Cerebellum (Metencephalon) Flashcards
Where is the Cerebellum located?
- largest part of the hindbrain
- located in the posterior cranial fossa
- behind the pons and medulla oblongata
- separated by the 4th ventricle
What is tentorium cerebelli?
an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.
Role of cerebellum
- Maintenance of Equilibrium - balance, posture, eye movement
posture, gait
- Adjustment of Muscle Tone
- coordination of voluntary movements
- Motor Leaning – Motor Skills
- Cognitive Function
- does not initiate movement
Does the cerebellum relay directly to motor neurons
- no
- exerts action indirectly via circuits which terminate onto the UMN or the LMN
- major component of extrapyramidal motor system
How does the cerebellum communicate with other structures
via superior, middle and inferior cerebellar peduncles
- afferent and efferent connections run between the cerebellum, brainstem and SC travel through cerebellar peduncles
What are cerebellar peduncles
- a nerve tract that permits communication between the cerebellum and the other parts of the central nervous system
- Three pairs of cerebellar peduncles conduct this communication
Describe the structure of the cerebellum
- consists of two large cerebral hemispheres united in the middle by the vermis
- numerous transverse fissures divide the cerebellum into three lobes - anterior, posterior and flocculonodular
- longitudinal divisons - vermis, paravermal region and cerebellar hemisphere
- contain 8 lobules
Superior Cerebellar Peduncle - function, what borders do they form and what do they connect?
- brachia conjuctiva
- major efferent fibers of cerebellum
- emerge from the upper and medial part of the white matter of the cerebellum
- they form the upper and lateral boundaries of the fourth ventricle
- they connect the cerebellar nuclei, mainly the dentate nuclei of the cerebellum, with the midbrain structures and the thalamus
Inferior Cerebellar Peduncle -
- sometimes named restiform bodies
- formed by fibers of the posterior spinocerebellar tract and the axons of the inferior olivary nucleus
- they lie between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves
- contain mainly afferent fibers
- from SC and MO
Middle Cerebellar Peduncles
- brachia pontis
- largest peduncle
- contain only afferent fibers
- fibers of these peduncles come from the pontine nuclei of the opposite side, so, the middle cerebellar peduncles connect the cerebellum with the pons
- pontine nuclei receive input from the cerebral cortex, the stimuli arrive via the middle cerebellar peduncles in the cortex of the cerebellar hemispheres
- these fibers that arrive at the cerebellum from the pathway are part of the so-called mossy fiber system
How the peduncles bring about movement
- The inferior peduncles bring sensory information about the actual position of body parts such as limbs and joints
- The middle peduncles transmit information about the desired position of these parts.
- After integrating and analyzing, the cerebellum sends impulses through the superior peduncles to the midbrain
- In response, motor impulses are transmitted down through the pons, medulla oblongata, and spinal cord to stimulate or inhibit skeletal muscles at appropriate times and cause movements of body parts into the desired positions
- This activity makes rapid and complex muscular movements possible.
Longitudinal divisons of cerebellum
Transverse divisions of cerebellum
Function of Anterior lobe
responsible for mediating unconscious proprioception and receives input mainly from the spinal cord.
Function of Posterior Lobe
important role in fine motor coordination specifically in the inhibition of involuntary movement via inhibitory neurotransmitters especially GABA
- The posterior lobe receives input mainly from the brainstem and the cerebral cortex
Subdivisions of flocculonodular lobe
Nodulus and Flocculus
Subdivisions of anterior lobe
Subdivision of posterior lobe
What is cerebellum composed of?
- composed of grey cerebellar cortex, medullary core of white matter and 4 parts of intrinsic nuclei
- corpus medullare - white matter
- deep nuclei - fastigial, globose, emboliform and dentate - main centers of communication
- globose + emboliform = interposed nucleus
How is the white matter arranged in the cerebellum?
