The Cerebellum

I. Gross anatomy

- major divisions

- cerebellar peduncles (afferents and efferents)

- folia (= gyri)

- deep cerebellar nuclei

II. Functional anatomy

A. Spinocerebellum

B. Cerebrocerebellum

C. Vestibulocerebellum

III. Regional anatomyA. Cytoarchitecture and circuitry of the cerebellar cortex.

B. Cerebellar-associated nuclei of the spinal cord + medulla.

C. Pontine nuclei.

D. Deep cerebellar nuclei.

E. Midbrain pathways.

F. VLN of thalamus.

G. Clinical notes regarding cerebellar lesions.

I. Gross Anatomy

A. Location: dorsal to pons and 4th ventricle and medulla (cut it off to view dorsal surface anatomy of brainstem).

- separated from overlying cerebral cortex by tentorium cerebelli (a tough dorsal flap).

- 2 symmetrical halves, partly divided by posterior cerebellar incisure (also containing a dorsal flap, the falx cerebri).

B. Major anatomical divisions (reflecting functional regions):

- vermis

- intermediate hemisphere

- lateral hemisphere

Folds on terminal folia (equivalent to gyri in cerebral cortex)

Cortex = organized into groups of folia = 10 lobules and 3 lobes, which are functionally important:

Fig. 13-1

Fig. 13-1

Fig. 13-2A

I. Gross Anatomy

Anterior: I – V.

Posterior: VI – IX.

Flocunodular: X.

C. Cerebellar peduncles (Fig. 13-1B) – All axons travelling to and from the cerebellum course through these.

superior: efferents

middle: afferents

inferior: efferents + afferents

D. Deep cerebellar nuclei – key elements of neural circuit (Fig. 13-2B): 4 nuclei (med lat):

fastigial

globose

emboliform

dentate

Fig. 13-2B

Note: vestibular nuclei also play a role, as we will soon see…

II. Functional Anatomy of the Cerebellum

3 Major functional divisions:A. Spinocerebellum – inputs from sc; controls posture and

movement of trunk and limbs.

- provides some immediate feedback based on sensory input from the muscles.

- comprises the vermis + intermediate hemisphere of both anterior and posterior lobes.

- projects through fastigial and interposed nuclei.

- has a somatotropic organization.

Spinocerebellar tracts: 4 afferent tracts.

II. Functional Anatomy of the Cerebellum: 3 Major Functional Divisions

Muscles ofbody axis

Muscles oflimbs peripheral

Fig. 13-6A:Dorsal Spinocerebellar Tract

Cuneocerebellar Tract

Note from where these tractsoriginate.Travels in ipsilateral lateralcolumn.Both of these tracts enter cerebellum through theipsilateral ipsilateral inferiorcerebellar peduncle. Lower limbs,

trunk

Upper limbs,trunk

Sensory info comes from periphery.

Fig. 13-6B:Descending Pathways:

Ventral Spinocerebellar Tract travels aftera decussation in the ventral portion of thelateral column and enter cerebellum via thesuperior cerebellar peduncle.Once in cerebellum, fibres cross again; so, inputis ipsilateral!

Rostral Spinocerebellar

Both relay internal feedback signals reflectingamounts of neural activity in descendingpathways.

Lower limbs + trunk

Border ofventral andintermediatezone of sc

Fig. 13-4: Input-output organization.Inputs: All major inputs feed to dcn,As well as cerebellar cortex.Output = once again through dcn.

Fig. 13-7

Inferior cerebellar peduncles

Medial descendingpathways andreticulospinal andvestibulospinal

VL

1° motor ctxdescends

Medial(ventral)Corticospinal tract

Spinocerebellar Output:As noted earlier, the vermis willsend efferents through fastigial n.

Fig. 13-7

The intermediate hemisphere will send efferents through interposed n.

Superior cerebellar peduncle

Red nucleus (magnocellular)

VL

Lateral cortico-spinal tract

Rubrospinal tract

B. Cerebrocerebellum

-participates in the planning of movement

-located in the lateral hemisphere

-projects to the dentate nucleus

This part of the cerebellum is interconnected with the cerebral cortex, rather than receiving its input from the spinal cord.

Afferent input – See Fig. 13-8 – from entire contralateral cerebral cortex:

Fig. 13-8

Contralateral cerebral ctx

Middle pontine n.

Middle cerebellar peduncle

Contralateral cerebellar cortex

Efferent pathway

Dentate n.

Red n. (parvocellular) inferior olivary n. (ipsilateral)

VL 1° motor ctx and premotor ctx + prefrontal ctx (influences beh and learn)

C. Vestibulocerebellum

- functions in maintaining balance and controlling head and eye movements.

