Lecture 8 - Cerebellum Flashcards
What is the reticular formation composed of?
Composed of clusters of gray matter scattered throughout midbrain, pons and medulla
What is the reticular formation involved in?
Habituation
What is habituation?
a process in which the brain learns to ignore repetitive, inconsequential stimuli while remaining sensitive to others
What is the reticular formation inhibited by?
by sleep centres located in the hypothalamus & other brain regions
What is the reticular formation depressed by?
depressed by alcohol, sleep-inducing drugs & tranquilisers
What does brainstem injury of reticular formation cause?
permanent unconsciousness
(irreversible coma)
What does the reticular formation govern?
The arousal of the brain via thalamus
Where is the cerebellum located?
posterior cranial fossa
What is the cerebellum posterior to?
Superior and inferior medullary velum
Brainstem
4th Ventricle
Cerebellar peduncles
What does the cerebellum consist of?
cortex, white matter and deep nuclei
What is the cerebellum primarily concerned with?
synchronised, precisely timed movement across multiple joints = synergistic multi-joint limb movement
What does the cerebellum recieve?
receives vast amount of sensory information, but does not give rise to conscious sensory perceptions
What % of neurons in the brain does the cerebellum contain?
50%
What does the cerebellum have more of, afferent or efferent?
40x more afferents than efferents
What informs the cerebellum of intent to start voluntary muscle contractions?
Frontal motor association areas (eg. premotor cortex) via the corticopontine-cerebellar tract
What does the cerebellum recieve information for?
Proprioceptors throughout body
Visual input
Vestibular (balance) input
What does the proprioceptive information to cerebellum include?
Tension in muscles and tendons and the position of joints
What does proprioceptive information allow the cerebellum to do?
Allows the cerebellum to evaluate body position and momentum = where the body is and where it intends to go
What is the role of the cerebellar cortex and deep cerebellar nuclei?
The cerebellar cortex and the deep cerebellar nuclei calculate the best way to coordinate the force of each muscle contraction to prevent overshoot, maintain posture & ensure smooth coordinated movement.
What does the cerebellum dispatch to the motor cerebral cortex?
Blueprint for coordinating movement
What does the primary motor cortex influence?
The primary motor cortex then influences motor neurons in the spinal cord to produce movement
What is the effect of cerebellar lesion?
A patient with a cerebellar lesion is usually capable of carrying out general outlines of movement, but each movement is executed with suboptimal coordination and precision.
What does the cerebellum need to be connected to to achieve function?
Cerebellum needs to be connected to the motor input from cerebral cortex, the various sensory inputs and needs to send its output or blueprint back to the cerebral cortex.
What are the right and left hemispheres of cerebellum connected by?
Vermis
What are folia?
Parallel surface folds of cerebellum made of grey matter
What is the regional anatomy of the cerebellum?
Grey matter (cortex)
White matter (arbor vitae) - tree of life
Deep nuclei
What are the two main inputs of the cerebellar circuits?
mossy fibers/axons
climbing fibers/axons
Where are the climbing fibers/axons from?
mainly from inf. olivary nucleus = proprioceptive input. One ION neuron to 1 PC
Where are the mossy fibers/axons from?
from spinal cord or brainstem neurons
What do the mossy fibers/axons convey?
conveying motor or sensory input
What do the climbing fibers/axons convey?
Proprioceptive input
What do the climbing axons form?
Climbing axons form excitatory synapses directly with the Purkinje neurons/cells (PC) in the cerebellar cortex
What do the mossy axons form?
Mossy axons form excitatory synapses with granule neurons in the cerebellar cortex.
What does the granule neurons send their axon as?
The granule neurons send their axon as a “parallel fibre” to form excitatory synapses with the Purkinje neurons
What is the sole output neuron of the cerebellar cortex?
Purkinje neuron
What type of neuron is the Purkinje neuron in the cerebellar circuit?
Inhibitory
What does the Purkinje neuron work with/do?
Works with input axons to regulate the firing frequency and amplitude of the neurons in the deep cerebellar nuclei = “blueprint” sent to motor cortex
What do neurons in cerebellar deep nuclei integrate?
Synaptic input
What is the structure of Purkinje cells?
Oval-shaped cell body
Elaborate flattened, fanlike dendrite tree (sagittal section)
Where does the Flocculonodular lobe lie deep to?
Vermis
What surface is the Flocculonodular lobe on?
Inferior surface of cerebellum
What do the anterior and posterior lobes of cerebellum do?
Co-ordinate movement
What is the FNL?
Flocculonodular lobe
What is the role of the Flocculonodular lobe?
Balance
What is on the superior surface of the cerebellum?
Anterior lobe
vermis
Posterior lobe
folia
FNL
What are the zones on the superior surface of the cerebellum? and what do they correspond with?
Lateral to medial
Lateral zone
Intermediate zone
Vermis (median zone)
Corresponding to sagittal functional subdivisions
What is the deep cerebellar nuclei composed of?
Fastigial
Interposed/interpositus nucleus:
- Globose
- Emboliform
Dentate
What does the Vermis (median zone) project to?
Vermis (median zone) projects to the fastigial nucleus
What does the Intermediate zone in deep cerebellar nuclei project to?
Intermediate zone projects to the interposed/interpositus nucleus
What does the Lateral zone in deep cerebellar nuclei project to?
Lateral zone projects to the dentate nucleus
What are the functional divisions of the cerebellum?
three sagittal functional regions, with the flocculonodular lobe being a 4th non-sagittal functional region
What are the spinocerebellum divisions?
Vermis
Intermediate zone
What is the cerebrocerebellum division?
Lateral zones
What is the vestibulocerebellum division?
Flocculonodular lobe
What is the overall function of the cerebrocerebellar circuits?
controls multijointed movements of limbs
What is the function of the spinocerebellar intermediate zone circuits?
controls accuracy of movement of the limbs.
eg. precision at a joint
What is the function of the spinocerebellar medial/median/vermal zone circuit?
Controls posture via influencing axial muscles in trunk
What is the function of the vestibulocerebellar circuits?
maintain balance via axial and limb muscles
What does the inferior cerebellar peduncle convey?
Sensory information to the cerebellum
From muscle proprioceptors throughout the body
From the vestibular nuclei of the brainstem (equilibrium & balance)
What axons does the inferior cerebellar peduncle contain?
Contains both afferent (chiefly) & efferent axons
What axons does the middle cerebellar peduncle contain?
Contains only afferent axons (crossed axons from contralateral pontine nuclei). Eg CPCT
What does the superior cerebellar peduncle connect?
The cerebellum to the midbrain
What is the superior cerebellar peduncle formed by?
Formed by axons that arise from deep cerebellar nuclei (main efferent pathway)
Describe the fibres of the superior cerebellar peduncle
Fibres decussate at various levels
Crossed fibres ascend - either terminate in the red nucleus or continue rostrally to end within the thalamus (then to cerebral motor cortex)
What does each cerebellar hemisphere primarily exert its influence on?
Each cerebellar hemisphere exerts its influence primarily on the ipsilateral half of the body
What happens when there is cerebellar dysfunction?
Loss of co-ordination of muscle activity
What is ataxia?
Inaccuracy in the speed, force and distance of movement (staggering gait, dysmetria, slurred speech)
What is tremor?
Involuntary oscillation of the limbs or trunk
What is nystagmus?
rhythmic involuntary oscillation of the eyes
What is often the 1st symptom of cerebellar tumour?
Headaches and vomiting
Due to blockage of CSF drainage from 4th ventricle
