle Cerebellar Peduncle – attached to the Pons
 Inferior Cerebellar Peduncle – attached to the Medulla
Sagittal subdivisions
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Vermis
o Contributes to body posture
Hemisphere
Intermediate
Lateral Surface of the Cerebellar Hemisphere
Phylogenetic/functional divisions
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Archicerebellum
o Flocculonodular lobe
o Also called, Vestibulocerebellum
o Oldest Structure
Paleocerebellum
o Anterior lobe
o Also called, Spinocerebellum
Neocerebellum
o Largest and Newest Lobe
o Posterior Lobe
Cerebellar peduncles
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attachments of the cerebellar hemisphere into the brain stem
Superior cerebellar peduncle
o Also called as “Brachium conjuntivum”
o connects to the Midbrain
Middle Cerebellar Peduncle
o Also known as “Brachium pontis”
o connects to the Pons
o through Pons, receives fibers from parietal lobe
o Largest Cerebellar Peduncle
- Inferior Cerebellar Peduncle
o Also known as “Restiform and juxtarestiform bodies”
o attached to the Medulla
Major Connection Tracts of Cerebellar Peduncles
Peduncle
Inferior
Middle
Superior
Tracts
Restiform Body
Dorsal Spinocerebellar
Oliveocerebellar
Arcuatocerebellar
Reticulocerebellar
Juxtarestiform Body
Vestibulocerebellar
Cerebellovestibular
Pontocerebellar
Ventral Spinocerebellar
Trigeminocerebellar
Tectatorubrothalamic
Dentatorubrothalamic
Afferent/ Efferent
Afferent
Afferent
Afferent
Afferent
Afferent
Efferent
Afferent
Afferent
Afferent
Afferent
Efferent
Deep cerebellar nuclei (from median to lateral)
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Fastigial
o Located near Roof nucleus (of the 4th Ventricle)
- Globose (interposed)
- Emboliform (interposed)
- Dentate
o Largest
o Most lateral
- Note: Globose + Emboliform = Interposed Nuclei
*Mnemonics from Most Medial to Most Lateral: Fat Guys Eat Donuts
Cerebellar organization (triads)
Lobe
Afferent peduncle
Efferent peduncle
Deep nucleus
Floculonodular Inferior
Inferior
Fastigial
Anterior
Superior and inferior
Superior
Interposed (Globose & Emboliform)
Posterior
Middle
Superior
Dentate
*Cerebellar Lobes, Afferent/Efferent Peduncles and Deep nuclei can be arranged into triads
* Cerebellum – organized structure
Cerebellar cortex
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Structures in 3 parallel layers
Molecular
o outermost layer
Purkinje
o Single cell layer of Purkinje cells
o Purkinje Neurons
 Have a lot of connections
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 Largest neurons in the cerebellum
o Connects surface and deep nuclei
o Source of all efferent (outgoing) fibers
 All of the axons coming from the cerebellar cortex comes from the Purkinje layer
o Cerebellar cortex
White Matter/Granular Layer
Micro-circuitry
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Input into the cerebellum
o Mossy fiber and climbing fiber
o Both are excitatory (neurotransmitter: glutamate)
Output from the cerebellar cortex
o Purkinje cell axon (mainly)
o Inhibitory (GABA)
Output from cerebellum
o Deep cerebellar nuclei
o Excitatory
Cerebellar cortex: neuronal types
Neuron
Outer stellate
Inner stellate (basket)
Purkinje
Golgi type II
Granule
*Only excitatory neuron: Granule
Layer
Molecular
Molecular
Purkinje
Granular
Granular
Cerebellar input
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Climbing fiber system
o From Inferior olivary nuclei
Mossy fiber system
o From all other sources
Micro-circuitry
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Purkinje cell
o 2 dimensional dendritic tree
Function
Inhibitory
Inhibitory
Inhibitory
Inhibitory
Excitatory
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Only output of the cerebellar cortex
Receives input from climbing fiber and parallel fiber from the granule cell axon
Cerebellar circuitry
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Direct path
o input projects directly to motor systems via deep nuclei
o all pathways pass through the cerebellar peduncles
Indirect side loop
o Via the parallel fibers, involves granular cells
o mossy fiber input to granular cells, through parallel fibers to purkinje and back out to deep nuclei
o Used to correct the direct reflex responses (immediate correction of [intended] movement)
Climbing fiber [System] input to purkinje cells
o Like basal memory
o Error detection input
o Used for learning what needs correcting
Cerebrocerebellopyramidal pathway
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Cerebro-ponto-cerebello-dentato-rubro-thalamo-cerebro-spinal
Crosses the midline 2 times
Most important pathway (there are a lot of pathways in the cerebellum)
o Long pathway
Unique characteristic: crosses the midline twice – unilateral lesion usually presents as ipsilateral problems
Cerebellar triad
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Vestibulocerebellum
o Input: vestibular organs
o Output: legs, trunk, eye muscles
o Function: tunes balance (stance and gait) and VOR
o Disorders
 Ataxic gait: wide based stance (looks drunk, due to poor sense of balance)
