09 09 2014 Cerebelum Flashcards
Function of cerebellum
Balance, smooth coordination of movement
Where does sensory and motor inputs plus outputs go through?
- Superior peduncle
- Middle peduncle
- Inferior Peduncle
Superior peduncle
connects to midbrain and thalamus (VA/VL)
- outputs (crossed) to VA/VL and red nucleus
- some inputs from spinal cord
*decussates in midbrain at the level of the inferior colliculi
Middle peduncle
Connects to pons
- formed entirely by inputs coming from pons
- contralateral pontine nuclei
Inferior peduncle
connects to medulla/spinal cord
- inputs from medulla and spinal cord (olive)
- Outputs to vestibular and reticular nuclei
Ataxia
Uncoordinated movement
Hallmark of cerebellar sign
- appendicular (limbs)
- gait
- trunk
- Speech (no normal tempo)
- extraocular (stagmis)
What happens if there is a lateral lesion in the cerebellum?
Affect limbs ipsilaterally
What if there is a medial lesion in the cerbellum
Affect trunk and eye movements
Vermis
proximal and trunk muscle control plus vestibulo-ocular control
Intermediate part
control of more distal appendicular muscles in legs and arms
Lateral part
planning the motor program for extremities
primary fissure
1/3 from rostral
-Deep fissure that divides cerebellum from anterior vs posterior lobes
Who provides outputs?
Deep cerebellar nuclei.
* inputs come in here!
Deep cerebellar nuclei
- dentate
- Interposed nuclei (globose and emboliform)
- Fastigial nuclei
- Vestibular nuclei
Dentate nuclei
receives projections from lateral cerebellar hemisphere.
-Active before voluntary movements.
Interposed nuclei
globose and emboliform
-receive input from intermediate part of cerebellum.
Fastigial nuclei
most medial- receive input from vermis and small input from flocculonodular lobe
Vestibular nuclei
located in brainstem close to cerebellum
-output nuclei for flocculonodular lobe
-not part of deep cerebellar nuclei
Inferior olivary nucleus
located in medulla
- histology: look like dentate (but are in medulla)
- inputs from spinal cord and cortex.
- output to contralateral cerebellum via the interior cerebellar peduncle.
- IO neurons coordinate through gap junctions
- inputs throughout cerebellum
-motor learning
Cerebellum works as a comparator
An efferent copy of command is made and once it reaches the cerebellar cortex, the efferent command (copy) is compared to the feedback of original motor command and an error correction is made.
This error correction is then sent back to brainstem and cerebral cortex.
Inputs to deep cerebellar nuclei
- Mossy fibers– everywhere not from inferior olive.
2. Climbing fibers- come from contralateral inferior olivary nucleus.
Cerebellar cortex
modulate levels of feedback via purkinje fibers.
Layers of cerbellar cortex before hitting white matter
- molecular layer
- Purkinje cell layer
- Granual cell layer
Molecular layer
layer where purkinje dendrites are. they synaptic connections.
Purkinje layer
Cell bodies of purkinje neurons.
Granule cell layer
project upward toward molecular layer
-send axons to molecular layer to connect with purkinje cell dendrites.
Mossy fibers
go straight up into Granule layer and synapse with granule cells. Make end-on-end connection
Climbing fibers
Inputs from olive
- come in and go all the way up to the molecular layer (synapse at purkinje dendrite)
- activated when movement errors occur. When activated they change synaptic length of parallel fibers onto purkinje neurons – change cortical inhibitory loop
Cerebrocerebellum
Lateral hemisphere of cerebellum.
- motor planning
- active before movement
Spinocerebellum
vermis + intermediate part of cerebellum.
- feedback from spinal cord allows adjustments for movement.
- more for execution vs. planning
What are the three cerebellar circuits
- Cerebrocerebellum
- Spinocerebellum
- Vestibulocerebellum
Cerebrocerebellum circuit
Input: Cerebral cortex – pons– pontine nuclei
Controls pre-motor cortex output based on predictions. – active before movement.
* contralateral!! (Left cortex projects to right cerebellum)
-Input from cerebral cortex –> pontine nucleus–> (crosses Middle cerebellar peduncle) to get to lateral hemisphere of cerebellar cortex.
