Motor control Flashcards
How do motor neurons of the brainstem project?
Ipsilaterally in 4 tracts
- Vestibulospinal
- Reticulospinal
- Tectospinal
- Medullay reticulospinal
What do the basal ganglia and cerebellum do?
Indirectly influence movement by regulating the function of the upper motor neurons
What do upper motor neurons of the brainstem control?
Posture and balance
What do upper motor neurons do?
- Control motor function and are found the brain
What pathway do upper motor neurons from the brainstem follow and where do they travel to?
- Ventomedial pathway
- Synapse on more medial lower motor pools, controlling more axial muscles
Where do neurons cross the midline?
At the pyramidal decussation in the medulla
What is the primary function of the cerebellum?
To detect and correct differences between the intended movement and actual movement (motor error)
How does motor neuron disease affect the upper motor neurons?
- Muscle weakness
- Spasticity due to increase in muscle tone
- Hyperactive reflexes
- Loss of fine voluntary movements
- Patients usually die from bulbar (tongue and pharynx) involvement
How does motor neuron disease affect the lower motor neurons?
- Muscle weakness or paralysis
- Loss of muscle tone due to loss of stretch reflexes
- Leads to severe muscle atrophy
- Patients usually die from lung dysfunction (atrophy of intercostal muscles)
What does anticipation involve?
A circuit from the motor cortex to the brainstem nuclei
What subsystems in the brain influence the behaviours of central pattern generators?
1) Motor cortex
- Voluntary movements
2) Brainstem
- Basic movements and postural control
3) Basal ganglia
- Gating proper initiation of movement
4) Cerebellum
- Sensory motor coordination
What are central pattern generators?
- Neuronal circuits that when activated can produce rhythmic motor patterns such as walking
- Between the muscle and the spinal chord
- In the absence of sensory or descending inputs (from the brain)
What is the motor cortex?
- Precentral gyrus
- Stimulation of part of it elicits contraction of the CONTRALATERAL body muscles
What pathway do upper motor neurons from the motor cortex follow and where do they travel to?
- Via the lateral pathway
- Synapse onto more laterally located lower motor neurons (or interneuron circuitary)
- Controlling more distal structures
- Upper body inputs go lateral
- Lower body inputs go medial
- Project contralaterally
Where do inputs to the motor cortex come in at?
Layer IV to stellate cells
How does the basal ganglia initiate movement?
- With no initiating cortical input, the globus pallidus tonically inhibits the thalamus
- Due to tonic activation form the striatum
- When the striatum is activated it inhibits the globus palidus, allowing the thalamus to activate area 6 of the motor cortex and initiate movement
Describe the loop that the cerebellum forms with the motor cortex?
- Cerebellum receive massive massive input from many areas of the cortex, corticopontocerebellar projection and sensory input from the spinal cord and vestibular system
- In turn, projects back onto the motor cortex via the thalamus but no direct output to the spinal cord
What is a ‘motor pool’?
All the alpha motor neurons which innervating the fibres of a single skeletal muscle
What does lesions in the cerebellum cause?
Cerebellar ataxia - poorly integrated movement
Where do axons of the cortiocospinal tract dervie from?
Betz (pyramidal) cells in layer V
How are the neurons involved in motor control similar to that of the somatosensory system?
- They are topographically mapped
- Proportions reflect density of innervation and behavioural significance
although not identical
What ultimately initiates all skeletal muscle movements?
Lower motor neurons
Where do outputs from the motor cortex leave from?
Layers III, V and VI
What is the indirect pathway from the cortex which influences the spinal cord?
- Via the reticular formation to the muscles
- Corticoreticulospinal tract
How are motor pools arranged?
- Grouped into rod-shape clusters within the spinal cord
- Innovation for each muscle occupies a distinct mediolateral and rostrocaudal postion with within the ventral horn of the spinal cord
Organised somatotopically in the ventral horn:
- Distal muscles located laterally
- Proximal muscles located medially
How do the upper motor neurons in the cortical influence the spinal cord circuits?
- 2 different routes, both starting with planning and initiation in the premotor cortex
Indirect projection
Direct projection:
What is the motor loop?
- Basal ganglia feedback to the premotor area via the ventrolateral complex of the thalamus to control the initiation of movement
- Via the caudate, putamen, globus pallidus
What is the cerebellum required for?
Proper execution of planned voluntary multijoint movements
What is the ‘feedforward’ mechanism?
Anticipatory, pre-adjusts body posture to compensate for forces that will be generated when doing an action
Where are upper motor neurons from the brainstem located?
1) Reticular formation
2) Vestibular nucleus (vestibular coordination)
3) Superior colliculus (visual coordination)
What do upper motor neurons of the motor cortex control?
- Muscles involved in precise limb movements (especially the hands)
- Initiate complex voluntary movements via the corticospinal tract
Where dos the input from many cortical regions converge?
On the striatum
What is the direct pathway from the cortex which influences the spinal cord?
- To the spinal cord via the corticospinal tract
- Pyramidal decussation to the lateral CS tract
What causes Huntington’s disease?
- Degeneration of the striatum, resulting in reduced inhibition of the thalamus by the golbus pallidus
- Increased initation of jerky movements (hyperkinesis)
What causes Parkinson’s disease?
- Degeneration of the substansia nigra
- Leads to tonic inhibition of the thalamus and suppresed inhibtion of movement
- Hypokinesis