 Imbalance becomes worse when eyes are closed (Romberg sign)
 Nystagmus
Spinocerebellum
o Anterior Lobe
o Input: spinal cord (somatosensory and muscle afferents), visual and auditory
o Output: spinal cord (via red reticular n. and motor cortex)
o Function: tunes motor execution by adjusting movements and muscle tone
o Disorders
 Ataxic gait
 Fail
Cerebro cerebellum
o Input: cerebral cortex (every time you do a motor command, a copy of motor command is sent down the spinal
cord, arrives through the [lateral cerebellar cortex] pontine nuclei
o Output: primary motor and premotor cortex
o Function: initiation of skilled movements
o Disorders
 Ataxia during skilled movement initiation: delay in initiation, dysmetic movements, tremor
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Unilateral lesion will present as ipsilateral symptoms
Cerebellar function (Summary)
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Vestibulocerebellum controls balance and eye movements
Spinocerebellum adjusts ongoing movements
Cerebroerebellum coordinates the planning of limb movements
Cerebellum participates in motor learning
Signs of cerebellar dysfunction
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Dysdiadochokinesia
o Clumsiness in altering movements
o Tapping, speech sound
Dysarthria
o Ataxic
o Scanning speech
o Slurred and disjointed speech (“Parang- Lasing”)
Dysmetria
o Error in judgment of range and distance of target
o Undershooting or overshooting
Intentional tremor
o Accessory movement during volitional task
 Tremor that happens with movement, voluntary movement or volitional task
o Vs. Parkinson’s disease where tremor lessens during volitional movement
 Tremor at rest
Hypotonia
o Reduced resistance to passive stretch in the muscle
Rebounding
o Inability to predict movement
o Cannot hold back movement
Disequilibrium
o Unsteady gait
Cerebellar syndromes
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Cerebellar hemisphere
o Ipsilataral side of the body is affected
o Mainly posterior lobe
o Dystaxia/hypotonia of ipsilateral extremities
Rostral vermis
o Anterior lobe
o Dystaxia of legs and trunk (mainly the legs are affected)
Caudal vermis
o Floculonodular and posterior lobes
o Mainly Truncal dystaxia
Pancerebellar
o All lobes affected
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All cerebellar signs
Case 1
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7 year old girl
5 mos histo of dizziness, diplopia and ataxia
Papilladema, bilateral 6th nerve palsy, (+) cerebellar signs
The Basal Ganglia
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You don’t see the basal ganglia in the surface. Only when cutting into the brain do you see this
People with basal ganglia problems: Michael J. Fox, Muhammad Ali, Pope John Paul II (Alzheimer's Disease)
About 5 structures will be encountered in the basal ganglia
o Caudate – Latin term for “having a tail”
 Putamen – Latin term for “husk” or outside covering (covers something)
o Globus Pallidus – Latin terminology for “Pale Globe”
 Covered by Putamen
o Substantia Nigra – Latin Terminology for “Black Body/Substance”
 Contains melanocytes
 Colored black because of the presence of melanin
o Subthalamic Nucleus
 Also called “Corpus Luys”
 “Underneath the Thalamus”
 Favorite Target for Deep Brain Stimulation Therapy for Parkinson’s Disease Patients
Terminology
- Corpus striatum
o Caudate nucleus
o Putamen
o Globus pallidus
- Striatum
o Caudate nucleus
o Putamen
- Lenticular/Lentiform nucleus
o Putamen
o Globus pallidus
- Subthalamic nucleus
- Substantia nigra
Additional Information to identify for Anatomy
- Head of the caudate – related to the anterior horn of the lateral ventricle
- Internal Capsule –pale V-shaped structure
o separate the following
 Head of the caudate nucleus
 Lentiform Nucleus (Putamen + Globus Pallidus)
 Thalamus
o Subdivided into
 Anterior Limb (Crus Anterius)
 Posterior Limb (Crus Posterius)
 Genu - bend in the V
- Claustrum – gray matter lateral to the Putamen, separated by the external capsule
o Not part of the basal ganglia
- External Capsule – white matter between the putamen (lentiform nucleus) and claustrum
- Extreme Capsule – white matter lateral to the claustrum
Function
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Disinhibits proposed actions
o Basal Ganglia output nuclei tonically inhibit the thalamic nuclei and the superior colliculus
 Thalamic nuclei - stimulates motor complex
 Normally you don’t have excessive movements because of the inhibitory function of the basal ganglia
o Released when input patterns excite principal neurons of the neostriatum
 Tailors/controls the automatic movements you do by releasing the inhibition
Striatum
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Major afferent center
o Where most of the cortical inputs enter the basal ganglia
Projects to Globus Pallidus
Mostly small neurons
Afferents:
o Corticostriatal – sensorimotor
o Thalamostriatal – VA, VL, IL (from the thalamus)
o Nigrostriatal
o Raphe-Striatal - brainstem
Efferents
o Striatopallidal
 Globus Pallidus
 “Comes from the Striatum going to the Globus Pallidus”
