Cerebellum

Question 1

What are the 4 main functions of the cerebellum?

How is it involved in movement?

Answer 1

• the cerebellum does NOT initiate movement - but it is needed for precise, controlled movements

Functions of the cerebellum:

1. important motor part of the brain
2. synergy of movement
3. maintenance of equilibrium** and **coordination of muscle contractions
4. contraction of muscles at an appropriate time and with an appropriate force

Question 2

On what side of the body does the cerebellum act?

Answer 2

the cerebellum acts IPSILATERALLY

• it receives information from muscles on one side of the body, and influences muscles on the same side of the body
• there may be some crossing over of fibres, but the muscles being coordinated are on SAME side of the body as the cerebellum

Question 3

How can the superior surface of the cerebellum be identified?

How is it divided into 2 lobes and what forms the most medial part?

Answer 3

• the superior surface can be identified as the cut surface of the midbrain is visible
• the primary fissure separates the cerebellum into an anterior (smaller) and posterior (larger) lobe
• the vermis is the most medial aspect of the cerebellum

Question 4

How can the inferior surface of the cerebellum be identified?

What structure is visible here?

Answer 4

• the inferior surface is visible as the cut surface of the medulla can be seen
• the cerebellar tonsils are visible on the inferior surface

these are the lowest hanging point of the cerebellum and are in close relationship with the medulla oblongata

Question 5

How can the ventral surface of the cerebellum be identified?

What key area can only be found here and how can it be identified?

Answer 5

• the ventral surface is identified by the superior, middle and inferior cerebellar peduncles
  
  • it is only visible once the brainstem has been detached
• the 3^rd lobe of the cerebellum is visible from this view - the flocculonodular lobe
• this is formed by the flocculus (2) and the nodulus (1)
  
  • the nodulus is an extension of the vermis onto the ventral surface
• the flocculonodular lobe is demarcated by the horizontal fissure

Question 6

What is meant by tonsillar herniation?

Answer 6

• if there is an increase in intracranial pressure, the skull cannot expand so the brain becomes compressed
• as the brain is compressed, there is herniation through the foramen magnum
• the cerebellar tonsils are often the first structure to herniate
• this can lead to compression of the medulla and compromise of its functions

Question 7

What is the relationship of the cerebellum to the 4^th ventricle?

Why is this clinically important and what side effects can be associated with this procedure?

Answer 7

• the posterior aspect of the 4^th ventricle is formed by the vermis of the cerebellum
• this is an important landmark for surgical access to the 4^th ventricle
• splitting of the vermis can lead to:

1. truncal ataxia
2. gait disturbances
3. equilibrium disturbances
4. nystagmus

Question 8

What are the cerebellar peduncles?

Answer 8

• they are bundles of white matter fibres that connect the cerebellum to the brainstem
• they carry both afferent and efferent fibres travelling to and from the cerebellum

Question 9

What are the afferent and efferent fibres carried by the superior cerebellar peduncle?

Answer 9

Afferent:

• dorsal spinocerebellar tract
• cuneocerebellar fibres
• vestibulocerebellar fibres

Efferent:

• cerebellovestibular fibres

Question 10

What are the afferent and efferent fibres carried by the middle cerebellar peduncle?

Answer 10

Afferents:

• pontocerebellar fibres

MCP carries AFFERENT fibres ONLY

Question 11

What are the afferent and efferent fibres carried by the inferior cerebellar peduncle?

Answer 11

Afferent:

• ventral spinocerebellar tract

Efferent:

• cerebellothalamic fibres
• cerebellorubral fibres

Question 12

How can the cerebellum be divided into 3 key functional areas?

Answer 12

Vestibulocerebellum (archi):

• formed by the flocculonodular lobe
• receives information relating to balance and posture

Spinocerebellum (paleo):

• formed by most of the anterior lobe and the medial portion of the vermis

Pontocerebellum (neo):

• this is the largest part of the cerebellum that has evolved the most recently
• it receives many connections from the pons and is involved in performing fine, coordinated motor movements
  • connections from the pons have originally come from the cortex

Question 13

What are the 4 central nuclei of the cerebellum?

