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Download Function of Basal Ganglia (Summary)
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Cerebellum and Basal Ganglia The Cerebellum - 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 Flocculonodular Lobe Most caudal lobe of vernus, nodulus and flocculus (hence, the name) Oldest part of the cerebellum Smallest lobe of the cerebellum - 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 - Vermis o Contributes to body posture Hemisphere Intermediate Lateral Surface of the Cerebellar Hemisphere Phylogenetic/functional divisions - - - 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 - - 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) - 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 - 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 - 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 - - - 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 - Climbing fiber system o From Inferior olivary nuclei Mossy fiber system o From all other sources Micro-circuitry - Purkinje cell o 2 dimensional dendritic tree Function Inhibitory Inhibitory Inhibitory Inhibitory Excitatory o o Only output of the cerebellar cortex Receives input from climbing fiber and parallel fiber from the granule cell axon Cerebellar circuitry - - - 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 - 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 - - - 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 Unilateral lesion will present as ipsilateral symptoms Cerebellar function (Summary) - 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 - - - - - - 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 - - - - 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 o All cerebellar signs Case 1 - 7 year old girl 5 mos histo of dizziness, diplopia and ataxia Papilladema, bilateral 6th nerve palsy, (+) cerebellar signs The Basal Ganglia - 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 - 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 - - - - - 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 Striatopallidal Subthalamic Fasciculus o Efferents H fields of Forel (G. Haubefeld or cap field) – at subthalamus VA, VL, IL(CM) thalamic nuclei Thalamic nuclei (H1 field) Lenticular fasciculus (H2 field) 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 o o o 2 pathways of modulating/controlling movement (parallel pathways) - - 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 - 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 - 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 - 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 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)