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The Cerebellum


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The cerebellum serves to:
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?
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:
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?
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?
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?
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?
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.)

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