Transcript Cerebellum13

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 anatomy
A. 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 of Muscles of
body axis
limbs
peripheral
Fig. 13-6A:
Dorsal Spinocerebellar Tract
Upper limbs,
trunk
Cuneocerebellar Tract
Note from where these tracts
originate.
Travels in ipsilateral lateral
column.
Both of these tracts enter
cerebellum through the
ipsilateral ipsilateral inferior
cerebellar peduncle.
Sensory info comes from periphery.
Lower limbs,
trunk
Fig. 13-6B:
Descending Pathways:
Ventral Spinocerebellar Tract travels after
a decussation in the ventral portion of the
lateral column and enter cerebellum via the
superior cerebellar peduncle.
Once in cerebellum, fibres cross again; so, input
is ipsilateral!
Rostral Spinocerebellar
Both relay internal feedback signals reflecting
amounts of neural activity in descending
pathways.
Border of
ventral and
intermediate
zone of sc
Lower limbs + trunk
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
Spinocerebellar Output:
As noted earlier, the vermis will
send efferents through fastigial n.
Inferior cerebellar peduncles
Medial descending
pathways and
reticulospinal and
vestibulospinal
VL
1° motor ctx
descends
Medial(ventral)
Corticospinal tract
Fig. 13-7
The intermediate hemisphere will
send efferents through interposed n.
Superior cerebellar peduncle
Red nucleus
(magnocellular)
Rubrospinal tract
VL
Lateral corticospinal 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 cerebellar
cortex
Vestibular nuclei
Med
Med and lat longitud
VS tracts
Fasciculus
(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 pathways
1. Scp and its decussation visible here (caudal midbrain).
Fig. 13-17
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.
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