Cerebellum physiology

guide

1. cerebellum

2. Overview Is located behind the Medulla and Pons Contains only 10% of the Brain’s volume Situated in posterior cranial fossa Also has two hemispheres

3. Receives two inputs; one from the muscles and joints and other from the motor area of the cerebral cortex After comparing it gives corrective signals to the motor cortex for the correction of voluntary movements

4. Functional Overview Basically evaluates and adjusts motor movement while it is in progress. Does a lot of integration and evaluation of incoming information. Is very important for balance and motor learning

5. Anatomically Cerebellum surface has many parallel convolutions called Folia (leaves) that run from side to side. Has three distinct lobes separated by two fissures Anterior lobe Middle lobe Posterior lobe

6. Longitudinal functional divisions of anterior and posterior lobes In the centre a narrow band separated from the remainder of cerebellum by shallow grooves is the Vermis Laterally on each side of the Vermis is cerebellar hemisphere, each divided into Intermediate and Lateral zones

7. Longitudinal functional divisions Cerebro cerebellum Vestibulo cerebellum Spinocerebellum

8. Phylogenetic history of cerebellum Archicerebellum (Vestibulocerebellar) is oldest part _flocculonodular lobe Paleocerebellum (Spinocerebellar) Neocerebellum (pontocerebellum)

9. Vermis Helps control the proximal muscles of the body and limbs e.g. axial body, neck, shoulders and hips. Generally governs posture, locomotion, and gaze.

10. Intermediate Zone Gets somatosensory information from limbs Helps control distal muscles of the limbs, hands and fingers, feet and toes Lateral zone Responsible for planning the sequence and timing of movements

11. Has Three Distinct Regions* Cerebellar cortex. Is the outer covering Is composed mostly of Gray Matter Internal White Matter Are Myelinated Axons/Fiber Tracts Three pairs of Deep Nuclei Fastigal Interposed Globose Emboliform Dentate

12. Cerebellar Nuclei Dentate nucleus Carries information important for coordination of limb movements (along with the motor cortex and basal ganglia) Emboliform nucleus and Globose nucleus Regulates movements of ipsilateral extremity Fastigial nucleus Regulates body posture Is related to the flocculo nodular lobe

13. Three layers of grey matter Outer molecular or plexiform layer Intermediate purkinje layer Inner granular layer

14. Molecular or plexiform layer It’s the outermost layer cells are arranged in two strata Superficial strata contains star shaped cells called stellate cells Deep strata contains basket cells In addition this layer contains parallel fibers, terminal portion of climbing fibers and dendrites of purkinje and golgi cells Basket cells and stellate cells are inhibitory, result in lateral inhibition of purkinje cells hence sharpens the signals

15. Purkinje layer Thinnest layer between molecular and granular layer Single layer of flask shaped purkinje cells Purkinje cells are the largest neurons Dendrites ascend and arborize in the molecular layer to end on climbing or parallel fibers Axons descend into white matter and terminate on the cerebellar nuclei Purkinje cells are “final common path "of cerebellar cortex

16. Granular layer Innermost layer of cerebellar grey matter Contains Granule cells and Golgi cells Granule cells are the only excitatory cells in the cerebellar cortex Axons of granule cells ascend into molecular layer and form parallel fibers which synapses with dendrites of purkinje cells, stellate cells, basket cells and golgi cells Dendrites of granule cells along with axons and dendrites of golgi cell synapse with mossy fibers in the synaptic area called the glomerulus

17. I-From other parts of brain a. Vestibulocerebellar Tract Info from Semicircular Canals through vestibular nuclei to cerebellum in flocculonodular lobe Maintains Upright Posture b. Reticulocerebellar Tract Information from reticular formation to cerebellum

18. c. Olivocerebellar Tract Info From Spinal Cord, basal ganglia, reticular formation Through Olivary N to Contralateral Cerebellar Hemisphere Source of Climbing Fibers for Direct Input to Cerebellum d. Cuneocerebellar Tract Mediate Proprioception From Upper Limbs and Neck

