Cerebellum Flashcards
True or False
The cerebellum influences the motor system through direct connection to LMNs
False
The cerebellum influences the motor system without direct connection to LMNs
What are the main functions of the cerebellum?
- Smoothen and coordinate ongoing movements (including balance and eye movements)
- Motor planning
- Motor learning
- Also involved in speech articulation, respiratory movements, and higher order cognitive processes
What is the clinical significance of cerebellar tonsils?
The tonsils can develop mass lesions which will increase intracranial pressure leading to the tonsils herniating through foramen magnum, this herniation will compress the medulla and cause death
Which cerebellar peduncle(s) deal with input signals?
Inferior and middle cerebellar peduncles
Which cerebellar peduncle(s) mainly deal with output signals?
Superior cerebellar peduncle
What is another name for the inferior cerebellar peduncle?
Restiform body
Does the cerebellum coordinate movement on the ipsilateral side of the body or contralateral side of the body?
The cerebellum coordinates movement on the ipsilateral side of the body
Since the cortex controls movement on the contralateral side of the body, any connections between the cerebellum and cortex must decussate (cross)
What are the functional regions of cerebellum?
- Cerebrocerebellum (lateral hemispheres)
- Spinocerebellum (intermediate hemispheres and upper vermis)
- Vestibulocerebellum (lower vermis and flocculonodular lobe)
What is the function of the lateral hemispheres of the cerebellum (cerebrocerebellum)?
Motor planning for the extremities by influencing the lateral corticospinal tract
What is the function of the intermediate hemispheres of the cerebellum (spinocerebellum)?
Distal limb coordination by influencing the lateral corticospinal tract and rubrospinal tract
What is the function of the vermis and flocculonodular lobes (vestibulocerebellum)?
- Proximal and trunk muscle control from the vermis by influencing the medial motor system (anterior corticospinal tract, reticulospinal tract, vestibulospinal tract, tectospinal tract)
- Balance and vestibulo-ocular control from the flocculonodular lobe by influencing the medial longitudinal fasciculus
Name the deep cerebellar nuclei
- Dentate nucleus
- Emboliform nucleus
- Globose nucleus
- Fastigial nucleus
Where does the dentate nucleus receive input from?
- Receives input from lateral cerebellar hemispheres
- Active immediately before voluntary movement
Where does the emboliform nucleus and globose nucleus receive input from?
- Together they are called the interposed nuclei
- Receives input from intermediate cerebellar hemispheres
Where does the fastigial nucleus receive input from?
Receives input from the vermis and some input from the flocculonodular lobe
What are the three layers of the cerebellar cortex?
- Granule cell layer
- Purkinje cell layer
- Molecular cell layer
Describe the contents of the granule cell layer
- Small granule cells
- Golgi cells
- Glomeruli (axons and dendrites surrounded by a glial sheath)
Describe the contents of the purkinje cell layer
cell bodies of large, flask-shaped purkinje cells
Describe the contents of the molecular layer
- Unmyelinated granule cell axons (parallel fibers)
- Purkinje cell dendrites
- Interneurons (basket cells, stellate cells)
Which cells provide input to the cerebellar cortex?
- Mossy fibers (excitatory)
- Climbing fibers (excitatory)
Which cells carry output from the cerebellar cortex?
Purkinje cells (inhibitory)
Describe mossy fibers
- Input cells to the cerebellum
- Arise from numerous regions
- Synapse on granule cells within the glomerulus
Describe climbing fibers
- Input cells to the cerebellum
- Arise from the inferior olivary nucleus and crosses in the medulla to enter the contralateral inferior cerebellar peduncle
- Wrap around cell body and proximal dendrite of purkinje cells (1 fiber per 10 purkinje cells, purkinje cell is excited by climbing fiber)
Describe granule cells
- In cerebellar cortex
- Sends axons to the molecular layer which bifurcate and create the parallel fibers
- Parallel fibers run perpendicular to purkinje fibers and have numerous excitatory contacts with purkinje fibers
Describe purkinje cells
- Carries output from cerebellar cortex to cerebellar white matter
- Has inhibitory synapses on deep cerebellar nuclei and vestibular nuclei
- When purkinje cell in excited, it will send inhibitory signal
Describe basket cells and stellate cells
- Cells bodies are in the molecular layer
- Excited by parallel fibers of granule cells
- Cause lateral inhibition of purkinje cells (when cell is excited, inhibits purkinje cell next to it)
- Stellate cells terminate on purkinje dendrites and basket cells terminate on purkinje cell bodies
Describe golgi cells
- Cell bodies are in the granule layer
- Excited by parallel fibers of granule cells
- Feedback inhibition to granule cells (information from parallel fibers relayed back to granule cell as feedback)
- Axon terminals occupy glomeruli along with mossy fiber axon terminals and granule cell dendrites
What is the cerebellar glomerulus?
