Cerebellum Flashcards
(13 cards)
Describe the cerebellar peduncles:
Superior peduncle:
- connects cerebellum to the midbrain
- fibres originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus)
Middle peduncles:
- connect cerebellum to the pons and to axis of the brainstem
- cerebellum receives information advising it of voluntary motor activities initiated by motor cortex
Inferior peduncles:
- connect cerebellum to the medulla
- afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (medulla oblongata)
These cerebellar peduncles carry all information in tracts to and from the cerebellum and it is important to remember that the cerebellum has no direct pathway to the lower motor neurons, but exerts its control via the cerebral cortex and the brainstem
What is the cerebellum ?
The cerebellum functions as a rapid, corrective feedback loop, smoothing and coordinating movements
Motor plan leaves the motor cortex (intended movement) and goes to the basal nuclei and cerebellum (actual movement)
The blood supply to the cerebellum is from three vessels from the vertebral basilar system; the anterior inferior cerebellar artery, the posterior inferior cerebellar artery and the superior cerebellar artery
functions:
- the maintenance of muscle tone
- the maintenance of upright posture with respect to ones position in space
- an association with movements that are properly grouped for the performance of selective responses that
require specific adjustments
Describe the gross anatomy of the cerebellum:
Cerebellum is located in the posterior cranial fossa and is separated from cerebral cortex by the tentorium cerebelli
It lies over the fourth ventricle and is connected to the brainstem by 3 cerebellar peduncles through which all tracts to and from the cerebellum run
Located dorsal to the pons and medulla
Two cerebellar hemispheres (right & left) joined medially by the vermis
Has extensive folds (folia) and each folia contains a core of white matter known as the arbor vitae
External grey matter folia – transversely arranged gyri
Each hemisphere divided into 3 lobes by the primary &
posterolateral fissures:
- anterior
- posterior
- flocculonodular
Anterior and posterior lobes further divide into:
- vermal zone occupying vermis
- intermediate zone
- lateral zone
Describe the functional anatomy of the cerebellum:
The cerebellum is divided into 3 major functional divisions
Vestibulocerebellum:
- composed of the flocculonodular lobe
- functioning as maintenance balance, control of eye movement
Spinocerebellum:
- composed of the vermis and paravermal zone
- functioning as regulation of muscle tone, coordination of skilled movement
Cerebrocerebellum:
- functions are planning and initiation of voluntary movement
- composed of the lateral zones of the cerebellar hemispheres
Describe the cerebellar inputs/ afferents
Posterior (dorsal) spinocerebellar tract:
- enters cerebrum via inferior cerebellar peduncle
- conveys signals mainly from muscle spindles and Golgi tendon organs in the muscles of the lower limb
Anterior (ventral) spinocerebellar tract:
- enters cerebrum via superior cerebellar peduncle
- the synergy of movement conveys signals from the Golgi tendon organs which detects whole limb movement
Cuneocerebellar tract:
- enters cerebellum via inferior cerebellar peduncle
- conveys signals mainly from muscle spindles and Golgi tendon organs in the muscles of the upper limb
Describe the brainstem nuclei that provide afferent fibres to the cerebellum:
Inferior olivary nuclei:
- receives info from cutaneous and joint afferents and muscle spindle
- axons pass to the contralateral cerebellar cortex via the inferior cerebellar peduncle
- also receive axons from the sensorimotor cortex directly and indirectly via the red nucleus
Deep pontine nuclei:
- primary route by which the cerebral cortex communicates with the cerebellum is via the basilar pons
- fibres from the cerebral cortex synapse with deep pontine nuclei which then give rise to the transverse pontine fibres that enter the contralateral middle cerebellar peduncle and are distributed to corresponding areas of the cerebellum
Reticular formation:
- regulates spinal reflexes
- provides input to the cerebellum that relates to the manner in which reticular neurons regulate extensor motor tone at any given time
Tectum:
- cerebellum also receives fibres arising from the superior and inferior colliculi of the tectum to provide visual and auditory information respectively
- project to pontine nuclei
Red nucleus - serves as a relay from the sensorimotor cortex to the spinal cord via the rubrospinal tract
Trigeminal system - secondary proprioceptive fibres associated with muscle spindle activity of the face and jaw reach the cerebellum through the mesencephalic trigeminal nucleus
Describe the deep cerebellar nuclei:
Signals will leave the cerebellar cortex via cerebellar Purkinje Cells and travel to the deep cerebellar nuclei
The cerebellar cortex is composed of outer grey matter which is extensively folded overlying a large expanse of white matter
Separated from the cortex by the white matter are underlying, deep, cerebellar nuclei which are represented bilaterally
From lateral to medial;
Dentate nucleus:
- project contralaterally through superior cerebellar peduncle to neurons in the contralateral thalamus &
from thalamus to motor cortex - function = influence of planning and initiation of movement
Emboliform and Globose nuclei:
- project mainly to the contralateral red nuclei & a small group is projected to the motor cortex
- function = Red Nuclei → Rubrospinal Tract control of proximal limb muscles
Fastigial nuclei:
- project to the vestibular nuclei & to the pontine and medullary reticular formation
- function = vestibulopsinal and reticulospinal tracts
Describe the efferent connections of the cerebrocerebellum:
The cerebrocerebellum sends outputs mainly through the dentate nucleus.
