Neuro Exam 2: Cerebellum

Front 1

What is the cerebellum comprised of?

Back 1

A midline vermis and two lateral cerebellar hemispheres. The paired cerebellar tonsils are parts of the hemispheres located on the inferior surface near the midline.

Front 2

How many fissures divide the cerebellum into how many lobes?

Back 2

Two transversely oriented fissures divide the cerebellum into three lobes.
Primary fissure: On superior surface, separates anterior and posterior lobe
Posterolateral fissure: One inferior surface, separates posterior lobe from flocculondular lobe.
-The cerebellar lobes are divided by fissures into lobules

Front 3

What does the flocculonodular lobe consist of?

Back 3

Nodulus: small part of vermis
Flocculi:

Front 4

What are the gyri of the cerebellum called?

Back 4

Folia. Each folium consists of a thin gray cortex with a core of white matter.

Front 5

How many layers of cortex are there in the cerebellum?

Back 5

3. From the surface to the white matter of the folium, these are the molecular, Purkinje, and granular cell layers.
-Note: Purkinje cells, which are the output cells of the cerebellar cortex, are extremely sensitive to ischemia (insufficient blood flow to a tissue)

Front 6

How many deep nuclei lie within the deep cerebellar white matter?

Back 6

4.
-Fastigial (most medial)
-Globose and emboliform (interposed nuclei)
-Dentate (most lateral)

Front 7

What do the deep cerebellar nuclei do?

Back 7

Transmit almost all the output of the cerebellum back to the brainstem and cerebral cortex

Front 8

What connect the cerebellum with the rest of the nervous system and how many are there?

Back 8

Three paired white matter structures called cerebellar peduncles.
-Superior cerebellar peduncle: contains most of the output tracts (especially the dentatorubrothalamic tract) and projects into contralateral midbrain (lateral roof of 4th ventricle, enters lower midbrain and crosses here, projects to contralateral red nuclei in upper midbrain)
-Middle cerebellar peduncle: contains one input tract (smooth & coordinate tract #2) to cerebellum that projects
from contralateral pons (pontine nuclei).
-Inferior cerebellar peduncle: contains most of the input tracts (smooth & coordinate #1) to the cerebellum and contains many projections from ipsilateral spinal cord.

Front 9

What is each cerebellar hemisphere and the vermis concerned with the function of?

Back 9

Each cerebellar hemisphere is concerned with the function of the ipsilateral body. The vermis is concerned with the function of midline or axial body structures.

Front 10

What is the major function of the cerebellum?

Back 10

To smooth and coordinate voluntary movements of trunk and extremities (does this via two independent pathways)

Front 11

Describe "smooth & coordinate circuit #1"

Back 11

1. Input about movement in progress projected to cerebellum from spinal cord via the three spinocerebellar tracts (3 per side of body)
2. Input is projected to interposed and fastigial nuclei and to cortex of medial cerebellar hemispheres and vermis. Interposed/fastigial nuclei independently do part of smooth/coordinating movements. Input to cortex results in inhibitory/modulatory output from Purkinje cells to interposed/fastigial nuclei, helping them do task better.
3. Interposed/fastigial nuclei give rise to cerebellar output that exit in superior cerebellor peduncle. These fibers cross in the midbrain and pass through and around the red nucleus to synapse in the thalamic nucleus VLp.
4. Thalamic neurons project to primary motor cortex. Fastigial nucleus projects to regions of motor cortex involved in control of axial/proximal muscles (gives rise to anterior corticospinal tract). Interposed nuclei project to regions of motor cortex controlling distal limb movements (give rise to lateral corticospinal tracts).

Front 12

What happens if there is a lesion below VLp?

Back 12

Ipsilateral unsmooth/uncoordinated movements

Front 13

What happens if there is a lesion of VLp (or above)?

Back 13

Contralateral unsmooth/uncoordinated movements

Front 14

Part of the cerebellum is part of what other system?

Back 14

The vestibular system (sometimes cerebellar lesion looks like a vestibular lesion)

Front 15

What is the specific purpose of "smooth & coordinate circuit #2"?

Back 15

To help plan and organize voluntary movements, particularly those that will be too fast to be smoothed in progress (aka too fast for circuit #1). This circuit is independent of somatosensory feedback and is a more evolutionarily developed pathway.

Front 16

Describe "smooth and coordinate circuit #2"

Back 16

1. Primary sensory and motor cortices, premotor cortex, posterior parietal cortex project axons through corona radiata and anterior limb of internal capsule
2. Project through medial and lateral fifths of the crus cerebri of the midbrain
3. Synapse on ipsilateral pontine nuclei which are scattered throughout basis pontis
4. The pontine nuclei then project through contralateral middle cerebellar peduncle (meaning they crossed in the pons) as mossy fibers to dentate nucleus and cortex of the lateral part of cerebellar hemisphere.
5. The cortex of each lateral hemisphere projects to ipsilateral dentate nucleus
6. The cerebellar output for planning/organizing movements arises from dentate nucleus. It projects through the crossed cerebellar peduncle through and around the red nucleus to the VLp nucleus of the thalamus. These projections are called the dentatorubrothalamic tract
7. Cells in the VLp then project to the motor and premotor cortex.