assumes a laminar organisation and on sagittal sections has a branching appearance
Dentate Nucleus
- center of corpus medullare
- convex, indented lamina of grey matter with a hillum open anteromedially
- interior if filled with efferent white fibers - leave the nucleus and form the major part of the superior cerebella peduncle
Emboliform Nucleus (interposed)
- lies at the hillum of the dentate nucleus
- youngest of the cerebellar nuclei (w/ dentate)
- receives input from cerebrocerebeullum (lateral parts/hemispheres)
- projects axons to the contralateral red nucleus and thalamus via SCP
Globose Nucleus
- includes several small cellular groups found medially to the emboliform nucleus
- associated with spinocerebellum
Fastigial nucleus
- it is close to the midline
- oldes nucleus
- associated with vestibulocerebellum
- receives afferents from it and projects it to the vestibular nuclei in the pons and RF
Cerebellar Cortex
- modulate information flowing through the deep nuclei
- 3 layers - molecular, purkinje cell layer and granular layer
Describe the molecular layer of the cortex
- contains two types of inhibitor neurons - (outer) stellate and (inner) basket cells
- external layer
- deep to pia mater and contain very few cells
Describe stellate and basket cells
- molecular layer
Stellate cells
- small interneurons; their processes do not extend beyond the external layer
- their axons form inhibitor synapses with the dendrites of the purkinje cells
- NT: taurine
Basket Cells
- larger, with numerous dendrites
- axon of each cell forms a basket-like plexus around the bodies of a group of purkinje cells, establishing axo-somatic inhibitory synapses
- NT: GABA
Describe the purkinje layer of the cortex - function, arrangement, pathway, collateral branches
- primary neurons of cortex and provides its sole output
- made up of bodies of the purkinje cells
- arranged in a singular layer, but the processes penetrate other layers
- they are relatively large
- the dendrites branch heavily with the molecular layer
- their axons arise at the base of the cell bodies and pass through the granular layer
- when they enter white matter, they get myelin sheaths and terminate at the cerebellar nuclei with inhibitor synapses (GABA)
- collateral branches of the axons form inhibitor synapses with other purkinje, basket and golgi cells (afferent?)
Describe Golgi cells
- granular layer
- distributed in the upper part of the granular layer, near the purkinje cells
- their dendrites branch in the molecular layer in their axons - in the granular layer itself
- they form axodendritic inhibitor synapses with the granule cells at the site of the glomeruli
Mossy fibers
- other afferent cerebellar tracts (exc. olivocerebellar) terminate at the cerebellar cortex via mossy fibers
- thick axons, branch heavily
- in granular layer, their thin terminations synapse with the dendrites of the granule cells, forming globular structures (cerebellar glomeruli)
- stimulatory effect of mossy fibers is then transferred by the granule cells to the purkinje cells
- through these numerous connections, they can stimulate thousands or purkinje cells - more diffuse excitatory effect on purkinje cells
Describe the detail of the glomerulus
- input comes from mossy fibers (afferent) - (except inferior olivary input) which terminate there and synapse with golgi and granule
- granular cell dendrite - main afferent input
- golgi cell axon - synapse on granule cell dendrite, GABA, surrounded by astrocyte foot process
Classification of phylogenetic and ontogenetic development, afferent connection and efferent connection of cerebellum respectively
Archicerebellum - Vestibulocerebellum - Vermis
Paleocerebellum - Spinocerebellum - Paravermal Region
Neocerebellum, Pontocerebellum, Cerebellar Hemisphere
Vestibulocerebellum
- archeocerebellum
- represented by nodulus and flocculus and fastigeal nucleus
- bilaterally connected to the vestibular nuclei
- involves consecutive input from the vestibular nuclei in the pons (vestibulocerebellar tract)
- rise to vestibulospinal tract - descends to LMN
- influence of the ipsilateral extensor muscle tone associated with maintenance of eqm.
Main connections of vestibulocerebellum
Spinocerebellum
- paleocerebellum
- vermis and medial hemisphere
- emboliform and (part of fastigeal which has connections with SC)
- trunco-cerebellar citcuitry - red nucleus and inferior olivary nucleus
- rubroolivary tract and olivocerebellar tract
- maintenance of posture, muscle tone, movements of the axial and proxomal musculature
Main connections of Paleocerebellum
Cerebrocerebellum
- neocerebellum
- dentate
- linked to basilar part of pons
- most advanced module
- involved in motor precision, learning and memory
- corticopontine tract - pontocerebellar tract
Main connections of neocerebellum
Where do the afferent tracts of the superior peduncle terminate into?
in the spinocerebellar cortex as mossy fibers
Where do the tracts from the inferior cerebellar peduncle terminate in?
cortex of the vestibulo and spino-cerebellum
Pyramidal tract and associated circuits
Cerebellum and Automatic Motor Control
Olivocerebellar connections
- caudal (post.) portion of medial and dorsal accessory olivary nucleus, vermis of cortex (A,B), fastigial and vestibular nucleus
- rostral (near nose) portion of medial and dorsal accessory olivary nucleus, paravermal region (C1,2,3) and nucleus interpositus
- principal inferior olviary nucleus - cerebellar hemisphere (D1,2) and dentate nucleus