o Striatonigral
 Substantia Nigra Pars Reticulata
 “Comes from the Striatum going directly to Substantia Nigra (specifically Pars Reticulata)”
Caudate Nucleus
o Input: Association Areas Of The Cerebral Cortex
o Projects Mostly To Prefrontal Areas
o Cognitive Function
Putamen
o Input: Motor And Somatosensory Cortex
o Projects Mostly To Supplementary Motor Area
o Motor Functions
Globus Pallidus
o Lateral And Medial Medullary Laminae (separates internal and external Globus Pallidus)
Multipolar Neurons
Final Common Pathway From Basal Ganglia To The Thalamus
Afferents
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Striatopallidal
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Subthalamic Fasciculus
o Efferents
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H fields of Forel (G. Haubefeld or cap field) – at subthalamus VA, VL, IL(CM) thalamic nuclei
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Thalamic nuclei (H1 field)
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Lenticular fasciculus (H2 field)
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Ansa leticularis
o Prerubral field (H field)
o Zona incerta
Subthalamic Nucleus (Corpus Luys)
o Reciprocal (Two-Way_ connections with Globus Pallidus via the Subthalamic Fasciculus
Substatia Nigra
o Large multipolar neurons
o 2 groups
 Pars compacta
 Dorsal, efferents, dopamine
 Pars reticulata
 Ventral, afferents
Main Function of Basal Ganglia (Summary)
Selection, triggering and generation of basic motor commands in the Central Nervous Systems.
- Doesn't regulate, just releases the basic motor commands
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2 pathways of modulating/controlling movement (parallel pathways)
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Terminology:
o GPi – Globus Pallidus Interna
o GPe – Globus Pallidus Externa
o STN – SubThalamic Nucleus
Basic Circuit of the Basal Ganglia
o From the Cerebral Cortex  Striatum (afferent )  Globus Pallidus  Thalamus  back to the Cerebral Cortex
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Indirect
o GPi-STN-GPe-thalamic-cortical circuit
o Roundabout pathway
o Inhibits unwanted/inappropriate movement
o Net Effect: Inhibition of the Thalamus and Unwanted Movement
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Direct
o Facilitates/reinforces intended behaviorally relevant behavior or programmed movement
o Shorter pathway
o Excitatory
o Reinforces Intended Movements
o Net Effect: Stimulation Of The Thalamus
Additional Notes:
- Globus Pallidus – main output
- Striatum – main input
- Basal Ganglia (Caudate, Putamen and Globus Pallidus) - GABA (Inhibitory)
- Cortex, Thalamus, STN - Glutamine (Excitatory)
- There are many parallel pathways of the basal ganglia
o Motor Loop - simplest out of the many pathways of the Basal Ganglia
Clinical-anatomical correlation
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2 types of disability
o Negative (deficiency) signs
 Affects the indirect pathway
 Akinesia
 Loss of normal motor function, resulting in impaired muscle movement.
 Difficulty in initiating movement
 Bradykinesia
 Slow movement
 Basically difficulty in moving
o Positive (release) signs
 Basically tremors or rigidity
 Hypertonia/rigidity
 Abnormal increase in tightness of muscle tone and a reduced ability of a muscle to stretch
 Dystonia
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Posturing movements which in both agonist and antagonist muscles contract at the same time, creating
abnormal movements
 Has genetic type found in the Philippines (Sex-linked Recessive Dystonia Parkinsonism of Panay
 Usually occurs in the 3rd or 4th decade of life (late 30's)
 Striatal degeneration, dystonia - parkinsonism
Athetosis
 Movements are involuntary, slow, squirming, and continuous during flexing, extending (the opposite of
flexing), supination (turning the palm up), and pronation (turning the palm down) of the hands and
fingers
 Involuntary (uncontrollable) writhing movements of face, arms and hands
Chorea
 Syndenham’s chorea
o Complication of rheumatic fever
o Fine, disorganized, random movements of face, extremities and tongue
o Muscular hypotonia
o Typical exaggeration of associated movements during voluntary activity
o Usually recovers spontaneously in 1-4 months
o Still happens in the Philippines
o Usually temporary
o Disappears with treatment
 Huntington’s chorea
o Autosomal dominant
o Degeneration of striatal neurons
o Also discovered in New York
o Affects both sexes, appears usually during 4th decade of life
o Atrophy of the caudate
o Not found in the Philippines
o Sometimes with cognitive problems
o Rapidly progressing disease
o Hyperkinetic (theoretically)
Hemiballismus
 Excessive movement (Wild, flinging movements)
 Less inhibition of the thalamus
o Leads to excess stimulation of the cortex leading to the hyperkinetic state
Movement disorder
Chorea (dance-like movements)
Athetosis
Dystonia
Hemiballismus
Parkinsonism (paralysis agitans)
Triad: tremor, rigidity, akinesia
Lesion
Striatum
Corpus striatum + thalamus
Site unclear
Subthalamic nucleus
Substantia nigra (degeneration)