What is their function?

Answer 13

• there are 4 pairs of nuclei that are embedded within cerebellar white matter:
• from medial to lateral:

1. fastigial nucleus
2. globose nucleus
3. emboliform nucleus
4. dentate nucleus

• the globose and emboliform nuclei make up the interposed nuclei
• the central nuclei contain cell bodies that are the output sites from the cerebellum

Question 14

Which of the central nuclei are associated with the different functional lobes of the cerebellum?

What do they connect to?

Answer 14

Vestibulocerebellum:

• contains the fastigial nucleus
• this connects to the reticular formation and vestibular neurones

Spinocerebellum:

• contains the interposed nuclei
• this connects to the red nucleus and the VA & VL nuclei of the thalamus

Pontocerebellum:

• contains the dentate nucleus
• this connects to the red nucleus and the VA & VL nuclei of the thalamus

The VA & VL nuclei are those that deal with information regarding motor function

Question 15

What is this?

Answer 15

Question 16

What are the roles of the vestibulocerebellum?

Answer 16

• it receives ipsilateral information from the vestibular system about balance
• it regulates balance and eye movements
• it adjusts muscles and eye movements in response to vestibular stimuli (i.e. changes in balance)

Question 17

Describe the afferent and efferent pathways to the vestibulocerebellum

Answer 17

Afferent pathway:

• vestibular nuclei in the brainstem receive afferent fibres from the vestibular division of VIII
• they send vestibulocerebellar fibres to the ipsilateral cerebellum via the inferior cerebellar peduncle (ICP)
• vestibulocerebellar fibres can do 2 things:

1. travel directly to the flocculonodular (vestibulocerebellar) cortex
2. synapse at the fastigial nucleus and then continue to the vestibulocerebellar cortex

Efferent pathway:

• the cerebellum computes the information and sends cerebellovestibular fibres to the vestibular nuclei via the ICP
• this information regulates balance and eye movements via the vestibulospinal tract and MLF

Question 18

How are the vestibulospinal tract and MLF involved in regulating balance and eye movements?

Answer 18

Vestibulospinal tract:

• this is involved in coordination of the muscles that maintain equilibrium
• the lateral VST is associated with the extensor posturing muscles and the medial VST is associated with muscles that can move the neck

MLF:

• the ascending portion of the MLF connects cranial nerve nuclei that can coordinate eye movements in response to changes in balance
• the MLF descends with the vestibulospinal tract

Question 19

What would a lesion to the vestibulocerebellum lead to?

Answer 19

1. problems maintaining balance
2. inaccurate eye scanning
3. truncal ataxia (inability to stand upright)

Question 20

Complete the summary of the vestibulocerebellum

Answer 20

Question 21

What is the role of the spinocerebellum?

Answer 21

• it receives unconscious proprioception from the Golgi organs / muscle spindle
  
  • this includes level of tension, length of muscle & speed of movement
• it sends outputs to regulate body and limb movements
• it influences corticospinal and rubrospinal pathways to adjust muscle tone and execution of movements

Question 22

What are the 3 spinocerebellar tracts and what information do they carry?

Answer 22

Dorsal spinocerebellar tract:

• carries information about unconscious proprioception from below C8

Ventral spinocerebellar tract:

• carries information about unconscious proprioception from below C8

Cuneocerebellar tract:

• carries information about unconscious proprioception from C1-C8
  
  • this is information relating to the upper limb and neck muscles

Question 23

Describe the afferent and efferent pathways of the spinocerebellum

Answer 23

Afferent fibres:

• the spinocerebellum receives afferent fibres from:

1. dorsal spinocerebellar tract (via ICP)
2. ventral spinocerebellar tract (via SCP)
3. cuneocerebellar tract (via ICP)

• these fibres can do 2 things:

1. project directly to the spinocerebellar cortex
2. stop and synapse within the interposed nuclei before continuing to the spinocerebellar cortex

Efferent fibres:

• the cerebellum processes the information and then sends efferent fibres:

cerebellothalamic fibres (via SCP) travel to the VA / VL nuclei of the thalamus

cerebellorubral fibres (via SCP) travel to the red nucleus of the brainstem

• the cerebellum influences both the corticospinal and rubrospinal pathways that control muscle tone and execution of movements

Question 24

What is significant about how the cerebellothalamic and cerebellorubral fibres travel?

