The Cerebellum
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- The cerebellum serves to:
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1-integrate sensory and other inputs from many regions of the spinal cord and brain.
2-smooth movements/ coordination; functions in motor planning.
3-involvement of lower motor neurons (not directly) through motor system of cortex & brainstem. - What condition is typically related to lesions of the cerebellum?
- Ataxia - irregular, uncoordinated movements
- What function does the inferior vermis or flocculonodular lobes serve?
- Regulates balance and eye movement in conjunction with the vestibulatory circuitry. Also works with other parts of vermist to regulate medial motor systems (e.g., proximal trunk & limb muscles).
- What do the intermediate hemispheres do?
- These regions serve the lateral motor systems, such as distal appendicular muscles.
- Which region of the cerebellum functions in motor planning?
- The lateral cerebellar regions.
- Is ataxia ipsilateral or contralateral to the side of the cerebellar lesion?
- Ipsilateral
- Unsteady gait, such as truncal ataxia and eye movement abnormalities result from what type of lesions?
- Midline lesions of the cerebellar vermis or flocculonodular lobes
- Midline lesions can cause what type of symptoms (other than the unsteady gait)?
- Intense vertigo, nausea, and vomiting
- Ataxia of the limbs, for example, appendicular ataxia, result from lesions where?
- Lesions lateral to the cerebellar vermis.
- Identify four additional functions of the cerebellar pathways:
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1 - speech articulation
2 - respiratory movements
3 - motor learning
4 - higher order cognitive functions - How is the cerebellum attached to the dorsal region of the pons and medulla?
- It is attached by the superior, middle, and inferior cerebellar peduncles.
- The roof of what ventricle is formed by the cerebellum?
- Fourth ventricle
- Herniation of the cerebellar tonsils can be caused by and lead to what conditions?
- Caused by mass lesion of the cerebrum or cerebellum, brain swelling, intracranial pressure. Herniation can lead to tonsils being pushed into foramen magnum, compress the medulla, & possible death secondary to medulla respiratory centers being affected.
- Which cerebellar peduncle carries mainly output from the cerebellum?
- Superior cerebellar peduncle.
- Which peduncle (s) carry mainly input to the cerebellum?
- Middle and Inferior cerebellar peduncles.
- What are the main functions of the lateral hemispheres?
- Motor planning for extremities.
- Which region is the largest part of the cerebellum?
- The lateral hemispheres.
- Which motor pathways influence the lateral hemispheres?
- Lateral corticospinal tract
- What is the function of the intermediate hemispheres of the cerebellum?
- Distal limb coordination, particularly the appendicular muscles in the legs & arms.
- Which region of the cerebellum controls proximal limb and truck coordination?
- Vermis.
- The flocculonodular lobe controls what functions?
- Balance and vestibulo-ocular reflexes.
- What motor pathways are influenced in the intermediate hemispheres?
- lateral corticospinal trach & rubrospinal tract.
- What motor pathways are involved in the vermis?
- Anterior corticospinal tract, reticulospinal tract, vestibulospinal tract, & tectospinal tract.
- The motor pathway of the medial longitudinal fasciliculus is involved in which region?
- Flocculonodular lobe.
- If there is a lesion in the lateral cerebellum, what function may be affected?
- Distal limb coordination.
- Truck control, posture, balance, & gait can be affected by a lesion in what region?
- Medial cerebellum.
- Deficits in coordination are ipsilateral the the lesion because the pathways are "double crossed." Where are the crossings?
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1 - As the cerebellar output pathways exit in the decussation of the superior cerebellar peduncles.
2 - Occurs as the cortico -spinal and rubrospinal tract go down to the spinal cord. - Do lesions of the medial motor system cause unilateral, contralateral, or bilateral deficits?
- Bilateral, as the medial motor system influences the proximal trunk muscles bilaterally.
- Inputs to the cerebellum arise from various sources. Identify 4 regions:
- All regions of the CNS, sensory modalities, brainstem nuclei, & spinal cord.
- What is the major source of fibers in the cerebellum?
- Corticopontine fibers from the 4 lobes of cerebrum - travel in the internal capsule and cerebral peduncles.
- How is much of the cerebellum innervated?
- Pontocerebellar fibers cross the midline to enter the contralateral middle cerebellar peduncle. It branches to mossy fibers to innervate the cerebellum.
