75 - Cerebellar Function

Question 1

Dysmetria

Answer 1

Dysmetria - errors in the range and force of movement: this is the cause of past pointing

Question 2

Ataxia

Answer 2

Ataxia - loss of muscular coordination due to errors in the range, rate, force, and direction of movement. Movements are jerky and imprecise.

Question 3

Dysdiadochokinesia

Answer 3

Dysdiadochokinesia is a condition that can be found in patients with cerebellar lesions. Patients with dysdiadochokinesia have an impaired ability to perform the rapid alternating movements of diadochokinesia. This is probably caused by abnormal agonist – antagonist control.

Question 4

Dysarthria

Answer 4

Dysarthria - disorder in articulating speech

Can be of cerebellar origin (ataxic dysarthria)
- Cerebellar lesions can cause slurring and slowing of speech, slurring dysarthria or scanning dysarthria with words broken up into syllables with variable intonation.

Question 5

Intention tremor

Answer 5

AKA action tremor

Involuntary, oscillatory motion during a voluntary movement. Tremor disappears when limb at rest. “Tremor” is most noticeable towards the end of a movement when the patient attempts to achieve the greatest precision. Apparent tremor may be due to dysmetria.

Question 6

Static tremor

Answer 6

Static tremor – tremor seen when patient with cerebellar lesions is not moving but is holding limb up against gravity. If patient stands with the arms extended can see this tremor. There is rhythmic movement of the shoulders that also involves the arms.

Question 7

Nystagmus

Answer 7

• Cerebellar nystagmus - nystagmus or oscillatory movements of the eye due to cerebellar-vestibular dysfunction. Movements are involuntary.
• There are many types of acquired nystagmus. If the nystagmus is caused by a cerebellar injury the lesion is usually in the flocculonodular lobes.

Question 8

Hypotonia

Answer 8

Hypotonia - diminished resistance to passive movement. Patient with hypotonia might have greater than normal range of movement at a joint.

Question 9

Synergy

Answer 9

Synergy - in neurology can mean that movements are coordinated over two or more joints to make one smooth movement. Patients with cerebellar damage often exhibit asynergia – lack of this synergy

Question 10

Asynergy

Answer 10

Asynergia - or decomposition of complex movements - errors in the timing of the components of complex multi joint movement. Joints are moved sequentially rather than simultaneously.

Question 11

Decomposition of movement

Answer 11

Another name for asynergy

Question 12

Pendular knee jerk

Answer 12

Pendular muscle stretch reflexes. A pendular knee jerk response to a tap on the patellar tendon is a sign of cerebellar damage. The lower leg swings back and forth like a pendulum probably because of lack of damping by muscle stretch reflexes.

Question 13

Titubation

Answer 13

Titubation is a tremor of the entire trunk or head during stance and gait. It can be caused by cerebellar midline lesions.

Question 14

Rebound phenomenon

Answer 14

AKA “lack of check”

Rebound phenomena (impaired check) - inability of the agonist and antagonist to adapt to rapid changes in load.

Question 15

What are the functional divisions of the cerebellum?

Answer 15

• Vestibulocerebellum
• Spinocerebellum (vermis portion)
• Spinocerebellum (paravermal portion)
• Cerebrocerebellum or pontocerebellum

Question 16

Describe the location of the vestibulocerebellum

Answer 16

Found in the flocular-nodular lobe

Question 17

What is the function of the vestibulocerebellum?

Answer 17

• Regulates equilibrium
• Regulate gait and posture especially through vestibulospinal reflexes (Note - muscles involved in stance and gait are also under control of the fastigial nuclei which are also connected to the vermal cortex of the spinocerebellum)
• Control of eye movements and coordinate movements of the head and eyes
• Role in visual guidance of eye movements

Question 18

Describe the location of the spinocerebellum (vermis portion)

Answer 18

The vermis is midline

Question 19

What is the function of the spiocerebellum (vermis portion)?

Answer 19

• Main functions - regulates axial and proximal musculature; concerned with ongoing motor execution and regulation of muscle tone
• Vermis is involved in the control of saccades and smooth pursuit eye movements. Lesions cause deficits in accuracy of these movements.

Question 20

Describe the location of the spinocerebellum (paravermal regions)

Answer 20

Intermediate part of the hemispheres on either side of the midline vermis

Question 21

What is the function of the spinocerebellum (paravermal regions)?

Answer 21

functions - regulates distal muscles; concerned with ongoing motor execution and regulation of muscle tone
 

Question 22

Describe the location of the cerebrocerebellum or pontocerebellum

Answer 22

Lateral part of the hemispheres of the cerebellum

Question 23

What is the function of the cerebrocerebellum or pontocerebellum?

