Neuro Block 3 - L06 Cerebellum

parts of the vestibulocerebellum

Vermal and floccular parts of the flocculonodular lobe.

Three fiber bundles carry the input and output of the cerebellum.

cerebellar peduncles

"little brain"

cerebellum

only part that when damaged leads to ipsilateral deficits

cerebellum only

The error signal is believed to be conveyed by the __ inputs. >they are known to be especially active when an *unexpected* event occurs, such as 1. when a greater load than expected is placed on a muscle or 2. when a toe is stubbed.

climbing fiber

The Purkinje cell spikes that are generated by __ are calcium-spikes

climbing fibers

The powerful inputs from __occur less frequently (~1 spike/sec); thus, they have a minor influence on the overall firing rate of the Purkinje cell.

climbing fibers

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

climbing fibers signal this error & trigger a calcium spike in the Purkinje cell. >> The influx of calcium changes the connection strengths between parallel fibers & Purkinje cells, >> so that the next time the same behavioral context occurs, the motor output will be *modified to more closely approximate* the desired output.

1. decomposition of mvmt 2. intention tremor 3. dysdiadochokinesia 4. deficits in motor learning

damage to cerebellum causes...

The __ is the largest of the cerebellar nuclei, located (lateral to the interposed nuclei.) > It receives input from 1.lateral hemisphere 2.cerebellar afferents that carry information from the cerebral cortex (via the pontine nuclei). >It projects to the 1. contralateral red nucleus 2. the ventrolateral (VL) thalamic nucleus.

dentate nucleus (cerebrocerebellum path)

inputs to the cerebellum are conveyed primarily through the

inferior and middle cerebellar peduncles,

all cerebellar nuclei and all regions of cerebellum get special inputs from the

inferior olive of the medulla

the cerebellum is involved in motor function by

modifying motor commands of the descending pathways to make mvmts MORE ADAPTIVE & ACCURATE

The outer layer, the __layer, is made of the >axons of granule cells >dendrites of Purkinje cells, >as well as a few other cell types.

molecular

the __ inputs to the cerebellum convey the sensory information used to evaluate the overall sensory context of the movement. >respond to sensory stimuli; >also correlated with different movements >>These fibers convey such information as: 1. Where are the appropriate body parts (proprioceptors), 2. what is the current load on the muscle (proprioceptors, somatosensory receptors, etc.), 3. what other sensory information can predict a useful response (e.g., the tone in the eye blink conditioning), 4. what are the desired movements (motor cortex).

mossy fiber

outputs are conveyed primarily through the

superior cerebellar peduncle

In addition to the major cell types (purkinje & granule cells) the cerebellar cortex also contains

various interneuron types, including 1. the Golgi cell, 2. the basket cell, 3. the stellate cell.

The spinocerebellum contains the...

vermis and intermediate zone of the anterior and posterior lobes.

The __ are located *outside* the cerebellum, *in the medulla*. Hence, they are not strictly cerebellar nuclei, but they are considered to be functionally equivalent to the cerebellar nuclei because their connectivity patterns are identical to the cerebellar nuclei. >receive input from 1. flocculonodular lobe 2. vestibular labyrinth. >They project to various motor nuclei and originate the vestibulospinal tracts.

vestibular nuclei (vestibulocerebellum path)

This reflex allows us to maintain gaze on an object when the head is rotated >Vestibular signals detect the head movement, >send signals through the cerebellum >to the eye muscles to >1. recisely counter the head rotation and 2.maintain a stable center of gaze. >>The motor commands to the eyes must be calibrated precisely with experience, and this calibration appears to be the job of the cerebellum

the vestibuloocular reflex (VOR).

All outputs from the cerebellum originate from the

cerebellar deep nuclei.

__ constitute the sole output of the *entire* cerebellum

cerebellar nuclei

What are the 3 layers of the cerebellar cortex?

1. granule cell layer 2. purkinje cell layer 3. molecular layer

functions of the cerebellum

1. maintenance of balance and posture 2. coordination of voluntary mvmts 3. motor learning 4. cognitive functions

functional subdivisions of the cerebellum

1. vestibulocerebellum 2. spinocerebellum 3. cerebrocerebellum

cerebellum accounts for approximately __% of the brain's volume,

10

cerebellum contains over __% of the total number of neurons in the brain.

50

The key distinction between a feedback and feedforward system is that

>feedback system uses sensory information to *generate an error signal* DURING the control of a movement, >feedforward system *uses sensory information IN ADVANCE of a movement* -FF(*error signal about the final* output is used only to *change its programming of future* movements).

cerebellar INPUT vs OUTPUT Ipsi vs contralateral

ALL CONTRALATERAL

Functions, such as language

Cognitive functions

Most movements are composed of a number of different muscle groups acting together >Timing and force of these different muscle groups to produce fluid limb or body movements.

Coordination of voluntary movements

touching one's finger to one's nose requires the coordinated activity of shoulder, elbow, and wrist joints. Cerebellar patients must first perform the shoulder movement, then the elbow movement, and finally the wrist movement in sequence, rather than as one, uniform motion.

Decomposition of movement

lesions to the cerebellum prevent this adjustment of the VOR./ can't calibrate VOR >ex 1 > the image moves along the retina (termed "retinal slip") in the direction opposite to the movement of the head. >ex 2 > can't compensate for prism >ex 3 > can't produce the eyelid closure in response to the tone. (Pavlovian classical conditioning of the eye blink reflex - doesn't work in pts with ___)

Deficits in motor learning.

