A&P IL2 Structure & Function of Cerebellum

Cerebellum is the largest part of the hindbrain and lies posterior to the fourth ventricle, the pons, and the medulla oblongata. Name the structures connecting the cerebellum to the posterior aspect of brainstem.

Three symmetrical bundles of nerve fibers called the superior, middle, and inferior cerebellar peduncles.

Cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem. True or False.

True.

Cerebellum is divided into three main lobes. Describe briefly 3 lobes of cerebellum.

1. Anterior lobe - on the superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure. 2. Middle lobe (posterior lobe) - largest part of the cerebellum, is situated between the primary and uvulonodular fissures. 3. Flocculonodular lobe - posterior to the uvulonodular fissure.

Spinal cord sends information to the cerebellum from somatosensory receptors by three pathways. Name the pathways.

1. Anterior spinocerebellar tract. 2. Posterior spinocerebellar tract. 3. Cuneocerebellar tract.

Name three morphological subdivisions of the cerebellum.

1. Archicerebellum (vestibulocerebellar). 2. Paleocerebellum (spinocerebellar). 3. Neocerebellum (corticoponto-cerebellar).

Describe briefly two afferent fibers entering cerebellar cortex.

1. Climbing fibers - terminal fibers of olivocebellar tracts. Wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell. 2. Mossy fibers - terminal fibers of all other cerebellar afferent tracts. A single mossy fiber may stimulate thousands of Purkinje cells through the granule cells. * Both climbing and mossy fibers are EXCITATORY

Neocerebellum is the most recent part of cerebellum to develop. State the features of Neocerebellum: 1. Components. 2. Nucleus. 3. Chief connections. 4. Function.

1. Components - Middle lobe (posterior lobe) except pyramid & uvula. 2. Nucleus - Dentate. 3. Chief connections - corticoponto cerebellar. 4. Function - smooth performance of highly skilled voluntary movements of precision.

Describe briefly the efferent fibers of white matter in cerebellum.

1. Constitute the output of the cerebellum and commence as the axons of the Purkinje cells of the cerebellar cortex. 2. The great majority of the Purkinje cell axons pass to and synapse with the neurons of the cerebellar nuclei. 3. Axons of the neurons then leave the cerebellum. 4. A few Purkinje cell axons in the flocculonodular lobe and in parts of the vermis bypass the cerebellar nuclei and leave the cerebellum without synapsing. 5. Fibers from the dentate, emboliform, and globose nuclei leave the cerebellum through the superior cerebellar peduncle. 6. Fibers from the fastigial nucleus leave through the inferior cerebellar peduncle.

Describe briefly three functional areas of cerebellum: 1. Cortex of vermis. 2. Immediately lateral to the vermis. 3. Lateral zone of each cerebellar hemisphere.

1. Cortex of vermis - influences the movements of the long axis of the body (neck, shoulders, thorax, abdomen, and hips). 2. Immediately lateral to the vermis - control the muscles of the distal parts of the limbs (hands & feet). 3. Lateral zone of each cerebellar hemisphere - planning of sequential movements of the entire body & is involved with the conscious assessment of movement errors.

Cerebral cortex sends information to the cerebellum by three pathways. State them.

1. Corticopontocerebellar pathway: enter through middle cerebellar peduncle. 2. Cerebro-olivocerebellar pathway: enter through inferior cerebellar peduncle. 3. Cerebroreticulocerebellar pathway: enter through inferior and middle cerebellar peduncles.

Four masses of gray matter are embedded in the white matter of the cerebellum on each side of the midline. Name four intracerebellar nuclei. State the largest intracerebellar nuclei.

1. Dentate - largest. 2. Emboliform. 3. Globose. 4. Fastigial. The intracerebellar nuclei are composed of large, multipolar neurons with simple branching dendrites. The axons form the cerebellar outflow in the superior and inferior cerebellar peduncles.

What is the triad of motor dysfunctions manifested by patient with cerebellar disease?

1. Disequilibrium - loss of balance characterized by gate and truncal ataxia. 2. Hypotonia - loss of resistance normally offered by muscles on palpation. 3. Dyssynergia - loss of coordinated motor activity.

Explain why cerebral cortex lesions affect contralateral limbs whereas cerebellar hemisphere lesions cause incoordination of ipsilateral limbs.