- input from vestibular labyrinth.

- located in floculonodular lobe.

- projects to vestivular nuclei (taking the place of the dcn here).

Afferent input:- 1° vestibular afferents (note only 1° sensory n.

projecting directly to cerebellum).- 2° vestibular neurons in vestibular nuclei.

Efferent path: See Fig. 13-9.

Fig. 13-9

Vestibular cerebellarcortex

Vestibular nuclei

Med and latVS tracts

MedlongitudFasciculus(eyes, head)

III. Regional Anatomy

A. Cytoarchitecture and circuitry of the cerebellar cortex.

- 3 cell layers: molecular, purkinje, granular

Fig. 13-10

Folium

Fig. 13-10: Cellular resolution

5 Cell Types:1. Purkinje (inhibitory – GABA)

- contacted by climbing fibres

- the major output neuron (the only neuron projecting outside the cerebellar cortex).

Location: PCL

- projects to dcn

- projects to vestibular nuclei through inferior cerebellar peduncle (icp).

2. Granule cell (this and remaining 3 are interneurons)

- contacted by mossy fibres.

- the only excitatory neuron.

- puts out just 1 parallel fibre up into molecular layer purkinje dentrites.

5 Cell Types (Cont’d):3. Stellate Cells – contact Purkinje cell dendrites (inhibitory).

- location: outer molecular layer (inhibitory, taurine).

4. Basket Cells – contact Purkinje soma (“basket” around it) – inhibitory.

- location: inner molecular layer (inhibitory, GABA).

5. Golgi Cells – contacts granule cell within “glomeruli” (inhibitory) – glial capsule and specificity of connections.

- location: granule cell layer (inhibitory, GABA).

See Fig. 13-11 for topology of cells.

Fig. 13-11

B. Cerebellar-associated nuclei of the spinal cord and brainstem (medulla).

Clarke’s Nucleus and accessory cuneate nucleus relay sensory info to spinocerebellum.

1. Spinal cord:

- Clarke’s n. (Fig. 13-14) courses from C8 to L2 within the medial portion of the intermediate zone.

somatic sensory info from lower limbs and trunk

- Axons travel in dorsal spinocerebellar tract icp (medulla).

- also visible: ventral spinocerebellar tract scp (pons) [originating from spinal border cells].

Fig. 13-14

2. Brainstem:

- Accessory cuneate nucleus (Fig. 13-15).

- visible in caudal medulla

- somatic sensory info from upper limbs and trunk.

- trunk served by cuneate fascicle and feeds to icp.

Go back and refer to Fig. 13-8: The 1 input is the red nucleus-parvocellular.

- Inferior olivary nucleus – origin of all climbing fibres.

- Medial and inferior vestibular nuclei (“dcn” for vestibulocerebellum) – receives Purkinje cell axons from flocculonodular lobe vestibulospinal tracts and the medial longitudinal fasciculus (eye muscle control).

Fig. 13-15

C. Pontine nuclei (Fig. 13-16) – These relay input from cerebral cortex cerebrocerebellum.

Motor, sensory cortices (1° and 2°) [LAYER 5] pontine nuclei

Internal capsule,

basis pedunculi

axons decussate in pons, later

cerebellum via mcp

[review: efferent from cerebellum through dentate back to cerebral cortex].

Fig. 13-16

D. Deep cerebellar nuclei

- visible in section through caudal pons (Fig. 13-17).

- within deep wjite matter underlying the cerebellar cortex.

- fastigial n. of pons, medulla (medial descending systems: reticulo, vestibulospinal).

- descending projections from all dcn course in the scp.

Fig. 13-17

Fig. 13-17

E. Midbrain pathways1. Scp and its decussation visible here (caudal midbrain).

2. Interposed n. magnocellular red nucleus rubrospinal tract (note also the corticopontine fibres).3. Dentate n. parvocellular red nucleus central tegmental tract

inferior olivary nucleus.

Fig. 13-17

Ascending via the VL to motor cortices and prefrontal cortex (Fig. 13-18).

Fig. 13-18

F. VL (thalamic) nucleus.Cerebellar tract can be followed in Fig. 13-18.VL is rostral to VPL (for somatic sensory relay).VL 1° motor cortex and premotor cortex.

G. Clinical notes regarding cerebellar lesions 3 classic signs of cerebellar dysfunction:

1. Ataxia – inaccuracy (undershoot, overshoot), staggering.

2. Nystagmus – rhythmic oscillations of the eyes.

3. Tremors – involuntary oscillations of limbs (“intention tremor”). symptoms are ipsilateral to lesion.

[note the many unusual and doubly-crossed pathways]

On the next slide, we have some behavioral problems associated with cerebellar lesions