Lecture 13: Cerebellum Flashcards
What is the largest part of the hindbrain?
The cerebellum
What sits in the Posterior Cranial Fossa?
The Cerebellum
Where in the skull does the cerebellum sit?
In the posterior cranial fossa
What part of the dura does surrounds the dura mater?
The tentorium cerebelli
What sits under the tentorium cerebelli?
The cerebellum
What forms 2/3 walls of the fourth ventricle?
The cerebellum
What is the fourth ventricle surrounded by?
CSF
How does the CSF get to the cerebellum?
Through the median and lateral aperatures
What is the Cisterna Magna?
The big CSF cistern that allows CSF to reach the subarachnoid space
How does the cerebellum connect to the Brainstem?
Via the three peduncles
What percent of brain volume and neurons is the cerebellum?
10% of total brain volume; >50% of neurons
What is the overall purpose of the cerebellum?
It is the overall consultant on rapid movement - keeps the stride steady and balanced
Where does the cerebellum provide input to?
The Thalamus and the Cortex
What kind of input does the cerebellum receive?
Afferent input from all muscles and joints
Why does the cerebellum receive afferent input from all muscles and joints?
Because it needs to know where muscles and joints are in space before performing a function
What does the cerebellum consult on?
Rapid and ongoing movements to tweak motor skills
Where does the efferent information coming from the cerebellum need to go before reaching the cortex?
The thalamus
What does Cerebellum mean?
Little brain
What is the cerebellum considered part of the motor system?
Because if the cerebellum is damaged movement is still possible but the patient has deficits
What deficits may a patients have if the cerebellum is damaged?
- Gait imbalance, poor postural control
- Poor coordination of voluntary movements ex. Slurred speech or tremor when moving
Why are there deficits when the cerebellum is damaged?
Because the cerebellum, basal ganglia and motor systems are disinhibiting to all for motor movement
What happens to people with cerebellar damage when performing intentional motor movements?
They have a tremor
Why do people with cerebellar damage have a tremor when performing intentional motor movements?
Because the cerebellum is no longer inhibiting extraneous motor movement
What are the functions of the cerebellum?
- Controls equilibrium/balance
- Controls posture and muscle tone
- Coordinates smooth and purposeful movement
How does the cerebellum control equilibrium and balance?
By using the vestibular pathway using information from the inner ear to control core musculature to balance
Is the cerebellum involved in sensory processing?
Yes, the cerebellum is a huge sensory processor
What is meant by the cerebellum is the great comparator?
It compares cortical command with muscle and joint positioning and tone
Through what tracts does the cerebellum compare muscle joint positioning and tone?
The ipsilateral spinocerebellar tracts (and cuneocerebellar tracts)
What are the spinocerebellar tracts and cuneocerebellar tracts?
Sensory afferents from all the muscles, joints and tendons from one side of the body that go to the ipsilateral side of the cerebellum
After receiving ipsilateral information from the spinocerebellar tracts what does the cerebellum do?
Sends information through the thalamus to and advises the cortex on how much, how many, and how fast
What happens after the cerebellum advises the cortex on a movement?
The motor cortex sends the revised command down the corticospinal tract
What are the three steps in the cerebellum being a comparator?
- Receives muscle and joint positioning from spinocerebellar tracts
- Advises the cortex on how much, how many and how fast
- Motor cortex sends the revised command down the corticospinal tract
How many afferent tracts does the cerebellum receive?
Two afferent tracts
What are the two afferent tracts that the cerebellum receives?
The Corticopontocerebellar tract and the spinocerebellar tracts (ipsilateral)
What are the corticopontocerebellar tracts?
Axon tracts from the premotor and supplementary motor cortex that connects to the cerebellum
What is the pathway of the Corticopontocerebellar tracts?
- Premotor cortex/supplementary motor cortex to the pons
- Pons through the middle cerebellar peduncle to the cerebellum
Which cerebellar peduncle doe the corticopontocerebellar tract travel through?
The Middle Cerebellar Peduncle (MCP)
What tract travels through the middle cerebellar peduncle?
The Corticopontocerebellar tract
Where does the Corticopontocerebellar tract synapse?
