Modulation of Movement: Basal Ganglia and Cerebellum Flashcards
What does the motor cortex do?
Initiation of voluntary movement Skilled, dexterous movements Integration of movement with - Maintenance of postural stability - Goals - Physical environment
What kind of motor patterns does the motor cortex coordinate?
Extended patterns of movement
Does the motor cortex exert ipsilateral or contralateral control of the body?
Contralateral
Where is the motor cortex located?
Pre-central gyrus
What happens when areas more rostral to the motor cortex are stimulated?
More complex movements produced
What is the topographical mapping of the motor cortex?
Lower limb medial Upper limb more lateral - Fingers and hands have large areas Head and face lateral - Large area from lips and mouth
What areas of the cortex are activated with simple movement?
Pre-central gyrus
Post-central gyrus in similar area
What areas of the cortex are activated with complex movement?
Pre-central gyrus
Post-central gyrus in similar area
Pre-motor areas
What areas of the cortex are activated with mental rehearsal of complex movment?
Motor association area only
What is really represented in the primary motor cortex?
Wherever hand is at start of stimulation of cortex, activation of area of motor cortex moves hand to particular region
Produces ecologically logical movements
Describe the experiment that demonstrates what mirror motor neurons are
Neurons would fire when monkeys observed experimenters doing things
These neurons recognised those tasks
When monkey performed same task, same neuron fires as well
What do mirror motor neurons recognise?
Same pattern of movements rather than same end goal
What is the likely reason for the existence of mirror motor neurons?
How we learn - people and monkeys learn a lot of things by watching
Where are the inputs to the primary motor cortex from
Association areas
Somatosensory cortex
Posterior parietal area
What does the posterior parietal area do?
Synthesises sensory information into egocentric map
Where do the pre-motor areas receive input from?
Posterior parietal areas
Pre-frontal areas responsible for salience of objects and tasks
- Goal driving
- Planning
What are the visual streams coming into the motor areas?
Dorsal
Ventral
What do the visual streams provide information to the motor cortex on?
Where things are
What things are
What types of movement do the visual streams “control”?
Dorsal = where > reach Ventral = what > grasping - hand shaping
What are the functions of the basal ganglia?
Allow selection of complex patterns of voluntary movements
Evaluate success of actions in achieving goals of actions
Initiating movements
What is the relationship between the basal ganglia and motor cortex?
Basal ganglia modulate what happens in motor cortex
How do the basal ganglia project to the motor cortex?
Only via thalamus
Do the basal ganglia project to other cortical regions?
Yes
Which basal ganglia is destroyed in Parkinson’s disease?
Substantia nigra
With what level of damage to the substantia nigra do clinical signs of Parkinson’s disease appear?
80% of neurons lost
Why is the substantia pigmented black?
Presence of black pigment melanin in dopaminergic neurons
What basal ganglia are affected in Huntington’s disease?
Caudate
Lenticular nucleus
What are the characteristics of the Parkinsonian gait?
Stooped posture
Turning by small shuffling steps
Tremor in limbs
Bradykinesia
What is the role of dopamine in the basal ganglia?
Facilitates pathway of information from basal ganglia to motor cortex
What are the characteristics of chorea in Huntington’s disease?
Quick irregular involuntary muscle twitches
Hyperactivity of hands, feet, and sometimes entire limb
Where does input from the motor cortex come into the basal ganglia?
Striatum
How many pathways are there from the basal ganglia to the motor cortex?
Two, via thalamus
Describe the direct pathway from the basal ganglia to the motor cortex?
Facilitates movements
Selects movement patterns to go together to make coherent motor plan
Facilitated by dopamine
Removes inhibition
Describe the indirect pathway from the basal ganglia to the motor cortex?
Stops movement from happening, especially those that interfere with those that are happening
Excites inhibitory neurons to inhibit these pathways
Dopamine reduces activity
What is the role of having both a direct and indirect pathway?
Movements selected stand out more clearly by inhibiting all others
What are the functions of the cerebellum?
Coordinating timing and sequence of muscle actions and movements
Maintenance of tone
Motor learning
Planning sequences of muscle activation for complex movements
What inputs does the cerebellum receive?
Copies of motor commands from motor cortex
Ascending information to see how motor command went
What does the cerebellum do with the information it receives from the motor cortex and ascending information?
Compares two to adjust movement
What cortical structures does the cerebellum link with?
Primary and associated motor cortices
What is the gross structure of the cerebellum?
Tightly folded
Three lobes
Cerebellar peduncles attach it to brainstem
Where do fibres in the cerebellar peduncles connect to?
Medulla
Pons
Midbrain
What is the functional organisation of the cerebellum?
Approx medial to lateral
What is ataxia?
Inability to appropriately integrate/coordinate movement
What happens with a lesion in the cerebellum?
Ataxia
Does a unilateral lesion in the cerebellum have a contralateral or ipsilateral effect?
Generally ipsilateral
What is anterior lobe syndrome?
Ataxic gait
Loss of inter-limb coordination
Why does anterior lobe syndrome occur?
Chronic ethanol toxicity > anterior Purkinje cells in cerebellum preferentially lost
How does anterior lobe syndrome progress?
Progression of pathology posterioly involves upper limbs and facial muscle dys-coordination
What is posterior lobe syndrome?
Dysemtria Dysdiadochokinesia Speech abnormality - Loss of natural rhythm - Slurring across syllables - Overcompensation by explosive speech
What is dysemtria?
Overshoot in precision speech
What is dysdiadochokinesia?
Inability to rapidly alternate movements
What is flocculonodular lobe syndrome?
Truncal ataxia
- Difficulty walking
- In severe cases: difficulty standing and sitting
Why are cerebellar lesions ipsilateral to deficits?
One side of cerebellum sends output > crosses midline > info received by contralateral motor cortex
Motor cortex sends information to body on contralateral side
= double cross
