neuro lab 8 cerebellum intro

what connect cerebellum to brainstem?

cerebellar peduncles

cerebellum

important center for the integration of sensory input with information about motor commands. Its activity helps to produce smoother and more accurate movement.

Morphologically, the cerebellum consists of a medial region known as

the vermis (Latin for "worm," which it resembles) and two lateral hemispheres.

rostral peduncle

• carries mossy afferents, mainly from the visual and auditory systems. It is dominated by efferent axons traveling from the cerebellum toward the midbrain and thalamus.

Input reaches the cerebellum via

all 3 cerebellar peduncles

In summary, the mediolateral organization of afferent/input topography is reflected in the efferent/output patterns of the different regions of the cerebellum.

• Medial vermal regions of cerebellar cortex and the flocculonodular lobe receive information from the neck, trunk and inner ear. They exert control (via the fastigial or vestibular nucleus outflow) over the muscles in these same axial and proximal limb regions via their vestibulospinal tract and reticulospinal tract connections. • The adjacent paravermal zone receives input from the distal limbs and digits. • The lateral zone (lateral to the paravermis) receives input from corticopontocerebellar tracts about motor planning. The paravermal and lateral zones influence movements of distal limb and digit muscles via the rubral and cortical connections of the interpositus (paravermal zone) and dentate (lateral zone) nuclei. • Each zone of the cerebellum modifies muscle activity in the same region from which it receives its input.

excitation of a Purkinje cell results in an inhibitory outflow from the cerebellar cortex to cells in the deep cerebellar or vestibular nuclei.

This inhibitory control by Purkinje cells over excitability of the deep cerebellar nuclei appears to be a key aspect of cerebellar function. Since the final outflow from the cerebellum as a whole (from the deep cerebellar nuclei) is excitatory, the inhibitory output from the cerebellar cortex can be viewed as a way of "sculpting" or "fine tuning" the (otherwise excitatory) cerebellar output to provide appropriately modulated feedback to the motor systems. Purkinje output to the deep nuclei is itself "fine-tuned" by other inhibitory neurons in the cerebellar cortex (e.g. stellate cells, etc.) that limit the Purkinje inhibition (leading to a disinhibition of cerebellar output).

posterolateral fissure of cerebellum

This caudally-located fissure pinches off a portion of the vermis (known as the nodulus), and a portion of each hemisphere (the flocculus).

folia

are the fundamental anatomical and functional units of the cerebellum. They give the cerebellar surface a corrugated appearance, and significantly increase the total cortical area available for information processing.

mossy fibers

arrive at the cerebellum from several sources, including: • Dorsal and ventral spinocerebellar tracts • the Cuneocerebellar tract • Vestibular pathways, • Trigeminal pathways, • the Reticular formation, or • the Pontine nuclei.

what carry the sole output of the cerebellar cortex?

axons of purkinjes

The cerebellum has rostral (anterior) and caudal (posterior) lobes: fxn?

both of these lobes receive tactile and proprioceptive input, and both compare feedback from the body with motor commands from the motor cortex.

caudal peduncle

carries both climbing (from IO) and mossy (from spinal cord & brainstem) afferents; its role is primarily to bring afferent axons to the cerebellum. It is also is a pathway by which some axons exit the cerebellum on the way to the vestibular nuclei, reticular formation, or spinal cord

middle penduncle

carries mossy afferent axons to the cerebellum from the pontine nuclei (part of the corticopontocerebellar tract).

mossy fibers: Almost all of these pathways enter the cerebellum via the

caudal cerebellar peduncle. The exceptions are the ventral spinocerebellar tract (which utilizes the rostral cerebellar peduncle) and the pontine nuclei (which utilize the middle cerebellar peduncle).

As in the cerebrum, grey matter is located on the surface of the cerebellum, forming the

cerebellar cortex

molecular layer

contains few cell bodies, but has many axons - especially the axons of granule cells. These axons are known as parallel fibers. It also contains dendrites from cell bodies in other layers, especially the dendrites of Purkinje cells.

Most of the interpositus axons terminate on cell bodies in the

contralateral red nucleus (NR) of the midbrain, although some axons continue to the diencephalon and terminate in the contralateral ventrolateral nucleus (VL) of the thalamus.

most lateral regions of cerebellar cortex, the lateral hemispheres, receive and process motor command information from the

corticopontocerebellar pathway hemispheres, receive and process motor command information from the corticopontocerebellar pathway. This information is associated with motor planning, mental rehearsal of complex motor actions, and motor memory.

