Cerebellum

Dr. Safaa

Objectives• Identify the major lobes and regions of cerebellum.• Summarize the structure of the cerebellar cortex• Identify the deep cerebellar nuclei and their

connections.• List the afferent and efferent connections of the

cerebellum and their arrangement in cerebellar peduncles.

• Describe the major functions of the cerebellum and how each side of the cerebellum controls the ipsilateral side of the body.

• Explain the effects of lesions of cerebellum and motor disorder associated with cerebellar lesions.

Gross Appearance of the Cerebellum • The cerebellum is situated in posterior cranial

fossa • Covered superiorly by tentorium cerebelli.• Lies posterior to the fourth ventricle, the pons, and

the medulla oblongata.• It consists of two cerebellar hemispheres joined

vermis. • The cerebellum is connected to the posterior

aspect of the brainstem by:• Superior cerebellar peduncles (midbrain).• Middle cerebellar peduncles (pons).• Inferior cerebellar peduncles (medulla oblongata).

Cerebellum

• The cerebellum is divided into three main lobes:

• Anterior lobe which is separated from the middle lobe primary fissure.

• Middle (posterior) lobe which is situated between

the primary and uvulonodular fissures.

• Flocculonodular lobe. which is situated

posterior to the uvulonodular fissure

A deep horizontal fissure separates the superior from the inferior surfaces.

• Structure of the Cerebellum

• The cerebellum is composed of:

• Outer cortex of gray matter.

• Inner white matter. • Three masses of gray

matter (intracerebellar nuclei) are embedded in the white matter.

• The cerebellar cortex is formed of folds called folia.

• Each fold or folium contains a core of white matter covered superficially by gray matter.

• A section made through the cerebellum parallel with the median plane has a branched appearance, called the arbor vitae.

• The gray matter of the cortex may be divided into three layers:

• (1) Molecular layer (stellate & basket cells).

• (2) Purkinje cell layer (Purkinje cells) .

• (3) Granular layer (granular & golgi cells).

Intracerebellar Nuclei: 1.Dentate: The largest of the

cerebellar nuclei. It has the shape of a crumpled bag

2. Emboliform:Is ovoid3. Globose: consists of one or more

rounded cell groups 4. Fastigial:Lies near the midline in

the vermis.• Afferents to these nuclei from:• Inhibitory from Purkinje cells.• Excitatory from climbing and

mossy fibers. • Efferents from these nuclei form

the cerebellar outflow in the superior and inferior cerebellar peduncles.

• White Matter:• The white matter is made up of three groups of fibers: • (1) Intrinsic. • (2) Afferent.• (3) Efferent.

Afferent fibers (mossy & climbing fibers):

1. From cerebral cortex(Conveys control from cerebral cortex) :

• Corticopontocerebellar through pontine nuclei in middle peduncle & terminates as mossy fibers to cerebellar cortex.

• Cerebroreticulocerebellar through reticular formation in inferior and middle peduncles& terminates as mossy fibers to cerebellar cortex.

• Cerebro-olivocerebellar through inferior olivary nuclei in inferior peduncle & terminates as climbing fibers to cerebellar cortex.

2. From spinal cord (conveys information from muscles and joints):

• Anterior spinocerebellar from nucleus dorsalis (Clarke's column) majority crossing and enter cerebellum through superior peduncle & terminates as mossy fibers to cerebellar cortex.

• Posterior spinocerebellar from nucleus dorsalis (Clarke's column) NOT crossing and enter cerebellum through inferior peduncle & terminates as mossy fibers to cerebellar cortex.

3. Cuneocerebellar (Conveys information from muscles and joints of upper limb) originate in nucleus cuneatus of medulla oblongata NOT crossing and enter cerebellum through inferior peduncle& terminates as mossy fibers to cerebellar cortex.

4. Vestibular nerve (conveys information of head position and movement) originate in inner ear NOT crossing and enter cerebellum through inferior peduncle& terminates as mossy fibers to flocculonodular lobe.

5. In addition, cerebellum receives small bundles of afferent fibers from red nucleus & tectum.

• Efferent fibers (to red nucleus, thalamus, vestibular complex, and reticular formation) :

• Purkinje cell axons synapse with all cerebellar nuclei (fastigial, globose, emboliform, and dentate).

• From dentate, emboliform, and globose nuclei through the superior cerebellar peduncle.

• From fastigial nucleus leave through the inferior cerebellar peduncle.

• Each cerebellar hemisphere influences the voluntary muscle tone on the same side of the body (ipsilateral).

• The cerebellum has no direct neuronal connections with the lower motor neurons but exerts its influence indirectly through the cerebral cortex and brainstem.