Cerebellum- Wilson Flashcards
What are interesting facts about cerebellum?
- means little brain
- constitutes only 10% of the brain’s volume
- contains over 50% of all neurons
Is the cerebellum a sensory or motor structure? What is the embryology of the cerebellum?
a motor structure
-you don’t have any cerebellum (insult)
lesion of cerebellum could result in loss of balance and not movement
the cerebellum comes from the alar plate (so embryonically speaking it is coming from sensory primordium)
What does the cerebellum receive?
all sensory input from essentially all sensory receptors
What is the major output of the cerebellum?
is the ventral lateral nucleus of the thalamus which projects to areas 4 and 6 of the cortex
Why do people not think of cerebellum as sensory?
if there is lesion you don’t get loss of sensory innervation but you do get lack of coordination in body movements
-no sensory information, transmitted to the cerebellum reaches consciousness
How do you control a motor system?
1) Feed-Forward Control
2) Feedback Control
Visual reflex is how fast?
at least 200 m/s
Describe the Feed-Forward Control
for a behavior or activity, you set an initial motor activity and don’t change it; if you don’t make the right motor program then this system misses its mark (point of no return)
- . starting position
- (anticipated) target position
- properly timed sequence of muscle contractions of appropriate velocities/strengths
Feedback Control
-constantly developing feed forward control
and monitoring how the program is and adjusting it according to how far you are off the mark (you have unexpected changes,v the world is constantly changing)
What happens if there are unanticipated perturbations in the feed forward motor response because of program error and/or changes in the environment and/or target position?
you will not reach your goal
Pre central gyrus have close connections with the primary motor cortex. Explain.
Neural activity during flexion of the arm to a target
most of the signals come from the cerebellum (the primary generator to an adjustment due to unexpected changes)
somatosensory gyrus has close links with the primary motor cortex
Cerebellum is involved in generating the metric/numbers that are necessary to make the movement work.
The cerebellum is a comparator. Explain.
it compares the intended movement with the actual performance
if intention and performance match the cerebellum can go to sleep
if there is no match, the target is off, the cerebellum has to make it match, make the adjustment
Cerebellum must have what factors to make an adjustment?
- corollary discharge: cerebellum must have information about the intended movement (the movement you expect to make); gets corollary discharge or internal feedback or efferent copy for the intended movement
- reafference or external (sensory) feedback for the actual movement response; as you’re executing a movement the cerebellum is monitoring that movement and getting feedback to see if there needs to be any adjustments
The sensory information that the cerebellum receives is used for what?
- autonomic regulation and control of motor function (including posture)
- for the limbs and the axial musculature
Through comparisons of external and internal feedback signals, the cerebellum is able to what?
- correct ongoing movements when they deviate from the intended course (efferent copy)
- modify motor programs in the CNS so that future movements attain their goals, ie. greatly involved in motor learning
The cerebellum receives what external (sensory) feedback?
- vestibular
a. primary afferents: (ipsilateral)
b. vestibulocerebellar: vestibular nuclei (bilateral) - spinal cord
a. dorsal spinocerebellar tract
b. ventral spinal cerebellar tract
c. cuneocerebellar tract
d. rostrospinocerebellar tract
What is the internal feedback (efferent copy) of the cerebellum?
NEED to KNOW
- cerebral cortex
a. pontocerebellar (contralateral)***
-cortex reaches the cerebellum through the PONS
What is the major output of the cerebellum?
cerebellum goes to the motor systems of the brain: primary and lateral premotor cortex
cerebellum structure
- forms a roof over the 4th ventricle
- divided into two regions: vermis and hemispheres
- vermis is the oldest part of the cerebellum
The cerebellar tonsils are clinically important when there is a increase in intracranial pressure (epidural hematoma). Explain.
- tonsils are located on the posterior lobe of cerebellum
- as they herniate through the foramen magnum they put pressure on the medulla thus putting pressure on the cardio and pulmonary centers
They can:
herniate through the foramen magnum
compress the medulla
cause death
The surface of the cerebellum is extensively folded by what?
