Lecture 8- The Cerebellum Flashcards
What is the reticular formation?
Composed of clusters of gray matter scattered throughout midbrain, pons and medulla
Neurons project up via the thalamus
What is the reticular formation’s functions?
- Governing the arousal of the brain
- involved in habituation (a process in which the brain learns to ignore repetitive, inconsequential stimuli while remaining sensitive to others)
What is the reticular formation depressed by?
- depressed by alcohol, sleep-inducing drugs & tranquilisers
- inhibited by sleep centres located in the hypothalamus & other brain regions
What happens if the reticular formation is damaged?
-brainstem injury: permanent unconsciousness (irreversible coma)
Where is the cerebrum located in terms of the cranial fossas?
Posterior cranial fossa
What meningeal fold sits above the cerebellum?
The tentorium cerebelli separating the cerebrum from the cerebellum
What does the cerebellum consist of?
Consists of cortex, white matter and deep nuclei
What is the cerebellum’s primary function?
-synchronised, precisely timed movement across multiple joints = synergistic multijoint limb movement
Eg. throwing a ball, finger-to-nose test
• control of muscle tone (posture)
• maintenance of balance
Does the cerebellum receive more sensory or motor output?
receives vast amount of sensory
information, but does not give rise
to conscious sensory perceptions
• 40x more afferents than efferents
How much of the neurons of the brain does the cerebellum contain? What allows this?
- containing 50% of the neurons in the entire brain in order to synchronize movements
- It’s very ordered structure allows this
How is synergistic multijoint movement achieved?
-Frontal motor association areas (eg. premotor cortex)
via the corticopontine-cerebellar tract, inform cerebellum
of intent to start voluntary muscle contractions.
-At the same time, the cerebellum receives information
from proprioceptors throughout the body, as well as visual
and vestibular (balance) input.
-The proprioceptive information includes tension in
muscles and tendons and the position of joints.
-This information allows the cerebellum to evaluate body
position and momentum = where the body is and where it
intends to go.
-The cerebellar cortex and the deep cerebellar nuclei then
calculate the best way to coordinate the force of each
muscle contraction to prevent overshoot, maintain posture
& ensure smooth coordinated movement.
-Then, the cerebellum dispatches to the motor cerebral
cortex its “blueprint” for coordinating movement. The
primary motor cortex then influences motor neurons in
the spinal cord to produce movement.
What is the cerebellar lesion patient usually capable and not capable of?
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.
In order to be able to carry out it’s function what anatomy does the cerebellum need?
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
Needs the cerebellar peduncles
Where are the different cerebellar peduncles located in the brain stem
- Superior cerebellar peduncle= midbrain
- Middle cerebellar peduncle= pons
- Inferior cerebellar peduncle= medulla
Label the peduncles on anterior and superior views of the cerebellum…
One note
What is the cerebellum posterior to?
Brainstem, 4th Ventricle, Vela, Cerebellar Peduncles
What meningeal fold does the Posterior cerebellar incisure contain?
Falx cerebelli
What are the parallel surface folds on the cerebellum called and what are they made of?
- Folia (leaves)
- Made of gray matter
Complete the diagram on OneNote showing the deep anatomy of the cerebellum…
OneNote
Describe the cerebellar circuits…
Two main inputs
• mossy fibers/axons from spinal cord or
brainstem neurons conveying motor or sensory input
• climbing fibers/axons, mainly from inf. olivary nucleus
= proprioceptive input. One ION neuron to 1 PC
Climbing axons form excitatory synapses directly with
the Purkinje neurons/cells (PC) in the cerebellar cortex
Mossy axons form excitatory synapses with granule
neurons in the cerebellar cortex.
The granule neurons send their axon as a “parallel fibre”
to form excitatory synapses with the Purkinje neurons.
Purkinje neuron is sole output neuron of the cerebellar
cortex. Is inhibitory. 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 does the purkinje cells look like?
- oval-shaped cell body
- elaborate flattened, fanlike dendrite tree (sagittal section)
What lobe of the cerebellum lies deep to it’s surface? What is it’s function as opposed to the anterior and posterior lobes?
- Flocculonodular lobe (FNL) on inferior surface
- Ant. & post. lobes: co-ordinate movement. FNL: balance
Label the diagram of the cerebellum in anterior view on OneNote.
Answers on OneNote
How is the cerebellum divided superiorly?
-Lateral zone, Intermediate zone and the median zone (vermis)
What deep cerebellar nuclei exist in the cerebellum? What two structures make up the Interposed/ Interpositus Nucleus?
Fastigial
Globose
Emboliform
Dentate
Interpositus nucelus= Globose and Emboliform
What do each of the functional sagittal sections of the cerebellum project to?
- Vermis (median zone) projects to the fastigial nucleus
- Intermediate zone projects to the interposed/interpositus nucleus
- Lateral zone projects to the dentate nucleus
What are the two Spinocerebellum Divisions of the cerebellum?
- Vermis (median)
- Intermediate zones
What is the Cerebrocerebellum Division of the cerebellum?
-Lateral zone
What is the fourth non-sagittal division of the cerebellum? What is it know as?
Flocculonodular lobe= Vestibulocerebellum
What do the cerebrocerebellar circuits control?
controls multijointed movements of limbs (refer to OneNote to study specfic pathways/ neurons in tract)
What do the Spinocerebellar intermediate zone circuits do?
-controls accuracy of movement of the limbs. eg. precision at a joint
What do the spinocerebellar median zone circuits do?
-Controls posture via influencing axial muscles in trunk
What does the Vestibulocerebellar circuits do?
maintain balance via axial and limb muscles
What does the inferior cerebellar peduncle do?
conveys sensory information to the cerebellum
-from muscle proprioceptors throughout the body
- from the vestibular nuclei of the brainstem
(equilibrium & balance)
• contains both afferent (chiefly) & efferent axons
What does the middle cerebellar peduncle do?
contains only afferent axons (crossed axons
from contralateral pontine nuclei). Eg CPCT
What does the Superior cerebellar peduncle do?
• connects the cerebellum to the midbrain
• fibers decussate at various levels
• crossed fibers ascend - either terminate in the red
nucleus or continue rostrally to end within the
thalamus (then to cerebral motor cortex)
• formed by axons that arise from deep cerebellar
nuclei (main efferent pathway)
How are ballistic or rapid movements carried out? Is there cerebellar input here?
No time to pre-program these movements. Coordination
thought to be based on a learned motor program/sequence,
involving modifications of synaptic strengths in cerebellum
Is cerebellar influence primarily ipsilateral or contralateral?
ipsilateral due to decussation at both the Superior cerebellar
peduncle and in the Corticospinal tract (doubly crossed).
What does cerebellar dysfunction result in?
-Loss of coordinated muscle activity :
• Ataxia - inaccuracy in the speed, force and distance of
movement (staggering gait, dysmetria,
slurred speech)
• Tremor - involuntary oscillation of the limbs or trunk
• Nystagmus - rhythmic involuntary oscillation of the eyes
Headache & vomiting - often 1st symptoms of cerebellar tumour
- due to blockage of CSF drainage from 4th ventricle
