02_Cerebellum Flashcards
Why does electrical stimulation of the cerebellum not cause sensation and rarely cause movement?
like the basal ganglia, cerebellar neurons have no direct connections to spinal cord ventral horn motoneurons
From where and what type of input does the cerebellum receive?
-The cerebellum receives continuously updated information from the higher brain centers on the intended motor program. -It also receives continuous sensory information from several sensory modalities (vestibular and visual systems; peripheral muscle spindles and tendon organs) regarding actual movement including body position, rate of movement, muscle length and muscle force.
Cerebellar diseases and disorders (e.g. tumor, infarction, degeneration due to chronic alcoholism) produce what types of conditions (3 cardinal signs of cerebellar disease/disorder)?
-ataxia (incoordination of movements without paralysis) -hypotonia to passive stretch -intention tremors (loss of muscle synergy)
What are the four overall functions of the cerebellum?
-Compare actual and intended movements -Aid the cerebral cortex in planning sequential movements -Participate in the process of learning coordinated movements -Produce a synergy of movement
Cerebellar function (1 of 4) Comparing actual and intended movements-Description
Then when necessary, send appropriate corrective signals to the motor system to increase or decrease the levels of activation of specific muscle groups to make corrective movements.
Cerebellar function (2 of 4) Aid the cerebral cortex in planning sequential movements-Description
While a movement is on-going the next sequential movement is planned a fraction of a second in advance, thus enabling movements to progress smoothly.
Cerebellar function (3 of 4) Participate in the process of learning coordinated movements. -Description
If a movement error is made, the cerebellar circuitry “learns” to adjust its output to produce a stronger or weaker movement, as appropriate, the next time the movement is performed.
Cerebellar function (4 of 4) Produce a synergy of movement. -Description
To produce smooth, coordinated muscle activation.
Anatomy of Cerebellum: Anterior lobe
- Medial border is the vermis, - Separated from the posterior lobe by the Primary Fissure
Anatomy of Cerebellum: Posterior lobe
- Separated from the anterior lobe by the Primary Fissure - Separated from the Flocculonodular lobe by the Posterolateral Fissure
Anatomy of Cerebellum: Flocculonodular lobe
- Can be observed on the ventral surface of the cerebellum - consists of 2 Flocculi (flocculus is singular) and 1 nodulus - Separated from the posterior lobe by the Posterolateral Fissure
Cerebellar tonsils
These lie lateral to the nodulus and medial to the cerebellar peduncles.
Anatomy of Cerebellum: Deep Cerebellar Structures (Nuclei)
- Dentate – most lateral, projection neurons of the cerebrocerebellum 2. Globose and Emboliform (Interposed) Nuclei – intermediate, projection neurons of the spinocerebellum. 3. Fastigial Nucleus – medial, projection neurons of the vestibulocerebellum.
Anatomy of Cerebellum: Cerebellar White Matter Pathways
- Gross Structures (Peduncles) 2. Axons
Where is the major output pathway of the cerebellum located?
Superior Cerebellar Peduncle – mainly axons leaving the cerebellum, “output pathway”
Where is the major input pathway of the cerebellum located?
Middle Cerebellar Peduncle – mainly axons entering the cerebellum, “input pathway”
Where is the major input & output (combined) pathway of the cerebellum located?
Inferior Cerebellar Peduncle – mainly axons entering the cerebellum, “input pathway and output”
Describe the cortico-ponto-cerebellar tract
The ponto-cerebellar fibers originate from nuclei in the pons that receive input from the frontal, parietal, temporal, and occipital lobes of the cerebral cortex. The enter the cerebellum via the middle cerebellar peduncle.
Describe the dorsal (posterior) spinocerebellar tract and ventral (anterior) spinocerebellar tract
a. Axons of the DSCT arising from cell bodies in the spinal cord (Clarke’s column) enter the cerebellum via the inferior peduncle. The spinal cord neurons receive input from peripheral proprioceptors in the trunk and lower extremities b. Axons arising from cell bodies in the spinal cord enter the cerebellum via the superior cerebellar peduncle.
Describe the spinocuneocerebellar tract and rostral spinocerebellar tract
a. Axons arise from neurons in the cuneate nuclei enter the cerebellum via the inferior cerebellar peduncle. Neurons in the cuneate nucleus receive input from peripheral proprioceptors in the upper trunk and upper extremities b. Axons arising from neurons in the cervical spinal cord enter the cerebellum via the inferior and superior cerebellar peduncles.
A subset of vestibular nerve axons enter the cerebellum via which peduncle?
inferior cerebellar peduncle
What are the input sources for climbing fibers?
cortex, basal ganglia, red nucleus and other extrapyramidal pathways
Which fibers play an important role in error correction and timing of motor tasks in the cerebellum?
Climbing fibers (they arise from cell bodies in the inferior olivary nucleus)
Through which peduncle do climbing fibers pass as they enter the cerebellum?
Inferior cerebellar peduncle
What are the two input and one output systems of the cerebellar cortex?
dual-input system (mossy and climbing fibers)
single-output system (Purkinje cell axons)
The cerebellar cortex consists of how many layers and cell types?
