Cerebellum Flashcards
What is the function of the cerebellum?
Important motor part of the brain:
- Production of coordinated movement (speed, direction)
- Maintain equilibrium, balance and posture
- Co-ordinates appropriate time, force and duration of muscle contraction (synergy: two or more actions come together to produce an effect e.g. information from the primary motor cortex and information from the limbs)
- May store instruction for patterns of movement
- May have linguistic and cognitive functions
Does the cerebellum act ipsilaterally or contralaterally?
Cerebellum acts ipsilaterally: receives information from the same side and acts for the same side.
Which 2ary vesicle does the cerebellum develop from?
metencephalon
Where is the cerebellum located? In which cranial fossa?
- Found under the occipital lobes of the cerebral hemispheres
- In the posterior cranial fossa
How is the cerebellum separated from the occipital lobes?
By the tentorium cerebelli (tough layer of dura mater)
How is the cerebellum attached to the brainstem?
By 3 paired cerebellar peduncles
Which part of the brainstem does the cerebellum lie posterior to?
It lies at the same level of and posterior to the pons
How is the cerebellum separated from the pons?
By the 4th ventricle
The cerebellum consists of two hemispheres. What are these connected by?
Vermis; a narrow midline area
How many anatomical lobes does the cerebellum have?
3; the anterior lobe, the posterior lobe and the flocculonodular lobe.
How are the lobes of the cerebellum separated?
These lobes are divided by two fissures – the primary fissure and posterolateral fissure.
The cerebellum also has tonsils (2 small areas at the bottom). What can happen in situations of increased
Tonsils can herniate through the foramen magnum and compress the medulla.
The cerebellum can also be divided by function. How many functional areas are there? What are they?
There are three functional areas of the cerebellum:
- Cerebrocerebellum
- Spinocerebellum
- Vestibulocerebellum
What forms the vestibulocerebellum (archicerebellum)?
- Comprised of the flocculonodular lobe and part of the vermis
- Seen here in blue
What is the spinocerebellum also referred to as?
paleocerebellum
What is the vestibulocerebellum also referred to as?
archicerebellum
What is the cerebrocerebellum also referred to as?
neocerebellum
What comprises the spinocerebellum?
Comprises most of the vermis and adjacent region of hemispheres (seen here in purple)
What comprises the cerebrocerebellum?
- Comprises lateral parts of the hemispheres
- Seen here in green
The cerebellum is somatotopically organised. What does this mean?
Cerebellar homunculus: homunculus matches up to the function of specific subdivisions
Function of the vestibulocerebellum?
- Has a role in the vestibular system of the Inner ear, controlling balance
- Coordinates muscles involved in maintaining balance and constancy of visual fields
- Receives input from the vestibular apparatus of the inner ear
Function of the spinocerebellum?
- Receives connections from the spinal cord
- Co-ordinates muscles involved in posture and locomotion
Function of cerebrocerebellum?
- Receives input from the cerebrum/cortex
- Co-ordinates movements of distal limbs. Particularly fine, skilled and targeted movements of hands (also involved in learning, linguistic and cognitive functions
Which functional division of the cerebellum is only seen in higher functioning animals?
Cerebrocerebellum; region developed later on in evolution
Which functional division of the cerebellum regulates balance and eye movement?
Vestibulocerebellum
Where does the vestibulocerebellum receive info from? Is this info ipsi or contralateral?
- Receives input from the vestibular apparatus and nuclei of the inner ear
- Ipsilateral info from balance
Describe how detection of change in balance leads to muscle/eye movements (Vestibulocerebellum)
- Neurons in vestibular apparatus (inner ear) detect change in balance
- Fire action potentials using the vestibular division of the vestibulocochlear nerves
- Information reaches brainstem (vestibular nuclei in medulla)
- Information then sent to flocculus and nodulus of cerebellum
- Response: Adjusts muscles and eyes movements in response to vestibular stimuli.
Which divison of the cerebellum deals with a change in balance?
Vestibulocerebellum
Function of the vestibular apparatus?
