Location• Sits in the posterior fossa• Straddles the brainstem• Forms the roof of the fourth ventricle
Main Functions• Entirely motor and operated at an unconscious level• Maintains balance• Maintains posture and controls eye movement (vestibulocerebellum)• Influences posture and muscle tone (spinocerebellum)• Coordinates movement (pontocerebellum, cerebrocerebellum)
• Separated into 3 areas – spino, cerebro andvestibulocerebellum• And also into lobes – anterior, posterior andflocculonodular lobes
Cerebellar structures• Separated by tentorium cerebelli dura mater from occipital lobes and joined in the middle by vermis.• 3 sets of deep nuclei: interposted nucleus (spinocerebellum, green), fas tigial nucleus (vestibulocerebellum, blue), dentate nucleus (pontocerebellum, red)
Microscopic StructureCortex:• granular layer (granule and golgi cells)• Piriform layer (purkinje cells)• Molecular layer (stellate and basket cells)
More info on these layers...• Purkinje cells have fan shaped dendritic trees that extend into the molecular layer.• Mossy fibres take info into the granular layer and climbing fibres to the molecular layer (to the dendritic trees of the purkinje cells). These two systems take info to the cerebellar deep nuclei, as well as the purkinje fibres.
Main Nerve pathways• Recieves large amount of input from sensory sytems and motor system. Role in motor control can be thought of as sensory-motor integration.• Output is to the brainstem (especially vestibular nuclei), the extrapyramidal system and cerebral motor cortices (via the thalamus)
Nerve pathway of Spinocerebellum• Influences muscle tone and posture• Afferents: dorsal and ventral spinocerebellar tract neurones. Carry info from muscle, joint and cutaneous receptors. Enter through the superior, middle and inferiour peduncles respectively. Terminate in cortex of ipsilateral and paravermis.• Efferents: From Cerebellar cortex to the globose and emboliform nuclei and the fastigial nucleus. These nuclei project to the contralateral red nucleus via the superior cerebellar peduncle.• In the red nucleus: influence activity of cells giving rise to the descending rubrospinal tract.
Nerve pathways of vestibulocerebellum• Maintenance of balance• Many connections with the vestibular and reticular nuclei (brainstem) through Inferior cerebellar peduncle.• Afferents: from vestibular nuclei to cortex of ipsilateral flocculonodular lobe.• Efferents: from cortex to fastigial nucleus (by purkinje fibres), then from the fastigial nucleus to the vestibular nuclei and the reticular formation.• Many of the fastigial efferents cross to the contralateral side of the brainstem, making the influence of the vestibulocerebellum bilateral on the LMN.
Nerve pathways of pontocerebellum• Muscular coordination, trajectory, speed and force of movements.• Afferents: pontocerebellar fibres from the pontine nuclei, crossing to the other side and passing through the middle peduncle to terminate in the lateral parts of the cerebellar hemisphere.• Efferents: From the neocerebellar cortex to dentate nucleus. From the dentate nucleus to the contralateral red nucleus and ventral lateral nucleus of the thalamus. From the red nucleus, rubrothalamic cells. From the ventral lateral nucleus of the thalamus to the motor cortex. From the motor cortex to the pontine nuclei.• It exerts its effects through action on the cerebral cortex which gives rise to the descending corticospinal and corticobulbar pathways.
Disorders of the cerebellum• Ataxia – incoordination of both arms, staggering, wide based and unsteady gait. – bilateral dysfunction of the cerebellum caused by alcoholic intoxication, hypothroidism, inherited cerebellar degeneration, multiple sclerosis or paraneoplastic disease.