CEREBELLUM Chris Cohan, Ph.D. Dept. of Pathology/Anat Sci University at Buffalo Objectives: Describe the anatomy of the cerebellum, its 3 functions and associated regions Describe how the cerebellum influences other components of the motor system Understand the general scheme of information flowing to the cerebellum and leaving the cerebellum Have a general understanding of the functions and pathways of the vestibulo-, spino-, cerebro- cerebellum Understand the effects/symptoms of lesions of each unit of the cerebellum and the CNS areas where lesions produce cerebellar symptoms Describe the clinical tests used to assess cerebellar function I) FUNCTIONAl COMPONENTS: Function Component Deficits Start Basal Ganglia Spontan movements Move Cerebral Cortex/ Weak/Paralyzed Brainstem/SpCord Plan Cerebellum Ataxia Adjusts Cerebellum Ataxia Balance/EyeMove Cerebellum Falling/ nystagmus Desire to move originates in motor cortical areas. Subsequently, the cerebellum cooperates in planning the movement (which muscles will be activated and in what sequence). When the movement starts, its progress is monitored continuously by sensory and motor feedback to adjust the movement to achieve its goal. Balance is also monitored by cerebellum to ensure postural steadiness. FUNCTION: It COORDINATES movement HOW IT WORKS Thalamus Cerebral Cortex Basal Ganglia Cerebellum head muscles Brainstem body muscles Spinal Cord How does the cerebellum influence movement: 1) by influencing corticospinal and corticobulbar neurons in the cerebral cortex 2) by influencing the descending brainstem pathways that project to the spinal cord. There are NO direct efferent projections from the cerebellum to the spinal cord. SYMPTOMS of cerebellar disease: uncoordinated movement ataxia, nystagmus BIG PICTURE: the cerebellum controls 3 functions relating to coordination of movement (planning, adjusting, balance/eye movements) these 3 functions are controlled by 3 specific areas of the cerebellum the cerebellum affects movement by regulating UMN activity (cortex and brainstem) damage to the cerebellum or its pathways causes ataxia Not so Simple: how the cerebellum is able to perform these functions and the pathways it uses to do it. 1
II) Cerebellar Anatomy -cerebellum is composed of 2 lateral hemispheres joined by a central portion called vermis. -Fissures separate the cerebellum into 3 lobes: primary fissure separates anterior lobe and posterior lobes; posterolateral fissure separates post. lobe from flocculonodular lobe. -there are 4 pairs of deep nuclei within the cerebellum: Fastigial, Interpositus, and Dentate. -all fibers going to or coming from the cerebellum travel via the cerebellar peduncles: Inferior (restiform body), Middle (brachium pontis), Superior (brachium conjunctivum). -review cerebellar anatomy in your text and lab manual. superior surface anterior surface Deep Nuclei III) Functional subdivisions of cerebellum Vestibulocerebellum, Spinocerebellum Cerebrocerebellum Functional Unit 1.Vestibulocerebellum Structure Flocculus, nodulus Inputs from Vestib Nuc&Nerve To Deep Nuclei (Vestibular Nuc) 2a.Spinocerebellum Vermis. Fastigial Nuc 2b.Spinocerebellum Lateral hemisphere (Intermediate zone) Lateral hemisphere Spinal cord (Vest.nuc,, visual, auditory, face) Spinal cord Cerebral Cortex via pons Dentate Nuc. 3.Cerebrocerebellum (or Pontocerebellum Interpositus Function Balance & eye movements adjust movement of axial musc adjust movement of distal musc motor planning IV) Cerebellar Pathways Sensory or Motor info Brainstem UMNs Cerebral Cortex UMNs (via thalamus) Cerebellum Control Axial/Proximal muscles Control Distal limb muscles Vestibulospinal Tracts Reticulospinal Tracts Lateral Corticospinal Tract Rubrospinal Tract Abbreviations SCP- superior cerebellar peduncle MCP- middle cerebellar peduncle ICP- inferior cerebellar peduncle DSCT- dorsal spinocerebellar tract VSpCerT- ventral spinocerebellar t. 2
Cerebellum uses multiple pathways to affect movement, but all are based on above scheme. Afferent (sensory and motor) info arises from spinal cord, vestibular nuclei, cerebral cortex (via pontine nuclei), and brainstem nuclei. ALL fibers leaving the cerebellum arise from the deep nuclei, except for axons from the flocculonodular cortex to the vestibular nuclei. V) FLOCCULUS and NODULUS Vestibulocerebellum How it works: cerebellum uses vestibular information to control balance and eye movements. It does this by controlling the vestibular nuclei. Sensory or Motor info ICP Cerebellum ICP UMNs Vestibular system Vestibular nuclei: Vestibulospinal Ts MLF Flocculus/Nodulus Role of Vestibulospinal Tracts (UMNs) in Motor System Antigravity fighters! - provide excitatory activity to LMNs controlling antigravity muscles (predominantly extensors) to maintain balance and posture. controlled by cerebellum via the vestibular nuclei UMN LVST Tactile fibers + +/ Extensor LMN + Info to and from vestibulocerebellum via ICP. Lesions: loss of balance and consequent gait problems (ataxia); nystagmus, vertigo, nausea. 3
