Cerebellum Flashcards
What does the word cerebellum mean ?
Little brain- 1 or the 3 main divisions of the brain
What is the overall structure of the cerebellum?
mini version of cerebral
- has outer cortex which consist of grey matter and neruron cell bodies
- and white matter under neath that cortex with deep nuclei within the deep white matter like the thalamus
What is the cerebellum main functions?
- brain in miniuture
- is in sensory and motor integration with a specific purpose of smoothly coordinating our voluntary movements.
What is the general principal of control of voluntary movements ?
3 events occur when you make a voluntary movement
- plan the movement
- initiate the movement
- execute the movement
How is the planning of voluntary movements made?
- occurs in the pre motor area (PMA) of the frontal cortex
- sit infront of primary motor
- Brocas area is part of the pre motor cortex which is responsible for planning our ability to speak
- mediated by the PMA of the frontal cortex
What do these pre motor areas of the frontal cortex contain ?
stored motor programmes which have been acquired from practice and rehearsal from procedural memory
-accquired to generate complex movements and sequences from our part experience e.g our speak, reaching out to an object
How does the initiation occur?
area of frontal cortex send signals to M1 in pre central gyrus
- role of neurons in M1 to activtate the intended motor plan or programme
- M1 initiates the signals which initiate the movement
How does execution occur?
- while movement is executed it is supervised and coordinated by 2 things:
- PPC - posteror parental cortex which is in the cerberbral cortex- sits behind the S1 cortex
- Cerebellum
How is the PMA always used?
In FMRI - Brian imaging findings- looking at brain acitivity- when people imagine making a movement
- e.g person lying in the scanne- asked to tap right index finger on forearm- a region of PMA will be activated , then M1 is activated and parts of cerebellum will be activated (as responsible for co-rodinating movement)
- Then ask px to imagine tapping their forearm with finger- PMA is still activated however because they dont initiate it M1 and cerebellum is not activated
What is the important sensory aspects to control of voluntary movements ?
- Motor plan/programme- takes account of sensory information about- because can change
need to know current head, eye, body & limb positions in space
which are rarely ever the same. - Execution of the Movement itself:
-generates sensory feedback, in different systems, for example:
changes in head position (vestibular system)- when you are walking head bops up and down
muscle contraction & joint positions (proprioceptive system)- in your hand if you are grasping an object
body parts moving in the field of view (visual system)- reaching out the grasp object
3.The Cerebellum receives all this information:about motor plan from the PMA - and receives info from sensory feedback-
And calculates the best way to coordinate the timing, force & amplitude of the desired muscle contractions
How is cerebellar damage caused?
Its normal sensory-motor coordination
functions involve regulating:
-Proper force & sequences of muscle contraction (timing)
-Accurate movement sizes & amplitudes (space)
THEREFORE THE damage to the cerebellar cortex leads to loss of timing and spatial accuracy - which is called Ataxia
What are the 3 features cerebellar ataxia is characterised by ?
A disorder characterized by clumsy & misdirected movements:
- Timing:
Intention Tremor-before you move to lift hand - it will go into spasm before you even go into movement. & ‘Decomposition’
- mis-timing of muscle forces & contraction sequences -
-Dysmetria
- inaccurate movement amplitudes (over- or under-shooting) - too big or little a force
What does the cerebellum receive ?
the Motor plan- what the intention actually is- receives those signals from the PMA -sent directly to cerebellum
along with sensory feedback rom the action inn progress
-integrates motor and sensory signals and thinks - if there is a mismatch to the intention of the action and actually doing the action- yes there is.
Why is there a mismatch in intention and action ?
- motor plans contain inherent errors in them
- these motor plans we develop in the PMA
- glitches and errors
- send signals back up to PMA to tell them the current state (remember motor plan has to take into account the current situations ) that’s called updating the motor plan. - route between cerebellum and PMA.
What are the 2 main parts of the cerebellum ?
[1] Outer Cortex:
has 3 sub-regions, which receive & integrate sensory & motor inputs:
- Midline region = Vermis (‘worm’)
- Lateral regions = 2 Hemispheres- one extends on left then right
[2] Deep Nuclei: receive information from neurons from the outer cortex and they send motor outputs involved with co-ordinating movements and updating motor plans
3 pairs = Fastigial, Interposed & Dentate
(Like the cerebral cortex, these 3 regions of cerebellar cortex have grey matter on
the outside and white matter inside & are deeply folded)
(Unlike the cerebral cortex, they are concerned with events on
the same side of the body)