(largely) transversely running folia
The cerebellum is composed of what 3 major lobes?
anterior lobe
posterior lobe
flocculonodular lobe
What separates the anterior and posterior lobes?
primary fissure
What separates the focculonodular and posterior lobes?
posterolateral Fissure
What type of fibers form the arbor vitae ‘tree of life’?
white matter
What organization have functional and clinical significance?
flocculonodular organization
Each hemisphere is composed of an intermediate (paravermal) and lateral part.
These parts represent distinct functional subdivisions with distinct connections.
????
What is the 3 functional divisions of the cerebellum?
- Vestibulocerebellum
- Spinocerebellum:
has direct connections with the spinal cord - Cerebrocerebellum
has massive connections with the cortex via the basilar pons ?????
What are the inputs into the cerebellum?
- corticopontine: the lateral hemisphere is primarily connected to the pons; receives cortical input through the corticopontine and pontocerebellar system
- spinal (limbs)
- trigeminal (and trunk: located in the vermis
- vestibular: has a lot of primary afferents from vestibular nuclei and it even goes into the spinocerebellum region in the vermis
- visual and auditory: are located in the vermis
spinocerebellar tract projects primarily into the vermis and intermediate lobe
Describe the Somatotopic Organization of Inputs to the Cerebellum.
Spinocerebellum
- intermediate zone: sensory input from the limbs
- medial zone: vermis is related to the control of the axial musculature
Cerebrocerebellar
-lateral hemisphere
Vestibulocerebellum
- flocculus
- nodulus
The descending motor systems are organized into what two major fiber columns?
Lateral Descending System
(limb muscles)
1. lateral corticospinal
2. rubospinal
Medial (Anterior) Descending System (axial muscles)--these are all BILATERAL input 1. anterior corticospinal 2. vestibulospinal 3. reticulospinal
What is the cerebellar output for the spinocerebellum, cerebrocerebellum, and vestibulocerebellum?
spinocerebellum: axial (medial descending system) and limb (lateral descending system) musculature for motor execution
cerebrocerebellum: to areas 4 and 6 for motor planning and coordination
vestibulocerebellum: for balance and eye movements
How is the cerebellum connected to the brainstem?
3 cerebellar peduncles: large axon tracts
Describe the 3 cerebellar peduncles.
-superior cerebellar peduncle (connects to cerebellum to the midbrain); for the most part the OUTPUT of the cerebellum
In general, the cerebellum sends its efferents (…to cortex) through the superior cerebellar peduncle.
-middle cerebellar peduncle
(connects cerebellum to the pons); cortical INPUT through the basilar pons
-inferior cerebellar peduncle
(connects the cerebellum to the medulla); mainly INPUT
In general, the cerebellum receives its afferents through the:
- inferior cerebellar peduncle (spinal cord & medulla)
- middle cerebellar peduncle (pons - cortical input)
Know the reference slide
The Inputs and Outputs of the Cerebellum Pass Through the Peduncles
Have to know:
-Middle Peduncle: pontocerebellar (contralateral)*** INPUT!!
Superior Peduncle outputs: a. cerebellothalamic b. cerbellorubal input: 1. ventrospinocerebellar
rubal is the red nucleus (the other target of outputs to the cerebellum)?????
The cerebellum has gray matter of what two types?
- has a cortex (which is gray matter) which is organized into 3 distinct layers:
1. molecular layer
2. Purkinje cell layer
3. granular layer
-there are 4 deep cerebellar nuclei (output):
gray matter embedded in the white matter deep to the cerebellum cortex
- fastigial
- emboliform
- globose
- dentate
emboliform and globose are the interposed nuclei (won’t ask about this)
What are the 5 types of neurosn found in the cerebellum?
1) granular cells: found in the deepest layer (granular cell layer); their axons run to the surface and split running parallel to the folia
2: Purkinje cells: project long inhibitory axons that go to the deep cerebellar nuclei
- stellate cells
- basket cells
- golgi cells
will only ask about the 1st two layers and not 3-5 which are all inhibitory
Describe Purkinje cell.
