Lecture 12: Contributions of Cerebellum & Basal Nuclei to Motor Function I Flashcards
What does the primary motor cortex (area 4) signal?
Motor neurons to contract skeletal muscle fibers.
What tract does the primary motor cortex signal via?
Via the corticospinal (pyramidal tract) tract.
What are the executed commands of the primary motor cortex preceded by?
Extensive processing by cerebellum and basal nuclei.
What does the premotor cortex (area 6) plan?
Movements based on sensory and visual cues.
What does the supplementary motor area (area 6) function to do?
Retrieves and coordinates memorized motor sequences.
Which cortex retrieves and coordinates memorized motor sequences?
supplementary motor area (area 6)
Which cortex plans movements based on sensory and visual cues?
pre-motor cortex (area 6)
Which cortex signals motor neurons to contract skeletal muscle fibers?
primary motor cortex (area 4)
Which cortex provides most of the activating signals to the spinal cord?
motor cortex system
True or False:
Cord patterns are mainly determined by heredity and are “hard wired”.
True
What does the motor cortex system issue?
Sequential and parallel commands that initiate various cord patterns.
List basic functions of the cerebellum.
- NOT essential for locomotion
- helps sequence motor activities
- monitors and makes corrective adjustments to motor activities while they are being executed
- compares actual movements with intended movements
- aids cortex in planning next sequential movement
- learns by its mistakes
- functions with spinal cord to enhance the stretch reflex
- functions with brain stem to make postural movements
- functions with cerebral cortex to provide accessory motor functions
- turns on antagonist at appropriate time
- helps program muscle contraction in advance
- functions mainly when muscle movements have to be rapid
What does the cerebellum play a major role in?
Timing of motor activities and in rapid, smooth progression from one muscle movement to the next.
What does removal of the cerebellum cause?
Body movements to become highly abnormal.
True or False:
Electrical excitation of the cerebellum does not cause any conscious sensation and rarely causes any motor movement.
True
What 3 lobes is the cerebellum anatomically divided into?
> Anterior Lobe
Posterior Lobe
Flocculonodular Lobe (associated with vestibular system)
What are the two hemispheres of the cerebellum separated by?
vermis
each hemisphere is divided into an intermediate zone and a lateral zone
What zones are the two hemispheres of the cerebellum divided into?
intermediate zone and lateral zone
What lobe of the cerebellum is evolutionarily the oldest?
flocculonodular lobe
What and where is the vermis; with what functions is it associated?
> the vermis separates the hemispheres of the cerebellum
> vermis -> location for control functions for muscle movements of the axial body, neck, shoulders, and hips.
What does the intermediate zone control?
Concerned with controlling muscle contractions in the distal portions of the upper and lower limbs, especially hands, feet, fingers, and toes.
What is the lateral zone associated with?
Associated with cerebral cortex with planning of sequential motor movements.
Does the cerebellar cortex have 6 layers?
No - only 3
What are the characteristics of the cortex of the cerebellum?
- like the cerebral cortex, this is gray matter and consists of multiple layers of cells, dendrites, and synapses.
- consists of transversely arranged narrow gyri called folia
What do the intracerebellar nuclei of the cerebellum make up?
Make up an inner layer of gray matter and include the following pairs of nuclei: > dentate > emboliform > globose > fastigial
What would lesions in the dentate nuclei, emboliform nuclei, and globose nuclei cause?
extremity ataxia
ataxia is abnormal movements of the limb, especially distal part of limb
What would a lesion in the fastigial nuclei cause?
trunk ataxia
Where do fibers from the dentate nuclei, emboliform nuclei, and globose nuclei project to?
red nucleus
Which intracerebellar nuclei are related to limb musculature and fine manipulative movements?
- dentate nuclei
- emboliform nuclei
- globose nuclei
Where do fibers from the fastigial nuclei project to?
- reticular formation
- vestibular nuclei
Which intracerebellar nuclei is related to postural activity and limb movements via reticulospinal and vestibulospinal tracts (balance and equilibrium)?
- fastigial nuclei
Which cells make up the cerebellar cortex?
> granular cells
golgi cells
basket cells
stellate cells
Which two cell types of the cerebellar cortex provide lateral inhibition on adjacent Purkinje cells to provide damping?
- basket cells
- stellate cells
What is the only cell type in the cerebellar cortex that is excitatory?
granular cells
What is the only cell type in the cerebellar cortex that is excitatory?
granular cells
What do axons from granular cells form?
Axons from parallel fibers in cortex (excitatory)
Where do golgi cells project from and to?
From parallel fibers to granular cell bodies (inhibitory)
Where do basket cells project from and to?
From parallel fibers to Purkinje axon hillock (inhibitory)
Where do stellate cells project from and to?
From parallel fibers to Purkinje dendrites (inhibitory)
What are the three layers of the cerebellar cortex?