- Spinocerebellar fibers are another greast source into the cerebellum. What information is conveyed via this route?
- Information about limb movements via the dorsal spinocerebellar tract and cuneocerebellar tract.
- Why would you get ipsilateral limb ataxia if there was a lesion within the spinocerebellar tract?
- The input is either ipsilateral or double-crossed.
- What are the 2 types of synaptic input into the cerebellum?
- Mossy fibers (excitatory synapses) and Climbing fibers (also powerful excitatory synapses).
- Which cells carry all of the outputs of the cerebellum?
- Carried out by the axons of purkinje cells, which form inhibitory synapses onto deep cerebellar nuclei and vestibular nuclei - then outputs from the cerebellum to other regions (excitatory).
- Cerebellar inhibitory interneurons include:
- Basket cells and stellate cells (located in the molecular layer).
- Axons projecting upward are excitatory. These include:
- mossy fibers, climbing fibers, granule cell parallel fibers.
- All axons projecting downward are inhibitory. These include:
- Purkinje cells, stellate cells, basekt cells, and Golgi cells.
- What branches of arteries supply the cerebellum?
- Posterior inferior cerebellar artery, anterior inferior cerebellar artery, & superior cerebellar artery.
- Do the arteries above supply blood to the cerebellum exclusively?
- No, they also supply blood to portions of the lateral medulla & pons.
- Infarcts are most common in which arteries?
- Posterior inferior cerebellar artery and Superior cerebellar artery.
- What are the common symptoms seen in cerebellar infarcts?
- headache (occipital, frontal, upper cervial), nausea/vomiting, horizontal nystagmus, vertigo, unsteady gait, & limb ataxia.
- If the cerebellum is spared (in an infarct), can the patient have ataxia?
- Yes, because many signs/symptoms of cerebellar artery infarcts result from lateral medulla/pons infarcts - it is because of its involvement with the cerebellar peduncles.
- What kind of infarct may have occured if the brainstem was spared but involved primarily the cerebellum?
- Superior cerebellar artery infarct.
- Which infarcts would involve both lateral brainstem and cerebellum?
- Posterior inferior and Anterior inferior cerebellar arteries.
- Compression of the fourth ventricle can be caused by what type of infarct?
- Large cerebellar infarcts involving areas supplied by the posterior inferior and superior cerebellar arteries. This can lead to hydrocephalus
- Why would compression of the posterior fossa be life threatening?
- Respiratory centers & other equally vital brainstem structures can be affected.
- What primary medical conditions can lead to cerebellar hemorrhage?
- Chronic hypertension, ateriovenous malformation, hemmorhage 2ndary to inschemic infarct, & metastases.
- What can be caused by a large cerebellar hemorrhage?
- hydrocephalus, 6th nerve palsy, impaired consciousness, brainstem compression, death.
- What is ataxia?
- Problems with both contractions of agonist and antagonist muscles. It's the lack of normal coordination btwn movement at different joints.
- What are characteristics of ataxia?
- irregular movements, with a wavering course that can present with "overshoots," overcorrecting and then overshooting again around the intended target.
- What are the characteristics of ataxic movements?
- Problems with timing (dysrhythmia) and problems with trajectories through space (dysmetria).
- What type of ataxia is caused by lesions of the cerebellar vermis?
- Truncal ataxia - wide-based, unsteady, drunk-like gait. One can have some difficulty sitting upright in severe cases.
- What portions of the cerebellum are affected in appendicular ataxia?
- Lesions of the intermediate and lateral portions.
- Which motor system leads to a bilateral (truncal ataxia)?
- Lesions affecting the medial motor system - while bilateral, patient may lean towards side of lesion.
- With intact cerebellum, lesions in the cerebellary peduncles or pons can lead to what?
- Severe ataxia.
- Gait abnormalities, similar to truncal ataxia, can result from lesions/hydrocephalus in which brain region, other than cerebellar hemispheres?
- Lesions within the prefrontal cortex or hydrocephalus, which may damage frontopontine pathways.
- Another false localization of ataxia can occur where in the CNS?
- Spinal cord.
- What syndrome is caused by lacunar infarcts in the cerebellum?
- Ataxia-hemiparesis.
- What is the clinical presentation of ataxia-hemiparesis?
- Includes a combination of ataxia and unilateral motor signs. Both ataxia & hemiparesis are contralateral to side of lesion.
