Cerebellum and Control Systems (continued)
The cerebellum may be a feedforward control system
The cerebellar involvement in the VOR may be explained in terms of the learning requirements of a feedforward controller. When the head moves, a compensatory eye movement must be made to maintain a stable gaze. The cerebellum receives sensory input from the vestibular system informing it that the head is moving. It also receives input from eye muscle proprioceptors and other relevant sources of information about current conditions in order to make an accurate compensatory eye movement. It evaluates all of this advance sensory information and calculates the proper eye movement to exactly counterbalance the head movement. What if the eye movement does not match the head movement, however, and the visual image moves across the retina (such as in the experimental condition in which a prism was worn, or in a real-life situation in which an individual wears new prescription eyeglasses)? The retinal slip constitutes an error signal to tell the cerebellum that next time these conditions are met, adjust the eye movement to decrease the retinal slip. This trial and error sequence will be repeated until the movement is properly calibrated; moreover, these mechanisms will ensure that the movements stay calibrated.
As another example, the coordination of movements requires that muscle groups be activated in precise temporal sequence. Not only do the different joints need to be coordinated temporally, but even antagonist muscles that control the same joint need precise temporal coordination. For example, an extensor muscle needs to be activated to start a reaching movement, and the corresponding flexor muscle needs to be activated at the end of the movement to stop the movement appropriately. The precise timing of muscle contractions and the force necessary for each contraction varies with the amount of load placed on a muscle, as well as on the inherent properties of the muscle itself (e.g., elasticity). These variables are constantly changing throughout life, as one grows, gains/loses weights, and ages. Moreover, a similar movement will require different patterns of motor activity depending on the weight being born by the muscle (for example, if an extended hand is empty or holding a heavy weight). The cerebellum appears necessary for the proper timing and coordination of muscle groups, very likely through a trial-and-error learning mechanism discussed previously. Such a role helps explain the deficits seen in dysdiadochokinesia, in which patients cannot perform rapidly alternating sequences of movements.
It is believed that the mossy fiber inputs to the cerebellum convey the sensory information used to evaluate the overall sensory context of the movement. Mossy fibers are known to respond to sensory stimuli; they are also correlated with different movements (Figure 5.11). These fibers convey such information as: Where are the appropriate body parts (proprioceptors), what is the current load on the muscle (proprioceptors, somatosensory receptors, etc.), what other sensory information can predict a useful response (e.g., the tone in the eye blink conditioning), what are the desired movements (motor cortex). The error signal is believed to be conveyed by the climbing fiber inputs. Climbing fibers are known to be especially active when an unexpected event occurs, such as when a greater load than expected is placed on a muscle or when a toe is stubbed. Thus, the large divergence of input from the mossy fibers to the granule cells to the parallel fibers is believed to create complex representations of the entire sensory context at present and the desired motor output. When the desired output is not achieved, the climbing fibers signal this error and trigger a calcium spike in the Purkinje cell. The influx of calcium changes the connection strengths between parallel fibers and Purkinje cells, such that the next time the same behavioral context occurs, the motor output will be modified to more closely approximate the desired output.
- Question 1
- A
- B
- C
- D
- E
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes.
B. Vermal and floccular parts of the flocculonodular lobe.
C. Lateral portions of the cerebellum.
D. Posterior lobe and interposed nuclei.
E. Anterior lobe and dentate nuclei.
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes. This answer is CORRECT!
B. Vermal and floccular parts of the flocculonodular lobe.
C. Lateral portions of the cerebellum.
D. Posterior lobe and interposed nuclei.
E. Anterior lobe and dentate nuclei.
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes.
B. Vermal and floccular parts of the flocculonodular lobe. This answer is INCORRECT.
These are parts of the vestibulocerebellum.
C. Lateral portions of the cerebellum.
D. Posterior lobe and interposed nuclei.
E. Anterior lobe and dentate nuclei.
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes.
B. Vermal and floccular parts of the flocculonodular lobe.
C. Lateral portions of the cerebellum. This answer is INCORRECT.
These are parts of the cerebrocerebellum.
D. Posterior lobe and interposed nuclei.
E. Anterior lobe and dentate nuclei.
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes.
B. Vermal and floccular parts of the flocculonodular lobe.
C. Lateral portions of the cerebellum.
D. Posterior lobe and interposed nuclei. This answer is INCORRECT.
Not all of the posterior lobe is part of the spinocerebellum.
E. Anterior lobe and dentate nuclei.
The spinocerebellum contains the...
A. vermis and intermediate zone of the anterior and posterior lobes.
B. Vermal and floccular parts of the flocculonodular lobe.
C. Lateral portions of the cerebellum.
D. Posterior lobe and interposed nuclei.
E. Anterior lobe and dentate nuclei. This answer is INCORRECT.
Not all of the anterior lobe is part of the spinocerebellum, and the dentate nuclei are part of the cerebrocerebellum.
- Question 2
- A
- B
- C
- D
- E
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus
B. Purkinje cells
C. Basal ganglia
D. Thalamus
E. Deep cerebellar nuclei
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus This answer is INCORRECT.
The red nucleus is not analogous to the lateral vestibular nuclei.
B. Purkinje cells
C. Basal ganglia
D. Thalamus
E. Deep cerebellar nuclei
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus
B. Purkinje cells This answer is INCORRECT.
Purkinje cells are not analogous to the lateral vestibular nuclei.
C. Basal ganglia
D. Thalamus
E. Deep cerebellar nuclei
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus
B. Purkinje cells
C. Basal ganglia This answer is INCORRECT.
The basal ganglia are not analogous to the lateral vestibular nuclei.
D. Thalamus
E. Deep cerebellar nuclei
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus
B. Purkinje cells
C. Basal ganglia
D. Thalamus This answer is INCORRECT.
The thalamus is not analogous to the lateral vestibular nuclei.
E. Deep cerebellar nuclei
The lateral vestibular nuclei are functionally analogous to the...
A. Red nucleus
B. Purkinje cells
C. Basal ganglia
D. Thalamus
E. Deep cerebellar nuclei This answer is CORRECT!
The lateral vestibular nuclei, although not contained within the cerebellum, are considered to be functionally analogous to the deep cerebellar nuclei because of their functional connectivity with the cerebellum.
