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HNNS > HNS22 Cerebellum > Flashcards

HNS22 Cerebellum Flashcards

1
Q

Motor control regulation

A

3 main neural areas

  1. Motor cortex
    - Corticospinal tract
  2. Basal ganglia
  3. Cerebellum
    - connect to cerebral cortex (Superior peduncle)
    - connect to brainstem reticular formation (Reticular nuclei, Vestibular nucleus, Red nucleus) —> descending projection
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2
Q

Key functional role of cerebellum

A
  1. Sensorimotor integration
  2. Coordination and control of movements
  3. Cognitive processes
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3
Q

Clinical test for cerebellar function

A
  1. Finger to nose test (Past-pointing sign) —> Abnormal trajectory + Intention tremor (Errors in range / force of movement)
  2. Dysdiadochokinesia test (Errors in rate / regularity of movement)
  3. Heel to shin test
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4
Q

Basic structure of cerebellum

A

Lobules division:

  • 10 lobules
  • lobule 1-8 —> Anterior + Posterior lobe —> Subdivided into Sagittal zones
  • lobule 9, 10 —> Flocculonodular lobe —> ***Vestibulocerebellum

Sagittal zones:

  1. Vermis
    - Fastigial nucleus (paired)
  2. Intermediate hemisphere
    - Globose nucleus
    - Emboliform nucleus

—> Vermis + Intermediate hemisphere = ***Spinocerebellum

  1. Lateral hemisphere —> ***Cerebrocerebellum
    - Dentate nucleus

Purkinje cells / Cortex cells of cerebellum (外面) —> Zonal projection to Subcortical cerebellar nuclei (connect with its own deep nuclei in each region)
e.g. cortex cells of Vermis connect to Fastigial nucleus (+ Vestibular nucleus)

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5
Q

Connections of cerebellum to brainstem

A
  1. Superior cerebellar peduncle
    - Output to Thalamus and Cortex —> fine tune and control movement
    - Output from:
    —> Fastigial nucleus
    —> Globose nucleus, Emboliform nucleus
    —> Dentate nucleus
  2. Middle cerebellar peduncle
    - Input from Pons (e.g. Corticopontine fibres / descending tract)
  3. Inferior cerebellar peduncle
    - Input from Medulla (esp. Inferior olive) / Spinal cord (e.g. Spinocerebellar tract (proprioceptive information))
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6
Q

2 types of input fibres (via middle and inferior cerebellar peduncle)

A

Cerebellar inputs converge on Purkinje cells

  1. Mossy fibres (MAJOR)
    - Middle + Inferior peduncle
    - Indirect excitatory input:
    —> ***Granule cell (also in cortex) —(ascend)—> Parallel fibres —> Purkinje cell (cortex cells)
    —> Subcortical cerebellar nuclei
  2. Climbing fibre (from inferior olive)
    - Inferior peduncle only
    - Direct excitatory input:
    —> Purkinje cell (cortex cells) (each climbing fibre contact <10 Purkinje cells)
    —> Subcortical cerebellar nuclei
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7
Q

Purkinje cell

A

Top layer of cortex

Huge but thin dendritic tree —> staggered layer

***ONLY cortical output neuron

Input:
—> receive **Excitatory input from 1. Granule cell parallel fibres (from Mossy input) + 2. Climbing fibre (both innervate dendritic tree)
—> receive **GABA Inhibitory input from 1. Stellate cell + 2. Basket cell + 3. Golgi cell

Output:
—> Integrate excitatory / inhibitory input in soma
—> ***GABA inhibitory output (out of cortex)
—> Subcortical cerebellar nuclei (majority) / Brainstem (vestibular nuclei of reticular formation)

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8
Q

Stellate cell and Basket cell

A
  • Both in cortex
  • GABAergic inhibitory
  • receives collateral Climbing fibres + Granule cell parallel fibres (excitatory)
    —> Transverse fibre
    —> GABAergic inhibition
    —> control excitability of Purkinje cell

Stellate cell:
- inhibit ***dendritic tree of Purkinje cell

Basket cell:
- inhibit ***soma of Purkinje cell

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9
Q

On-beam (射程範圍內) and Off-beam (射程範圍外) excitation / inhibition

A

Mossy fibre
—> excite Granule cell (Parallel fibre)

Initially:
—> excite On-beam Purkinje cell

Then:
—> excitatory signals spread to other regions
—> excite On-beam Stellate cell + Basket cell

Excited Stellate cell + Basket cell
—> inhibit adjacent Off-beam Purkinje cell

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10
Q

On-beam and Off-beam Purkinje cell

A

On-beam Purkinje cell (excited by Parallel fibres):
- ***Inhibition of:
—> Subcortical cells (majority)
—> Brainstem cells

Off-beam Purkinje cell (inhibited by Basket cell + Stellate cell):
- ***Dis-inhibition of:
—> Subcortical cells (majority)
—> Brainstem cells

Inhibition / Dis-inhibition of a particular subcortical / brainstem cell:
- depend on Spatial temporal arrangement of output of cerebellum

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11
Q

Output of Subcortical cerebellar nuclei

A
  • Excitatory
  1. Thalamus —> then to Cerebral cortex
  2. Brainstem nuclei (i.e. Red nucleus, Vestibular nuclei, Reticular formation)

(唔會直接落spinal cord影響LMN)

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12
Q

***Inputs to Cerebellum

A

Vermis and Intermediate hemisphere:

  1. Spinal input (Sensory discrimination: Globose nucleus + Emboliform nucleus)
  2. Trigeminal input
  3. Visual input
  4. Auditory input
  5. Vestibular input (Vermis only)
  6. Cerebral cortex input (Intermediate hemisphere only)