19. e. Pontocerebellar tract Info from cerebral cortex(motor and premotor cortex and also somatosensory cortex) to pontine nuclei From pontine nuclei to Cerebellar Hemisphere OTHERS; Tectocerebellar, Rubrocerebellar and Trigeminocerebellar tract

20. II-Afferent from the spinal cord Dorsal Spinocerebellar Tract Unconscious Proprioception From Muscle Spindles, Golgi Tendons and Tactile Receptors Ventral Spinocerebellar tract Excited by motor signals arising in anterior horn of spinal cord from Brain through corticospinal and rubrospinal tracts Internal motor pattern generated in cord itself

21. The Ventral spinal pathway provides efference copy of the anterior horn motor drive . And the dorsal Spinocerebellar tract apprise the cerebellum of momentary status of Muscle contraction degree of tension in the muscle tension Positions and rates of movements of different parts of body

22. Cerebellar Afferent Pathways mossy fibers

23. Cerebellar Inputs Vermis Receives input from spinal cord regarding somatosensory and kinesthetic information (intrinsic knowledge of the position of the limbs) Damage leads to difficulty with postural adjustments

24. Intermediate Zone Receives input from the red nucleus and somatosensory information from the spinal cord Damage results in rigidity & difficulty in moving limbs

25. Lateral Zone Receives input from the motor and association cortices through the Pons Projects to the dentate nucleus, which projects back to primary and premotor cortex Damage leads to 4 types of deficits: - Ballistic movements ( cerebellar ataxia ) - Coordination of multi-joint movement (lack of coordination: asynergia ) - Muscle learning - Movement timing

26. Inputs to cerebellum from spinocerebellar tracts have a somatotopic organization. 2 maps of body Primary fissure Signals from the motor cortex, which is also arranged somatotopically , project to corresponding points in the sensory maps of the cerebellum.

27. Cerebellar Efferent Pathways* From midline structures of cerebellum ( vermis ) to Fastigial nuclei: project to the vestibular nuclei & to the pontine and medullary reticular formation Fibers pass in Vestibulospinal & Reticulospinal tracts Function: Maintains posture and equilibrium

28. From lateral zone of cerebellar hemisphere to Dentate nuclei: to ventrolateral and ventroanterior nuclei of the thalamus to motor cortex Function: helps in coordinate sequential motor activities initiated by the cerebral cortex

29. Cerebellar Peduncles Superior peduncles (mainly efferents) Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus) ventral spinothalamic tract Middle pedun cles (mainly afferents) Cerebellum receives information advising it of voluntary motor activities initiated by motor cortex Inferior peduncles (mainly afferents) Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord)

30. Cerebellar Cortical Circuits Inputs to the cerebellar cortex (mossy and climbing fibers) excite the deep nuclei cells as they enter. The outputs of the cerebellar cortex (Purkinje cell axons) inhibit the deep nuclei cells. *

31. Go P B Gr Deep cerebellar nuclei P Mossy fibers Climbing fibers Gr : Granule cells Go: Golgi cells P: Purkinje cells St: Stellate cells B: Basket cells Excitatory (Glutamate) Inhibitory (GABA) Parallel fibers St Spinal cord and brainstem Molecular layer Purkinje cell layer Granule cell layer White matter SC Vestibular n. Reticular n. Motor cortex (via thalamus) Sup Col inferior olivary nucleus Collaterals Collaterals Intrinsic circuitry

32. Direct stimulation of deep cerebellar nuclei from mossy and climbing fibers leads to excitation. Signals from purkinje fibers leads to inhibition. Normally balanced and output from deep cerebellar nuclei is constant moderate level of excitation. The inhibitory signal from purkinje fibers resemble a delay line ,negative feed back signal and is effective in damping.

33. Turn-On/Turn-Off and Turn-Off/Turn-On Output Signals from the Cerebellum * Purkinje Cells "Learn" to Correct Motor Errors-Role of the Climbing Fibers The degree of motor enhancement by the cerebellum at the onset of contraction, the degree of inhibition at the end of contraction, and the timing of these all are learned by experience.

34. Function of Cerebellum Error Control Device - Monitor, Quality Control Monitors outputs to muscles from motor cortex and sensory signals from receptors. Compares the efferent project plan with execution at motor action site. Considers related factors and makes adjustment.