- has a fan shaped dendritic organization that have a perpendicular orientation to the folia
- looks like a Chinese fan????
Purkinje cells project to the deep cerebellar nuclei* and are the sole (inhibitory) output of the cortex.
SO ALL OUTPUT (inhibitory) from the cerebellar cortex goes through the purkinje fibers
exception is the Purkinje cells in the flocculonodular lobe which project t o the 4 vestibular nuclei which can be thought of as the deep cerebellar nuclei
What are the three types of afferents that come into the cerebellum/ conduct nerve impulses to the cerebellum?
- aminergic fibers (modulatory)
- they change the excitability of different modules of the cerebellum
- cerebellum can go to sleep if it is not doing anything - mossy fibers (excitatory)
- climbing fiber (excitatory)
Aminergic fibers come from what sources and where do they terminate?
Two sources
- raphe nuclei: serotonin
- locus coeruleus: norepinephrine
Fibers terminate in all layers of cortex.
They modulate cerebellar excitability.
REFERENCE SLIDE
Climbing fibers come from what sources and where do they terminate?
- come from inferior olivary complex (ONLY ONE SOURCE) ; axons from these cells go to the contralateral side to the cerebellum
- climbing fibers wrap around the soma and climb the dendrites of Purkinje cells making numerous excitatory contacts
- climbing fiber terminations looks just like the dendritic tree of the Purkinje
very close relationship between axon termination of the climbing fibers and the purkinje neurons; they are not superimposed
Each Purkinje cells receives input from how many climbing fibers? How many synapses will climbing fibers make on Purkinje cells?
Each Purkinje cells receives input from 1 climbing fiber.
a single climbing fiber synapses on 1-10 Purkinje cells
climbing fibers run perpendicular to the folia
climbing fibers provide powerful excitatory and low frequency input (1 spike/s)
climbing fiber input is “all-or-nothing,” (ie., a single action potential in a climbing fiber evokes a complex spike in the Purkinje cell)
The Climbing fiber input into a Purkinje cells is one of the most powerful in the nervous system. Explain this.
A single action potential in a climbing fiber evokes a ‘complex spike’ and a large Ca2+ influx.
they underlie the plasticity (cerebellar learning is somehow involved with climbing fibers and the use of calcium to modify synapses)
Most climbing fibers also send collaterals to which nuclei?
the deep cerebellar nuclei
What is the major type of input into the cerebellum?
Mossy fibers
-all other input coming from the pons, brainstem, spinal cord, reticular etc. form mossy fiber
it is the MAJOR INPUT to the cerebellum
Describe Mossy fibers.
- they synapse with granular cells in the granular cell layer that will then synapse on Purkinje cells
- has to be a massive amount of these fibers firing at the same time at a high frequency
- provides a high frequency (50-100 spikes/s), excitatory input that must be summated to cause spiking of the Purkinje cells
Why do you need summation of Mossy fibers?
- to excite purkinje cells
- input coming from a single parallel Mossy fiber is minor
- Simple Spike will be evoked by spatiotemporal summation of Mossy Inputs
How do Mossy fibers indirectly influence many Purkinje cells? What is their type of influence
When you have intersections of mossy and climbing fiber, what happens?
Mossy fibers enter into the granular cell layer then synapse onto the granule cells. The granule cells axons will then go up into the molecular layer and form parallel fibers that will run through many Purkinje cells.
Granule cells are EXCITATORY
-there is coincidence which is what the cerebellum will start processing
????
- Climbing fibers are perpendicular to the folia.
- Granule cell axons split parallel to folia.
Inhibitory (gabanergeric) interneurons integrate the excitatory inputs into Punkinji cells. Where are these cells found?
These cells are found in the granular and molecular layers.
What are the 3 deep cerebellar nuclei?
- fastigial: closest to the nuclei; directly underneath the vermis
- interposed nuclei
- dentate nuclei: largest of the 3
Purkinje cells go where????