1. Each cerebellar hemisphere receives a major input from the contralateral cerebral cortex via pontine nuclei and the middle cerebellar peduncles. 2. The major output from the cerebellum cross to the contralateral red nucleus & thalamus, thence to spinal cord & basal ganglia & cerebral hemispheres via the superior cerebellar peduncles. + Left cerebellar - Right cerebral hemisphere - Left side body.

Compare the signs between Parkinson's disease & Cerebellar disease.

1. Gait: Festinant gait (bends forward & walks with short shuffling steps) in Parkinson's disease while Drunken gait (abnormal wide-based & unsteady gait) in Cerebellar disease. 2. Tremor: Rest tremor in Parkinson's disease while Intention tremor in Cerebellar disease. 3. Speech: Slow, slurred speech in Parkinson's disease while Scanning speech in Cerebellar disease. 4. Muscle Tone: Increased tone (rigidity) in Parkinson's disease while Hypotonia in Cerebellar disease.

Describe briefly inner granular layer of cerebellar cortex.

1. Granular layer is packed with small cells with densely staining nuclei and scanty cytoplasm (granule cells). 2. Each cell gives rise to four or five dendrites, which make claw like endings and have synaptic contact with mossy fiber input. 3. The axon of each granule cell passes into the molecular layer, where it bifurcates at a T junction, the branches running parallel to the long axis of the cerebellar folium.

There is a large amount of white matter in each cerebellar hemisphere. The white matter is made up of three groups of fibers. Name the fibers of white matter of cerebellum.

1. Intrinsic fibers. 2. Afferent fibers. 3. Efferent fibers.

Describe the location of cerebellum.

1. Largest part of hindbrain. 2. Located in the posterior cranial fossa underneath tentorium cerebelli and behind pons and medulla oblongata. 3. Separated from the pons and medulla by cavity of fourth ventricle. 4. Connected to brainstem by cerebellar peduncles.

State 3 functions of cerebellum.

1. Maintenance of posture. 2. Maintenance of muscle tone. 3. Coordination of voluntary motor activity.

[EXTRA] Name three longitudinal subdivisions of the cerebellum.

1. Median. 2. Paramedian. 3. Lateral.

Name 3 layers of cerebellar cortex.

1. Molecular layer. 2. Single Purkinje cell layer. 3. Inner Granular layer.

State the Charcot's neurologic triad in cerebellar disease.

1. Nystagmus - repetitive, uncontrolled eye movements. 2. Intention tremor. 3. Scanning speech.

Name 5 different type of cells in cerebellar cortex.

1. Purkinje cell. 2. Golgi cell. 3. Basket cell. 4. Granule cell. 5. Stellate cell.

Describe briefly single Purkinje cell layer of cerebellar cortex.

1. Purkinje cells are large Golgi type I neurons. 2. They are flask shaped and are arranged in a single layer. 3. Collateral branches of the Purkinje axon make synaptic contacts with the dendrites of basket and stellate cells of the granular layer in the same area or in distant folia. 4. A few of the Purkinje cell axons pass directly to end in the vestibular nuclei of the brain.

State three other signs of cerebellar disease.

1. Scanning/Staccato speech: "Walk (pause) ing is good ex (pause) er (pause) cise". 2. Hypotonia. 3. Dysmetria / past pointing: overshooting in attempt to touch an object with a finger. 4. Rebound phenomenon : cannot brake movement (pendular knee jerk). 5. Intention tremor.

Name three arteries supplying blood to the cerebellum.

1. Superior cerebellar artery (SCA). 2. Anterior Inferior cerebellar artery (AICA). 3. Posterior Inferior cerebellar artery (PICA).

The axons of the Purkinje cells project with few exceptions on the deep cerebellar nuclei. Name the deep cerebellar nuclei which receive the output from: 1. Vermis. 2. Intermediate region. 3. Lateral part.

1. Vermis - projects into Fastigial nucleus. 2. Intermediate region - projects to Globose & Emboliform nuclei. 3. Lateral part - projects to Dentate nucleus. VF-IGE-LD + Purkinje axons exert an inhibitory influence on the neurons of the cerebellar nuclei and the lateral vestibular nuclei.