- Special region of complex synaptic interaction within the granule cell layer
- Can be visualized as small clearings among granule cells
- Contains axons and dendrites encapsulated in a glial sheath
- Axon terminals receive excitatory input from mossy fibers and inhibitory input from golgi cells
- Dendrites sends out signals to granule cells
What locations can the cerebellum receive input from?
- Almost all cortical areas
- Multiple sensory modalities (vestibular, auditory, visual, somatosensory)
- Brainstem nuclei
- Spinal cord
From which side of the body does the cerebellum receive input?
Ipsilateral
Describe the corticopontine fibers
- First part of the cerebellar input pathway from the cortex
- Carry information from frontal, parietal, temporal, and occipital cortex through the internal capsule and cerebral peduncles
- Synapse on ipsilateral pontine nuclei
Describe pontocerebellar fibers
- Second part of the cerebellar input pathway from the cortex
- Carries information from pontine nuclei, crosses midline, and enters the middle cerebellar peduncle and gives rise to mossy fibers
Describe the spinocerebellar pathway
- Cerebellar input pathway from the body
- Made up of 4 tracts (Dorsal Spinocerebellar, Cuneocerebellar, Ventral Spinocerebellar, and Rostral Spinocerebellar)
What are some characteristics of the dorsal spinocerebellar tract?
- Sends afferent information to the cerebellum about LE limb movements
- Pathway: LE proprioceptors > nucleus dorsalis of clark > ipsilateral inferior cerebellar peduncle
What are some characteristics of the cuneocerebellar tract?
- Sends afferent information to the cerebellum about UE and neck movement
- Pathway: UE proprioceptors > external cuneate nucleus > ipsilateral inferior cerebellar peduncle
What are some characteristics of the ventral spinocerebellar tract?
- Sends information to the cerebellum about activity of spinal cord interneurons for LEs
- Double-cross (remains ipsilateral)
- Pathway: LE interneurons > cross in ventral white commissure > cross with superior cerebellar peduncle
What are some characteristics of the rostral spinocerebellar tract?
- Sends information to the cerebellum about activity of spinal cord interneurons for UEs
- Pathway: UE interneurons > ipsilateral superior and inferior cerebellar peduncle
Where does the inferior olive receive inputs from?
- Red nucleus
- Cortex
- Brainstem nuclei
- Spinal cord
Describe vestibular inputs to the cerebellum
- There are primary (enter directly) and secondary (synapse to enter) vestibular neurons projecting to the cerebellum
- Enter via the juxtarestiform body along side inferior cerebellar peduncle
- Project to ipsilateral cerebellar vermis and flocculonodular lobe
Describe visual and auditory inputs to the cerebellum
- Inputs are relayed from brainstem nuclei
- Provide additional information about body position and motion
- Visual inputs to flocculus allow smooth control of pursuit eye movements
What is the juxtarestiform body?