???
vermis: fastigial
intermediate: interposed
cerebrocerebellum: dentate
flocculonodular lobe go to all four vestibular nuclei
What is the largest part of the cerebellum?
corticocerebellum
1. afferents 2. efferents 3. lesions
The cerebellum receives its MAJOR input from the cortex which is relayed through the pons.
The corticopontine tract originates primarily from where?
- premotor cortex (area 6)
- motor cortex (area 4)
- somatosensory cortex (areas 3, 1, 2)
- higher order somatosensory cortex (area 5)
Compare the size of the corticopontine tract to the corticospinal tract.
CPT: 10 million fibers
CST: 1 million fibers
Where are the corticopontine fibers located in the crus cerebri and where to they terminate?
Corticopontine fibers pass through the cerebral peduncle on either side of the corticospinal tract
Corticopontine fibers terminate in nuclei found in the basile pons
pontine nuclei form the white (fiber stain) matter laced between fiber tracts
Where do the corticopontine fibers cross?
Pontocerebellar fibers cross in the pons and reach the cerebellum via the middle cerebellar peduncle
Efferents from pontine nuclei form mossy fibers terminating primarily in the contralateral cerebrocerebellum
???????
Principle Efferent Connection of the DENTATE Nucleus*
- decussate go to the VL of thalamus then to area 4 and 6
- A small portion of dentate efferents synapse in the red nucleus (parvocellular part) before being relayed to thalamus & cortex
???
Where will the contralateral fibers synapse?
Cerebellar signs are usually ipsilateral because the decussations of the corticopontine-cerebellar tract and the cerebellothalamic tract .
Principle Efferent Connections of the INTERPOSED Nucleus To the Cortex & Red Nucleus
-they go to the magnocellular part of the nucleus of the rubrospinal tract
Where do the efferents from the fastigial nucleus go and what are their effects?
1) via inferior cerebellar peduncle
2) targets
a. vestibular nuclei (vestibulospinal pathways)
b. reticular formation (reticulospinal pathways)
3) effects
a. posture
b. automatic movements (e.g., locomotion)
What occurs with lesions of the cerebellar cortex? What is the triad of cerebellar dysfunction?
- there are delays of initiation of movement
1) Hypotonia (loss of cerebellar facilitation of motor cortex)
2) Disequilibrium (loss of balance)
a. trunk ataxia
b. limb ataxia
3) Dyssynergia (loss of coordinated muscle activity)
a. ataxia
b. dysmetria: when you try to touch your nose you either under or over shoot
c. decomposition or fragmentation of movement
d. dysarthria (scanning or robotic speech)
e. dysdiadochokinesia (pronation/supination Dr. Graf talked about)
f. intentional tremor
g. nystagmus
Dystonia, hyper-reflexia and clonus
????
Describe ‘Flocculonodular’ & ‘Anterior Lobe’ Syndromes”* (disturbances in equilibrium).
seen in alcoholics where they have disequilibrium
gait ataxia: limbs are spread apart and they teetering back and forth as though they are drunk
Patient teeters back, forth & sideways
Wide-based gait (gait ataxia).
- degeneration of the anterior lobe is characteristic of alcoholics and thiamine deficiency
?????
Describe the finger-to-nose test.
Patient cannot direct finger accurately to nose with eyes close.
a. hypometria: under measured b. hypermetria: over measured
Patient cannot rapidly repeat
alternating movements
(adiadochokinesia).
Patients with vermal damage can be differentiated from patients with lesion of the dorsal columns by the Romberg Sign. What is the romberg sign?
Vermal lesion: patients loose balance with their eyes open falling towards the lesion.
Dorsal column lesion – patients loose balance with their eyes closed; often occurs in syphillis
What is Fredrick’s Ataxia?
What are symptoms of it?
An inherited autosomal recessive disease resulting in low levels of frataxin required for mitochondrial electron transport.
Symptoms:
a) muscle weakness in extremities
b) ataxia and loss of coordination and dysmetria
c) dysarthria and dysphagia
The cerebellum is involved in what type of motor learning?
error-based motor learning
