2. Control of movement 3/ The cerebellum Flashcards
The cerebellum modulates motor output based on integration of which 3 sources of info?
- Activity in the pre-motor and motor areas as well as spinal motor circuits (information about potential motor output)
- Sensory feedback from vestibular system, visual system and ascending proprioceptive information (about real motor output)
- Modulation by the cerebellum is effected at the motor cortex and brainstem
All an automated ability, so any damage then requires patient to put conscious thought into movements.
Name the structural lobes and columns of the cerebellum?
Columns: Vermis, intermediate part of the hemisphere, lateral part of the hemisphere
Lobes: Anterior, posterior, flocculonodular
Layers of the cerebellar cortex?
3 main layers:
OUTER: Molecular
MIDDLE Purkinje cell layer: Contains purkinje cell bodies, forms main output of cerebellum via deep nuclei
INNER Granule cell layer: Vast array of synapses
BELOW is white matter containing tracts from rest of body
Where is the input transmitted by the climbing fibre from?
The olives
Fibre that carries input into granular cells
Mossy fibres from pontine nuclei and other sources
What are the principal afferents of the cerebellum? Where do they come from and insert on the cerebellum?
From the…
- Pre- and Primary motor cortex AND the somatosensory cortex via pontine nuclei and middle peduncle (in cerebrocerebellum)
- Reticular nuclei and olives via inferior peduncle
- Vestibular nuclei via inferior peduncle
- Dorsal ascending spinal proprioception via inferior peduncle
- Ventral ascending spinal proprioception via the superior peduncle
3 structural units of cerebellum?
Spinoserebellum
Cerebrocerebellum
Vestibulocerebellum
Vestibular system afferents to the cerebellum?
- Inputs from vestibular nuclei (balance) project to the vestibulocerebellum (flocculonodular lobe) and vermis
- The flocculonodular is involved with maintaining balance and posture
Proprioceptive feedback afferent to the cerebellum?
- Inputs from ascending sensory spinal pathways derived principally from proprioceptors to the spinocerebellum (= Anterior lobe + Vermis + Intermediate vermis)
- The spinocerebellum modulates axial or antigravity muscles and eye movement
- The spinocerebellum contains a somatotopical map of the body
What makes up the spinocerebellum?
Anterior lobe
Vermis
Intermediate Vermis
What is the cortical input into the cerebellum?
- Inputs from the motor & pre-motor cortex as well as somatosensory cortex via multiple pontine nuclei project to the cerebrocerebellum
- Functions to sequence and coordinate distal muscles esp. during locomotion or juggling etc.
Function of cerebrocerebellum?
The cerebrocerebellum is involved with motor planning, and feeds information back towards the cerebra
What are the deep nuclei of the cerebellum?
(Lateral to medial) Dentate nucleus Emboliform nucleus Globose nucleus Fastigial nucleus
ALL INVOLVED IN CEREBELLAR OUTPUT
What makes up the interposed nucleus?
Emboliform nucleus
Globose nucleus
Each functional division projects to its target via a d_____ ________
Each functional division projects to its target via a deep nucleus
What are the functional divisions of the cerebellar input?
Vestibular system (balance)
Proprioceptive feedback
Cortical input
What are the two outputs of the cerebellar fastigial nucleus?
- For motor execution
Via descending systems (for trunk and proximal via the reticular formation) - Head and eye movements
Via vestibular nuclei, tectum and cranial nerve nuclei
What is the output of the cerebellar interposed nuclei?
Interposed nuclei made up of Emboliform nucleus +Globose nucleus
For motor execution: Via lateral descending system (for distal and extremities via spindles)
What is the output of the cerebellar dentate nuclei?
For motor planning
Via motor and premotor cortices
Which cerebellar nuclei is in charge of:
- Motor execution
- Motor planning
- Head and eye movement
- Motor execution: Fastigial and interposed nuclei
- Motor planning: Dentate
- Head and eye movement: Fastigial
Function of reticular formation?
4 categories: motor control, sensory control, visceral control, and control of consciousness.
- Motor control refers to physical movements or activities such as walking or running.
