Module 6 - the cerebellum

Question 1

What is the anatomical positioning of the cerebellum?

Answer 1

It it posterior to the brainstem, and inferior to the temporal and occipital lobes.

It sits in the posterior fossa, and is separated from the cerebrum by the tentorium cerebelli.

It is separated from the brainstem by the 4th ventricle.

Question 2

What are the gray matter folds on the surface of the cerebellum called?

Answer 2

Folia.

Question 3

Where is the anterior lobe located?

Answer 3

Above and anterior to the primary fissure.

Question 4

Where is the posterior lobe located?

Answer 4

Below and posterior to the primary fissure.

Question 5

Where is the flocculonodular lobe located, and what are its components?

Answer 5

It is located next to the posterolateral fissure. It is composed of a flocculus on either side, and a central nodulus.

Question 6

What is the vermis?

Answer 6

The central region of the cerebellum.

Question 7

What is the intermediate zone?

Answer 7

It encompasses the medial third of the anterior and posterior lobes.

Question 8

What is the lateral zone?

Answer 8

It encompasses the lateral two thirds of the anterior and posterior lobes.

Question 9

What is the flocculonodular zone?

Answer 9

It encompasses the nodulus and the flocculi.

Question 10

What is the dentate nucleus?

Answer 10

It is the largest of the deep cerebellar nuclei. It is located in the lateral zone.

Question 11

What are the interposed nuclei?

Answer 11

Composed of the emboliform and globose nuclei. It is located in the intermediate zone.

Question 12

What is the fastigial nucleus?

Answer 12

The nucleus along the midline - in the vermis and flocculonodular zone.

Question 13

What are the cerebellar peduncles, and what are their functions?

Answer 13

They are broad bands of white matter surrounding the pons that carry information to and from the cerebellum.

Inferior and middle peduncles -> inputs.

Superior peduncle -> outputs.

Question 14

What is the general processing path of cerebellar information?

Answer 14

Middle and inferior peduncles -> processing in the cerebellar cortex -> axons project through Purkinje cells to the deep cerebellar nuclei -> exit through superior peduncle

Question 15

What is the function of motor cerebellar inputs?

Answer 15

To carry copies of motor commands (efferent copies) from the PMC to the contralateral cerebellum. These copies are carried through corticopontine and pontocerebellar fibers.

Question 16

Explain the pathway of information between the pons and the cerebellum.

Answer 16

Neurons from the cortex -> corticopontine fibers -> synapse onto ipsilateral pontine nuclei -> axons cross the midline -> pontocerebellar fibers -> enter into the cerebellum via the middle peduncle

Question 17

What is the function of sensory inputs to the cerebellum?

Answer 17

To detect ongoing sensory information throughout movement via afferent copies from the SSC. The cerebellum receives sensory input from the ipsilateral side.

Question 18

Explain the path and function of the cuneo-spinocerebellar tract.

Answer 18

It carries information from the upper trunk and upper body, and travels in the dorsal column of the SC.

Primary sensory neurons synapse on second order neurons in the external cuneate nucleus (caudal medulla). Axons then enter the ipsilateral cerebellum via the inferior peduncle.

Question 19

Explain the path and function of the dorsal spinocerebellar tract.

Answer 19

It carries information from the legs and the lower trunk. It travels in the dorsal column of the SC.

Primary sensory neurons synapse on second order neurons in the nucleus dorsalis of Clark. Axons travel to the lateral SC and ascend to the ipsilateral cerebellum via the inferior peduncle.

Question 20

Which spinal segments does the nucleus dorsalis of Clark span across?

Answer 20

C8 - L2/L3 in the intermediate zone of the SC.

Question 21

How does vestibular information reach the cerebellum?

Answer 21

Both primary vestibular sensory neurons and vestibular nuclei have branches that project to the ipsilateral cerebellum.

They travel through the juxtarestiform body, which is a subsection of the inferior peduncle.

Question 22

What is the primary target of cerebellar outputs?