- Granular Layer
- Purkinje Cell Layer
- Molecular Layer
Which layer of the cerebellar cortex is the innermost layer?
Granular Layer
Which layer of the cerebellar cortex is the middle layer?
Purkinje Cell Layer
Which layer of the cerebellar cortex is the outermost layer?
Molecular Layer
What cell types make up the granular layer of the cerebellar cortex?
Made up of:
> granule cells
> Golgi type II cells
> glomeruli
Axons of what fibers synapse with granular cells and Golgi type II cells in the glomeruli?
mossy fibers
What cell types are found in the molecular layer of the cerebellar cortex?
Contains: > stellate cells > basket cells > Purkinje dendrites > Golgi type II cells > axons of granule cells (parallel fibers)
What cell type does the Purkinje layer of the cerebellar cortex contain?
Purkinje cells
True or False:
Purkinje cells are ONLY output from the cortex.
True
Is the Purkinje cells ouput always inhibitory.
True
What are the characteristics of Purkinje cells?
> extensive dendritic branching
> receive input from parallel fibers (20,000 synapses between parallel fibers and one Purkinje cell).
> project to intracerebellar nuclei (inhibitory)
To which nuclei do Purkinje cells project to?
intracerebellar nuclei (inhibitory)
Which fibers in the cerebellar cortex are afferent fibers?
- climbing fibers
- mossy fibers
What are the characteristics of climbing fibers (afferent)?
> originate from medullary olives
> make multiple synapses with Purkinje cells
> provide high frequency bursts (complex spikes)
> “condition” the Purkinje cells
> play a role in motor learning
What are the characteristics of mossy fibers?
> originate from multiple centers in brainstem and spinal cord, including:
- vestibulocerebellar tracts
- spinocerebellar tracts
- pontocerebellar tracts
> make multiple syanpses on Purkinje cells and result in simple spikes
> synapse on granule cells in glomeruli
Where do climbing fibers (afferent) originate from?
medullary olives
Where do mossy fibers (afferent) originate from?
multiple centers in brainstem and spinal cord, including vestibulocerebellar, spinocerebellar, and pontocerebellar tracts
Where do mossy fibers (afferent) of the cerebellar cortex synapse?
On granule cells in glomeruli.
What cell makes up the efferent axons of the cerebellar cortex?
Purkinje cell axons
What are the characteristics of Purkinje cell axons (efferent)?
> only output from cerebellar cortex
> output is always inhibitory
> GABA
> projects to deep cerebellar nuclei and vestibular nucleus
> modulates output of cerebellum and provides synergy (regulates rate, range, and direction of movement)
Which efferent axon from the cerebellar cortex modulates output of cerebellum and provides synergy?
Purkinje cell axons
Where do Purkinje cell axons project to?
To deep cerebellar nuclei and vestibular nucleus.
Where do all climbing fibers originate from?
Inferior Olives
True or False:
Mossy fibers send excitatory collaterals to deep nuclear cells and then synapse in granular layer with thousands of granule cells.
True
How many functional units are there in the cerebellar cortex?
30 million
Output from a functional unit is from what type of cell?
From a deep nuclear cell
Fill in the Blank:
Each functional unit is centered on a _____ cell and a corresponding _____ _____ cell.
Purkinje; Deep Nuclear
Afferent inputs to the cerebellum are mainly from what fibers?
> mossy fibers
> climbing fibers
Do basket and stellate cells function as inhibitory cells in the cerebellar cortex?
Yes
What type of cell does Purkinje cells inhibit?
Deep Nuclear Cells
True or False:
Granule cells send axons to outer cerebellar surface; axons brach in two directions parallel to folia.
True
Study Figure 57-7
“Neuronal circuit of the cerebellar cortex and Intracerebellar nuclei”
What three levels does the nervous system use the cerebellum to coordinate motor control functions?
- vestibulocerebellum
- spinocerebellum
- cerebrocerebellum
What part of the cerebellum does the vestibulocerebellum consist of?
> flocculonodular lobe
> vermis
What does the vestibulocerebellum control?
balance and eye movements
What two systems does the vestibulocerebellum receive fibers from?
> vestibular system
> oculomotor system (pontocerebellar fibers)
Where does the vestibulocerebellum primarily send output to?
vestibular system
What happens if you have loss of flocculonodular lobes?
extreme disturbance of equilibrium and postural movements
True or False:
The vestibulocerebellum evolved at about the same time as the vestibular system.
True
What changes can occur when the cerebellum is removed?
> movements are slow to develop
force developed is weak
movements are slow to turn off
What is the relationship of vestibulocerebellum to pendular movements?
- most body movements are pendular (swing back and forth)
- all pendular movements have tendency to overshoot
- appropriate learned subconscious signals from intact cerebellum can stop movement precisely at intended point (= damping system)
What parts of the cerebellum does the spinocerebellum mostly consist of?
- vermis
- intermediate zone
What is the function of the spinocerebellum?
Synergy: control of rate, force, range, and direction of movement.
