The cerebellum week 6 Flashcards
Where does the cerebellum reside within the cranium?
What are the functions of the cerebellum?
The cerebellum resides within the brainstem in the posterior fossa beneath the tentorium cerebelli. It is responsible for coordination (taxia) of movements, muscle tone, flexor extensor synergies, and the metrics and precision of movement. These activities constitute unconscious proprioceptive functions that distinguish them from the conscious proprioceptive perception of the dorsalcolumn-lemniscal system.
Where is the vermis of the cerebellum? The hemispheres?
What are the two lobes? What are they divided by?
What are cerebellar folia?
Where are the cerebellar tonsils located?
The cerebellar cortex has a midline vermis and two lateral hemispheres. It is divided rostral-caudally into an anterior and a larger posterior lobe by a transverse primary fissure. This main fissure is paralleled by a number of secondary fissures that define minor cerebellar lobules.
Cerebellar folia form small transverse “gyri” across the entire surface. The tonsils are eminences on the medial-inferior posterior surface.
What can happen to the cerebellar tonsils with increased ICP or masses in the cranium?
Individuals with what disorder are particularly at risk for this?
The tonsils can herniate through the foramen magnum as a result of increased intracranial pressure or masses in the cranium. Such translocations can compress cardiorespiratory centers in the lower medulla. Individuals with Arnold-Chiari malformations are particularly at risk for herniations of cerebellar tonsils.
Where is the floculonodular lobe located? What is the function of this lobe?
Name the cerebellar peduncles.
What travels in each of the cerebellar peduncles?
Beneath its posterior lobe, a primitive flocculonodular lobe has rich connections to the nearby vestibular nuclei. This relationship is important for controlling descending extensor systems involved in balance and posture.
The cerebellar peduncles are the relay station for fibers into and out of the cerebellum. Efferent fibers go through the SUPERIOR cerebellar peduncle, pontine fibers through the MIDDLE cerebellar peduncle, and AFFERENT fibers through the inferior cerebellar peduncle.
Explain the somatotopy within the cerebellum.
The somatotopy of the cerebellar cortex is actually rather simple. Legs are represented heavily in the anterior lobe. Arms and legs have a second representation more posteriorly. The distal extremities are represented most laterally in the hemispheres (neocerebellum). The axial musculature, neck and head are represented in the midline in the vermis. Consistent with this layout, the paravermal zones deal with more proximal limb musculature.
Extra: With cerebellar atrophy in alcoholism, starts in vermis and moves laterally into hemispheres
What arteries supply the cerebellum?
Three arteries:
- Superior cerebellar (SCA)
- Anterior inferior (AICA)
- Posterior inferior (PICA)
How many layers of cortex does the cerebellum contain? Name the layers.
What underlies the cortex?
The cerebellum consists of a three-layered cortex and underlying white matter consisting of afferent and efferent pathways that enter and exit the cerebellum through its three cerebellar peduncles.
Three layers of cortex:
- Molecular
- Purkinje
- Granule cell
Where are the deep cerebellar nuclei located?
Name the deep cerebellar nuclei.
What is the function of the deep crebellar nuclei?
Deep cerebellar nuclei are embedded in the white matter of the cerebellum.
Deep cerebellar nuclei receive afferent information and project efferent information to the contralateral cortex via the superior cerebellar peduncle.
Deep cerebellar nuclei:
- Dentate – largest, pontine fibers
- Emboliform
- Globose
- Fastigial
(Don’t Eat Greasy Foods)
What is the prinicple neuron of the cerebellar cortex?
What NT do they release? What is the function of these cells?
Purkinje cells are the principle neurons of the cerebellar cortex (see next section). These have GABAergic output, but their axons, for the most part, do not project outside of the cerebellum. Instead they modulate the activity of the deep nuclei which are the main source of efferent pathways to the brainstem or cortex.
Explain the inputs Purkinje cells receive and whether they are excitatory or inhibitory.