35. Vestibulocerebellum – controls tone & movements of muscles involved in equilibrium & posture, by receiving impulses from vestibular apparatus. Vestibulocerebellum calculates in advance where the different parts will be in a movement and uses information from the periphery as feed back for Anticipatory correction of postural signals to maintain equilibrium.

36. Spinocerebellum – coordinates mainly movements of distal parts of limbs, such as the fast ballistic movements (in association with cerebrocerebellum), & also coordinates saccadic eye movements. It receives impulses from proprioceptors in muscles, tendons & joints, tactile receptors, visual receptors & auditory receptors.

37. Corticocerebellum – coordinates timing & planning involved in fast sequential movements like writing, running, talking etc. It perform its function by the intensive to & fro connection with the cerebral cortex ( cerebro - cerebello -cerebral connections).

38. Functions of Corticocerebellum 1- Servomechanism 2- damping function 3- Coordination of ballistic movements 4- Planning and timing of Sequential Movements 5-comparator function

39. The patterns of cerebellar activity are learned by trial and error, over many repetitions. Many of the basic patterns are established early in life: 1. The fine balancing adjustments you make while standing and walking. 2. The ability to fine-tune a complex pattern of movement improves with practice, until the movements become fluid and automatic.

40. 1-Damping function Prevents exaggerated muscular activity. Makes voluntary activities smooth and accurate. Voluntary movements are initiated in motor areas of cerebral cortex. Corticocerebellum receives information from motor cortex as well as feedback signals from the muscles as soon the muscular activity starts Sends information back to motor cortex to cut off extra impulses

41. 2- Coordination of ballistic movements Ballistic movements are the rapid alternate movements in different parts of body while doing skilled or trained work e.g. typing, cycling, dancing etc. Corticocerebellum plays an important role in preplanning these ballistic movements during learning process.

42. 3- Planning of Sequential Movements Plays an important role in timing and programming the movements during learning process Corticocerebellum plans the sequential movements and also time of each movement All the information from corticocerebellum is communicated to sensory motor area of cerebral cortex and stored in memory

43. 4-Comparator function This function is responsible for integration and coordination of various muscular activities Receives messages from both cerebral cortex and muscles( proprioceptive impulses) Compares the both and corrects

44. 5-Servomechanism It is the correction of any disturbance or interference in performing skilled work. Once skilled works are learnt, the sequential movements are performed without interruption However in case of disturbance corticocerebellum immediately influences the cortex to correct.

45. 6- Extra motor Predictive Functions of the Cerebellum The cerebrocerebellum (the large lateral lobes) also helps to "time" events other than movements of the body. For instance, the rates of progression of both auditory and visual phenomena can be predicted by the brain, but both of these require cerebellar participation. As an example, a person can predict from the changing visual scene how rapidly he or she is approaching an object. is particularly helpful in interpreting rapidly changing spatiotemporal relations in sensory information

46. Clinical Considerations Some Signs of Dysfunction Hypotonia -Reduced Muscle Tone Ataxia -Lack of Order and Coordination in Activities

47. Bradykinesia : Slow Movement Asthenia : Mild Muscular Weakness Asynergia : Inability to perform two acts simultaneously

48. Clinical Considerations Dysdiadochokinesia Clumsiness in Alternating Movements Dysarthria Ataxic Dysarthria Scanning Speech Slurred and Disjointed Speech

49. Dysmetria and Ataxia Error in Judgment of Range and Distance of Target Undershooting or Overshooting (past pointing) Intentional Tremor the movements tend to oscillate, especially when they approach the intended mark, first overshooting the mark and then vibrating back and forth several times before settling on the mark

50. Hypotonia Reduced Resistance to Passive Stretch Due to loss of cerebellar facilitation of the motor cortex and brain stem motor nuclei by tonic signals from the deep cerebellar nuclei. Rebounding Inability to Predict Movement Cannot Hold Back Movement Disequilibrium Unsteady Gait, Body Wavering

51. Drunken gait Pendular knee jerk Cerebellar nystagmus : involuntary movements of eyeballs due to lesion in flocculonodular lobe