What kind of information does the spinocerebellum receive?
- information from motor cortex and red nucleus telling cerebellum intended sequential plan of movement for the next few fractions of a second.
- feedback information from periphery telling cerebellum what actual movements result.
Where does the spinocerebellum send corrections to that it has compared from the two sources that it receives information from?
- motor cortex via thalamus
- magnocellular potion of red nucleus
What part of the cerebellum does the cerebrocerebellum consist of?
lateral parts of hemispheres
What areas of the cerebral cortex are the cerebrocerebellum associated with?
- premotor cortex
- primary motor cortex
- association somatosensory areas
What projections do the cerebrocerebellum receive?
corticopontcerebellar
What is the cerebrocerebellum involved in coordinating?
skilled movement and speech
True or False:
The cerebrocerebellum plans as much as tenths of a second in advance of actual movements.
True
**referred to as “motor imagery”
What is the definition of dysmetria?
Refers to a lack of coordination of movement typified by the undershoot or overshoot of intended position with hand, arm, leg, or eye.
It is a type of ataxia.
An inability to judge distance or scale.
What is the definition of ataxia?
The loss of full control of bodily movements.
What is the definition of past pointing?
In cerebellar disease, a patient attempting to reach a point with finger will overshoot it.
What is the definition of dysdiadochokinesia?
Is a feature of cerebellar ataxia and may be the result of lesions to either the cerebellar hemispheres or the frontal lob, it can also be a combination of both.
What is the definition of dysarthria?
Difficult or unclear articulation of speech that is otherwise linguistically normal.
What is the definition of cerebellar nystagmus?
Disease affecting the vestibular organ in the inner ear causes an imbalance that leads to a mixed horizontal - torsional nystagmus usually associated with vertigo. Disease affecting the central connections of the vestibular system, including the cerebellum, may cause several forms of nystagmus.
What is the definition of hypotonia?
Also known as floppy baby syndrome, is a state of low muscle tone (the amount of tension or resistance to stretch in a muscle) often involving reduced muscle strength.
What afferent tracts go to the cerebellum?
- Corticopontocerebellar
- Vestibulocerebellar
- Reticulocerebellar
- Spinocerebellar
> ventral
> dorsal - Olivocerebellar
What are the efferent tracts from the cerebellum?
- cerebelloreticular
- cerebellothalamocortical
- cerebellorubral
- cerebellovestibular
What is the route of the corticopontocerebellar to the cerebellum?
motor and premotor cortices/Somatosensory cortex -> pontine nuclei -> lateral divisions of cerebellum
Where does the vestibulocerebellar terminate in the cerebellum?
terminates in flocculonodular lobes
Where does the reticulocerebellar tract primarily terminate in the cerebellum?
Terminates primarily in vermis.
What afferent tracts to the cerebellum form the mossy fibers that terminate on the granule cells in the cerebellar cortex (excitatory)?
- corticopontocerebellar
- vestibulocerebellar
- reticulocerebellar
- spinocerebellar
Where do dorsal spinocerebellar tracts come from and terminate in the cerebellum?
Muscle Spindles -> ipsilaterally in vermis and intermediate zones.
What does the dorsal spinocerebellar apprise the cerebellum of momentary status of?
- muscle contractions
- degree of tension on the muscle spindles
- positions and rates of movement of parts of the body
- forces acting on surfaces of the body
True of False:
The ventral spinocerebellar tract terminates both ipsilaterally and contralaterally.
True
The ventral spinocerebellar tract is excited by signals coming from?
- cortex via corticospinal and rubrospinal tracts
- internal motor pattern generators within spinal cord
What does the ventral spinocerebellar tracts tell the cerebellum?
- Which motor signals have arrived at the anterior horns.
- This feedback = efference copy of the anterior horn motor drive.
What do axons of the olivocerebellar form?
climbing fibers
Where do tracts from cerebelloreticular come from and to?
Fastigial nuclei -> reticular nuclei in pons and medulla
Where do tracts from cerebellothalamocortical come from and to?
dentate, emboliform, globose nuclei -> thalamus -> motor cortex
Where do tracts from cerebellorubral come from and to?
dentate, emboliform, globose nuclei -> red nucleus
Where do tracts from cerebellovestibular come from and to?
cerebellum -> vestibular nuclei
What do climbing fibers from the olivocerebellar (afferent) tracts cause?
Climbing fiber causes a single, prolonged (up to one second) action potential on each Purkinje cell with which it connects (one climbing fiber per 5-10 Purkinje cells).
What is a complex spike?
Each signal (from climbing fiber) starts out as a strong spike and is followed by a series of weak secondary spikes.
What do mossy fibers send excitatory signals to?
granule cells
True or False:
In the olivocerebellar afferent tracts to the cerebellum, neurons project from inferior olivary nuclei (in medulla) to Purkinje cell dendrites (+) and to intracerebellar nuclei.
True
