Cerebellum Flashcards
What are the 2 control centres that regulate the activity of descending pathways?
Basal ganglia:
- involved in learned tasks and making decisions
cerebellum:
- coordinates movement initiated by the precentral gyrus
- allows movement to be precise
What are the 5 functions of the cerebellum?
- 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
What is meant by synergy?
How is the cerebellum involved in synergy?
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
On which side of the body does the cerebellum act?
The cerebellum acts ipsilaterally
it receives information from ipsilateral body parts and works on them
Where is the cerebellum found?
How is it attached to the rest of the brain?
It is found under the occipital lobes of the cerebral hemispheres
it is attached to the brainstem by three paired cerebellar peduncles
What do each of the cerebellar peduncles attach to?
Superior cerebellar peduncle attaches to the midbrain
middle cerebellar peduncle attaches to the pons
inferior cerebellar peduncle attaches to the medulla
What are the following structures of the cerebellum?
What is shown by numbers 2 and 3?
2 is the cerebral aqueduct
3 is the cerebral peduncles (crux cerebri)
What are the 3 lobes of the cerebellum?
- Anterior lobe
- posterior lobe
- flocculonodular lobe
- the anterior and posterior lobes are separated by the primary fissure
- the flocculonodular lobe is formed from the flocculus and nodule
What can happen to the tonsils if there is increased intracranial pressure?
Increased intracranial pressure (e.g. CSF) can lead to tonsillar herniation
the tonsils leave through the foramen magnum and compress the medulla
What are the 3 functional subdivisions of the cerebellum?
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
What are the following regions of the cerebellum?
Blue = vestibulocerebellum
purple = spinocerebellum
green = cerebrocerebellum
What is meant by the cerebellar homunculus?
The homunculus matches up to the function of specific subdivisions
the cerebellum is somatotopically organised
What is the function of the vestibulocerebellum?
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)
what is the function of the spinocerebellum?
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
What is the function of the cerebrocerebellum?
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
What is the main function of the vestibulocerebellum?
It regulates balance and eye movements
Where does the vestibulocerebellum receive an input from?
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
What happens when the vestibular apparatus detects changes in balance?
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
What are the efferent and afferent fibres travelling to and from the vestibular nucleus in the medulla?
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
How do the vestibulocerebellar afferents and cerebellovestibular efferent travel to and from the cerebellum?
Via the inferior cerebellar peduncle
this is connected to the medulla, where the vestibular nucleus is located
What type of fibres do the efferent cerebellovestibular fibres synapse with?
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
What is the role of the fibres travelling via the medial longitudinal fasciculus?
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
What is the role of fibres travelling in the vestibulospinal tract?
It coordinates actions in the muscles in response to changes in balance
it is an extrapyramidal descending pathway
Where is the vestibular nucleus located?
In the pons and rostral medulla
it is part of the vestibulospinal pathway which controls posture
What is the main role of the spinocerebellum?
It regulates body and limb movements related to gait and locomotion
What information does the spinocerebellum receive?
How does it respond to this?
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
What side of the body does the spinocerebellum control?
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
How does a muscle send information to the spinocerebellum?
Via spinocerebellar tracts (afferents)
it analyses sensory information and generates a response to adjust movement by modifying descending pathways
What is the role of spinocerebellar tracts?
How do they enter the cerebellum?
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
What is the role of the cerebrocerebellum?
Control of fine motor skills and targeted movements of the limbs, particularly the hands
also involved in learning, linguistic and cognitive functions
Where does the cerebrocerebellum receive information from?
It receives information on intended movements that are in progress from the cerebral cortex
it receives this information via corticopontine and olviocerebellar fibres
What pathway must information take when travelling from the cortex to the cerebrocerebellum?
- 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
What is the role of the cerebrocerebellum after receiving information about planned movement from the cerebral cortex?
It ensures a smooth and orderly sequence of muscle contractions with intended precision, force and direction
this is particularly important for upper limb activities
How do the fibres from the cerebral cortex reach the cerebrocerebellum?
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
What must be remembered about the influence of the cerebellum?
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
How do the spinocerebellum and cerebrocerebellum work together?
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
What are the efferents sent from the spinocerebellum?
Cerebellothalamic and cerebellorubral efferents are sent to the thalamus and red nucleus
they travel via the superior cerebellar peduncle
How does the spinocerebellum influence descending pathways?
It influences descending pathways to control muscle tone and execution of movements via rubrospinal and corticospinal tracts
What afferents are received by the cerebrocerebellum?
It receives pontocerebellar afferents from the contralateral pontine nucleus via MCP
it receives olivocerebellar afferents from the contralateral inferior olivary nucleus via ICP
What efferents are sent from the cerebrocerebellum?
Cerebellothalamic efferents are sent to the contralateral thalamus via SCP decussation
from the thalamus, these fibres project to the motor cortex
What pathways does the cerebrocerebellum influence?
It influences descending pathways to ensure intended movements are precise via:
- corticospinal tracts
- corticorubral (rubrospinal) pathways
- corticoreticular (reticulospinal) pathways
What are the roles of the reticulospinal and rubrospinal pathways?
Reticulospinal pathway:
- involved in voluntary movement, breathing & consciousness
- runs from the reticular formation
Rubrospinal pathway:
- controls muscle tone
- runs from the red nucleus
In general, what are the effects of cerebellar damage?
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
What is truncal ataxia?
What type of lesion causes this?
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)
What is meant by gait ataxia?
Which region of the cerebellum is lesioned?
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
What happens if there is a lesion of a cerebellar hemisphere?
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)
