Exam 3 Week 12 pp 7-9 3 sections of cerebellum Flashcards
Vestibular afferents project to _____
cortex of vestibulocerebellum and to the fastigial nucleus through the inferior cerebellar peduncle
Where do primary vestibular afferents start from?
direct from ispilateral CN VIII
Where do secondary vestibular afferents start from?
from ipsilateral vestibular nuclei
Why do I care about vestibular afferents?
because they influence distribution of tone in limbs, trunk, neck, and extraocular eye muscles
How does the visual systems project to vestibulocerebellum?
indirectly to vestibulocerebellum through climbing fibers of the inferior olivary nucleus
Function of visual system input
Assists in regulating the vestibular ocular reflex (VOR)
What are the two places in the brain stem that receive outputs from the vestibulocerebellum?
- Vestibular nuclei
- From vestibular nuclei to influence extraocular motor neurons via MLF
- From vestibular nuclei to influence body and limb tone and responses via the vestibulospinal tracts
- –Reticular formation
- Descending fibers of reticulospinal tracts
- Ascending fibers to extraocular motor nuclei
Where does the vestibulocerebellum have outputs?
to the brainstem Vestibular nuclei
Purpose of the projections through the vestibular nuclei: (2)
- influence extraocular motor neurons via the medial longitudinal fasciculus
- play a role to influence body and limb tone and responses via the vestibulospinal tracts
Second location where vestibulocerebellum outputs to the brainstem end and why
-nuclei of the Reticular formation -These nuclei send both Descending fibers forming the reticulospinal tracts and Ascending fibers to extraocular motor nuclei
Functions of the vestibulocerebellum (Flocculonodular lobe): (3)
- Balance in sitting, standing & gait
- Plasticity of vestibulo-ocular reflex
- Nodule function related to sensitivity to motion sickness (ablated this makes subject immune to motion sickness
Nyanduk’s favorite animal
monkeys
major role of spinocerebellum
comparator -defined on interwebs as a device for comparing a measurable property or thing with a reference or standard. an electronic circuit for comparing two electrical signals. something used as a standard for comparison.
So what makes spinocerebellum a comparator? (3)
- Information about intended movement is sent to the cerebellum – efference copy, a copy of the outgoing command to move – Feed forward signal from inferior olive
- Patterns of peripheral proprioceptor discharge are also sent to the cerebellum - feedback
- Cerebellum constantly updates movement as it is evolving
Functions of Vermis (2)
- Movement coordination of axial & proximal limb musculature
- Probable regulation of postural muscle tone
Where do the inputs from vermis come from? (types of input)
Proprioception, Vision & Vestibular sensory systems
What happens if spinal proprioceptive input to vermis is damaged? (4)
Damage results in sensory ataxia:
- Ataxic symptoms without visual support
- Increased postural sway
- Difficulty in standing with narrow base of support and eyes closed (Romberg sign)
- Uncoordinated gait
How is body mapped on cerebellum?
somatotopically mapped on the cerebellum with separate somatopic maps on anterior and posterior lobes of cerebellum
How many homunculi are on the cerebellum?
two
How are homunculi distributed?
Two homunculi are inverted images of one another Neck & trunk are vermal & extremities paravermal
Afferent tracts of the Spinocerebellum (5)
- Dorsal spinocerebellar tract (DSCT)
- Cuneocerebellar tract (CCT)
- Ventral spinocerebellar tract (VSCT)
- Rostral spinocerebellar tract (RSCT)
- Trigeminocerebellar projections
Pathway of Dorsal spinocerebellar tract (DSCT)
- Arises from cells of Nucleus dorsalis (Clarke’s) in spinal segments T1 to L2 or L3
- Axons rise ipsilaterally in dorsal lateral funiculus to enter thru inferior peduncle -Axons end in areas representing LE & trunk in anterior & posterior lobes
Pathway of Ventral spinocerebellar tract (VSCT)
- Arises from nuclei scattered in based of dorsal horn -Axons decussate to rise in peripheral lateral funiculus just ventral to contralateral DSCT
- Axons ascend thru medulla & pons to decussate again and enter thru superior cerebellar peduncle
- Axons end in LE representation of anterior lobe and paramedian lobule
What type of activity do Ventral spinocerebellar tract (VSCT) and Dorsal spinocerebellar tract (DSCT) have in common?