The vestibular system is the sensory apparatus of the inner ear that helps the body maintain its postural equilibrium.
Which afferent neurons does the vestibulocerebellum receive?
Recieves vestibulocerebellar afferents from the vestibular nuclei of the same side, travelling via the inferior cerebellar peduncle
Describe the afferent and efferent pathway for the vestibulocerebellum.
Afferent:
- Vestibulocerebellar afferents receives (ipsilateral) information from the vestibular apparatus
- Information is sent via the vestibular division of the vestibulocochlear nerve to the vestibular nuclei of the brainstem
- Vestibulocerebellar afferents have their nuclei (vestibular nuclei) in the medulla
- Reach cerebellum via the inferior cerebellar peduncle (due to nuclei being in medulla)
Efferent:
- Cerebellovestibular efferent fibres leave cerebellum via inferior cerebellar peduncle
- They reach vestibular nuclei in the medulla then enter:
- Vestibulospinal tract –> LMNs to co-ordinate muscles to contract in relation to balance.
- Medial longitudinal fasciculus –> LMNs to cranial nerve nuclei (3, 4, 6) which control movements of the eyes.There will also be LMNs to the neck, to allow for head turning
What are the afferent fibres of the vestibulocerebellum called?
vestibulocerebellar afferent fibres
What are the efferent fibres of the vestibulocerebellum called?
cerebellovestibular efferents
Cerebellovestibular efferents can enter 1 of 2 tracts when responding to a change in balance. What are these 2 tracts and what is the response?
- Vestibulospinal tract –> LMNs travels via the vestibulospinal tract which will co-ordinate muscles to contract in relation to balance –> help keep you upright
- Medial longitudinal fasciculus –> LMNs to cranial nerve nuclei (3, 4, 6) which control movements of the eyes. There will also be LMNs to the neck, to allow for head turning.
Which tract connects the vestibular nuclei to the neck LMNs and cranial nerve nuclei (III, IV and VI)?
Medial longitudinal fasciculus
What are semicircular canals?
Your semicircular canals are three tiny, fluid-filled tubes in your inner ear that help you keep your balance.
Which cranial nerves are responsibe for eye movement?
III, IV and VI
Vestibulospinal pathway summary:
- Vestibular nuclei in caudal pons and medulla
- Send fibres down to modify LMNs
- Ipsilateral
- Vestibulospinal pathway works together with vestibulocerebellum to modify posture and balance
Where are the vestibular nuclei located?
In the pons and medulla
Vestibulocerebellum: Summary
- Receives vestibulocerebellar afferents from the vestibular nuclei of the same side - travel via ICP
- Sends cerebellovestibullar efferents back to vestibular nuclei – travel via ICP
- Regulates balance and eye movements via:
1. Vestibulospinal tract –> Coordinates the actions of muscles that maintain equilibrium
2. Medial longitudinal fasciculus: - Coordinates the actions of eye movement
- Also descends with vestibulospinal tract (similar role)
Which functional division of the cerebellum controls body and limb movements?
Spinocerebellum
What information does the spinocerebellum receive and from which receptors?
Receives unconscious proprioception (status of the whole limb) from the Golgi organs/muscle spindle. This includes:
- Length of muscle
- Speed of movement
- Level of tension
Describe the afferent and efferent pathway of the spinocerebellum
- Golgi organs/muscle spindle detect unconscious proprioception
- Send afferent spinocerebellar tracts, through spinal cord
- Fibres reach cerebellum via the inferior cerebellar peduncle
- Cerebellum analyses info in the vermis and adjacent area; decides how to adjust descending pathways
- Efferent fibres sent to muscles; adjust muscle tone and execution of movements
N.B.
- Right cortex controls left side of body BUT left side of body brings information to left cerebellum
- Some information is sent to the primary motor cortex (must cross the midline) and then sent to muscles.
- Left cerebellum must modulate information coming from the right to influence the ipsilateral left side of the body
The spinocerebellum receives unconscious proprioception (status of the whole limb) from the Golgi organs/muscle spindle. Is this ipsilateral or contralateral?
