Cerebellum structure and function Flashcards
1
Q
Differences in lesions btwn U/LMNs, basal ganglia, and cerebellum
A
- UMN and LMN lesions result in paralysis/weakness and either hyperreflexia or hyporeflexia
- Basal ganglia lesions result in hypo/hyperkinetic disorders (not weakness/paralysis)
- Cerebellar lesions result in poor coordination (cerebellar ataxia), not weakness/paralysis
2
Q
Function of cerebellum
A
- Coordinates and predicts motor activity by adjusting the timing and speed of muscle contraction/relaxation
- Works through the cortical UMNs and sum cortical UMNs
- Cerebellar control of extremities is ipsilateral and control of trunk is bilateral
3
Q
Anatomy of the cerebellum
A
- Divided into 3 lobes: anterior, posterior and flocculondular (at the inferior end)
- The fine grooves of the cerebellum are the folia
- There are 3 cerebellar peduncles (inferior, middle, superior)
- Superior cerebellar peduncle (SCP): connects midbrain w/ cerebellum (mostly efferent)
- Middle cerebellar peduncle (MCP): connects the pons w/ the cerebellum (afferent)
- Inferior cerebellar peduncle (ICP): connects the medulla w/ the cerebellum (afferent + efferent)
- Nuclei of the cerebellum: dentate, emboliform, globose, and fastigial (Don’t Eat Greasy Foods)
4
Q
Microanatomy of the cerebellum
A
- Has white matter (inside) and grey matter (outside) and 3 layers
- Molecular layer (most outer) contains dendrites of purkinje cells and axons of granule cells (and other stuff)
- Purkinje layer contains cell bodies of purkinje cells (reside in the border btwn the granular layer and molecular layer), dendrites project to molecular layer, axons project to deep cerebellar nuclei
- Granular layer contains cell bodies of granule cells who’s axons project to the molecular layer (for purkinje cells)
5
Q
Fibers (afferents) of the cerebellum
A
- All afferents of the cerebellum ultimately activate purkinje cells (3 fiber types)
- Mossy fibers come from the SC, pontine nucleus, and vestibular nucleus and synapse on granule cells
- Climbing fibers come from the inferior olivary nucleus and synapse on purkinje neurons
- Parallel fibers come from granule cells and synapse on purkinje neurons
6
Q
Functional subdivisions of the cerebellum
A
- From medial-> lateral/anterior: fastigial, globose, emboliform, dentate (emboliform+dentate together called interposed nucleus)
- There is a homunculus of the cerebellum: trunk is controlled by the midline (vermis) w/ limbs being controlled by the hemispheres: proximal limbs medial and distal limbs lateral (both anterior and posterior sections have their own homunculi)
- 3 functional subdivisions: vestibulocerebellum, spinocerebellum, cortico/pontocerebellum
7
Q
Vestibulocerebellum subdivision
A
- The 2 flocculi on either side connected by a part of the inferior vermis (nodule) together form the flocculonodular lobe
- This subdivision projects to the deep nucleus fastigial nucleus
- Receives info from the vestibular nucleus regarding balance
- Pathway: vestibular nucleus->fastigial nucleus-> vestibular nucleus
8
Q
Spinocerebellum subdivision
A
- Superior and inferior vermis except nodule, the medial and lateral zones of the hemispheres
- Projects to the interposed nucleus
- Receives information about proprioception form the SC
- Pathway: SC-> interposed nucleus-> SC and cortex
9
Q
Cortico/pontocerebellum subdivision
A
- Receives info from cortex but on the way to cerebellum it synapses in pons
- Comprises most of the lateral cerebellar hemispheres
- Projects to the dentate nucleus
- Receives info from cortex about the planning of movements and sends info back to cortex fine tuning those movements
- Pathway: cortex-> dentate-> cortex
10
Q
Vestibulocerebellum pathway 1
A
- Responds to changes in movements detected by inner ear
- Coordinates contractions of muscles of the trunk and proximal parts of the limbs to maintain balance, also controls eye muscles
- Afferents: arise from VIII (vestibular) nerve, cell bodies in vestibular ganglion, and synapse on the vestibular (VIII) nuclei in the upper medulla
- From the vestibular nucleus, the afferents enter the inferior cerebellar peduncles as mossy fibers, to terminate on the granule cells (flocculonodular lobe). These cells then synapse on the purkinje cells
11
Q
Vestibulocerebellum pathway 2
A
- Efferents: the purkinje cells project to the fastigial nucleus. From here axons leave the cerebellum via the ICP and synapse back on the vestibular nucleus and also on the reticular formation (also upper medulla)
- These motor centers influence the LMNs controlling trunk and proximal limb muscles via descending tracts arising from the 2 nuclei (vestibulospinal and reticulospinal tracts)
12
Q
Spinocerebellum pathway
A
- Monitors all ongoing movements in real time in all parts of the body (particularly the distal limbs) to ensure coordination
- Vermal and medial part of hemispheres control trunk/proximal limbs and lateral parts control the distal limbs
- 2 tracts: posterior which conveys info about joint position/muscle activity and anterior which relays info about the influence of CST on muscle activity
- Afferents: convey unconscious proprioceptive info from neuromuscular spindles and neurotendinous organs (golgi)
- Tracts are either truly ipsilateral (posterior) or cross twice to thus be ipsilateral as well (anterior)
13
Q
Posterior spinocerebellar tract
A
- First neuron is in the DRG of spinal nerves T1 and below (only for lower limbs- don’t need to know upper limbs)
- Fibers conveying proprioception (from spindles and golgi) enter the dorsal horn and synapse in the nucleus of clarke (T1-L2) which resides in the intermediate gray horn (just lateral to white commissure)
- The axons from here extend to the lateral funiculus (just posterior to the anterior spinocerebellar tract and lateral to the CST, on the lateral wall of the SC), which ascends all the way to the medulla
- In the upper medulla the tract enters the ICP to reach the spinocerebellar cortex (purkinje cells) in the anterior lobe on the ipsilateral side of info origin
- Purkinje axons projected to interposed nucleus
14
Q
Anterior spinocerebellar tract
A
- Arises form scattered spinal border cells of the anterior horn (around the anterior/lateral border of the ant horn)
- These cells receive info from muscles (sensory- where am I?) and from the CST (where I should be) to monitor what movements should happen vs what movements are happening
- These axons cross (also only for lower limbs) the anterior commissure to form the tract (just posterior to the STT, lateral to anterior horn) which travels up to the pons
- In the upper pons the tract enters the SCP to reach the cerebellar white matter where it crosses back to the side of origin and ends on the spinocerebellar cortex on the ipsilateral side
- The purkinje cells receiving this info project to the interposed nucleus
15
Q
Efferents of the spinocerebellar tract
A
- Axons of the interposed nucleus cross at the decussation of the SCP in the lower midbrain to reach 2 contralateral targets: red nucleus and ventral lateral (VL) nucleus of the thalamus
- The red nucleus axons will cross back over to the ipsilateral side (of info origin) before ending on LMNs that regulate muscles of trunk and proximal extremities
- The VL axons project to the motor cortex on the same side as the VL, which is contralateral to info origin. Since the motor cortex operates the muscles on the contralateral side, the VL projects to the motor cortex that will control muscles on the ipsilateral side of the info origin
- Thus all spinocerebellar information receives info from and generates corrections for muscles on the ipsilateral side of the interposed nucleus