- Sensory control consists of all the senses including pain.
- Visceral control encompasses breathing, heart rate and blood pressure.
- Control of consciousness refers to alertness, sleeping, and various conscious states.
Role of vestibular nuclei?
The vestibular nuclei function in the maintenance of equilibrium and posture, the perception of head position and acceleration, as well as general muscle tone.
Describe the processes that occur in the vestibulocerebellum to maintain posture?
Input:
Information from the vestibular nucleus is passed to the vestibulocerebellum and the vermal /paravermal areas and processed. Feed forward from Cortex and feedback from vestibular + olivary information.
Olivary information enables the calculation of predicted posture in advance of it happening, so feed forward posture adjustment allows fast postural changes e.g. sprinting or fast dancing.
Output:
Motor instructions/corrections are sent to the Fastigial nucleus and then on bilaterally to the vestibular nuclei and medullary reticulum (inhibitory).
Medullary reticular output and both medial and lateral vestibulospinal output (extensor excitation) act to stabilise balance by acting on axial and proximal muscles.
Other name for vestibulocerebellum?
Flocculonodular lobe
What is cerebellar hypoplasia?
Presentation?
Cerebellar hypoplasia is characterized by reduced cerebellar volume even though cerebellar shape is (near) normal.
It consists of a heterogeneous group of disorder of cerebellar maldevelopment presenting as early onset non progressive ataxia, hypotonia, and motor learning disability.
Condition known as Truncal ataxia
What is the difference between the course of proprioceptive information and motor intention information, when arriving at the spinocerebellum?
Proprioceptive information arrives at the spinocerebellum via the spinocerebellar and cuneocerebellar (cuneate nucleus) tracts.
Motor intention information is sent to the spinocerebellum from the motor cortex
When and how are planned and actual motor outs compared?
Motor intention is relayed to the spinocerebellum along with ascending sensory information.
Planned and actual motor output are compared, and corrective signals sent VIA THE THALAMUS to the cerebra, the red nucleus and vestibular nuclei.
Planned and actual motor output are compared in the spinocerebellum, what is it called when there are errors in this mechanism?
Errors in these corrections are classified as anterior lobe syndrome and include: 1. Overshoot (Dysmetria) 2. Intention tremor 3. Lack of movement damping
What is the role of cerebrocerebellum area in sequencing and timing complex movements
Input:
Pre-motor and sensory areas in cortex make plan for a complex movement. This signals is sent to the lateral cerebrocerebellum via pontine nucleus.
Output:
The plan has now been processed by cerebellum so that order and timing is arranged. This new plan is sent back to the cortex through the dentate nucleus first THEN to through the thalamus and red nucleus.
All these abilities of the cerebellum improve with ____ (plasticity and ________)
All these abilities of the cerebellum improve with practice (plasticity and learning
Why do unilateral cerebellar lesions have ipsilateral effects?
Output from the cerebellum is contralateral to the motor centres, which then crosses back at the pyramids
= DOUBLE CROSS
Why are medial lesions to the vermis bilateral?
Medial lesions to the vermis are bilateral for trunk and proximal because the medial motor system innervation is bilateral
Result of medial cerebellar lesions?
Medial cerebellar lesions affect medial descending pathways, causing unsteady gait (truncal ataxia), problems with balance, posture and eye movement abnormalities (nystagmus)
Result of lateral cerebellar lesions?
Lateral cerebellar lesions affect:
control of distal muscles
motor planning
i.e. areas of cerebellum that control muscles of extremities.
Results in limb ataxias
How to localise lesions to cerebrocerebellum?
Cause:
- Delay in initiation of movement
- Decomposition of multi-joint movements
e. g. loss of complex motor skills
How to localise lesions to vermis (in spinocerebellum) and the fastigial nucleus?
Affect axial and trunk muscles
Makes balance unsteady –> wide stance
Some facial muscles have feed-forward from the vermis. Lesions produced slowed and slurred speech
How to localise lesions to intermediate lobe (in spinocerebellum)?
Affect distal muscles and causes limb ataxia and action tremor