Ipsilateral
Which functional division of the cerebellum is involved in control of fine motor skills and targeted movements of limbs, particularly hands?
Cerebrocerebellum (also involved in learning, linguistic and cognitive functions)
Where does the cerebrocerebellum mainly receive its afferent fibres from?
The cerebrum e.g. frontal/temporal/parietal lobes
The cerebrocerebellum receives information (afferent fibres) on intended movements that are in progress from the cerebral cortex via the cortico-ponto-cerebellar pathway. What is this pathway composed of?
- Corticopontine tract
- Pontocerebellar tract
What are corticopontine fibres?
Corticopontine fibres are projections from the cerebral cortex to the pontine nuclei.
Depending upon the lobe of origin, they can be classified as frontopontine fibers, parietopontine fibers, temporopontine fibers or occipitopontine fibres.
Via which peduncle does the cortico-ponto-cerebellar pathway enter the cerebellum?
Middle cerebellar peduncle
Via which peduncle does olivocerebellar fibres enter the cerebellum?
Via the inferior cerebellar peduncle
Where do the corticopontine fibres cross the midline?
Transverse pontine fibres (decussation of pyramids)
Where do the transverse pontine fibres arise from/go to?
Arise from pontine nuclei in pons and go to cerebellum
Where do the olivocerebellar fibres arise from/go to?
Arise from inferior olivary nucleus and go to cerebellar hemispheres
After receiving afferent fibres from the cerebrum, the cerebrocerebellum analyses it and then decides what to do? What is the result?
Ensures a smooth and orderly sequence of muscle contractions with intended precision, force and direction = particularly important for upper limb activities
The cerebrocerebellar receives afferent fibres via which peduncles?
Middle and inferior cerebellar peduncles
Via which 2 fibres does the cerebellum receive input from the motor cortex?
- Pontocerebellar (2nd order neurons to corticopontine fibres)
- Inferior olivary nucleus
Via which cerebellar peduncle does olivocerebellar fibres enter the cerebellum?
Inferior
Via which cerebellar peduncle does pontocerebellar fibres enter the cerebellum?
Middle
Is the influence of the cerebellum ipsilateral or contralateral?
Ipsilateral i.e. right half of cerebellum co-ordinates action of muscles on the right side of body.
Cerebellum receives information from ipsilateral side of body, and for ipsilateral side of body, and acts on it.
Via which peduncle does proprioception and other sensory information from spinal cord pass into the cerebellum? (i.e. knows what the muscles are doing)
Via the inferior cerebellar peduncle
Describe the spinocerebellum and cerebrocerebellum connections for proprioception and other sensory information?
Input from; cortex (including motor cortex via nuclei in pons), cortex (including motor cortex via inferior olivary nucleus) and proprioception information via spinocerebellar fibres.
- Proprioceptive information:*
1. Proprioceptive information from muscles on right hand side of body relays to ipsilateral side of cerebellum (tension, length of muscle etc) via inferior cerebellar peduncle –> these are the spinocerebellar fibres - Input from cortex:*
- Information from left side of cerebrum reaches the pons and olivary nuclei on the left
- This information then needs to cross the midline:
- Pontocerebellar fibres cross the midline via the MCP
- Olivocerebellar fibres cross the midlnie via the ICP
The cerebellum needs to know what the CEREBRUM wants to do with these muscles (the left primary cortex will eventually control these muscles).
Output to: (via the SCP)
- Motor cortex (via thalamus)
- Reticular nuclei
- Red nucleus
This ensures the intended movement is coordinated and controlled.
Via which cerebellar peduncles does the cerebellum;
a) receive proprioception and other sensory information from?
b) send output to cortex?
a) MCP and ICP
b) SCP
Which division of the cerebellum communicates with the cortex?
