Cerebellum

Question 1

What are the 2 control centres that regulate the activity of descending pathways?

Answer 1

Basal ganglia:

• involved in learned tasks and making decisions

cerebellum:

• coordinates movement initiated by the precentral gyrus
• allows movement to be precise

Question 2

What are the 5 functions of the cerebellum?

Answer 2

• Production of coordinated movements
• maintain equilibrium, balance and posture
• coordinates appropriate time, force and duration of muscle contraction (synergy)
• may store instructions for patterns of movement
• may have linguistic and cognitive functions

Question 3

What is meant by synergy?

How is the cerebellum involved in synergy?

Answer 3

When 2 or more systems come together to produce a greater effect

the cerebellum receives information about intended movement from the precentral gyrus and from the limbs and muscles about their state

it then generates an adjusted coordinated outcome

Question 4

On which side of the body does the cerebellum act?

Answer 4

The cerebellum acts ipsilaterally

it receives information from ipsilateral body parts and works on them

Question 5

Where is the cerebellum found?

How is it attached to the rest of the brain?

Answer 5

It is found under the occipital lobes of the cerebral hemispheres

it is attached to the brainstem by three paired cerebellar peduncles

Question 6

What do each of the cerebellar peduncles attach to?

Answer 6

Superior cerebellar peduncle attaches to the midbrain

middle cerebellar peduncle attaches to the pons

inferior cerebellar peduncle attaches to the medulla

Question 8

What are the following structures of the cerebellum?

What is shown by numbers 2 and 3?

Answer 8

2 is the cerebral aqueduct

3 is the cerebral peduncles (crux cerebri)

Question 9

What are the 3 lobes of the cerebellum?

Answer 9

1. Anterior lobe
2. posterior lobe
3. flocculonodular lobe

• the anterior and posterior lobes are separated by the primary fissure
• the flocculonodular lobe is formed from the flocculus and nodule

Question 10

What can happen to the tonsils if there is increased intracranial pressure?

Answer 10

Increased intracranial pressure (e.g. CSF) can lead to tonsillar herniation

the tonsils leave through the foramen magnum and compress the medulla

Question 11

What are the 3 functional subdivisions of the cerebellum?

Answer 11

Vestibulocerebellum (Archicerebellum):

• comprises flocculonodular lobe and most medial part of vermis

Spinocerebellum (paleocerebellum):

• comprises most of the vermis and adjacent region of hemispheres

Cerebrocerebellum (neocerebellum):

• comprises the lateral parts of the hemispheres

Question 12

What are the following regions of the cerebellum?

Answer 12

Blue = vestibulocerebellum

purple = spinocerebellum

green = cerebrocerebellum

Question 13

What is meant by the cerebellar homunculus?

Answer 13

The homunculus matches up to the function of specific subdivisions

the cerebellum is somatotopically organised

Question 14

What is the function of the vestibulocerebellum?

Answer 14

It coordinates muscles involved in maintaining balance and constancy of visual fields

it receives input from the vestibular apparatus of the inner ear

the trunk and central muscles are involved in balance (blue)

Question 15

what is the function of the spinocerebellum?

Answer 15

It coordinates muscles involved in posture and locomotion

these are the muscles such as thighs and hips (purple)

it controls gait - this is the way in which we walk

Question 17

What is the function of the cerebrocerebellum?

Answer 17

It coordinates movements of the distal limbs (green)

it is particularly involved in fine, skilled and targeted movements of the hands

it is also involved in learning, linguistic and cognitive functions

Question 18

What is the main function of the vestibulocerebellum?

Answer 18

It regulates balance and eye movements

Question 19

Where does the vestibulocerebellum receive an input from?

Answer 19

It receives ipsilateral information about balance from the vestibular apparatus & nuclei in the inner ear

this area detects changes in balance as the fluid in the semicircular canals moves around

Question 20

What happens when the vestibular apparatus detects changes in balance?

Answer 20

Information is sent to the vestibular nuclei in the medulla via the vestibular division of the vestibulocochlear nerve

Information is then sent to the vestibulocerebellum which generates a response

Question 21

What are the efferent and afferent fibres travelling to and from the vestibular nucleus in the medulla?

Answer 21

Afferent fibres:

• vestibulocerebellar fibres carry information about balance from the vestibular nucleus to the vestibulocerebellum

Efferent fibres:

• cerebellovestibular fibres carry information about the response from the cerebellum to the vestibular nucleus

Question 22

How do the vestibulocerebellar afferents and cerebellovestibular efferent travel to and from the cerebellum?

Answer 22

Via the inferior cerebellar peduncle

this is connected to the medulla, where the vestibular nucleus is located

Question 25

What type of fibres do the efferent cerebellovestibular fibres synapse with?

Answer 25

They synapse within the vestibular nucleus fibres travel to CN nuclei III, IV and VI via the **medial longitudinal fasciculus** fibres travel to LMNs in the neck fibres travel to LMNs via the **vestibulospinal tract**

Question 26

What is the role of the fibres travelling via the medial longitudinal fasciculus?

Answer 26

They travel to CN nuclei of III, IV and VI in the brainstem they then travel to the muscles of the eyes they control the movement of the eyes to keep the visual field focused at a certain point

Question 27

What is the role of fibres travelling in the vestibulospinal tract?

Answer 27

It coordinates actions in the muscles in response to changes in balance it is an extrapyramidal descending pathway

Question 28

Where is the vestibular nucleus located?

Answer 28

In the pons and rostral medulla it is part of the **vestibulospinal pathway** which controls posture

Question 29

What is the main role of the spinocerebellum?

