Cerebellum Flashcards
What does cerebellum mean?
Little brain
Where is the cerebellum found?
In the posterior cranial fossa
What is the vermis?
seen from above
gyri lying along the midline
many narrow gyri
What divides the anterior and posterior lobe of the cerebellum in a sagittal section?
Primary fissure (sulcus)
What is the 3rd lobe of the cerebellum?
Seen on the ventral view of the brainstem
- between the anterior and posterior lobes
- flocculus: part of the flocculo-nodular lobe
- forms part of the roof of the 4th ventricle
How would the cerebellum look like unrolled?
- anterior lobe at the top (head)
- posterior lobe (body)
- flocculo-nodular lobe (tail)
- primary fissure between anterior and posterior
- horizontal fissure in the middle of posterior lobe
- posterior fissure between posterior lobe and flocculonodular lobe
Which arteries supply blood to the cerebellum?
Superior cerebellar
Anterior inferior cerebellar
Posterior inferior cerebellar
What is the most common site of an infarct in the posterior circulation?
PICA
What are the 3 main layers seen in the cerebellar cortex?
- pale outer molecular layer with axons
- middle layer with Purkinje cells
- thick inner layer with granule cells
What is input and output to the cerebellum mediated by?
Cerebellar peduncles
What are the roles of the superior, middle and inferior cerebellar peduncles?
- superior: output fibres
- middle: input from contralateral cerebral cortex and cranial nerves
- inferior: input from spinal cord
What is the pathway of the dorsal (posterior) spinocerebellar tract?
Ipsilateral
- carries afferents muscle spindles and golgi tendon organs -> passes up into brainstem -> enters cerebellum in inferior peduncle on same side
What is the function of the dorsal (posterior) spinocerebellar tract?
Carries info. from proprioceptors (joints - Golgi tendon organs and muscle spindles)
What is the pathway of the ventral (anterior) spinocerbellar tract?
Contralateral in the spinal cord
- but then recrosses in the brainstem so ends up on the same side it enters the cord in
- essentially information is passed to the same side in the cerebellum meaning cerebellar signs are on the same side as the lesion
What is the function of the ventral anterior spinocerebellar tract?
Carries info. about state of reflexes in the cord
What are the inputs and outputs to the cerebellar cortex routed by?
Through deep cerebellar nuclei
- lie in white matter below the cortex
What do the cerebellar nuceli connect to?
- hemispheres connect to dentate nuclei (lateral)
- anterior lobe connects to the globose and emboliform (interposed nuclei)
- vermis connects to the fastigial nucleus (most medial)
- flocculo-nodular lobe connects to the lateral vestibular nuclei of the pons
What is the role of the cerebellum in movement?
- helps motor cortex produce accurate and smooth movements
- modulates and refines motor cortex commands using feedback from proprioceptors and sensory organs
How does cerebellar damage affect movement?
Produces clumsiness, abnormal fatigue and instability
- extraocular eye muscles affected
- deep nuclei damage = persisting disability
What are the 3 functional zones of the cerebellum?
- vestibulocerebellum (flocculonodular lobe connected to lateral vestibular nucleus in the pons)
- spinocerebellum (anterior lobe and vermis connected to fastigual, globose and emboliform nucleus)
- cerebrocerebellum (posterior lobe/cerebellar hemisphere connected to dentate nucleus)
What is the function of the vestibulocerebellum?
Co-ordinates head and eye movments ensuring stability of gaze
- controls balance of head on body
- helps balance of body on ground
How does the vestibulocerebellum function?
vestibular apparatus sends info. about movements of head -> vestibular nuclei (in pons and medulla) -> combined with info from extra-ocular eye muscles and neck muscles -> vestibular nuclei computes muscle actions -> eyes kept balanced in head and head balanced on body and body on ground
How are motor commands sent from the vestibulocerebellum?
- to neck and eye muscles via medial longitudinal fasciculus and medial vestibulospinal tract
- to legs via lateral vestibulospinal tract
- motor programs stored in cortex of flocculo-nodular lobe
What is the function of the spinocerebellum?
Controls locomotion and limb co-ordination
- sends motor commands down reticulospinal tracts to co-ordinate postural and locomotor movements
What is the function of the cerebrocerebellum?
- coordinates movements initiated by the motor cortex (speech, voluntary hand and arm movements, hand-eye coordination)
What are the parts of the neocerebellum?
- cortex: cerebellar hemispheres
- deep nuclei: dentate
- input: from cerebral cortex via the middle cerebral peduncle
- output: to motor thalamus via superior cerebral peduncle
What are the 3 major distinguishable cerebellar syndromes?
- flocculonodular syndrome
- anterior lobe syndrome
- neocerebellar syndrome
What are flocculonodular syndromes characterised by?
- little control of axial muscles
- wide based ataxic gait/swaying
- tendency to fall to side of lesion
- nystagmus
- severe = cannot sit/stand without falling
Who is flocculonodular syndrome most common in?
Young children with medulloblastoma in 4th ventricle
What is medulloblastoma?
One of cranial primitive neuroectodermal tumours
What are the features of anterior lobe syndrome?
- correlated with damage to spinocerebellum
- inco-ordination of the limbs
- ataxia
- hypotonia (generalised muscle weakness and fatigue)
- reflexes (depressed or pendular)
- often seen in alcoholics due to malnutrition and lack of B vitamins
What are the features of neocerebellar syndrome?
- loss of hand eye co-ordination
- dysmetria: inaccurate reaching with intention tremor (not resting)
- dysdiadochokinesis (irregular rapid alternating movements of hands)
- intention tremors (when attempt to touch an object, finger to nose and heel to knee tests)
- loss of good speech articulation (slurred) as loss of co-ordination of muscles involved
- loss of cognitive eye movement
- selective attention & perception
What are the most common causes of neocerebellar syndromes?
stroke, tumour, trauma, degenerative diseases
What are the 2 main signs of cerebellar stroke?
1) headache/vertigo/nausea/vomiting (sudden, severe, intense, persistent, debilitating)
2) eye changes (typically only affect 1 eye, contribute to vertigo, nystagmus, ptosis)
3) dysarthria & dysphagia (drooling, difficulty chewing, inco-ordination/weakening of throat and oesophageal muscles)
4) ataxia (feet wide apart, wobble, lean)
5) arm weakness and inco-ordination (clumsiness, weakness, usually in 1 arm, trembling)
Why may alcohol intoxication mimic features of cerebellar damage?
Cerebellum has many GABA-ergic interneurons which are sensitive to the effects of alcohol
