Ataxia- The cerebellum

Question 1

What is the function of the cerebellum?

Answer 1

The function of the cerebellum is coordination; timing andd precision of fine movements, adjusting ongoing movements, motor learning of skilled tasks

**Lesions lead to Ataxias**

Question 2

Ataxia:

dysrhythmia

dysmetria

Answer 2

Ataxia literally means lack of order

it refers to the disordered contractions of agonist and antagonist muscles, and the lack of coordination between movements

dysrhythmia: abnormal timing
dysmetria: abnormal trajectories through space

Question 3

Simple principles:

1. Ataxia is ________ to the side of the cerebellar lesion
2. Midline lesions of the vermis or flocculonodular lobes mainly cause _______ and _______. These are accompanied by ________, ________, and _______.
3. Lesions lateral (in the hemispheres of the cerebellum) to the vermis mainly cause ataxia of the _______.

Answer 3

Simple principles:

1. Ataxia is ipsilateral to the side of the cerebellar lesion
2. Midline lesions of the vermis or flocculonodular lobes mainly cause unsteady gait and eye movement abnormalities. These are accompanied by intense vertigo, nausea, and vomiting.
3. Lesions lateral (in the hemispheres of the cerebellum) to the vermis mainly cause ataxia of the limbs (appendicular ataxia).

Question 4

Anatomiacal Organization

1. The inferior vermis and flocculonodular lobes regulate _____ and _____ through interactions with the vestibular system. These regions together with other regions of the vermis are involved in control of the ________.
2. the intermediate hemispheres control the ________.
3. The lateral hemispheres control the ________ and are important in ________.

Answer 4

Anatomiacal Organization

1. The inferior vermis and flocculonodular lobes regulate balance and eye movements through interactions with the vestibular system. These regions together with other regions of the vermis are involved in control of the medial motor systems (proximal and trunk motor control).
2. the intermediate hemispheres control the lateral motor systems (more distal muscles in the arms and legs).
3. The lateral hemispheres control the lateral corticospinal tract and are important in motor planning.

Question 5

Organization of the Descending Tracts

1. Lateral descending tracts modify ________.
2. Medial descending tracts modify _________.

Answer 5

Organization of the Descending Tracts

1. Lateral descending tracts modify extremities and distal musculature.
2. Medial descending tracts modify trunk and proximal muscles.

Question 6

1. The lateral hemispheres influence the ______ motor pathway.
2. The intermediate hemispheres influence the _____ motor pathway.
3. the Vermis and flocculonodular lobe influence the ______ motor pathway.

Answer 6

1. The lateral hemispheres influence the Lateral cortiocospinal tract.
2. The intermediate hemispheres influence the Lateral corticospinal tract and rubrospinal tract.
3. the Vermis and flocculonodular lobe influence the Anterior corticospinal tract, reticulospinal tract, vestivulospinal tract and tectospinal tract (proximal limb coordination) and the medial longitudinal fasciculus (Balance and vestibulo-ocular reflexes).

Question 7

All outputs from the cerebellum are relayed by ____ nuclei.

what are they named specifically?

Answer 7

All outputs from the cerebellum are relayed by Deep cerebellum nuclei.

Dentate, Emboliform, Globose, and Fastigial (don’t eat greasy foods. lateral → medial organization)

Question 8

Dentate nuclei

1. receives projections from:
2. projects to:

Answer 8

Dentate nuclei- they are the largest nuclei

1. receives projections from: lateral cerebellar hemispheres
2. projects to: superior cerebellar peduncle → the thalamus →motor cortex to influence the lateral corticospinal system
3. The dentate nucleus also projects to:
   
   1. parvocellular red nucleus → inferior olivary nucleus→lateral hemisphere (forms a loop)
   2. dentate nucleus→thalamus→ prefrontal cortex (cognition)

Question 9

Emboliform and globose nuclei

1. receive input from:
2. Project to:

Answer 9

Emboliform and globose nuclei

aka: interposed nuclei

1. receive input from: intermediate part of the cerebellar hemispheres
2. Project to:
   
   1. →superior cerebellar peduncle →thalamus (VL) → motor cortex influence lateral corticospinal system output (distal limb coordination)
   2. →magnocellular red nucleus to influence the rubrospinal tract

Question 10

Fastigial Nucleus

1. receives projections from:
2. projects to:

Answer 10

Fastigial Nucleus

1. receives projections from: vermis and a small input from the flocculonodular lobe
2. projects to:
   
   1. → thalamus (VL) → motor cortex to influence anterior corticospinal system output (proximal limb and trunk coordination)
   2. → tectum, retucular formation, and the vestibular nuclei to influence the remaining medial motor pathways (balance and vestibulocular reflexes)

Question 11

Vestibular Output Pathways

1. the inferior vermis and flocculonodular lobes project to the _________.
2. These nuclei are linked to nuclei involed in eye movements through the ________.
3. These connections are important for _______ and _____ and for influencing _______, ________, and __________.