Answer 29

It regulates body and limb movements related to gait and locomotion

Question 30

What information does the spinocerebellum receive? How does it respond to this?

Answer 30

It receives unconscious **proprioception** (status of the whole limb) from Golgi organs / muscle spindles * length of muscle (spindle) * speed of movement * level of tension (Golgi tendon) it responds by adjusting muscle tone and execution of movements through modifying descending pathways

Question 31

What side of the body does the spinocerebellum control?

Answer 31

The right side of the cortex sends out signals for intended movement of the left side of the body the left side of the body brings information to the cerebellum the spinocerebellum acts on the ipsilateral side, so must exert an influence on the descending pathways from the right side of the cortex

Question 32

How does a muscle send information to the spinocerebellum?

Answer 32

Via **spinocerebellar tracts** (afferents) it analyses sensory information and generates a response to adjust movement by modifying descending pathways

Question 33

What is the role of spinocerebellar tracts? How do they enter the cerebellum?

Answer 33

Proprioception and other sensory information from the spinal cord passes into the cerebellum via the **inferior cerebellar peduncle** this allows the cerebellum to **know what muscles are doing**

Question 34

What is the role of the cerebrocerebellum?

Answer 34

Control of fine motor skills and targeted movements of the limbs, particularly the hands also involved in learning, linguistic and cognitive functions

Question 35

Where does the cerebrocerebellum receive information from?

Answer 35

It receives information on intended movements that are in progress from the cerebral cortex it receives this information via **corticopontine** and **olviocerebellar** fibres

Question 36

What pathway must information take when travelling from the cortex to the cerebrocerebellum?

Answer 36

* The left side of the body is controlled by the right side of the cortex * for information to reach the cerebellum, there must be crossing over at the midline * descending fibres stop in the pons and olives of the medulla and then descend to the cerebellum after crossing the midline

Question 37

What is the role of the cerebrocerebellum after receiving information about planned movement from the cerebral cortex?

Answer 37

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 38

How do the fibres from the cerebral cortex reach the cerebrocerebellum?

Answer 38

It receives input from motor cortex via: * **pontine nuclei** - fibres enter the cerebellum via the **medial** cerebellar peduncle * **inferior olivary nucleus** - fibres enter the cerebellum via the **inferior** cerebellar peduncle the cerebellum **knows about intended movements**

Question 39

What must be remembered about the influence of the cerebellum?

Answer 39

The influence of the cerebellum is **ipsilateral** the right side of the cerebellum coordinates action of muscles on the right side of the body and vice versa

Question 40

How do the spinocerebellum and cerebrocerebellum work together?

Answer 40

**Spinocerebellum:** * proprioception & other sensory information from the spinal cord passes into the cerebellum via ICP on ipsilateral side * ***Knows what muscles are doing*** **Cerebrocerebellum:** * input from cortex via nuclei in the pons and inferior olivary nucleus * ***Knows about intended movements*** **Output:** * output to motor cortex (via thalamus), reticular nuclei and red nucleus via **SCP** * ***ensures intended movements are coordinated and controlled***

Question 41

What are the efferents sent from the spinocerebellum?

Answer 41

**Cerebellothalamic** and **cerebellorubral** efferents are sent to the thalamus and red nucleus they travel via the **superior cerebellar peduncle**

Question 42

How does the spinocerebellum influence descending pathways?

Answer 42

It influences descending pathways to control muscle tone and execution of movements via **rubrospinal** and **corticospinal tracts**

Question 43

What afferents are received by the cerebrocerebellum?

Answer 43

It receives **pontocerebellar afferents** from the contralateral pontine nucleus via **MCP** it receives **olivocerebellar afferents** from the contralateral inferior olivary nucleus via **ICP**

Question 44

What efferents are sent from the cerebrocerebellum?

Answer 44

**Cerebellothalamic** efferents are sent to the contralateral thalamus via **SCP decussation** from the thalamus, these fibres project to the motor cortex

Question 45

What pathways does the cerebrocerebellum influence?

Answer 45

It influences descending pathways to ensure intended movements are precise via: * corticospinal tracts * corticorubral (rubrospinal) pathways * corticoreticular (reticulospinal) pathways

Question 46

What are the roles of the reticulospinal and rubrospinal pathways?

Answer 46

**Reticulospinal pathway:** * involved in voluntary movement, breathing & consciousness * runs from the reticular formation **Rubrospinal pathway:** * controls muscle tone * runs from the red nucleus

Question 47

In general, what are the effects of cerebellar damage?

Answer 47

Depending on the subdivision of the cerebellum damaged, predictable deficits will be observed leads to **uncoordinated movements** or **ataxia** (no order) the person is still able to move as the cortex is initiating movements, but in a disordered manner

Question 48

What is truncal ataxia? What type of lesion causes this?

Answer 48

An inability to stand or sit without falling over to one side it is a midline lesion affecting **vestibulocerebellum** it is most commonly due to **medulloblastoma** (an overgrowth in the medulla compressing the flocculonodular lobe)

Question 49

What is meant by gait ataxia? Which region of the cerebellum is lesioned?

Answer 49

The lower limbs are most affected with staggering and wide-based gait due to a lesion of the **spinocerebellum** most common in chronic alcoholics due to degeneration of cerebellar neurones in paravermal areas

Question 50

What happens if there is a lesion of a cerebellar hemisphere?

Answer 50

This is a lesion of the **cerebrocerebellum** in coordination of voluntary movement, particularly in the upper limb there are many possible causes and patients show: * tremor of intent * past pointing or dysmetria (cannot estimate distance or force) * adiadochokinesia (unable to perform fast movements) * dysarthria (problems with speech)