Front 17

What is the lateral cerebellum particularly important for?

Back 17

skilled movements at optimal velocity which can't depend on substantial corrections from sensory feedback

Front 18

What else is the cerebellum involved in?

Back 18

Learning of new motor skills

Front 19

Would lesions of the cerebellar cortex or lesions of the deep cerebellar nuclei be expected to produce more severe and long-lasting cerebellar deficits.

Back 19

Deep cerebellar nuclei. If a lesion only destroys cerebellar cortex still will have uncoordinated and unsmooth movements, but not as bad because the deep cerebellar nuclei can process input and send output independent of the cerebellar cortex.

Front 20

What is the purpose of "smooth and coordinate circuit #1"?

Back 20

To convey unconscious proprioceptive information and information about final motor command. Correcting ongoing movements when they deviate from their intended course and modifying the central motor program so that subsequent similar movements are correct.

Front 21

What is ataxia?

Back 21

Clumsiness or incoordination that is not due to weakness or sensory loss. This is the most obvious abnormality produced by a lesion of the cerebellar system

Front 22

What is produced by a lesion of the vermis?

Back 22

Truncal ataxia: difficulty maintaining smooth trunk over feet.
-To maintain stability, patient must keep feet apart when walking.
-If lesion extends into one cerebellar hemisphere, patient will fall to this side
-Lesion of flocculonodular lobe produces similar findings

Front 23

What is produced by a lesion of a cerebellar hemisphere?

Back 23

Ataxia of the ipsilateral extremeties: purposeful movements are clumsy because of abnormal rate, range, direction, timing, and force of movement.
-Decomposition of movements: when attempting to do purposeful movement requiring several joints, components may not be properly coordinated
-Dysmetria: inability to stop movements at the desired point
-Adiadochokinesia (aka dysdiadochokinesia): failure of smoothness of rapid movements
-Intention "tremor": uncontrolled shaking of the affected extremity that is only present with purposeful movement and is worse at end of the movement (due to lesion of dentate nucleus or dentatorubrothalamic tract)
-Note: Can't distinguish lesions involving medial vs. lateral portions of cerebellar hemisphere

Front 24

What is produced by bihemispheric or vermal lesions?

Back 24

Characteristic cerebellar speech disorder. It is a type of dysarthris (speech disorder) called scanning or ataxic speech.
-Due to incoordination of muscles used in speech production
-Harsh, metallic, equal emphasis on each syllable

Front 25

What is produced by disorders of the deep nuclei or their projections in the superior cerebellar peduncle?

Back 25

More severe symptoms than disorders of the cerebellar cortex. With time there is often considerable improvement following a cerebellar lesion, especially if the deep nuclei are spared (allows cerebellum to be sacrificed if necessary).

Front 26

Why is the spinocerebellar system (aka "smooth/coordinate circuit #1) clinically important?

Back 26

Spinal cord lesions involving the spinocerebellar tracts may produce symptoms and signs suggestive of a cerebellar lesion.
-Remember these tracts convey trunk and extremity proprioceptive information to cerebellum
-Lesions of "descending" corticopontocerebellar fibers also sometimes produce symptoms and signs suggestive of cerebellar dysfunction

Front 27

A cerebellar lesion will also produce ipsilateral decreased muscle tone known as?

Back 27

ipsilateral hypotonia

Front 28

Do thalamic VL lesions produce cerebellar system dysfunction?

Back 28

No (actually therapeutic lesions are sometimes surgically placed into VL to reduce intention tremor due to cerebellar lesions)

Front 29

What type of medications typically also cause a cerebellar syndrome (particularly dysarthria and midline gait ataxia)?

Back 29

Medications that have dose-related sedative side effects

Front 30

What kind of treatment is used for cerebellum dysfunction?

Back 30

There is no effective medical treatment for cerebellar dysfunction.
-Physical therapy for gait disorders
-Occupational therapy to help people who have difficulty using their hands
-Speech therapy for those with dysarthria
-Neurosurgical procedures may improve intention tremor

Front 31

Describe the clinical signs of a cerebellum disorder

Back 31

Muscle bulk: Normal
Muscle tone: Hypotonia
Strength: Normal
Deep tendon reflexes: Normal
Pathological reflexes: None
Movement disorders: None
Coordination: Ataxia and intention "tremor"