Answer 11

Vestibular Output Pathways

1. the inferior vermis and flocculonodular lobes project to the vestibular nuclei.
2. These nuclei (the vestibular nuclei) are linked to nuclei involed in eye movements through the medial longitudinal fasciculus (MLF).
3. These connections are important for equilibrium and balance and for influencing vestibulo-ocular reflexes, smooth pursuit, and other eye movements.

Question 12

Cerebellar Input

1. Two types of inputs:

Answer 12

Cerebellar Input

1. Two types of inputs:
   
   1. Climbing fibers: Olivocerebellar- directly synapse (+) on purkinge neurons
   2. Mossy fibers (all other inputs) synapse (+) on Granule cells

**Climbing fibers and granule cells excite purkinge cells which in turn inhibit neurons in deep nuclei**

Question 13

Inferior Olivary Complex

(olivocerebellar fibers)

1. receive input from:
2. projects to:

Answer 13

Inferior Olivary Complex

fibers form the major component of the inferior cerebellar peduncle

1. receive input from: red nucleus, cerebral cortex, brainstem nuclei, and spinal cord
2. projects to: entire cerebellar cortex

Question 14

Corticopontine fibers:

1. recive input from:
2. project to:

Answer 14

Corticopontine fibers:

1. recive input from: frontal, temporal, parietal, and occipital lobes
2. project to: pontine nuclei

**Pontocerebellar figers cross the midline to enter the middle cerebellar peduncle and project to the entire cerebellar cortex**

Question 15

Spinocerebellar fibers

1. recive input from:
2. project to:

Answer 15

Spinocerebellar fibers

1. recive input from: the for spinocerebellar tracts. they enter through the inferior or superior cerebellar peduncle to provide proprioceptive information from the upper and lower extremities
2. project to: HA! trick question sucker… they don’t project nowhere!!!!

Question 16

Primary Vestibular sensory neurons

1. Located in:
2. project to

Answer 16

Primary Vestibular sensory neurons

1. Located in: Scarpa’s vestibular ganglia and secondary vestibular neurons in the vestibular nuclei
2. project to: inferior vermis and flocculonodular lobe

**these connections are important in balance and in equilibrium and vestibulo-ocular reflexes. The flocculus also reeives visual inputs related to control of smooth pursuit eye movements**

Question 17

Truncal Ataxia:

Answer 17

Truncal Ataxia:

lesions are confined to the cerebellar vermis and affect mainly the medial motor systems. Patients with lesions of the vermis have a wide-based, unsteady, drunk-like gait

Question 18

Appendicular ataxia:

Answer 18

Appendicular ataxia:

Lesions are in the intermediate and lateral cerebellar hemispheres and affect the lateral motor systems. Patients have ataxia on movement of the extremities such as during finger-nose-finger test

Question 19

Sensory Ataxia

where is the lesion?

how does a patient present?

Answer 19

Sensory ataxia occurs when the dorsal column/medial lemniscal pathway is disrupted resulting in loss of joint position sense.

Pt. with sensory ataxia have overshooting movements of the limbs and a wide-based, unsteady gait resembling patients with cerebellar lesions.

However, these patients have impaired joint position sense on exam and sensory ataxia is worse when the eyes are closed or in the dark

Question 20

What pathways are influenced by:

1. Lateral cerebellar hemispheres
2. Intermediate hemispheres
3. Vermis and flocculonodular lobe

Answer 20

What pathways are influenced by:

1. Lateral cerebellar hemispheres: Lateral corticospinal tract- functions in movement of the contralateral limbs
2. Intermediate hemispheres- lateral corticospinal tracts and rubrospinal tracts- both tracts are invloved with movement of the contralateral limbs
3. Vermis and flocculonodular lobe- yokes the eye movements together