The PURKINJE CELL is INHIBITORY (GABA) to the deep nuclei. It receives strong direct inputs from axons arriving from the inferior olivary nucleus that terminate in climbing fibers along its dendrite. The balance of non-climbing fiber inputs, called mossy fibers, activate Purkinje cells indirectly. These inputs are directed first to a small neuron called the granule cell which has a T-shaped axon that ascends to the cerebellar surface (molecular layer) and joins bundles of other granule cell axons (parallel fibers) – all running parallel to the folia. These synapse with the dendrites of Purkinje cells which have a planar distribution perpendicular to the orientation of the parallel fibers. The remainder of cells (basket, stellate) are inhibitory interneurons.
All the cells located in the cerebellar cortex, with the exception of the granule cell, are inhibitory. This includes the main output neuron, i.e. the Purkinje cell. This is a great story of an inhibitory control system all directed to controlling the activity of cerebellar output from the deep nuclei.
What tract provides proprioceptive input to the cerebellum?
From what receptors does the cerebellum receive information from?
What areas does the cerebellum project to? (What are its outputs for motor control?)
What is the major feedback loop?
The cerebellum receives its proprioceptive input from spinocerebellar pathways (4) that convey information from stretch receptors, specifically muscle spindles and Golgi tendon organs. Its output for motor control is not directly back to the cord or muscle but is to the brainstem and cortex:
1) motor and premotor cortex via Va/Vl nuclei of the thalamus.
2) brainstem postural systems (vestibulospinal, reticulospinal)
The cerebellum is truly multimodal in that it also receives a multiplicity of inputs that provide information about somatosensory, visual, auditory, and ongoing motor activity. The major feedback loop is the cortico-ponto-cerebellar pathway. The cerebellum is considered a timing system that can monitor activities going on at many distributed locations.
Inputs from the body to the cerebellum are made via what pathways? Are they ipsilateral or contralateral? Explain the travel of these pathways.
Feedback to the cerebellum is via what pathway? Explain the travel of this pathway. Does it come from the ipsilateral or contralateral side?
Inputs from the body are made via four spinocerebellar pathways inputs that are mostly ipsilateral. The posterior spinocerebellar pathway is the main service from the legs. Fibers from muscle spindles and joint receptors synapse in Clarke’s nucleus in the spinal cord, ascend in the spinocerebellar tract, enter the inferior cerebellar peduncles, and into the hemispheres of the cerebellum.
The feedback pathway from the contralateral cerebral cortex is mediated by corticopontocerebellar inputs. These arise widely from the cerebral cortex, pass through the crus cerebri, synapse in pontine gray matter (pontine nuclei) and decussate to enter via the middle cerebellar peduncle. Other inputs include include visual and oculomotor.
What is the name for the output pathway of the cerebellar hemispheres? Explain the route of travel for this pathway.
What deep nucleus of the cerebellum does this pathway relay in? What is the overall function of this pathway?
Output from the laterally-located cerebellar hemispheres is directed upstream to the cerebral cortex via the dentatorubrothalamocortical pathway. This pathway through the thalamus (Va/VL) modulates corticospinal outflow which, as you know, is directed primarily to distal extremities and the flexor system. Lateral cerebellar cortex (hemispheres) relay through the laterally positioned deep nucleus (DENTATE) and through the dentatorubrothalamocortical pathway to motor cortex - exerting control of fine motor corticospinal system. Note that this pathway decussates at the lower midbrain.
Where do the vermis and flocculonodular lobe (medial cerebellar regions) project to?
What deep cerebellar nuclei do they relay through?
What do they control?
Medially located cerebellar regions (vermis and flocculonodular lobe) have output directed to the brainstem affecting posture and especially extensor muscle tone. Medial cerebellar cortex (vermis and flocculonodular lobe) relay through medial deep nuclei (fastigial and interpositus) to the brainstem vestibular and reticular nuclei: exerting control of the brainstem-derived postural systems in the anterior funiculus of the cord (vestibulospinal and reticulospinal tracts).
Explain why cerebellar lesions cause ipsilateral symptoms.
The upstream dentatorubrothalamocortical pathway decussates at the lower midbrain. This means that while the left cerebellum receives ipsilateral inputs from the left body via spinocerebellar pathways, its output crosses the midline to reach the right motor cortex. The right corticospinal pathway then crosses to control the musculature on the left. This double cross results in ipsilateral effects of cerebellar lesions.
What are the classifications of causes of ataxia?
