14 - Cerebellum Flashcards
Cerebellum function
- The cerebellum’s function is to correlate cerebral instructions with information from muscles and provide corrective feedback to the motor cortex.
- Specifically, it’s role is to calculate velocity, duration, force and timing of muscle action to ensure body movements are carried out with precision.
What else is the cerebellum involved in?
- Related roles of the cerebellum are integrating vestibular information with proprioceptive feedback to maintain balance and upright posture at rest and during locomotion, and integrating eye and head movements.
- The cerebellum is also involved in “procedural memory”, complex motor learning such as riding a bike, playing a piano.
Three lobes of the cerebellum
Anterior lobe
Posterior lobe
Flocculonodular lobe
What separates the anterior and posterior lobes?
Primary fissure
What separates the two hemispheres of the cerebellum?
Vermis
There are three functional areas of the cerebellum. What are they?
1 - Vestibulocerebellum
2 - Spinocerebellum
3 - Cerebrocerebellum
Where is the vestibulocerebellum located?
Flocculonudular lobe
What is the function of the vestibulocerebellum?
Posture, balance, eye/head movement
What is the input to the vestibulocerebellum?
Vestibular system (inner ear and nucleus)
What is the output of the vestibulocerebellum?
Vestibular nuclei
Vestibulospinal tracts
Medial longitudinal fasiculus
What is the function of the medial longitudinal fasiculus output of the vestibulocerebellum?
It integrates CN III, CN IV and CN VI in order to coordinate eye/head movement
Which deep cerebellar nuclei are associated with the vestibulocerebellum?
The vestibular nucleus
Where is the spinocerebellum located?
In the vermal/paravermal areas
What is the function of the spinocerebellum?
Muscle tone and adjusting movements of axial trunk and proximal limbs
What is the input to the spinocerebellum?
Dorsal and ventral spinocerebellar tracts
Cuneocerebellar
Trigeminocerebellar
What is the function of the trigeminocerebellar input to the spinocerebellum?
Proprioception
What is the output of the spinocerebellum?
Vestibulospinal and reticulospinal tracts
What deep nuclei of the cerebellum are associated with the spinocerebellum?
Fastigial and interposed nuclei
The interposed nucleus consists of the globose and emboliform nuclei
Where is the cerebrocerebellum located?
In the lateral hemispheres
What is the function of the cerebrocerebellum?
Percise control of executed movements
Timing, duration, force, velocity and trajectory of movements, of extremities, especially hands and fingers.
What is the input to the cerebrocerebellum?
Corticopontocerebellar tracts (for motor cortex intent) Olivocerebellar tract
What is the output of the cerebrocerebellum?
Dentorubrothalamic tract (for feedback to motor cortex via VL nuclei of thalamus)
Rubrospinal tracts
Which deep cerebellar nuclei are associated with the cerebrocerebellum?
Denate nuclei
What fibers do deep nuclei of the cerebellum receive?
Purkinje fibers
What role do deep nuclei play in the cerebellum?
They are the major output of the cerebellum
Match the deep nuclei of the cerebellum to their location in the cerebellum and what functional division they are part of
Fastigial nucleus
- vermis
- spinocerebellar
Interposed nuclei
- paravermal
- spinocerebellar
Dentate nucleus
- hemispheres
- cerebrocerebellum
Vestibular nuclei
- flocculonodular lobe
- vestibulocerebellum
All the deep nuclei of the cerebellum have one thing in common… What is it?
They all send collaterals back to the cerebellar cortex
Are the purkinje cells excitatory or inhibitory on deep cerebellar nuclei?
ALWAYS INHIBITORY
What is the climbing fiber system?
The climbing fiber system consists of the olivocerebellar tract
The climbing fiber system synapses on purkinje cells. What type of synapse and what is the ratio?
- Excitatory synapses
- One to one ratio
What is the mossy fiber system?
The mossy fiber system includes all other inputs to the cerebellar cortex
What do the climbing fiber system and the mossy fiber system have in common?
They BOTH send excitatory collaterals to deep nuclei
How would you summarize the deep cerebellar nuclei output?
G. Deep cerebellar nuclei output is a product of excitatory climbing and mossy fibers and inhibitory Purkinje fiber activity.
What is the inferior olivary nucleus?
It is a nucleus of the cerebellum that extends from the inferior olive to Purkinje cells and is involved in the following processes:
- Internal clock
- Procedural learning of motor skills
- Adaptive learning
- Corrective action taken by motor cortex
An example of this would be “practice makes perfect” when learning to do a skilled movement such as playing the guitar
What are peduncles?
Attachments of the cerebellum to the brainstem that serve as pathways
They provide pathways for input ad output to the cerebellum
There are three peduncles of the cerebellum - what are they?
1 - Superior peduncle
2 - Middle peduncle
3 - Inferior peduncle
Superior peduncle
Superior peduncle- connects the cerebellum with the midbrain
Major output to the cerebrum
Specifically sends information to the cerebral motor cortex
Middle peduncle
Middle peduncle- connects the cerebellum with the pons
Major input into the cerebellum
The middle peduncle is INPUT ONLY and the input comes from the cortiopontocerebellar tract
Inferior peduncle
Inferior peduncle- connects the cerebellum with the medulla
Both input and output are present here
Ataxia
Ataxia – abnormal gait/stance and abnormal control of voluntary motions, caused by a hemispheric cerebellar lesion
Dysmetria
Dysmetria – inability to estimate the distance between a moving body part and the target
Dysdiadochokinesia
Dysdiadochokinesia – inability to carry out rapid, alternating movements regularly
Nystagmus
Nystagmus – uncoordinated activity of the ocular muscles, resulting in eye deviation towards the side of the lesion
Does the motor cortex have unilateral or bilateral connections with the cerebellar hemispheres?
Unilateral - The motor cortex has contralateral connections with the cerebellar hemispheres
What about the connections between the cerebellum and the spinal cord/brainstem?
These connections are UNCROSSED
So when there is a lesion in the cerebellum, what will we see?
Lesions of the cerebellum typically show ipsilateral (same-sided) signs and symptoms
What muscles could be paralyzed from a cerebellum lesion?
NONE
Since no cerebellar neurons have direct control of any muscles, there is NO PARALYSIS
Case 13
A 72-year-old woman developed sudden severe vertigo about 5 hours prior to presentation in the emergency room. The vertigo has persisted and remained severe. She became nauseated and vomited a few times. She has not been able to walk, and cannot even sit on the side of the bed without falling over. There was initially some double vision but this has since resolved. She complains that her left arm is “weak” and heavy. Her speech is mildly slurred. She feels that she is being pulled to the left when she attempts to stand or sit up. Exam shows mild dysarthria (slurred speech), but language function is normal. Bilateral end gaze nystagmus is present, which is much more prominent toward the left. Facial strength and sensation is normal. Despite the patient’s complaint, exam shows strength throughout to be normal. However, there is dysmetria and ataxia involving the left arm, but the right arm is normal. The patient cannot stand or even sit up in bed on her own. Sensation is normal throughout. Head CT in the emergency room was normal.
