Basal ganglia and cerebellum Flashcards
What are the functions of the motor cortex?
Initiation of voluntary movement
Skilled, dextrous movements
Integration of movement with maintenance of postural stability and the physical envrionment
Where is the motor cortex located?
Immediately rostral/anterior to the central sulcus
Describe the mapping of the primary motor cortex?
Simple mapping in comaprison to other motor areas
Topographic arrangement
Motor homunculus
Contralteral actions with stimulation
Which areas of the brain are active in more complex motor movements?
In addition to primary motor area, areas outside of it are stimulated with more complex movements
eg. SMA and primary sensory cortex
Describe the suggested functions of the motor association areas?
Planning of movements
Performance of more complicated programs or sequences of movements
What is really represented by the motor cortex?
The types of movements that we actually need to perform
eg. bringing hand to chest to examine something or hand to face to eat something
How do cortical motor neurons differ from spinal motor neurons?
In cortex, neurons have different functional allocations
Neurons for particular types of tasks
Not like spinal cord, where neuron must be active if muscle is active
Describe the concept of mirror neurons?
Neurons respond to seeing a movement performed, as well as performing that movement ourselves
Preparatory, as well as a way of encoding the means by which a goal would be achieved
Important for motor learning
Describe the inputs to the motor areas?
Primary motor cortex: inputs from association areas and somatosensory cortex, particularly other parts of parietal cortex that synthesise higher order representations of our environment
Premotor areas: from high level representation of environment, as well as prefrontal areas, which suggests that prefrontal areas are telling us about the value/salience/meaning of things
Describe how motor pathways relate to visual pathways in the brain?
Dorsal pathway = where = reaching
Ventral pathway = what = grasping
Two motor pathways that feed into different areas of the motor cortex and association areas, and integrate behaviour about an object that we see to perform a goal
Describe the three main functions of the basal gangli?
1) Selection of complex patterns of voluntary movements
2) Evaluating the success of actions in achieving the goals of those actions
3) Initiating movements
Describe the basic anatomy of the basal ganglia?
Made up of five nuclei
3 in midbrain: caudate, putamen, globus pallidus
1 in diencephalon: subthalamic nucleus
1 in midbrain: substantia nigra
How are the basal ganglia affected in Parkinson’s disease?
Loss of dopaminergic neurons in substantia nigra > inability to initiate movement
How are the basal ganglia affected in Huntington’s disease?
Caudate and putamen reduced, almost lost
Describe the general principles of the pathways through the basal ganglia?
Two pathways by which the motor cortex connects back with itself
Direct pathway: selects patterns of motor activity
Indirect pathway: suppresses other movements, especially similar ones
Dopamine is critical
Describe the functions of the cerebellum?
Coordinating timing and sequence of movements
Maintenance of muscle tone
Motor learning
Planning sequences of muscle activation for complex movements
Which parts of the brain does the cerebellum interact with?
Motor cortex
Brainstem
Briefly describe the anatomy of the cerebellum?
Tightly folded
Three main lobes with three connections to brainstem (superior, middle and inferior peduncles)
Every part the same in terms of cellular structure
Describe the functional organisation of the cerebellum?
Medial to lateral
What is the major consequence of cerebellar lesions?
Ataxic movements
Inability to follow path/route
Effects are ipsilateral for a unilateral lesion
Describe the signs of anterior lobe syndrome of the cerebellum?
Ataxic gait
Loss of inter-limb coordination
What is a major cause of anterior lobe syndrome in the cerebellum?
Chronic ethanol toxicity
Describe the signs of posterior lobe syndrome of the cerebellum?
Dysmetria (overshoot in precision reach)
Dysdiadochokinesia (inability to rapidly alternate movements)
Speech abnormality
What is flocculonodular syndrome?
Which lobe of the cerebellum is it associated with?
Truncal ataxia (inability to stabilise trunk)
Associated with posterior lobe
On which side of the body do unilateral cerebellar lesions present?
Why?
Cerebellar lesions present ipsilaterally
Due to double cross
Output from cerebellum crosses over and projects to motor thalamus or brainstem and to cortex in crossed pathway
Damage to cerebellum > affects contralateral part of cerebrum > affects ipsilateral side of body
Describe the role of the cerebellum in learning and adaptation?
Cerebellum is required to make adaptations to motor programs
