Week 6 Cerebellum: structure and function Flashcards
Compare the general functions of the three major motor control systems.
- UMNs and LMNs
- initiates voluntary skilled movements and more automatic stereotyped movements for posture - Basal Ganglia: facilitates desired motor programs and activities, and inhibits unwanted motor programs and activities
- Cerebellum: coordinates and predicts motor activity by adjusting the timing, speed of contraction and relaxation of various muscle groups involved in voluntary activity
- coordinates muscles in postural adjustments and gait
What are the three types of fibers of the cerebellum?
- Mossy fibers: from spinal cord, pontine nuclei, vestibular nuclei to synapse on granule cells
- Climbing fibers: from inferior olivary nuclei and synapse with Purkinje neurons
- Parallel fibers: from granule cells and synapse with Purkinje neurons
What are the functional subdivisions of the cerebellum and which nuclei do they contain?
- Vestibulocerebellum:
- flocculus and nodulus (part of the inferior vermis that connects the two flocculi)
- deep nucleus: Fastigial nucleus - Spinocerebellum:
- superior and inferior vermis except for the nodule
- medial zone of cerebellar hemisphere
- deep nucleus: interposed nucleus (globose and emboliform nucleus) - Cortico/pontocerebellum
- most of the lateral cerebellar hemisphere
- deep nucleus: dentate nucleus
What is the function of the vestibulocerebellum?
- responds to changes in position and movements of the head detected by the inner ear
- coordinates contraction of muscles of the trunk and proximal parts of the limbs to maintain balance
- controls eye muscles and eye position changes with movements of the head
What are the afferents and efferents of the vestibulocerebellum?
- afferents: from VIII nerve and nucleus, go through ICP (inferior cerebellar peduncles) as mossy fibers to vestibulocerebellar cortex
- efferents:
- purkinje cells of cortex to fastigial nucleus
- fastigial axons exit cerebellum to vestibular nucleus and brain stem reticular formation via ICP
- influence LMNs via mainly reticulospinal and vestibulospinal tracts (not responsible for these)
What is the function of the spinocerebellum?
- monitors ongoing movements in all parts of body to ensure coordination
- vermal part: trunk and proximal muscles
- medial zones of hemispheres: distal parts of the limbs
- posterior spinalcerebellar tract: joint position and muscle activity information
- anterior spinocerebellar tract: conveys integrated info about the influence of descending tracts on muscle activity
What are the afferents of the spinocerebellum?
afferents: unconscious proprioceptive info from neuromuscular spindles and neurotendinous organs in the muscles
- records info to where the limb is located before and during movement
- receives info about state of activity at the terminals of corticospinal tracts to assess current motor plan
- ipsilateral (posterior spinalcerebellar) or cross twice to bring info from one side (anterior spinalcerebellar)
Trace the pathway of the posterior spinocerebellar tract.
- neuron 1:spinal ganglia (DRG) of T1 and below
- proprioception from trunk and lower limbs - Neuron 2: roots enter spinal cord and synapse on Nucleus of Clarke in T1-L2 intermediate gray horn
- axons pass into lateral funiculus ipsilaterally to form posterior spinocerebellar tract
- ascends all the way through spinal cord and medulla
- ls lateral to lateral corticospinal tract - upper medulla: tract enters ICP to reach spinal cerebellum in anterior lobe on the same side
Trace the pathway of the anterior spinocerebellar tract.
- from spinal border neurons in anterior horn of lumbar and sacral cord. axons cross white commissure to form anterior spinocerebellar
tract.
-compares current position in sale with input from descending motor tracts in real time. sends info back to spinocerebellum during ongoing motor activity to maintain postural stability of lower limbs - travels in lateral funiculus ventral to posterior spinocerebeallar tract and ascends to upper pons
- enters SCP to cerebellar white matter. Crosses back to side of origin to end in spinocerebellar cortex on same side as origin of tract
- spinocerebellar cortex projects to interposed nuclei
Describe the efferents of the spinocerebellum.
- axons of interposed nuclei cross in SCP decussation in lower midbrain and reach 2 different targets
1. Red nucleus - rubrospinal tract from red nucleus crosses in lower midbrain and end on LMNs that regulate musculature of trunk and proximal parts of extremities
- two sets of crossings so spinocrebellum ends up regulating motor activity ipsilaterally
2. Ventral Lateral (VL) nucleus of the thalamus - VL projects to motor cortex to influence corticospinal tracts that terminate on and regulate LMNs for distal parts of extremities for skilled movements
- ipsilateral bc of double crossings
Describe the afferents of the corticocerebellum.
- axons from cerebral cortex, mainly frontal and parietal lobe
- corticopontine fibers: axons pass through corona radiate and anterior limb of internal capsule
- descend in lateral and medial 1/3s of crus cerebri to enter pons
- end ipsilaterally on pontine nuclei (in gray matter of ventral pons)
- Pontocerebellar fibers: cross the midline and enter contralateral MCP, end on granule cells of cortex
- Perkinje cells relay output to ipsilateral dentate nucleus
- fibers exit from cerebellum in SCP and cross midline at midbrain
- some to red nucleus other to VL
- thalamic neurons relay info back to cerebral cortex via internal capsule
What is the function of the corticocerebullum?
Responds to information provided by all parts of cortex, primarily Premotor area and supplementary motor area, regarding intent to move and for planning and guiding movements
Describe the efferents of the corticocerebellum.
- axons of dentate nucleus, make up dentatothalamic tract
- crosses in decussation of SCP in lower midbrain
- Axons mostly end in VL of thalamus (contralateral)
- VL projections end in and influence primary motor cortex, PMA, and SMA of same side
- effect mainly on distal muscles, muscles in speech and eyes
- double crossing of pontocerebellar and dentatothalamic fibers, each side of corticocerebellum is connected with opposite motor cortex
- since motor cortex controls contralateral side of body, net effect is ipsilateral regulation by corticocerebellum
What are the signs and symptoms of a midline lesion of the cerebellum?
Damages to vermis
-truncal ataxia=loss of equilibrium, swaying from side to side when standing or walking
-normal limb movements when head and trunk supported (lying down)
-abnormal eye movements
Causes: medullablastoma
What are the signs and symptoms of a hemispheric lesion of the cerebellum?
Affect mostly corticocerebellum, possible medial spinocerebellum
- decrease in muscle tone
- Limb/appendicular ataxia=incoordination of motor activity on voluntary movements
- predominantly affect limbs
- dys(a)synergia: error in timing of multipoint movement (finger to nose to finger test)
- dys(a)diadochokinesia: lack of regular rhythm and force of repeated movements
- intention tremor, mostly toward end of movement. Absent during rest.
- dysarthria or slurred speech
- hypotonia of affected limbs with oscillating knee jerk
- causes: abscess, infarct, astrocytoma, hemangioblastoma