The pontine nuclei are part of the ------- which brings information about motor commands to the cerebellum.

corticopontocerebellar tract

cerebellum receives copies of outgoing motor commands ('intended movement' information) from the somatomotor cerebral cortices via the

corticopontocerebellar tract

motor cortex is the origin of the ----------, a motor system controlling fine voluntary movements.

corticospinal tract

granule cell layer

deepest composed chiefly of small, densely packed granule cells. The extreme cell density gives this layer a darkly stained appearance in Nissl-stained sections. Axons from the granule cells ascend to the molecular layer and bifurcate, forming axon collaterals (called parallel fibers) that run parallel to the surface of the cerebellar cortex. These axons are oriented at right angles to the two-dimensional dendritic arrays of the Purkinje cells and run parallel to the long axis of the transversely-oriented folium. Each granule cell axon therefore contacts the dendritic arborizations of a large number of Purkinje cells.

The lateral zone projects ipsilaterally to the

dentate nucleus

cerebellum receives inputs from numerous sensory systems. It acts as a modulator of

diverse neural activity, including visual, auditory and visceral functions. The cerebellum is also involved in motor learning.

3rd lobe

flocculonodular lobe, receives input from the organs of balance (the vestibular apparatus).

Together the nodulus and flocculus form the ventrally-located

flocculonodular lobe, the most ancient part of the cerebellum (the archicerebellum).

The anterior and posterior lobes are composed of subdivisions known as lobules. The lobules are further subdivided into transversely-arranged, long, narrow ridges called

folia

paravermis

intermediate; receives and processes sensory information from the distal limbs. It projects ipsilaterally to the interpositus nucleus, which lies just lateral to the fastigial nucleus.

origin of the rubrospinal tract, a motor pathway that influences distal limb musculature (especially flexors) to produce fine, graded movements of the limbs and paws/feet?

large neurons of red nucleus

what does the primary fissure divide?

main part of the cerebellum into rostral (anterior) and caudal (posterior) lobes

Cerebellar white matter is located centrally, in the

medullary core of cerebellum

Output from the cerebellum allows the somatomotor cerebral cortices (via cerebello-thalamo-cerebrocortical connectivity) to produce

more accurate, refined commands to the muscles

Afferent input reaches the cerebellar cortex via two excitatory systems -

mossy fibers and climbing fibers - which are axons from a variety of sources

vermis

most medial region It receives and processes sensory information from the head, trunk, and proximal limbs.

purkinje cell layer

only one cell thick. Purkinje cells are large, distinctive neurons with a two-dimensional, flask-shaped soma and a massive dendritic arborization that extends out into the molecular layer. The Purkinje cell axon passes through the deeper granule cell layer and enters a fingerlike extension of white matter known as a medullary ray (Fig. 6). It synapses on cells in the deep cerebellar nuclei or in the vestibular nuclei.

climbing fibers

originate from only one source: the contralateral inferior olive in the medulla. These olivocerebellar axons are the largest afferent component in the caudal (inferior) cerebellar peduncle. The information carried to the cerebellum by climbing fiber axons comes from the somatosensory, enteric, auditory, and visual systems. Each climbing fiber axon sends an axon collateral (which is excitatory) to the deep cerebellar nuclei as it enters the cerebellum. The main axon (also excitatory) ascends to the Purkinje layer, and ends directly on the Purkinje cell by twining around (i.e., 'climbing') its dendrites

ventrolateral nucleus

projection nucleus whose axons project primarily to motor areas of the cerebral cortex.

fastigial nuclei

receive vermal input concerning the trunk and proximal limbs, project their axons bilaterally to various brainstem regions, also via the inferior cerebellar peduncle

dentate nucleus

receives input from premotor cortex concerning planning and mental rehearsal of complex motor actions. It sends axons out the rostral (superior) cerebellar peduncle in a manner similar to the interpositus projection: the majority of these axons decussate in DSCP (see Figs. 9 & 10). Some dentate axons terminate in the contralateral red nucleus, but most proceed to VL of the thalamus before synapsing. Axons from the VL project to motor areas of the cerebral cortex, origin of the corticospinal tract. This tract is the most intimately involved with the control of fine digital movements utilizing (mainly) flexor muscles in the distal limb and hand/foot or paw.

interpositus nucleus

receives paravermal input about the distal limbs, sends efferent axons out through the rostral (superior) cerebellar peduncle *Most of these axons immediately decussate in the midbrain (decussation of the superior cerebellar peduncle)

flocculonodular lobe

receives significant input from the vestibular system. It plays a major role in maintenance of muscle tone, equilibrium, and posture by way of its efferent connections, which influence motor pathways that control postural muscles.