VI) VERMIS Spinocerebellum WHAT: coordinates axial/trunk muscles for postural stability HOW: The vermis communicates with the spinal cord. The cerebellum uses ( unconscious ) proprioceptive and motor information from limbs. Vermis controls trunk (axial musculature). Sensory or Motor info ICP/SCP Cerebellum ICP/SCP UMNs Ipsilateral effects For trunk (axial) control Spinal cord Vestibular nuc, Reticular Form, Motor Cortex Vestibulospinal T Reticulospinal T VCST VERMIS Fastigial nucleus Pathways from spinal cord to Vermis/spinocerebellum (2-neuron chains): transmit proprioceptive, tactile, and motor information from the upper and lower body 1. Cuneocerebellar tract diverted from fasciculus cuneatus 2. Dorsal spinocerebellar tract diverted from fasciculus gracilis 3. Ventral spinocerebellar tract From dorsal columns for Unconscious proprioception Body Region 1 neuron Relay Nucleus Tract Peduncle Side Upper Fasc. Cuneatus Lateral Cuneate Nuc Cuneocerebellar Inferior ipsilateral Lower Fasc. Gracilis Nucleus Dorsalis (T1-L2) Dorsal spinocerebellar Inferior ipsilateral Lower Spinal Border Cells Ventral spinocerebellar Superior ipsilateral 4
Axons from the vermis use the fastigial nucleus as relay on their way to the brainstem. Lesions of vermis cause trunkal/gait ataxia (uncoordinated proximal leg movements during walking) VCST VL fastigial vermis ICP/SCP 5
VII) CEREBELLAR HEMISPHERES (Spino and Cerebrocerebellum) WHAT: control movements of the upper and lower limbs assists in adjusting and planning movements. Adjusting movement involves correcting the speed, direction, and force of intended movement. HOW: cerebellar hemispheres communicate with both the spinal cord and cerebral cortex. Sensory or Motor info MCP Cerebellum SCP UMNs Spinal Cord Motor Cortex Brainstem Red Nucleus Motor Cortex - LCST 1. Spinal cord Cerebellar Hemisphere Nuc Interpositus Red Nucleus upper Limb flexors 2. Cerebral cortex LATERAL HEMISPHERES Interpositus and Dentate nucleus This pathway demonstrates a general feature of the cerebellum the cerebellum influences ipsilateral body movement because most of its pathways cross the CNS twice. Lesions: cause distal limb ataxia (difficulty controlling the smoothness and accuracy of arm and leg movements) and decreased muscle tone. 6
VIII) Cerebellar Cortex and Motor Learning consists of 3 layers: granular, purkinje cell, molecular all afferents entering cerebellar cortex are known as Climbing fibers or Mossy fibers. 1. Climbing fibers originate in contralateral inferior olivary nuclei and travel in ICP. 2. All other afferents to cerebellar cortex are mossy fibers that enter cerebellum through all 3 peduncles. Cerebellum plays a important role in motor learning. New movements are made automatic by action of the cerebellum with the motor cortex. Inferior olivary nucleus and its climbing fibers play a big role in this as a relay between motor cortex and cerebellum. PET studies indicate that the cerebellum also participates in cognitive functions, but we don t understand yet the basis for this. IX) Symptoms of Cerebellar lesions Flocculus/Nodulus (Vestibulocerebellar) Signs Loss of balance Ataxic Gait caused by loss of balance Nystagmus Vermis (Spinocerebellar) Signs Ataxic Gait due to uncoordinated trunk/proximal lower limb movements Cerebellar Hemisphere (spinocerebellar/cerebrocerebellar) Signs all related to uncoordinated upper and lower limb movements: Ataxia/Asynergia/Decomposition of movements - lack of coordinated contractions of agonist and antagonist muscles Dysmetria- inaccurate movement range or direction Hypermetria- excessive movement amplitude (overshoot) Hypometria- insufficient movement amplitude (movement falls short) Dysdiadochokinesia- inability to perform fine, repetitive movements(e.g. rapid pronation and supination of the hand) Tremor (kinetic or intention) - occurs during muscle contraction or during performance of a voluntary task. Lack of Check inability to readjust limb position when movement is disturbed Inappropriate force Delayed initiation of movement Hypotonia (due to decreased influence of LVST) Dysarthria- uncoordinated, slurred, or slow speech (word use is unaffected) XI) SUMMARY and General Principles of Cerebellar Pathways (be able to distinguish these) Floccululas/Nodulus Vestibular signs Falling Nystagmus Ataxic Gait 4 th ventricle tumor, MS Vermis Trunkal ataxia Postural instability ataxic gait Alcohol, MS, tumors Cerebellar Hemispheres Upper/lower limb ataxia Ataxic gair Intention Tremor Uncoordinated motion MS, tumors, infarcts 1. Cerebellar symptoms are caused by damage to cerebellum, its peduncles, or its CNS pathways. 