At the pons and cerebellum
What is the pathway of the Spinocerebellar tracts?
They go from the upper and lower limbs (muscle spindles and tendon organs) to the cerebellum through the inferior cerebellar peduncle (ICP)
What is the neuron pathway of the spincerebellar tracts?
- From muscle, joints and tendons they synapse at the spinal cord (at the dorsal nucleus of Clarke)
- From the spinal cord through the inferior cerebellar peduncle to the cerebellum
Where does the spinocerebellar tract synapse?
At the spinal cord (dorsal nucleus of Clarke) and cerebellum
Which pathway travels through the inferior cerebellar peduncle (ICP)?
The spinocerebellar tracts
Which peduncle does the spinocerebellar tract travel through?
The inferior cerebellar peduncle (ICP)
Which pathway travels through the middle and inferior cerebellar peduncles?
Middle Cerebellar Peduncle - Corticopontocerebellar tract
Inferior Cerebellar Peduncle - Spinocerebellar Tracts
What are the two dorsal spinocerebellar tracts?
- Spinocerebellar tract (lower limbs)
- Cuneocerebellar tract (upper limbs)
What do the spinocerebellar tracts sense?
Muscle spindles, tendons and tendon organs
What are the largest peripheral nerves?
The dorsal spinocerebellar tracts and cuneocerebellar tracts
What happens as a result of the spinocerebellar and cuneocerebellar axons being large?
They are the most myelinates and as a result they are faster than motor axons so they can adjust for sensory axons to advise motor axons
What synapses at the Dorsal Nucleus of Clarke?
The spinocerebellar and cuneocerebellar tracts
What happens when an individual is thinking about a movement?
The premotor and supplementary motor cortices send afferents down to the basal ganglia and cerebellum
What happens after the premotor and supplementary motor cortex sends afferents down to the basal ganglia and cerebellum?
The cerebellum processes this information and sends information back to the upper motor cortex to tell which muscles to contract or not to contract
Why is the middle cerebellar peduncle so big?
Because there are tons of afferent motor fibers from from the motor cortex to the cerebellum
What kind of afferents does the cerebellum receive?
Motor and sensory afferents
What do the motor afferents that the cerebellum receives refer to?
Information from the motor planning areas
What kind of sensory afferents does the cerebellum receive?
Afferent information from joints and muscle spindles
What side would a lesion to the cerebellum cause deficits?
Ipsilaterally
When advising the cortex, which side does the cerebellum project to?
It projects contralaterally
Why is a lesion to the cerebellum contralateral?
- The cerebellum receives cortical information from the contralateral side of the cortex
- The cerebellum sends information back to the contralateral side of the cortex
- The crotex then projects to muscles on the contralateral side
This means that there is a double crossover
What is the other name for the Lateral Corticospinal Tract?
Pyramidal Tract
What happens in the cerebellum once a movement is evoked?
The cerebellum continues to compare the movement that it tried to tell the muscle to do and corrects for errors
Where does the Corticospinal tract synapse and cross over?
It crosses over at the medulla and synapses at the spinal cord
How is the cerebellum continuously involved in ongoing movements?
The cerebellum compares the intended movement with actual movement and corrects for errors as the movement evolves in real time
What are five cerebellar disorders?
Ataxia
Dysmetria
Dysdiadochokinesia
Forces ‘intentional tremor’
Vertigo
What is Ataxia?
Lack of coordination of muscle movements
What can Ataxia look like?
Awkwardness of posture and gait
What does Awkwardness of posture and gait usually mean for the cerebellum?
There is a lesion to the midline cerebellum
What is an ipsilateral cerebellar sign?
When there is a tendency to fall to the same side as a lesion
What are two types of Ataxia?
Dysmetria
Dysdiadochokinesia
What is Dysmetria?
Overshooting a goal in reaching for a target
What is Dysdiadochokinesia?
Inability to perform rapid alternating movements
What is is called when overshooting a goal in reaching for a target?
Dysmetria
What is it called when a person in unable to perform rapid alternating movements?
Dysdiadochokinesia
What is a Forced Intentional tremor?
When an individual has a tremor when attempting to perform purposeful movements