- What areas are typically lesioned in the syndrome of ataxia & hemiparesis?
- Internal capsule or pons that involve both corticospinal & corticopontine fibers, and corona radiata. Also, frontal, parietal lobes, sensorimotor ctx, midbrain lesions (fibers involving superior cerebellar peduncles or red nucleus).
- What pathway is disturbed in sensory ataxia?
- Posterior column-medial lemniscal pathway
- What symptoms occur in sensory ataxia?
- It causes impaired or loss of joint position sense and is characterized by ataxic like overshooting movements of the limbs and wide-based, unsteady gait.
- What worsens symptoms of sensory ataxia? What improves symptoms?
- When eyes are closed or in the dark, symptoms worsen; visual feedback helps.
- What types of lesions will cause sensory ataxia in the ipsilateral side of the lesion?
- Typically involves lesions of the peripheral nerves or posterior columns.
- In contralateral ataxia, where are the lesions typically located?
- May occur secondary to lesions in the thalamus, thalamic radiations or somatosensory cortex.
- What are common symptoms/signs of lesions in the cerebellum that produce incipient tonsilar herniation?
- Depressed consciousness, brainstem findings, hydrocephalus, head tilt.
- What are some abnormalities that can confond the cerebellar exam?
- Upper motor neuron signs (corticospinal and cerebellar lesions), lower motor neuron signs (testing would not be possible), sensory loss, basal ganglia dysfunction,tremor, & dyskinesia.
- What is dysmetria?
- Abnormal under- or overshooting during movements toward a target.
- What is dysrhythmia?
- Abnormal rhythm and timing of movements.
- Name and describe one test for ataxia:
- Finger-to-nose test - alternately touches nose and examiner's finger.
- Name and describe a second test for ataxia:
- Heel shin - rubs heel up and down length of shin in a straigt line (lying down).
- What is dysdiadochokinesia?
- Abnormalities of rapid alternating movements.
- What type of ataxia is seen in a wide-based gait, like a drunk person or toddler, with cerebellar involvement?
- Truncal ataxia.
- Name and describe one type of test for truncal ataxia:
- Tandem gait testing - heel-toe walk (narrow stance). The patient will fall or deviate towards the side of the lesion.
- Name and describe another test for truncal ataxia:
- Romberg's Test - Feet together (1/2 minute), eyes closed then. + test: can stand w/ eyes open, but falls with eyes closed. Proprioception lesion, not test of cerebellar fxn.
- Where would the lesion be if the patient had a hard time standing with eyes open AND closed?
- Midline cerebellar lesions (also a peculiar tremor of the trunk or head-titubation-can occur).
- Define ocular dysmetria:
- saccades overshoot or undershoot their target.
- Define nystagmus, of the gaze paretic type:
- The patient looking at a target in the periphery shows slow phases toward the primary position and fast phases occur back towards the target.
- What is it called when a person's speech has an ataxic quality, in cerebellar disorders, with irregular fluctuations in rate & volume?
- Scanning or explosive speech.
- What are the most prevalent causes of acute ataxia in adults?
- Ingestion of toxins and ischemic or hemorrhagic stroke.
- Identify the common causes of chronic ataxia in adults:
- brain metastases, chronic exposure to toxins(e.g., alcohol), multiple sclerosis, degenerative disorders of the cerebellum or cerebellar pathways.
- In the pediatric population, what are the most common causes of acute ataxia?
- Accidental ingestion of drugs/toxins, varicella- associated cerebellitis, migraine.
- Also in children, what are common causes for chronic or progressive ataxia?
- Cerebellar astrocytoma, medulloblastoma, Friedreich's ataxia, ataxia-telangiactasia
- In understanding the neuroanatomy of the cerebellum, where is it located in the cranium?
- Posterior fossa
- The cerebellum consists of what brain structures?
- Midline vermis, intermediate part of the cerebellar hemisphere, lateral part of the cerebellar hemisphere.
- The cerebellum is attached to the brainstem via which structures?
- Superior cerebellar, middle cerebellar, and inferior cerebellar peduncles.
- What are the 3 functional zones of the cerebellar cortex and deep nuclei?
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1 - Vermis (via fastigial n.) & flocculonodular lobes (via vestibular n.)
2 - Intermediate part of cerebellar hemispher (via interposed n.)
3 - Lateral part of the cerebellum (via dentate n.)