3 layers (molecular, Purkinje cell and Granular cell layers) with 5 cell types (stellate, basket, granule, Purkinje and Golgi cells)
Which cells are associated with the molecular layer of the cerebellar cortex?
A. stellate cells B. basket cells C. parallel fibers (axons of granule cells) D. dendrites of Purkinje cells
Which cells are associated with the Purkinje cell layer of the cerebellar cortex?
Purkinje cell bodies
Which cells are associated with the Granular cell layer of the cerebellar cortex?
A. granule cells B. Golgi cells C. glomerulus
What are the three functionally significant regions of the cerebellar corex?
- vestibulocerebellum 2. spinocerebellum 3. cerebrocerebellum
Where is the location of the vestibulocerebellum?
Also known as the flocculonodular lobe and the archicerebellum, phylogenetically the oldest part of the cerebellum.
What are the inputs for the vestibulocerebellum?
from the inner ear and visual system via the inferior cerebellar peduncle
What are the outputs for the vestibulocerebellum?
via the fastigial nucleus through the superior and inferior cerebellar peduncles to the vestibular nuclei
What are the functions of the vestibulocerebellum?
- Maintains equilibrium and control of axial (proximal) muscles to maintain balance 2. Coordinates eye and head movements (VOR) 3. Maintains upright posture.
Where is the location of the spinocerebellum?
It is the intermediate region, including part of the vermis and the cerebellar cortices just lateral to the vermis. This region carries out the “comparator function” of the cerebellum.
What are the inputs for the spinocerebellum?
from the spinal cord via the superior and inferior cerebellar peduncle
What are the outputs for the spinocerebellum?
via the globose and emboliform (interposed) nuclei through the superior cerebellar peduncle to the reticular formation, contralateral thalamus, and contralateral red nucleus
What are the functions of the spinocerebellum?
- Contributes to modulation and control of the execution of a movement by providing corrections both to the command centers in the sensorimotor cortex and to the motoneurons in the spinal cord. (control of ongoing movements) 2. Regulates muscle tone by influence of descending pathways on gamma motoneurons that (innervate muscle spindles).
Where is the location of the cerebrocerebellum?
Also called the neocerebellum, it is the phylogenetically the newest cerebellar area and consists of the lateral cerebellar cortices.
What are the inputs for the cerebrocerebellum?
from the cerebral cortex via the middle cerebellar peduncle
What are the outputs for the cerebrocerebellum?
via the dentate nucleus through the superior cerebellar peduncle to the contralateral thalamus
What is the function of the cerebrocerebellum?
Formulation of motor plans and initiation of movements.
What are signs of cerebellar dysfunction?
Hypotonia, disequilibrium and dyssynergia (including dysarthria, dystaxia, dysmetria, dysdiadochokinesia, nystagmus, decomposition of movement, rebound, nausea and vomiting)
Signs of cerebral dysfunction-hypotonia
floppy, loose-jointed, rag-doll appearance with pendular reflexes; patient appears inebriated
Signs of cerebral dysfunction-disequilibrium
loss of balance, characterized by gait and trunk dystaxia
Signs of cerebral dysfunction-dyssynergia
loss of coordinated muscle activity that includes dysarthria, dystaxia, dysmetria, dysdiadochokinesia, nystagmus, decomposition of movement, rebound, nausea and vomiting
Signs of cerebral dysfunction (subset of dyssynergia)-dysarthria
difficulty speaking; slurred or scanning speech
Signs of cerebral dysfunction (subset of dyssynergia)-dystaxia (ataxia)
lack of coordination in the execution of voluntary movement (e.g., gait, trunk - truncal, and leg/arm ataxia - appendicular)
Signs of cerebral dysfunction (subset of dyssynergia)-dysmetria
inability to arrest muscular movement at the desired point (also called past-pointing)
Signs of cerebral dysfunction (subset of dyssynergia)-dysdiadochokinesia?
inability to perform rapid alternating movements (e.g., rapid supination and pronation)
Signs of cerebral dysfunction (subset of dyssynergia)-nystagmus
a form of dystaxia consisting of to-and-fro eye movements (ocular dysmetria)
Signs of cerebral dysfunction (subset of dyssynergia)-decomposition of movement
consists of breaking down a smooth muscle act into a number of jerky awkward component parts
Signs of cerebral dysfunction (subset of dyssynergia)-rebound
or lack of check: results from the inability to adjust to changes in muscle tension (test by having the subject flex his forearm at the elbow against resistance; sudden release results in the forearm striking the subject’s chest).
Signs of cerebral dysfunction (subset of dyssynergia)-fatal gastroenteritis
Nausea and Vomiting: Associated with cerebellar hemorrhages and lesions to the vetibulocerebellum. Sometimes referred to as “fatal gastroenteritis”.
Signs of cerebral dysfunction (subset of dysmetria)-intention tremor
occurs during a voluntary movement (a type of dysmetria); gets worse as subject approaches his target.
