Week 10: The Cerebellum Flashcards
What are the functions of the cerebellum?
- production of coordinated movements
- maintain equilibrium, balance and posture
- co ordinates appropriate time, force and duration of muscle contraction (synergy)
What is synergy
two or more systems come together to create a more powerful response
How does the cerebellum act; ipsilateral or contralateral?
ipsilateral –> receives information from the ipsilateral side of the body
i.e the right cerebellar hemisphere will receive information from AND for the right side of the body and will act on the right side of the body
Where is the cerebellum?
- under the occipital lobes
- attached to the brainstem by 3 paired cerebellar peduncles
What is the vermis?
separates the right and left hemispheres of the cerebellum
What are the 3 functional subdivisions of the cerebellum?
- Vestibulocerebellum (archicerebellum)
- Spinocerebellum (palaecerebellum)
- Cerebrocerebellum (neocerebellum)
What is the vestibulocerebellum made of?
flocculonodular lobe and part of vermis
What is the function of the vestibulocerebellum?
- co-ordinates muscle involved in maintaining balance and constancy of visual fields
- receives input from vestibular apparatus of inner ear –> the vestibular apparatus detects change in balance
- regulates balance and eye movements
What is the spinocerebellum comprised of?
most of the vermis and adjacent region of hemispheres
What is the function of the spinocerebellum?
- co ordinates muscles involved in posture and locomotion
- regulates body and limb movements
What is the cerebrocerebellum comprised of?
lateral parts of hemispheres
What is the function of the cerebrocerebellum?
co-ordinates movements of distal limbs, particularly fine, skilled and targeted movements of hands (also involved in learning, linguistic and cognitive functions)
How is the cerebellum organised?
somatotopically:
- the axial musculature is projected to the vermis
- lateral most to the limbs
Explain how the vestibulocerebellum maintains balance
- Vestibule detects a change in balance and fires axons to the vestibular nucleus in the medulla
- From the medulla, the vestibulocerebellar afferents reach the cerebellum via the ICP
- The cerebellum then sends efferent fibres back to the vestibular nuclei in the medulla
- Vestibulospinal pathway reach LMNs for the body to contract and stabilise the postural muscles
- Some axons (the medial longitudinal fasciculus) go to the neck and the eyeballs so we can look and maintain gait
What does the vestibulospinal pathway do?
- extrapyramidal pathway
- works with the vestibulocerebellum to modify posture and balance
- co ordinates the actions of muscles that maintain equilibrium
- vestibular nuclei in pons and rostral medulla
What is the function of the medial longitudinal fasciculus?
- co ordinates the actions of eye movements
- descends with the vestibulospinal tract
How does the spinocerebellum regulate body and limb movements?
- receives unconcious proprioception from golgi organs/muscle spindle:
- length of muscle
- speed of movement
- level of tension
How does the spinocerebellar tract work?
- afferent ipsilateral spinocerebellar fibres from the muscle spindle/golgi tendon reach via the ICP
- unconscious proprioception
Explain how the cerebrocerebellum controls fine motor skills and targeted movement of limbs
- Receives information of intended limbs
- Via corticopontine fibres (cortex to pons) or olivocerebellar fibres (cortex to olives)
- The fibres need to cross the midline as information from the left hand side of the cortex will eventually co ordinate the information to the right hand side of the body
The cerebrocerebellar afferents receive input from the motor cortex via the?
Fibres come from the contralateral:
- Pontine nucleus which reaches cerebellum via MCP
- Inferior olivary nucleus which reaches cerebellum via ICP
If there is a lesion on the right side of the cerebellum, where will the deficit be?
on the right (ipsilateral) side
How does information about proprioception and other sensory information from the spinal cord pass into the cerebellum?
Via the ICP
How does the cerebellum know about intended movements?
- Input from cortex via MCP and ICP (pontine and inferior olivary nucleus respectively)
- Cerebellum sends its response to above to the CNS by crossing the midline via the SCP so the output eventually goes to the motor cortex via the thalamus
Is the cerebellum concious or unconcious
unconcious
Which descending pathways does the spinocerebellum influence and how?
Rubrospinal and corticospinal tracts:
- spinocerebellar afferents travel via ICP
- sends cerebellothalamic and cerebellorubal efferents to thalamus and red nucleus - travel via SCP
What is the function of the reticulospinal pathway?
voluntary movement, breathing, conciousness
What does the ribrospinal pathway control?
muscle tone
What is ataxia?
no order
What is truncal ataxia?
- inability to stand or sit without falling over
- midline lesion affecting vestibulocerebellum (balance)
- in co ordination of eye movements commonly affected (nystagmus)
What is the most common cause of truncal ataxia?
medulloblastoma (tumour in the midline of the cerebellum)
If falling over to the left side, which side of cerebellum may be injured?
the left side
What is gait ataxia?
- staggering, wide based gait
- lower limbs mostly affected
- lesion of the spinocerebellum
- most common in chronic alcoholics due to degeneration of cerebellar neurones
A lesion of the cerebrocerebellum is a lesion where?
cerebellar hemispheres
What are the symptoms of a lesion of the cerebellar hemisphere?
- in-ordination of voluntary movement, particular in upper limb
- tremor of intent
- past pointing or dysmetria
- adiadochokinesia (inability to perform rapid alternating movements)
- dysarthria