Answer 23

functions - role in preparation for movement
• planning role especially important for multi-joint movements and those requiring fractionated finger movement. Very important for learned, skilled voluntary movement.
• timing functions

Question 24

What is the effect of a lesion in the vestibulocerebellum?

Answer 24

Lesions to vestibulocerebellum can cause ataxic gait and various eye movement disorders including a type of cerebellar nystagmus.

Vestibulocerebellar lesions can cause deficits in smooth-pursuit eye movements towards the side of the lesion. (A patient with a left vestibulocerebellar lesion could smoothly track a target moving to the right but had trouble tracking an object moving to the left. Patient made use mainly of saccades rather than smooth pursuit. [Only the vermis portion of the cerebellum is involved in controlling saccades so the patient could still make saccades.])

Patients tend to fall toward the side of the lesion. Patients try to compensate for balance problem by having a wide-based stance and gait. Patients move legs irregularly while trying to walk but can make accurate leg movements when lying down.

Question 25

What is the effect of a lesion in the spiocerebellum (vermis portion)?

Answer 25

Vermis is involved in the control of saccades and smooth pursuit eye movements. Lesions cause deficits in accuracy of these movements.

Question 26

What is the effect of a lesion in the spinocerebellum (paravermal regions)?

Answer 26

** Deficits produced by lesions of the intermediate zone affect limbs on the same side as the lesion. Symptoms are ipsilateral to the lesion. **

Lesions of the spinocerebellum (in general) cause hypotonia in humans. Lesions of the interposed or fastigial nuclei caused hypotonia in monkeys. There is a drop in fusimotor drive that results in a decrease in muscle spindle afferent activity during both rest and movement.

Question 27

What is the effect of a lesion in the cerebrocerebellum or pontocerebellum?

Answer 27

Effects of lesions of cerebrocerebellar cortex or dentate region include
• delays in initiating and terminating movements
• problems with multi-joint movements
• effect on patient’s ability to judge elapsed time in non-motor tasks Lesions affected ability to tell if one tone was longer or shorter than another or whether the speed of a moving object was faster or slower than that of another object.

Question 28

Which cell type is the source of axons leaving the cerebellar cortex?

Answer 28

Purkinje cells

ALWAYS inhibitory

Question 29

Which cerebellar cortex cell makes excitatory synapses?

Answer 29

Granules

These are excitatory cells in the cerebellar cortex - they are the origin of parallel fibers

Question 30

What are mossy fibers?

Answer 30

Input neurons to the cerebellum from the spinal cord and brain stem

Question 31

What are climbing fibers?

Answer 31

Input neurons to the cerebellum from the inferior olive

Each climbing fiber contacts from 1 to 10 Purkinje cells but each Purkinje cell is only contacted by one climbing fiber.

Question 32

What is the effect of each type of input (mossy fibers and climbing fibers) on the Purkinje cells?

Answer 32

a. one action potential in climbing fiber is enough to cause complex calcium-dependent spike in Purkinje cell. [Remember each Purkinje cell only receives one climbing fiber but it makes multiple synapses]
b. mossy fiber input results in smaller EPSP’s which must sum via spatial and temporal summation to cause a single action potential, a simple sodium-dependent spike, in a Purkinje cell.
c. The climbing fiber input causes changes in the Purkinje cell’s future responses to mossy fiber input and this interaction is believed to be responsible for motor learning.

Question 33

Describe how cerebellar damage can occur from alcoholism

Answer 33

Alcoholism: The thiamine (vitamin B1) deficiency associated with long term alcoholism can cause atrophy of the anterior lobe of the cerebellum. Patients can have difficulty walking and with leg control in general, but control of their arms and head is less affected.

Question 34

Describe how cerebellar damage can occur from multiple sclerosis

Answer 34

• Cerebellar systems commonly affected in patients with long term chronic MS. Lesions may be in cerebellum itself, cerebellar peduncles or brainstem pathways afferent or efferent to the cerebellum.

Question 35

Describe how cerebellar damage can occur from Friedreich ataxia

Answer 35

Genetic disease
• Friedreich Ataxia is a recessively inherited progressive spinocerebellar ataxia that is caused by an expanded repetition of the trinucleotide GAA in a gene on chromosome 9.
• There are also several dominantly inherited spinocerebellar ataxias due to a different expanded triple (CAG) repeat.

Question 36

Describe how cerebellar damage can occur from neoplastic disease

Answer 36

Either primary tumors or metastatic disease