Most output from the cerebellum travels through its --- peduncle.

rostral

It is connected to brainstem structures by three paired "bridges" or peduncles:

rostral (superior), middle, and caudal (inferior) cerebellar peduncles

The cerebellum, through its interpositus and dentate projections to the red nucleus and VL/motor cortex, is able to exert influence on the origins of these pathways

rubrospinal & corticospinal

Efferent cerebellar pathways originate

somatotopically in the deep cerebellar nuclei, except for some cortical (Purkinje) axons that project directly to the vestibular nuclei via the inferior (caudal) cerebellar peduncle

cerebellum gets sensory feedback from tactile and proprioceptive receptors in the body ('actual movement' information) via

spinocerebellar tracts

Lesions of the cerebellum cause characteristic types of uncoordinated limb movements

such as ataxia (uncoordinated movement) or dysmetria (overshoot or undershoot) - and can also cause altered muscle tone.

Thus there are really two gray matter distributions within the cerebellum:

the first is of these is the cerebellar cortex, and the second consists of the deep cerebellar nuclei.

3 cell layers of cerebellar cortex

the molecular layer (most superficial), the Purkinje cell layer (middle), and the granule cell layer (deepest).

These brainstem regions include:

1. The vestibular nuclei in the medulla, especially the medial and lateral vestibular nuclei. These nuclei are the origins of the medial and lateral vestibulospinal tracts, respectively. These motor pathways control neck, axial and proximal muscles for balance and posture. 2. The reticular formation, especially those areas in the pons and medulla that are the origins of the pontine and medullary reticulospinal tracts (see Lab 9). The pontine reticular formation gives rise to the medial reticulospinal tract, which is ipsilateral; the medullary reticular formation gives rise to the lateral reticulospinal tract, which travels bilaterally. These two motor pathways function synchronously to produce locomotion.

Mossy fibers from all these sources send an (excitatory) axon collateral

to one or more deep cerebellar nuclei and then synapse, via a characteristic type of axon terminal, on granule cell dendrites (excitatory). Each granule cell then synapses on a "strip" of Purkinje cells whose dendrites lie along the granule cell's parallel axon collaterals.

vermis projects ipsilaterally to

to the most medial of the deep cerebellar nuclei, the fastigial nucleus, which then projects bilaterally to the vestibular and reticular formation nuclei.

Functional subdivisions of the cerebellum

Cerebrocerebellum (lateral zone): cerebellar hemispheres Spinocerebellum: vermis and paravermis Vestibulocerebellum: flocculonodular lobe

cerebellar outputs

Cerebrocerebellum (lateral zone): cerebellar hemispheres Spinocerebellum: vermis and paravermis Vestibulocerebellum: flocculonodular lobe

Corticopontocerebellar Tract

Copy of motor command from M1 (intended movement)

Climbing fiber axons have a ----excitatory effect on Purkinje cells.

DIRECT

'parallel fiber' axons from granule cells have a ----- effect on Purkinje cells.

EXCITATORY

Beneath cerebellar cortex is white matter and deep cerebellar nuclei:

Fastigial - most medial Dentate - most lateral Interposed - in between

Mossy fiber axons have an -----excitatory effect on Purkinje cells by first activating a granule cell and its parallel fiber system

INDIRECT

subdivisions of cerebellum - mediolateral

vermis (median) paravermis cerebellar hem's flocculonodular lobe - flocculus (lateral) & nodulus (medial)

cortical output carried by axons of purkinjes has ---- effect on the deep cerebellar and vestibular nuclei, both of which have an excitatory output.

INHIBITORY

Functional organization of major outputs from cerebellum to cortical motor systems

Projections from the cerebellum What was intended is compared with what actually happened and the motor error signal is sent to cortex via VL/VA to correct ongoing and future movements Corrections can be stored for motor learning

dorsal spinocerebellar tract

Proprioception hindlimbs and lower trunk (actual movement info)

Cuneocerebellar Tract

Proprioception neck, forelimb, upper trunk (actual movement info)

Functional organization of major outputs from cerebellum to brainstem motor systems

Tectospinal tract - Orienting Reticuospinal tracts - Posture and locomotion Vestibulospinal tract - Balance

flocculonodular lobe

which receives and processes sensory information from the vestibular component of the eighth cranial nerve, and projects to the vestibular nuclei of the medulla.

where are the cerebellar nuclei?

white matter of the medullary core -medial to lateral they are the fastigial, interpositus, and dentate nuclei.