Cerebrocerebellum
Spinocerebellum summary
-
Receives unconscious proprioception from Golgi organs/muscle spindle via:
- spinocerebellar afferents travel via ICP
- Sends cerebellothalamic and cerebellorubral efferents to thalamus and red nucleus – travel via SCP
- Influences descending pathways, to control muscle tone and execution of movements via:
- Rubrospinal
- Corticospinal tracts
Cerebrocerebellum: Summary
- Receives pontocerebellar afferents from contralateral pontine nucleus - via MCP
- Receives olivocerebellar afferents from contralateral inferior olivary nucleus - via ICP
- Sends cerebellothalamic to contralateral thalamus via SCP decussation
- From thalamus project to motor cortex
- Influences descending pathways, to ensure intended movements are precise via:
- Corticospinal tracts
- Corticorubro (rubrospinal) pathways
- Corticoreticular (reticulospinal) pathways
What does the reticulospinal pathway control?
voluntary movement/breathing/consciousness
Where does the reticulospinal pathway originate?
Brainstem Reticular Formation (pons and medulla) –> this is an extrapyramidal pathway that can receive information from the cerebellum
What does the rubrospinal pathway control?
Muscle tone
Where does the rubrospinal pathway originate?
Red nucleus (midbrain) - this is an extrapyramidal pathway that can receive information from the cerebellum
What is ataxia?
Ataxia describes a lack of muscle control or coordination of voluntary movements
Why does cerebellar damage lead to ataxia but not paralysis?
As motor cortex is still intact
Describe the movements of a patient with cerebellar damage?
Incoordinated (ataxia); depending on the subdivision of the cerebellum damaged, predictable deficits will be observed. Person is still able to move, but in a disordered manner.
A unilateral lesion to cerebellar hemisphere, causes symptoms on the ___ side of the body?
Ipsilateral
What is truncal ataxia?
- Inability to stand or sit without falling over - instability of the trunk
- A wide-based “drunken sailor” gait characterised by uncertain starts and stops, lateral deviations and unequal steps.
- Coordination of eye movements commonly affected (nystagmus)
What part of the cerebellum is affected in truncal ataxia?
Midline lesion affecting vestibulocerebellum (flocculonodular lobe and part of vermis)
Most common cause of truncal ataxia?
Medulloblastoma (mainly seen in children) in the wall of the fourth ventricle
What is nystagmus?
Nystagmus is a condition whereby a person suffers with involuntary, uncontrollable eye movements.
If falling over to the left in truncal ataxia, which side of cerebellum may be injured?
Left
How can sensory ataxia be distinguished from cerebellar ataxia?
REMOVE VISUAL –> Sensory ataxia marked by the presence of near-normal coordination when the movement is visually observed by the patient, but worsening of coordination when the eyes are shut, indicating a positive Romberg’s sign.
What is sensory ataxia? Cause?
It is a form of ataxia (loss of coordination) caused not by cerebellar dysfunction but by loss of sensory input into the control of movement.
Due to lesion in dorsal column.
What is Romberg’s sign?
The Romberg test is positive when the patient is unable to maintain balance with their eyes closed
What type of ataxia is Romberg’s sign positive in?
Sensory ataxia
What is gait ataxia?
Lower limbs most affected. Staggering, wide-based gait.
What division of the cerebellum is affected in gait ataxia?
Lesion of spinocerebellum (most of vermis and adjacent region of hemispheres)
Who is gait ataxia commonly seen in?
Most common in chronic alcoholics due to degeneration of cerebellar neurons in paravermal areas
Lesions of the cerebellar hemispheres include which division of the cerebellum?
Lesion of cerebrocerebellum
How do lesions of the cerebrocerebellum present?
Inco-ordination of voluntary movement, particularly in the upper limb
Possible causes of lesions of cerebrocerebellum?
Many possible causes eg. vascular, degenerative, trauma. Patients show:
- Tremor of intent
- Past pointing or dysmetria
- Adiadochokinesia
- Dysarthria
What condition do midline lesions of the cerebellum lead to?
Truncal ataxia
What condition do anterior lobe lesions of the cerebellum lead to?
Gait ataxia