- Cerebellar corted –> dentate nucleus
- -> (crosses Superior cerebellar peduncle) to VA/VL and red nucleus (midbrain).
VA/VL –> signal back to motor cortex.
Spinocerebellum circuit
Input: Spinal cord
input travels up inferior cerebellar peduncle to Intermediate part and vermis of cerebellar cortex.
- Output to interposed and fastigial neurons.
- out puts sent to VA/VL, Red nucleus, and Reticular F., Vestibular n. and rubrospinal tract (flexors of arms)
VA/VL send signal to motor and premotor cortex.
Specific types of input from spinal cord to spinocerebellum circuit
From lower extremities:
- Dorsal spinocerebellar (Clarke’s nucleus)
- Ventral spinocerebellar (ventral horn)
From upper extremities:
- Cuneocerebellar (external cuneate n)
- Rostral spinocerebellar tract (unknown yet).
What information is sent via inputs to spinocerebellum circuit?
- proprioceptors
- Motor activation information from lumbosacral SC intermediate zone and ventral horn
Dorsal spinocerebellar tract
input to spinocerebellar tract
- muscle spindle and GTO information is sent up via gracile tract. Collateral to Clarke’s nucleus (C8-L2). Dorsal spinocerebellar tract continues ipsilatral to Inferior cerebellar peduncle
- proprioceptive information from lower limb
Cuneocerebellar tract
input to spinocerebellar tract
- muscle spindle and GTO information sent via cuneate tract –> collateral to accessory/lateral/external cuneate nucleus (located right next o cuneate nucleus– DCML) in medulla.
- ipsilateral pathway
- proprioceptive info from upper limb to inferior cerebellar peduncle
ventral spinocerebellar tract
input to spinocerebellar tract
- originates from interneurons in lumbosacral cord (intermediate zone). Cross medially all the way to the other side’s ventral spinocerebellar tract and continues contra laterally to the superior cerebellar pedunce. There, it crosses to the intermediate part and vermis of the cerebellar cortex.
- carries information of muscle activation
Vestibulocerebellum circuit
monitors and corrects eye movements, posture, and balance
- CN# 8 sends trajection to both flocullonodular lobe and (via ICP) to Vestibular n.
- Flocullonodular lobe sends projections to fastigial n. and vestibular n.
- Vestibular n. sends a descending vestibulospinal tract and an ascending MLF (eye movements)
Main points about lesion location?
- produce symptoms ipsilateral to lesion
2. posterior vermis and flocullonodular lobe lesions affect trunk and eye movements.
Clinical tests for cerebellar ataxia
Rapid movements:
- finger-to-nose
- heel-to shin
- Rebound and check reflex
- speech
- tandem walking
Dysmetria
undershooting or overshooting target.
incorrect movement amplitude (finger to nose)
Dysdiadochokinesia
difficulty with rapid alternating movements
other symptoms of cerebellar ataxia
- decreased muscle tone (floppiness ipsilateral to lesion)
- Intention tremor (at the end of a movement)
- Scanning or explode speech – irregular rhythm or volume
- Abnormal eye movements
Flocculonodular lobe (Vestibulocerebellar) syndrome
- Truncal ataxia
- reeling of trunk from side to side
- Titubation- tremor of the trunk
- patients walk with a wide base of support
- abnormal eye movements.
testing for vestibulocerebellar syndrome
station (position in standing still with eyes open)
walking
Tandem gait
Anterior lobe syndrome
– anterior lobe of cerebellar cortex.
–deficits that mainly affect lower extremity usually bilaterally.
- ingestion of toxin (ethanol or other)
- alchololism
-broad-based, staggering gait
What complications would you see in a tonsil hernia?
Cerebellum is also in posterior fossa
Chiari I:
-compression of medulla (respiratory center) and upper spinal cord
- compression of cerebellum
- trunk problems if compression is midline.
- disruption of CSF flow through foramen magnum
What complications/ signs would you see with significant herniation of cerebellar tonsils and vermis and lower brainstem through foramen magnum with aqueductal stenosis?
Chiari II: Meningomyocele
Blood supply to cerebellum?
- Posterior infereior cerebellar artery (PICA)
- Anterior infereior cerebellar artery (AICA)
- Superior cerebellar artery (SCA)
