Neuroscience Week 4: Cerebellar anatomy

Question 1

The oldest portion of cerebellum phylogenetically

Answer 1

Vestibulocerebellum AKA Archicerebellum

Question 2

Vestibulocerebellum is derived from

Answer 2

It is derived from the flocculonodular lobe and the anterior tip of the vermis (the lingula).

Question 3

The second oldest part of the cerebellum

Answer 3

Spinocerebellum AKA paleocerebellum

Question 4

Spinocerebellum consists of

Answer 4

It is derived from the anterior lobe and the majority of the vermian and paravermian posterior lobe.

Question 5

Vestibulocerebellum function

Answer 5

It is important for equilibrium and eye movements.

Question 6

Vestibulocerebellum Clinical Correlates

Answer 6

Nystagmus

A common definition of nystagmus is an involuntary, rhythmic, ocular oscillation. Numerous forms of nystagmus exist, so a practical approach to analyzing nystagmus is essential to determine its underlying cause.

The following steps provide a clinical approach to the evaluation of nystagmus.
A. Assess its PLANE: whether the nystagmus is horizontal, vertical, torsional, or some combination of these.
B. Assess its TYPE: pendular nystagmus denotes nystagmus in which both phases of eye movement are of equal amplitude whereas jerk nystagmus denotes nystagmus that involves a slow drift and quick correction.
C. If JERK NYSTAGMUS is present, assess its direction: unidirectional nystagmus denotes nystagmus that maintains a consistent direction whereas bidirectional nystagmus changes depending on the direction of gaze. For instance, spontaneous, vestibular nystagmus is unidirectional: it never changes direction but it increases as the patient looks in the direction of the fast component of the jerk nystagmus. On the contrary, gaze-evoked nystagmus is bidirectional: for instance, on right gaze, it is right beating and on left gaze, it is left beating. Note that the jerk nystagmus is named for direction of the fast component.
D. Assess the amplitude and rate: commonly, the smaller the amplitude, the faster the rate. See: descriptive terminology for rate and amplitude.
E. Assess for the NULL POINT where the nystagmus is minimal or absent: the patient may adapt a head turn or tilt to consistently place the eyes at the null point.
F. Assess whether the nystagmus is binocular or monocular and if it is binocular whether it is conjugate (both eyes move in the same direction) or disconjugate (the eyes move in different directions).
G. Assess whether changes in head position modulate the nystagmus. Spontaneous nystagmus denotes nystagmus that is unmodulated by changes in head position whereas positional nystagmus denotes nystagmus that is modulated by changes in head position (see The Dix-Hallpike Maneuver).
H. Assess for latent nystagmus: manifest nystagmus denotes nystagmus that is present when both eyes are viewing a target whereas latent nystagmus is nystagmus that occurs when one eye is covered. Latent nystagmus is a binocular, conjugate nystagmus — the quick phases of both eyes beat toward the uncovered (fixating) eye.
I. Assess for associated rhythmic movements of non-ocular structures, such as the face, palate, neck, or limbs, such as oculopalatal myoclonus.

Question 7

spinocerebellum is named from?

Answer 7

The spinocerebellum receives its name from its major input fibers: the spinocerebellar tracts.

Question 8

vestibulocerebellum is named from?

Answer 8

The vestibulocerebellum receives its name because of its midline vestibulo- and olivocerebellar fibers, which project to the deep, medial-lying cerebellar fastigial nuclei.

Question 9

Spinocerebellum Function

Answer 9

It plays a major role in postural stability.

Question 10

spinocerebellum Clinical Correlations

Answer 10

Ataxic Gait

A lateral cerebellar hemisphere lesion causes the patient to be unsteady and fall to the ipsilateral side.

The base is wide, the leg moves irregularly when flexed and extended and the patient sways and rocks to that side.

If there is bilateral hemispheric cerebellar disease, the patient has a broad-base, rocks
and sways from side to side.

Ataxia of the trunk is caused by midline vermian lesions.

When sitting, the patient has lost extensor tone of the paraspinal muscles and titubates
(sways).

If the arms are outstretched, the drift is upwards.

The patient is completely unstable when standing, reels in all directions including backwards and needs support to walk.

Anterior cerebellar gait: the patient has a stiff-legged extensor posture and tends to lean backwards (“martinette gait”).

Question 11

The phylogenetically newest portion of the cerebellum

Answer 11

Pontocerebellum

Phylogenetically the newest portion of the cerebellum and is referred to as the neocerebellum.

Question 12

Pontocerebellum consists of

Answer 12

It is derived from the remainder of the posterior lobe.

Question 13

Pontocerebellum is named for?

Answer 13

The pontocerebellum receives its name because it acts through the corticopontocerebellar pathway.

Question 14

Pontocerebellum Function

Answer 14

It is geared towards fine motor movements, which are typically goal-oriented.

Question 15

Pontocerebellum Clinical Correlation

Answer 15

Incoordination

Finger-Nose-Finger Test

• Patient touches examiner’s finger.
• Patient touches his/her own nose.
• Patient touches examiner’s finger, again.
• Past-pointing refers to when the patient cannot brake the movement and overshoots the examiner’s finger.

Cerebellar Drift

• With eyes closed, patient exhibits an upward drift with the arms outstretched.
• “Spooned” hand posture: uneven interplay b/w agonists and antagonists.
• Examiner lightly taps the outstretched arm to displace it downward.
• Patient overshoots as places arm in its former position.

Finger Tapping

• Patient taps the thumb and index finger, repetitively.
• In cerebellar disease: the amplitude and rhythm vary.
• In pyramidal disease: normal rhythm but slow and move in concert (failure to fractionalize).

Question 16

Acute alcohol intoxication parts of cerebellum affected

Answer 16

the entire cerebellum is affected

Question 17

Nystagmus occurs from toxicity to

Answer 17

vestibulocerebellum

Question 18

truncal ataxia occurs from toxicity to the

Answer 18

spinocerebellum

Question 19

incoordination occurs from toxicity to the

Answer 19

pontocerebellum

Question 20

Chronic Alcoholic cerebellar degeneration: sites of degeneration

Answer 20

• The pathology is predominantly restricted to the anterior superior cerebellar vermis. Because of this restricted area of injury, truncal ataxia is sometimes the sole deficit.
• We may miss this exam finding if we fail to ask our patients to stand during the exam.

Question 21

Unilateral cerebellar lesions affect which side of the body?

Answer 21

Unilateral cerebellar lesions affect the ipsilateral side of the body.

Question 22

The midline cerebellum plays a role in

Answer 22

• posture (to stand up)
• For instance, to stand upright, you need the midline cerebellum, and to play the piano, you need the lateral cerebellar hemispheres.

Question 23

the lateral cerebellum assists in

Answer 23

• fine motor, goal-oriented skills (to play the piano)
• For instance, to stand upright, you need the midline cerebellum, and to play the piano, you need the lateral cerebellar hemispheres.

Question 24

The somatotopic map of the cerebellum

Answer 24

the role of the spinocerebellar, anterior lobe is to provide postural stability, which requires the limbs and trunk, and the role of the neocerebellar, posterior lobe is to provide goal-oriented, fine motor movements, such as those of the fingers and mouth.