Answer 24

• they both must cross the midline to reach the contralateral red nucleus / thalamus
• they need to communicate with pathways that will act on muscles on the SAME side as the cerebellum receiving afferent fibres

Question 25

Describe the pathway of the ventral spinocerebellar tract

Answer 25

* primary afferent fibres from the muscle enter the **dorsal aspect of the spinal cord** * they have their cell bodies within the **dorsal root ganglion (DRG)** * primary fibres synapse with second order neurones **_within the dorsal horn_** of the spinal cord * the second order neurones rapidly **_cross the midline_** via the **_ventral white commissure_** to join the **ventral spinocerebellar tract** on the **contralateral side** * fibres ascend to the level of the **midbrain** within the **_contralateral ventral spinocerebellar tract_** * the fibres **_re-cross the midline_** via the **superior cerebellar peduncle (_SCP_)** to reach the ipsilateral side of the cerebellum

Question 26

Describe the pathway of the dorsal spinocerebellar tract

Answer 26

* primary afferent fibres enter the **dorsal aspect of the spinal nerve** * they have their cell bodies within the **dorsal root ganglion (DRG)** * these fibres project to **_Clarke's nucleus (C8-L2)_** and synapse there * second order neurones join the **_ipsilateral dorsal spinocerebellar tract_** and ascend to the **medulla** * they pass to the spinocerebellar cortex via the **_inferior cerebellar peduncle (ICP)_**

Question 27

Between which levels is Clarke's nucleus present? What happens if a proprioceptive fibre enters below this level?

Answer 27

**_C8 - L2_** * any proprioceptive fibre entering below this level must ascend within the spinal cord **with the _fasciculus gracilis_** * when the fibre reaches **L2**, it re-enters the grey matter and **_synapses in Clarke's nucleus_** to then ascend via the **_dorsal spinocerebellar tract_**

Question 28

Describe the pathway of the cuneocerebellar tract

Answer 28

* primary afferent neurones carry unconscious proprioception information from the **upper limb and neck** (**_above C8_**) * they enter the **dorsal root** of the spinal nerve and have their cell bodies within the **DRG** * they ascend within the ipsilateral **_cuneate fasciculus_** to the level of the **closed medulla** * they enter the **_accessory cuneate nucleus_** to synpase with the second order neurone * *this is located laterally to the cuneate nucleus* * the second order neurone ascends as the **_cuneocerebellar tract_** to reach the ipsilateral cerebellum via the **_inferior cerebellar peduncle (ICP)_**

Question 29

What would be the result of a lesion to the spinocerebellum?

Answer 29

* reduced muscle tone * gait ataxia * loss of coordination whilst walking

Question 30

Complete for the spinocerebellum:

Answer 30

Question 31

What are the roles of the pontocerebellum?

Answer 31

* it receives information about **_intended movement_** from the **cerebral cortex** * it is involved in the control of **fine motor skills** and **targeted movements** * it ensures a **_smooth and orderly_ sequence of muscle contractions** with **_intended precision, force_ and _direction_** * *this is particularly important for upper limb activities*

Question 32

What are the different fibres that travel from the cortex to the pons that have a relationship to the pontocerebellum?

