Cerebellum

Question 1

What are the names of the three bilateral pairs of deep cerebellar nuclei?

Answer 1

fastigial (most medial)

interposed

dentate (most lateral)

Question 2

How is the cerebellum divided into lobes?

How is the cerebellum divided through the midline?

Answer 2

Anterior lobe, posterior lobe, flocculo-nodular lobe

Vermin, paravermis and lateral hemispheres

Question 3

Three cerebellar peduncles connect the cerebellum to the brainstem. Which peduncles carry inputs to the cerebellum and which peduncles carry outputs from the cerebellum? Which nerve bypasses the peduncles and communicates directly with the cerebellum?

Answer 3

Inferior cerebellar peduncle - inputs from spinal cord and medulla

Middle cerebellar peduncle - inputs from cerebral cortex (relayed through the pons)

Superior cerebellar peduncle - outputs except vestibular output AND the afferent ventral spinocerebellar tract

The floccular-nodular lobe receives direct input from the vestibular portion of CN VIII and vestibular nuclei

Question 4

What are the four tracts that carry somatosensory information to the cerebellum? What types of information does each tract carry? From what part of the body does each tract originate?

Answer 4

There are four spinocerebellar tracts:

dorsal spinocerebellar tract - carries pure somasthesis from lower body. Muscle spindle afferents carrying proprioception from the lower body ascend in the gracile fasciculus to terminate in Clarke’s nucleus in the thoracic spinal cord (T1-L1). Axons of these secondary neurons form the dorsal spinocerebellar tract, which projects through the inferior cerebellar peduncle on the paravermis

Cuneocerebellar tract - carries pure somasthesis from the upper body. muscle spindle afferent carry proprioception from the upper body ascend in the cuneate fasciculus and terminate on the lateral cuneate nucleus. Axons of these secondary neurons form the cuneocerebellar tract, which projects through the inferior cerebellar peduncle on the paravermis

Ventral spinocerebellar tract - carries the error signal from lower body. Golgi tendon organ afferents synapse on interneurons in the spinal cord which integrate sensory info with motor commands and generate an error signal conveying the discrepancy between the motor plan and the executed movement. Axons project through superior cerebellar peduncle to the paravermis

Rostral spinocerebellar tract - carries the error signal from the upper body. GTO afferents synapse on interneurons. Axons project through the inferior cerebellar peduncle to the paravermis

Question 5

What is the pathway from the cerebral cortex to the cerebellum?

Answer 5

Cerebral cortex -> internal capsule -> terminate on ipsilateral pontine nuclei -> project contralaterally as the crossing fibers of the pons -> middle cerebellar peduncle -> lateral hemispheres of the cerebellum

Question 6

What are the main input tracts to the cerebellum?

Answer 6

4 Spinocerebellar tracts

Vestibular nerve and nuclei

pontine nuclei (relaying info from the cerebral cortex)

inferior olivary complex

reticular formation

Question 7

What are the main output destinations of the cerebellum cortex? What nerves make up these output tracts? What neurotransmitter do these nerves release?

Answer 7

Deep cerebellar nuclei (fastigial nucleus, interposed nucleus and dentate nucleus)

Axons of purkinje cells make up the output tracts of the cerebellar cortex and are all GABAergic

Question 8

What are the three layers of the cerebellar cortex? What cells are in each layer?

Answer 8

granular layer - Golgi cells (inhibitory interneurons) and granule cells

purkinje layer - cell bodies of Purkinje cells

molecular layer - dendrites of Purkinje cells, cell bodies of stellate and basket cells (both inhibitory interneurons)

Question 9

What is the difference between climbing fibers and mossy fibers?

Answer 9

climbing fibers - synapse directly on Purkinje cells; excited only a few Purkinje cells but synapses thousands of times on those cells; arise from the inferior olivary complex

mossy fibers - synapses indirectly on Purkinje cells (mossy fibers synapse on granule cells which synapse on Purkinje cells); excits many Purkinje cells; arise from non-olivary cerebellar inputs

Question 10

What are the main output destinations of the cerebellum deep cerebellar nuclei?

Answer 10

output destinations: thalamus, red nucleus, vestibular nuclei

Question 11

What is the cerebellar output pathway that maintains posture?

Answer 11

floccular-nodular lobe and vermis -> fastigial nucleus -> bilateral vestibular nuclei in brainstem -> reticulospinal and vestibulospinal tracts -> axial and neck muscles

This pathway is also very important in the control of eye movement (vestibulo-ocular reflex)

Question 12

What is the cerebellar output pathway that facilitate motor control?