Patients have difficulty performing rapidly alternating movements, such as hitting a surface rapidly and repeatedly with the palm and back of the hand.

Dysdiadochokinesia

__cells are very small, densely packed neurons that >account for the huge majority of neurons in the cerebellum. >account for more than half of the neurons in the entire brain. >>These cells 1. receive input from mossy fibers 2. project to the Purkinje cells.

Granule

if reaching for a cup, the hand starts out in a direct line toward the cup; as it gets closer, however, the hand begins to move back and forth as it attempts to make contact with the cup.

Intention tremor.

parts of the cerebrocerebellum

Lateral portions of the cerebellum and dentate nuclei

Through its input from vestibular receptors and proprioceptors, it modulates commands to motor neurons to compensate for shifts in body position or changes in load upon muscles

Maintenance of balance and posture

The cerebellum plays a major role in adapting and fine-tuning motor programs to make accurate movements through a trial-and-error process (e.g., learning to hit a baseball).

Motor learning

The middle layer, the __cell layer, is only 1-cell thick. >forms the border between the granule and molecular layers.

Purkinje

the __ cell is the SOLE source of outpur from the cerebellar cortex

Purkinje

__constitute the sole output of the cerebellar cortex,

Purkinje cells

__ are the sole output structures of the cerebellum. These nuclei are encased by a highly convoluted sheet of tissue called the *cerebellar cortex*

The cerebellar deep nuclei (or cerebellar nuclei)

primarily contains >afferent fibers from the *medulla*, as well as >efferents to the *vestibular nuclei*.

The inferior cerebellar peduncle (also called the restiform body)

primarily contains >afferents from the *pontine nuclei.*

The middle cerebellar peduncle (also called the brachium pontis)

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 (LEARNING) - trial and error sequence will be repeated until the movement is properly calibrated; moreover, these mechanisms will ensure that the movements stay calibrated.

primarily contains >efferent fibers from the *cerebellar nuclei,* as well as some >afferents from the *spinocerebellar tract*

The superior cerebellar peduncle (also called the brachium conjunctivum)

contains almost all of the neurons in the cerebellum

cerebellar cortex

The cerebellum appears necessary for the proper timing and coordination of muscle groups, very likely through __mechanism. Such a role helps explain the deficits seen in dysdiadochokinesia, in which patients *cannot perform rapidly alternating sequences of movements.*

a trial-and-error learning FEEDFORWARD

The lateral vestibular nuclei are functionally analogous to the...

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.

Patients with __damage suffer from balance disorders, and they often develop stereotyped postural strategies to compensate for this problem (e.g., a *wide-based stance*).

cerebellar

The__is the >most *medially* located of the cerebellar nuclei. >It receives input from the 1. vermis 2. cerebellar afferents that carry -vestibular, -proximal somatosensory, -auditory, -visual information. >It projects to the 1. vestibular nuclei 2. the reticular formation

fastigial nucleus (spinocerebellum path)

__is sufficient for slow movements, such as posture. >The *myotatic reflex* is an example in the spinal cord >takes several cycles to reach the desired point In order for __ to work well, sensory regarding actual output is fast relative to the actual output. (sense output faster than output RELEASE)

feedBACK control system

__ is effective for most of the fast movements we make routinely (such as an eye movement or reaching out for a cup)

feedFORWARD control

The cerebellum may be a __control system for slow mvmts

feedback ex. posture changes,

The cerebellum may be a __control system for fast mvmts

feedforward (mossy & climbing fibers) EX. VOR - It evaluates all of this ADVANCE sensory information and calculates the proper eye movement to exactly counterbalance the head movement. -The retinal slip (image moves head mvmt) constitutes an error signal to tell the cerebellum that next time these conditions are met, adjust the eye movement to decrease the retinal slip.

In a ___ when a desired output is sent to the controller, the controller *evaluates* sensory information about the environment and about the system itself BEFORE the *output commands are generated*. >uses the sensory information to program the best set of instructions to accomplish the desired output. >BUT in a purely__system once the commands are sent, *there is no way to alter them* >PRO: makes precise set of commands for the effector without needing to constantly check and correct (no cycles, but requires a period of trial-and-error learning before it can function properly) >creates a "look-up table"

feedforward control system

The innermost layer, the __cell layer, is made of 5 x 1010 small, tightly packed __cells.

granule

Thus, a lesion to the cerebellar nuclei

has the same effect as a complete lesion of the entire cerebellum.

The__comprise the (lateral to fastigial) 1. emboliform nucleus 2. globose nucleus. >receive input from the 1. intermediate zone 2. from cerebellar afferents that carry -spinal, -proximal somatosensory, -auditory, -visual information. >project to the contralateral red nucleus (the origin of the rubrospinal tract).

interposed nuclei (spinocerebellum path)

If the actual output is faster than the sensor's ability to provide feedback, then the system will tend to

oscillate between overshooting and undershooting the desired output.

almost all of the spikes generated by the Purkinje cell are caused by its __inputs. These inputs cause the Purkinje cell to fire at a high resting rate (~70 spikes/sec), tonically inhibiting its cerebellar nucleus targets.

parallel-fiber