phasic activity during gait stepping cycle
Section dorsal roots affects which tract during phasic activity
Dorsal spinocerebellar tract (DSCT) only
What happens to phasic gait cycle pattern if dorsal roots were cut
Ventral spinocerebellar tract continues its phasic gait cycle pattern
DSCT neurons of the Clarke’s column are driven by______
proprioceptive afferents – unconscious proprioception
VSCT cells at the base of the dorsal horn driven by__________
descending motor commands – efferent copy
Pathway of Cuneocerebellar tract (CCT)
- Primary afferents from upper extremity proprioceptors ascend in fasciculus cuneatus to end in accessory (lateral) cuneate nucleus (ACN) of caudal medulla
- CCT axons from ACN enter inferior cerebellar peduncle innervating areas representing UE
- CCT axons from ACN carry information from muscle spindles, GTOs & joints
- Cutaneous input enters cerebellum from neurons in main cuneate nucleus – providing proprioceptive input from hands and fingers
Pathway of Rostral spinocerebellar tract (RSCT)
- Arise from cells scattered thru cervical segments
- Rise ipsilaterally to enter thru inferior cerebellar peduncle but evidence for contralaterally rising axons which enter thru superior cerebellar peduncle
- End of both LE & UE representations of ipsilateral anterior & posterior lobes of cerebellum
Pathway of Trigeminocerebellar tract (TCT)
- Cells in mesencephalic, chief sensory and spinal tract nuclei of CN V all contribute to these projections
- Some fibers enter thru superior and others thru inferior cerebellar peduncles
- TCT axons end ipsilaterally in the posterior lobe area with face representation
Other inputs to cerebellum (2)
Visual & auditory inputs
Where do visual & auditory inputs in cerebellum end?
End in same region as face representation in posterior lobe
How do visual inputs function?
provide sense of verticality & horizontality from the visual space for maintenance of upright stance
In what ways does cerebellum participate in cognitive functions related to hearing? (6)
- Speech generation
- Auditory processing
- Auditory memory
- Abstract reasoning & solution of problems
- Sensorial discrimination & information processing
- Language processing & linguistic operations
Spinocerebellum outputs (nuclei)
fastigial and interposed nuclear outputs
Fastigial outputs: what three places does the vermis project to?
- Vestibular Nuclei
- Reticular formation nuclei
- Thalamus: ventral lateral (VA) nucleus
What do fastigial nucleus outputs include? (3)
Vermal outputs to vestibular & reticular nuclei
(and ventrolateral thalamic nucleus)
How do vermal outputs to vestibular & reticular nuclei project (unilateraly or bilaterally) and why?
project bilaterally to control axial muscles
Where else (besides vestibular and reticular nuclei) do vermal outputs project?
to ventral lateral nucleus of the thalamus
How do fastigial outputs from spinocerebellum function? (2)
- Most feel that these function in control of proximal musculature during movement
- Providing proximal stability for distal mobility
What make up the interposed nucleus?
Globose and emboliform nuclei
Two types of fibers of the globose and emboliform nuclei
Cerebellorubral fibers Cerebellothalamic fibers
Pathway of Cerebellothalamic fibers
-globose and emboliform nuclei axons exit & decussate in superior cerebellar peduncle -most ending in the VL nucleus of thalamus which in turn projects to motor cortex
Pathway of Cerebellorubral fibers
-globose and emboliform nuclei axons exit & decussate in superior cerebellar peduncle -Terminate in the magnocellular part of red nucleus. These outputs appear to activate rubrospinal pathways
Purpose of Globose and emboliform nuclei
Globose and emboliform nuclei pathways to both the red nucleus and through the thalamus to the motor cortex are involved in fine motor control of the upper extremity
What occurs if damage to Globose and emboliform nuclei?