- Part of the cerebellum that carries fibers in both directions between vestibular nuclei and the cerebellum
- Next to the inferior cerebellar peduncle
Describe cerebellar output from the lateral hemispheres
- Function: motor planning
- Projects to dentate nucleus and exits via the superior cerebellar peduncle
- Will decussate in the midbrain and project to the contralateral ventral lateral nucleus in the thalamus
- The VL nucleus projects to the motor cortex, premotor cortex, supplementary motor cortex, and parietal cortex to influence motor planning of the corticospinal systems
- Some fibers may also terminate in the rostral red nucleus after decussation and will then project to the inferior olive
Describe cerebellar output from the intermediate hemispheres
- Function: control of ongoing movement of distal extremities
- Projects to the interposed nuclei and exits via the superior cerebellar peduncle to then project to the contralateral ventral lateral nucleus in the thalamus
- VL nucleus projects to motor cortex, premotor cortex, and supplementary cortex area
- Some fibers terminate in caudal red nucleus after decussation and influence the rubrospinal tract
Describe cerebellar output from the vermis
- Function: influences trunk and proximal muscles through the medial motor pathways
- Projects to fastigial nucleus and exits via the superior cerebellar peduncle, the juxtarestiform body, or the uncinate fasciculus
Describe the cerebellar output pathway from the vermis that exits through the superior cerebellar peduncle
- Projects from peduncle to ventral lateral nucleus of the thalamus which will then project to the motor cortex
- Will influence the anterior corticospinal tract
- Some fibers terminate at the tectal area to influence the tectospinal tract
Describe the cerebellar output pathway from the vermis that exits through the juxtarestiform body
- Projects from juxtarestiform body to ipsilateral reticular formation and vestibular nuclei
- Influences reticulospinal tract and vestibulospinal tract
Describe the cerebellar output pathway from the vermis that exits through the uncinate fasciculus
Loops over the cerebellar peduncle and continues caudally via the contralateral juxtarestiform body to the contralateral vestibular nuclei
Describe the cerebellar output pathway from the flocculonodular lobes and inferior vermis
- Function: equilibrium and balance, eye movement
- Projects to vestibular nuclei
- Influences vestibulospinal tract
- Some fibers project to fastigial nucleus, in which case they project directly to upper cervical spine (the only time cerebellum or basal ganglia have direct contact with LMNs)
What becomes impaired if either the cerebellum or inferior olive are damaged?
- Error based learning
- Unable to adapt motor output
What role do climbing fibers play in motor learning?
- Fibers originate in the inferior olive, they wrap around the purkinje cell which sends output signals
- This wrapping can create powerful excitatory synapses that result in complex spikes
- Induces conditioning effect (elicits plastic change) on the synaptic activity of purkinje cells
What is a complex spike?
- An initial burst of Na+ followed by multiple smaller bursts of Na+
- Causes a opening of voltage gated Ca2+ channels
- Due to climbing fibers wrapping around purkinje cell
What gives vascular supply to the inferior 1/2 of the cerebellum, the inferior vermis, and the lateral medulla?
Posterior inferior cerebellar artery
What gives vascular supply to the superior 1/2 of cerebellum, deep cerebellar nuclei, superior vermis, superior cerebellar peduncle, and upper lateral pons?
Superior cerebellar artery
What gives vascular supply to the anterior strip of the cerebellum, the flocculus, middle cerebellar peduncle, and inferior lateral pons?
Anterior inferior cerebellar artery
What is ataxia?
Disordered contraction of agonist and antagonist muscles and a lack of normal coordination of movements at multiple joints
What is truncal ataxia?
- Wide-based, unsteady gait (lose balance towards side of lesion)
- Decreased sitting balance
- Associated in the lesions in the vermis
What is appendicular ataxia?
- Impaired coordination of limb movement
- Associated with lesions to the intermediate and lateral cerebellar hemispheres
What is dysrhythmia?
Abnormal rhythm and timing
What is dysmetria?
Abnormal undershoot or overshoot of target
What is dysdiadochokinesia?
Difficulty with rapid alternating movements
What is postural tremor?
Oscillation when actively holding a position
What it intention tremor?
Oscillation when moving in space toward an object
What is rebound?
Impaired ability to check (as in check reign) with sudden release of resistance
What is nystagmus?
Pupils beat unintentionally, may occur in direction of gaze or in a upward fashion
What is saccades?
Overshoot of undershoot a target with the eyes
What issue can arise during smooth pursuit if cerebellar dysfunction is present?
Jerky “saccadic” eye movement when following a target
What issues can arise in speech if cerebellar dysfunction is present?
Irregular fluctuations in volume and rate of speech
What is hypotonia?
Mild decrease in tone or reflexes