These signals travel to:
- The red nucleus (influences limb movements)
- The thalamus, which then communicates back to the motor cortex
This loop helps with coordination, planning, and timing of complex voluntary movements.
Describe the efferent fibres in the cerebellar peduncles:
Inferior:
- cerebellovestibular tract that feeds information from the flocculonodular lobe back to the vestibular nuclei
- Cerebello-olivary tract that feed information from the vermis back to the inferior olivary nuclear complex
Superior:
- dentatrubrothalamic tract from the dentate nucleus of the posterior lobe to the red
nucleus than on to the thalamus
Middle - no efferent signals/fibres leave the cerebellum via the middle cerebellar peduncle
Describe the afferent tracts from the cerebral cortex:
Areas of the cerebral cortex project to the ipsilateral pontine nuclei
they cross the midline as the
transverse fibres of the pons, form the cerebrocerbellum and enter the cerebellum via the middle cerebellar
peduncle
will leave the corresponding cerebellar cortical areas and travel within the cerebellum to the dentate and interposed nuclei before leaving the cerebellum
It informs the cerebellum about planned motor activity
describe the afferent tracts from the vestibular nucleus:
The cerebellar cortex of the flocculonodular lobe is the area primarily responsible for receiving vestibular inputs
vestibular neurons that regulate extensor motor neurons via the vestibulospinal and reticulospinal tracts
The vestibulocerebellar fibres will leave the corresponding cerebellar cortical areas and travel to the fastigial nucleus before exiting the cerebellum
The vestibular nuclei send afferent (incoming) signals to the vestibulocerebellum
These signals carry information about head position and movement and balance
Helps cerebellum adjust posture and eye movements in response
Describe the vestibular feedback circuit in relation to Efferent connections of the vestibulo and spinocerebellum:
Vestibular Feedback Circuit
The vestibulocerebellum (mainly the flocculonodular lobe) sends signals to the vestibular nuclei in the brainstem
These nuclei send outputs to:
- Eye muscles (to coordinate eye movements)
- Spinal cord (to maintain balance via the vestibulospinal tract)
Function: Adjusts head & eye position via medial longitudinal fasciculus & medial vestibulospinal tract. Controls limb and axial muscle tone through the lateral vestibulospinal tract.
Fastigial Nuclei Projections
Projects to vestibular nuclei and reticular formation (pons & medulla).
Influences extensor muscle tone and postural control via these pathways.
Describe the reticular feedback circuit with relation to Efferent connections of the vestibulo and spinocerebellum:
Reticular nuclei (pons & medulla) → Anterior & posterior vermis
Vermal & paravermal regions → Fastigial nuclei
Fastigial nuclei → Reticular formation → Extensor motor neurons in the spinal cord
Vestibulo- and spinocerebellum send outputs to the reticular formation via the fastigial nucleus
The reticular formation then sends motor signals back to the spinal cord to adjust muscle tone and reflexes
It’s a feedback loop that helps maintain balance and posture during movement