Answer 12

paravermis -> interposed nuclei -> superior cerebellar peduncle -> red nucleus -> rubrospinal tract -> distal muscles (facilitates flexor muscles and inhibits extensor muscles)

Question 13

What is the cerebellar output pathway that facilitates motor planning?

Answer 13

lateral hemispheres -> dentate nucleus -> superior cerebellar peduncle -> ventrolateral posterior (VLp) thalamus -> cerebral cortex -> corticospinal tract

Question 14

Why are cerebellar deficits always ipsilateral to the lesion?

Answer 14

All outputs form the cerebellum (except vestibular) go through the superior cerebellar peduncle, which decussates in the midbrain. The target structures of the cerebellar outputs give rise to descending motor tracts (rubrospinal and corticospinal) that decussate again.

Question 15

What are the cardinal signs of cerebellar dysfunction?

Answer 15

ataxia, hypotonia, dysarthria (difficulty saying words because of problems with the muscles that help you talk), tremor (intention or postural tremor, NOT resting tremor) and oculomotor dysfunction

Question 16

What are the characteristic symptoms of a vermis/midline cerebellum syndrome? What is the most common cause of vermis syndrome?

Answer 16

wide-based stance due to difficulty in maintaining balance in all directions

imbalance causes patient to fall in all directions

wide gait

gait abnormalities not improved by visual orientation

eye-movement disturbances and nystagmus

distal arm and leg movments are not impaired

large masses can compress the 4th ventricle and lead to hydrocephalus

Most commonly caused by chronic alcohol abuse

Question 17

What are the characteristic symptoms of hemispheric cerebellum syndrome?

What are the most common etiologies of hemispheric cerebellum syndrome?

Answer 17

Mostly affect the limbs

impaired rapidly alternating movements

loss of coordination in ipsilateral limb

intention tremor

dysmetria (inability to stop a movement at the proper place; undershoot or overshoot eye movements, seen in finger-to-nose and heel-knee-shin tests)

scanning speech (dysarthria)

imbalance causes patient to fall towards the side of the lesion

Main causes of this syndrome is metastasis, infarcts or abscesses

Question 18

What are the five types of tremors?

Answer 18

resting tremor

intention tremor

postural tremor

essential tremor

physiologic tremor

Question 19

What is asterixis? What disease is asterixis a sign of?

Answer 19

NOT a tremor. Muscle tone lapses when wrist extension is attempted, resulting in wrist flexion. Usually bilateral.

A sign of hepatic encephalopathy due to build up of urea because of liver failure

Question 20

What is myoclonus?

Answer 20

A quick movement of muscle that is NOT a tremor. Cannot be suppressed.

Question 21

What portion of the cerebellum does alcohol primarily damage?

Answer 21

The vermis. Leads to a midline/vermis cerebellum syndrome (wide-based stance, eye movement abnormalities, truncal ataxia)

Question 22

Any time a patient presents with parkinsonism symptoms, what must you keep on the differential?

Answer 22

manganese toxicity

Question 23

What are the neurological characteristics of Friedreich ataxia? What other diseases do these patient often get? What is the age of onset?

Answer 23

Chronic, slowly progressive, genetic cerebellar ataxia caused by degeneration of sensory neurons that direct muscle movement through connections in the cerebellum.

Also associated with cardiomyopathy and diabetes mellitus

Usual age of onset is 2-25 years

Question 24

Besides ataxia and telangiectasias, what other diseases/clinical findings are found in ataxia-telangiectasia?

Answer 24

Malignancies are frequent because AT is caused by a genetic mutation in the ATM gene that is involved in repairing double-strand breaks in DNA

Question 25

What are the characteristics of a resting tremor? What is its etiology?

Answer 25

resting tremor - maximal at rest and decreases with activity but comes back after awhile;

etiology = basal ganglia disorder, parkinson’s disease, supranuclear palsy, drug-induced parkinsonism

Question 26

What are the characteristics of an intention tremor? What are its etiologies?

Answer 26

intention tremor - maximal during movement towards a target and the closer you get to a target, the larger the tremor;

Test with finger-nose-finger

etiology = cerebellar lesions (hemispheric), multiple sclerosis, chronic alcohol abuse and Wilson’s disease

Question 27

What are the characteristics of a postural tremor? How can you test for it? What are the etiologies if acute onset? If slow onset?

Answer 27

postural tremor - maximal when patient holds affected limb out against gravity

ask patient to hold their arms out

etiology = if acute onset, then toxic or metabolic disorder. If slow onset, then physiologic or essential tremor

Question 28

What are the characteristics of an essential tremor?

Answer 28

Usually affects the hands, head, and voice. Postural or kinetic. Is minimal at rest. Usually bilateral. It tends to increase with aging and in 50% of patients, inheritance is autosomal dominant.