Answer 32

* **_corticopontine fibres_** travel via the **internal capsule** to the **_pontine nuclei_** * **_frontopontine fibres_** travel via the **anterior limb** of the internal capsule * **_parietopontine fibres_** travel via the **posterior limb** of the internal capsule * **_occipitopontine fibres_** travel via the **retrolenticular limb** of the internal capsule * **_temporopontine fibres_** travel via the **sublenticular limb** of the internal capsule * the pontine nuclei then project to the cerebellum via **_pontocerebellar fibres_**

Question 33

Describe the afferent and efferent fibres associated with the pontocerebellum

Answer 33

**_Afferent fibres:_** * the pontocerebellum receives afferent **pontocerebellar fibres** from the **_contralateral pontine nucleus_** via the **middle cerebellar peduncle (_MCP_)** * the pontocerebellar fibres can do 2 things: 1. travel **_directly_** to the **pontocerebellar cortex** 2. synapse at the **_dentate nucleus_** and then continue to the pontocerebellar cortex **_Efferent fibres:_** * the cerebellum computes the information and then sends efferent fibres: **_cerebellothalamic fibres_** travel to the **_contralateral VA / VL nuclei_** of the thalamus **_cerebellorubral fibres_** travel to the **_contralateral red nucleus_** of the midbrain they both travel via the **superior cerebellar peduncle (_SCP_)**

Question 34

How can the pontocerebellum exert an effect via fibres travelling from the thalamus and red nucleus?

Answer 34

**_Thalamus:_** * fibres from the thalamus project to the **motor cortex** to exert an influence over the **_corticospinal tract_** **_Red nucleus:_** * fibres from the red nucleus are able to influence the **_rubrospinal tract_** ***The pontocerebellum influences descending pathways to ensure _intended movements are precise_ via _corticospinal, rubrospinal_ & _reticulospinal tracts_***

Question 35

What would be the result of a lesion to the pontocerebellum?

Answer 35

* incoordination of voluntary movements * intention tremor * overshooting * reduced accuracy of reaching (clumsy finger to nose) / dysmetria

Question 36

Complete the summary of the pontocerebellum

Answer 36

Question 37

What areas of the cerebellum tend to be implicated in midline lesions? What is the main symptom and most common cause?

Answer 37

* tends to affect the **_vermis_** and **_vestibulocerebellum_** * most common cause is **tumours of the IV^th ventricle** * *e.g. medulloblastomas in children* * the main symptom is **_truncal ataxia_** * *this is the inability to stand upright without support*

Question 38

What are the symptoms resulting from a midline lesion affecting the pathway from the vermis to the vestibular nuclei?

Answer 38

* malfunction of the **_lateral_ vestibular nucleus** and **vestibulospinal tract** can lead to **_deficient antigravity function_** the patient will ***fall towards the more affected side*** when attempting to stand or walk * **_nystagmus_** can be elicited on tracking of a finger from side to side **scanning eye movements are inaccurate** due to poor control of the gaze centres by the vermis

Question 39

Which part of the cerebellum tends to be affected in anterior lobe lesions? Who tends to be affected by these lesions?

Answer 39

* anterior lobe lesions tend to affect the **_spinocerebellum_** * disease of the anterior lobe is commonly seen in **alcoholics**

Question 40

What are the symptoms of an anterior lobe lesion?

Answer 40

* the main symptom is **_gait ataxia_** * *a drunken, staggering gait is observed even when the patient is sober* * **tendon reflexes** may be **diminished** in the lower limbs * *due to loss of stimulation of neurones from the pontine reticulospinal tract*

Question 41

What structures can be implicated in a neocerebellar lesion? What is the main symptom?

Answer 41

* lesion can be located within the **superior cerebellar peduncle**, n**eocerebellar cortex** or **dentate nucleus** * the main symptom is **_incoordination of voluntary movements_** * the **upper limb** is most noticeably affected

Question 42

What are other symptoms / signs of a neocerebellar lesion?

Answer 42

* **_intention tremor_** occurs when a fine purposive movement is attempted * **_overshooting / past-pointing_** occurs when the hand passes the target * **_dysdiadochokinesia_** occurs when rapid alternating movements performed under command become irregular * *e.g. finger to nose / alternating pronation & supination* * **phonation and articulation of speech** may be affected