2. Lesions of any cerebellar peduncle cause limb ataxia, because each peduncle contains axons that connect with the cerebellar hemispheres. 3.. Lesions produce IPSILATERAL motor deficits. Two clinical tests to assess limb coordination (cerebellar hemisphere): finger-to-nose test and heel-to-shin test. These tests are easy to perform and reveal tremor and ataxia with cerebellar impairment. 7
Recognizing Cerebellar Signs IMPORTANT! Cerebellar Signs basically fall into 2 categories: 1) Vestibular Symptoms: falling, nystagmus, ataxic gait. Subsequent analysis must be used to determine whether these result from lesions of the vestibular system or flocculus/nodulus. 2) Ataxia vermis trunk/proximal lower limbs ataxic gait cerebellar hemispheres (including intermediate zone) upper and lower limbs tremor and other symptoms of uncoordinated movement. Summary Table for Cerebellar Peduncles (for clarification not memorization) Peduncle Input Output Function Inferior Dorsal spinocerebellar tract Vestibular Nuclei vestibulo and Cuneocerebellar tract Reticular Formation spinocerebellum Vestibular nerve/nuclei CN V, IX, XII (coordination) Inferior Olivary Nucleus Middle Cerebral cortex via pontine nuclei none cerebrocerebellum Superior Ventral spinocerebellar tract Red Nucleus spino and cerebro- VL of Thalamus cerebellum Reticular Formation 8
CASE 1: A mother brought her 6-year-old son to a physician because he had been falling frequently and vomiting over the past 3 weeks, but he had no fever. On examination, the boy complained that he had a stiff neck. He lost his balance easily when he stood unsupported and nystagmus was observed. Ocular exam revealed papilledema. Solution: The symptoms are falling, vomiting, nystagmus, which are signs of vestibular problems. The absence of fever (no infection) and presence of papilledema suggest increased intracranial pressure tumor. Medulloblastoma arises in roof of 4th ventricle; affects cerebellar nodulus/ vestibulocerebellum; is most common in children. CASE 2: A 70-year-old man with a long history of alcohol dependency was brought to the ED because he had fallen in the street and was unconscious. On examination, he stood with a broad base and exhibited a truncal tremor. His walking was wide-based and unsteady. Even when supported, his steps were irregular and uncoordinated. Solution: the cerebellar vermis is especially sensitive to chronic alcohol intoxication. As part of the spinocerebellum, it controls trunk muscles necessary for standing and walking. Damage to the vermis causes truncal tremor and gait ataxia. To compensate, patients stand/walk with their legs widely separated. His uncoordinated steps even while supported indicate that his ataxia in not due just to loss of balance (vestibulocerebellum). Acute alcohol intoxication impairs cerebellar function, causing trunk and limb ataxia. CASE 3: A 45-year-old women with a history of multiple sclerosis visited her physician because she had difficulty controlling her left arm. She complained that when she eats, her arm shakes as she tries to bring her fork towards her mouth and that she often misses her mouth with her left hand and injures her cheek. Her left arm and leg muscles were hypotonic. The finger-to-nose test showed a gross inaccuracy in her ability to touch her nose with her left hand and she developed a severe left hand tremor as her finger approached her nose. Findings were similar for the heel-to-shin test on the left. It was also difficult for her to perform rapid alternating movements with her left hand. Her speech was slurred, but there was no problem with comprehension, word use, or capacity to vocalize. 9
Solution: The symptoms indicate ataxia affecting limb movements: arm shaking during movement - intention tremor finger to nose inaccuracy/tremor dysmetria/intention tremor of upper limb heel to shin deficits dysmetria/intention tremor of lower limb difficulty with rapid alternating movements (dysdiadochokinesia) uncoordinated movements slurred speech without difficulty in comprehension/capacity to vocalize (dysarthria) uncoordinated tongue, laryngeal, jaw muscles used for vocalization. All are symptoms of damage to the lateral cerebellar hemisphere or cerebrocerebellar pathway that lead to ataxia in movements of the limbs. 10