Answer 22

To the contralateral cortex, via pathways going through the contralateral thalamus. Outputs arise from the deep cerebellar nuclei.

Question 23

Describe the output pathway from the lateral region of the cerebellum.

Answer 23

Axons project into the dentate nucleus via Purkinje fibers -> dentate nucleus projects out via superior peduncle -> crosses the midline at the midbrain -> goes to the contralateral thalamus -> neurons project to different regions of the cortex.

Question 24

What is the function of lateral zone outputs? Which regions of the cortex does it project to?

Answer 24

Motor planning and motor learning.

Projects to: Pre-MC, PMC, supplementary motor area, parietal cortex.

Question 25

Describe the output pathway from the intermediate region of the cerebellum.

Answer 25

Axons project to the interposed nuclei -> project out via superior peduncle -> crosses the midline at the midbrain -> goes to the contralateral thalamus -> projects to different regions of the cortex.

Question 26

What are the functions of intermediate zone outputs? Which regions of the cortex does it project to?

Answer 26

Online coordination of movement. Projects to: Pre-MC, PMC, supplementary motor area.

Question 27

What is the path and function of the motor outputs from the vermis?

Answer 27

Axons project to the fastigial nucleus -> project out via superior peduncle -> crosses the midline at the midbrain -> goes to the contralateral thalamus -> projects to motor regions of the cortex for the neck and trunk. This pathway affects the anterior CST, and updates + coordinates activity.

Question 28

What is the path and function of the vestibular outputs from the vermis?

Answer 28

Each fastigial nucleus projects bilaterally to the vestibular nuclei. It controls activity of the vestibulospinal tract and other reflex pathways.

Question 29

What is the uncinate fasciculus?

Answer 29

Bands of axons from the fastigial nucleus that loop around the superior peduncle to get to the contralateral vestibular nucleus.

Question 30

What is the path and function of the reticular outputs from the vermis?

Answer 30

Each fastigial nucleus projects bilaterally to to reticular formation in the central brainstem. It manages and controls reticular reflexes and parts of the reticulospinal tract. It manages tone and balance.

Question 31

What is the path and function of flocculonodular lobe and inferior vermis outputs?

Answer 31

Axons go directly to the vestibular nuclei on the ipsilateral side. It influences balance and eye movement.

Question 32

What is the somatotopic organization of the cerebellum?

Answer 32

The anterior lobe organization spans across the vermis. - head region points towards the center - arm region is above the head region - leg region is the most 'superior' The posterior lobe has no representation in the vermis. Only in the intermediate zone. - head region points towards the center - arm region is just below it - leg region is the most 'inferior' Lateral zone - nothing in here, responsible for motor learning.

Question 33

What is the general role of the cerebellum?

Answer 33

The 'error detector'. It compares expected motor/sensory information to actual motor/sensory information and makes online corrections by projecting back to the motor areas of the cortex.

Question 34

What happens when there is a lesion to the intermediate cerebellar hemisphere?

Answer 34

A loss of motor learning primarily seen in ipsilateral distal limbs. Ataxia involving... - dysrhythmia - dysmetria - intention/action tremor - dysdiadochokinesia - dysarthria (aka explosive speech) - pendular reflexes

Question 35

What are some tests for cerebellar lesions?

Answer 35

Finger-nose-finger test, heel-shin test, clapping w/ a constant rhythm, finger-thumb tapping.

Question 36

What happens when there is a lesion to the vermis?

Answer 36

Deficits in coordinating muscles of the trunk and proximal hip joints + neck muscles - mostly in the anterior lobe. Ataxia involving... - truncal ataxia - gait ataxia - balance ataxia - anterior lobe syndrome

Question 37

What is seen with a lesion to the flocculonodular lobe/inferior vermis?

Answer 37

There is an impact on the vestibular nuclei - impacts balance, gait, and eye reflexes. Balance is impacted when standing and walking, but normal when seated or reclined. Eye control - difficulty with voluntary eye movements - Dysmetria of the eye - Lack of smooth pursuit - inability to suppress the VOR