State the effects of cerebellar lesions in: 1. Vestibulocerebellum. 2. Medial spinocerebellum. 3. Lateral spinocerebellum. 4. Cerebrocerebellum.

1. Vestibulocerebellum - Ataxia, disequilibrium, nystagmus. 2. Medial spinocerebellum - disturbances in control of axial & trunk muscles during attempted antigravity postures. 3. Lateral spinocerebellum - disturbances in control of distal muscles. 4. Cerebrocerebellum - delays in initiating movements & decomposition of movements.

State the function for each functional divisions of cerebellum respectively.

1. Vestibulocerebellum - for equilibrium & eye movement. 2. Spinocerebellum - medial (control axial & proximal limb muscles) while lateral (control distal limb muscles). Also acts as comparator which compares plan with performance. 3. Cerebrocerebellum - plan & program movements along with motor cortex.

State the functional divisions of cerebellum & their output respectively.

1. Vestibulocerebellum - to vestibular nuclei for balance and eye movement. 2. Medial portion of spinocerebellum - vermis via Fastigial nucleus. 3. Lateral portion of spinocerebellum - via Emboliform & Globose nuclei. 4. Cerebrocerebellum - via Dentate nucleus to the ventrolateral thalamic nucleus.

State the inputs to the various part of cerebellum: 1. Vestibulocerebellum. 2. Spinocerebellum. 3. Cuneocerebellar. 4. Tectocerebellar. 5. Pontocerebellar. 6. Olivocerebellar.

1. Vestibulocerebellum - vestibular inputs from labyrinths. 2. Spinocerebellum - proprioceptive & exteroceptive impulses from dorsal (lower limb & trunk) and ventral (upper & lower limbs). 3. Cuneocerebellar - proprioceptive impulses from upper limb & upper thorax. 4. Tectocerebellar - auditory & visual impulses from superior & inferior colliculus. 5. Pontocerebellar - motor & other parts of cerebral cortex via pontine nuclei. 6. Olivocerebellar - proprioceptive input from whole body via inferior olive.

Archicerebellum is the oldest part of cerebellum. State the features of Archicerebellum: 1. Components. 2. Nucleus. 3. Chief connections. 4. Function.

Archicerebellum: 1. Components - Flocculonodular lobe & lingula. 2. Nucleus - Fastigi. 3. Chief connections - Vestibulocerebellar. 4. Function - Maintenance of equilibrium, tone & posture of trunk muscles.

What is the decomposition of movements?

Difficulty performing actions that involve simultaneous motion at more than one joint. They dissect such movements and carry them out one joint at a time.

Ataxia is the incoordination due to error in Rate, Range, Force, Direction of movement. State type of ataxia in cerebellar lesions.

Drunken gait: abnormal wide-based and unsteady gait.

What is dysdiadochokinesia or adiadochokinesia in cerebellar disease?

Dysdiadochokinesia (discomfort) or Adiadochokinesia (inability) to alternately pronate & supinate forearm while flexing & extending elbow as rapidly as possible.

Afferent fibers of white matter in cerebellum form the greater part of the white matter and proceed to the cerebellar cortex. They enter the cerebellum mainly through?

Inferior and middle cerebellar peduncles.

State the result of neural circuitry in cerebellum.

Modulating or timing the excitatory output of the deep cerebellar nuclei to the brainstem and thalamus.

Paleocerebellum is the next part of cerebellum to appear in terrestrial vertebrates. State the features of Paleocerebellum: 1. Components. 2. Nucleus. 3. Chief connections. 4. Function.

Paleocerebellum: 1. Components - Anterior lobe (except lingula), Pyramid & Uvula. 2. Nucleus - Globose & Emboliform. 3. Chief connections - Spinocerebellar. 4. Function - control tone, posture & crude movements of the limbs.

Describe briefly the intrinsic fibers of white matter in cerebellum.

The intrinsic fibers do not leave the cerebellum but connect different regions of the organ. Some interconnect folia of the cerebellar cortex and vermis on the same side; others connect the two cerebellar hemispheres together.

Describe briefly molecular layer of cerebellar cortex.

The molecular layer contains two types of neurons: 1. Outer stellate cell and the inner basket cell. 2. These neurons are scattered among dendritic arborizations and numerous thin axons that run parallel to the long axis of the folia. 3. Neuroglial cells are found between these structures