Lateral hemisphere:
1. Cerebral cortex input

Flocculonodular lobe:
1. Vestibular input

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13
Q

***Cerebellar output

A
  1. Flocculonodular lobe:
    - Vestibular nucleus + Reticular formation (Balance, postural control, ***eye movement) —> Vestibulospinal tract + Reticulospinal tract
  2. Vermis (Medial corticonuclear zone):
    - Vestibular nucleus + Reticular formation (Balance, postural control) —> Vestibulospinal tract + Reticulospinal tract
    - Medial descending pathway (Motor execution)
  3. Intermediate hemisphere (Intermediate corticonuclear zone):
    - Red nucleus —> Rubrospinal tract
    - Lateral descending pathway (Motor execution)
  4. Lateral hemisphere:
    - Motor / Premotor cortex (Motor planning) —> Corticospinal tract
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14
Q

***Functional units of cerebellum

A
  1. Vestibulocerebellum (Flocculonodular lobe)
    - **Vestibulo-spinal reflex (Postural **reflexive movement via axial motor system)
    —> **1. Reticulospinal tract + 2. Lateral vestibulospinal tract
    - **    Vestibulo-ocular reflex
  2. Spinocerebellum (Vermis + Intermediate hemisphere)

Error detector by comparing command signals (in form of neural replica of intended action) from cerebral cortex (Cortico-ponto-cerebellar pathway) with updated feedback (via Spinocerebellar pathway)

Vermis (Medial corticonuclear zone):
- Postural / Voluntary movement of **Axial + **Proximal body parts
—> **1. Reticulospinal tract + 2. Vestibulospinal tract
—> 3. Ascending: Thalamocortical projection affecting **Medial Corticospinal tract / Medial descending system

Intermediate hemisphere (Intermediate corticonuclear zone)
- Voluntary movement of **Distal body parts by Moment-to-moment correction
—> 1. **Rubrospinal tract
—> 2. Ascending: Thalamocortical projection affecting ***Lateral Corticospinal tract / Lateral descending system

  1. Cerebrocerebellum (Lateral hemisphere)
    - Lateral hemisphere (Lateral corticonuclear zone)
    —> Convert movement designs (by Association cortex via Cerebro-cerebellar tracts) to programs
    —> Premotor cortex for subsequent execution of
    —> **Goal-directed voluntary movements
    —> **    Voluntary Oculomotor control (eye-hand coordination)
    (—> Cognitive processes)
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15
Q

Vestibulo-spinal reflex + Vestibulo-ocular reflex

A 
Vestibulo-spinal reflex:
Vestibular nucleus + Spinal cord + Reticular formation
—> ***both Vermis + Vestibulocerebellum
1. Lateral vestibulospinal tract
2. Reticulospinal tract

Vestibulo-ocular reflex:

  • Only output from ***Vestibulocerebellum
  • Vestibulo-related eye movements
  • Flocculus controls open-loop reflex
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16
Q

Vermis circuitry pathway

A

Spinocerebellar pathway
—> Vermis
—> Fastigial nucleus
—> **Reticular formation (—> Mossy fibres —> feedback to Vermis) + **Vestibular nuclei
—> **1. Reticulospinal tract + **2. Vestibulospinal tract
—> Axial + Proximal muscles
—> Spinocerebellar pathway (afferent feedback about movement)
—> Mossy fibres
—> Vermis

Thalamocortical projection: Afferent feedback about movement
—> Thalamus
—> Motor cortex
—> ***Medial Corticospinal tract
—> Axial + Proximal muscles
17
Q

Intermediate hemisphere circuitry pathway

A 
***Motor cortex
—> ***Cortico-ponto-cerebellar pathway
(—> Pons)
—> Mossy fibres
—> Intermediate hemisphere
—> Globose nucleus + Emboliform nucleus
—> ***Red nucleus
(—> Inferior olive —> Climbing fibres —> feedback to Intermediate hemisphere)
—> ***Rubrospinal tracts
—> Distal muscles
—> Spinocerebellar pathway (afferent feedback about movement)
(—> Pons)
—> Mossy fibres
—> Intermediate hemisphere
Thalamocortical projection: Afferent feedback about movement
—> Thalamus
—> Motor cortex
—> ***Lateral Corticospinal tract
—> Distal muscles
18
Q

Lateral hemisphere circuitry pathway

A

簡單: Association cortex —> Cerebro-cerebellar tracts —> Cerebellum —> Premotor cortex —> Motor cortex —> Corticospinal tract

***Association cortex (movement design)
(—> Pons)
—> ***Cerebro-cerebellar tracts
—> Mossy fibres
—> Lateral hemisphere
—> Dentate nucleus (movement program)
(—> Red nucleus —> Inferior olive —> Climbing fibres —> feedback to Lateral hemisphere)
—> Thalamus
—> ***Premotor cortex
—> ***Motor cortex (Master of movement control)
—> Corticospinal tract
—> Muscles

(Also,
Dentate nucleus
—> Red nucleus
—> Rubrospinal tract)

19
Q

Clinical correlations

A
  1. Ataxia (errors in rate, range, force, direction)
    - decomposition of movement
    - asynergia
    - dysmetria
    - unsteady / uncoordinated of posture and gait (Clinical test: Tandem steps)
    - adiadochokinesia
    - asthenia
    - scanning / slurred speech
  2. Intention tremor (=/ Resting / unintention tremor (Basal ganglia disorder))
  3. Hypotonus
  4. Nystagmus (associated with Vestibulocerebellum —> problem with Vestibulo-ocular reflex)
    - alternate slow and fast eye movements

HNNS (58 decks)

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