Damage to these areas produces a 3-5 Hz Intention tremor during reaching tasks. But there is no similar effect of damage on gait or standing balance
Role of Pontocerebellum (2)
- Role in the governance of voluntary movement and motor learning
- Role in timing of muscle activation (and inactivation), as well as influencing the duration of muscle contraction
Does Pontocerebellum receive projections from peripheral receptors?
No
Where do Afferent projections to the neocerebellum originate?
originate in the motor and association cortices of the cerebrum via cortico-pontocerebellar projections
Where do Cortico-pontocerebellar projections travel? (6)
- -Descend from motor association cortex thru internal capsule & medial third of cerebral peduncle
- -End on neurons of pontine nuclei
- -Pontine nuclei axons decussate to enter thru contralateral middle cerebellar peduncle
- -Mossy fibers end on granule cells of lateral cerebellar cortex
- -Mossy fiber collaterals end on neurons in dentate nucleus
- -Carries information that cerebellum uses for movement initiation & execution
What do lesions of Cortico-pontocerebellartract & pontine nuclei result in?
contralateral deficits in arm & leg coordination
What does a lesion of the middle cerebellar peduncle results in?
ipsilateral deficits in arm & leg coordination
After pontocerebellum cortex project to the dentate nuclei, where do projections travel?
project out via the superior cerebellar peduncle to: Contralateral red nucleus & Contralateral VL thalamus
Where do dentate projections to red nucleus end?
end on Parvocellular neurons which project to inferior olivary nucleus. These neurons then project back into the cerebellum providing Regulatory feedback to the cerebellum
What happens to dentate projections to VL nucleus of thalamus?
project to motor & premotor cortex whch produce Direct and indirect actions on UMN via corticospinal pathways & corticobulbar pathways
What happens when dentate nucleus is damaged?
Movement initiation & voluntary execution of the movement is delayed
What do the resulting impairments due to dentate nucleus damage suggest?
Suggests that dentate projections to motor cortex via VL nucleus of thalamus are essential for the initial activation of corticospinal neurons at the beginning of a movement
What results when damage to the pontocerebellum produces delay of excitatory output from the motor cortex
results in a corresponding delay in muscle contraction
When damage to pontocerebellum produces delay in agonist and antagonist contraction, what also happens?
Reciprocal pattern of activation in agonists and antagonists that accompanies many movements is dramatically disrupted
Thinking about the pontocerebellum, what happens with damage that involves only the cerebellar cortex?
rarely results in permanent motor deficits
What happens if there is damage to both deep nuclei and the cerebellar cortex?
Damage to both cortex & nuclei or to nuclei alone results in a wide range of motor problems
Unilateral lesions of the cerebellum produce ________
ipsilateral deficits
Why do unilateral lesions to cerebellum produce ipsilateral deficits?
Right dentate and interposed nuclei influence the left motor cortex and red nucleus and projections of the Left motor cortex & red nucleus project to the right side of the spinal cord. So a lesion in the cerebellum on the right results in deficits on the right side of the body
What is the results with lesions of the lateral cerebellum?
- deterioration of coordinated movement (movement decomposition) or dyssynergia
- This deficit consists of the breakdown of movement into its individual component parts
- Symptoms: hypotonia Ataxia Dysarthria Ocular motor coordination defects Dysmetria Intention tremor Dysdiadochokinesia
What is dysmetria?
past pointing when pointing at stationary or moving objects
Characteristics of Ataxia
incoordinated limb movement Unsteady gait Tendency to lean or fall to the side of the lesion
Hypotonia
decrease in muscle tone & in deep tendon reflexes
dyssynergia
lack of harmonious association of its various components; usually used to describe abnormalities of movement caused by cerebellar disorders.
Dysdiadochokinesia
awkward performance of rapid alternating movements & also manifested by inability to perform repeated rhythmic movements
Intention tremor
oscillation of limb as target is approached - occurs with performance of a voluntary movement
Characteristics of Sensory ataxia (4)
- Disruption of proprioceptive afferents into the cerebellum
- Near-normal coordination when the movement in question is visually observed by the patient
- Marked worsening of coordination when the eyes are shut
- Positive Romberg sign & problem walking in dark
Characteristics of Motor Ataxia (2)
- Damage to the cerebellum
- Ataxia symptoms with or without vision
