Motor control

Question 1

How do motor neurons of the brainstem project?

Answer 1

Ipsilaterally in 4 tracts

• Vestibulospinal
• Reticulospinal
• Tectospinal
• Medullay reticulospinal

Question 2

What do the basal ganglia and cerebellum do?

Answer 2

Indirectly influence movement by regulating the function of the upper motor neurons

Question 3

What do upper motor neurons of the brainstem control?

Answer 3

Posture and balance

Question 4

What do upper motor neurons do?

Answer 4

• Control motor function and are found the brain

Question 5

What pathway do upper motor neurons from the brainstem follow and where do they travel to?

Answer 5

• Ventomedial pathway

- Synapse on more medial lower motor pools, controlling more axial muscles

Question 6

Where do neurons cross the midline?

Answer 6

At the pyramidal decussation in the medulla

Question 7

What is the primary function of the cerebellum?

Answer 7

To detect and correct differences between the intended movement and actual movement (motor error)

Question 8

How does motor neuron disease affect the upper motor neurons?

Answer 8

• 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

Question 9

How does motor neuron disease affect the lower motor neurons?

Answer 9

• 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)

Question 10

What does anticipation involve?

Answer 10

A circuit from the motor cortex to the brainstem nuclei

Question 11

What subsystems in the brain influence the behaviours of central pattern generators?

Answer 11

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

Question 12

What are central pattern generators?

Answer 12

• 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)

Question 13

What is the motor cortex?

Answer 13

• Precentral gyrus

- Stimulation of part of it elicits contraction of the CONTRALATERAL body muscles

Question 14

What pathway do upper motor neurons from the motor cortex follow and where do they travel to?

Answer 14

• 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

Question 15

Where do inputs to the motor cortex come in at?

Answer 15

Layer IV to stellate cells

Question 16

How does the basal ganglia initiate movement?

Answer 16

• 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

Question 17

Describe the loop that the cerebellum forms with the motor cortex?

Answer 17

• 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

Question 18

What is a ‘motor pool’?

Answer 18

All the alpha motor neurons which innervating the fibres of a single skeletal muscle

Question 19

What does lesions in the cerebellum cause?

Answer 19

Cerebellar ataxia - poorly integrated movement

Question 20

Where do axons of the cortiocospinal tract dervie from?

Answer 20

Betz (pyramidal) cells in layer V

Question 21

How are the neurons involved in motor control similar to that of the somatosensory system?

Answer 21

• They are topographically mapped

- Proportions reflect density of innervation and behavioural significance
although not identical

Question 22

What ultimately initiates all skeletal muscle movements?

Answer 22

Lower motor neurons

Question 23

Where do outputs from the motor cortex leave from?

Answer 23

Layers III, V and VI

Question 24

What is the indirect pathway from the cortex which influences the spinal cord?

Answer 24

• Via the reticular formation to the muscles

- Corticoreticulospinal tract

Question 25

How are motor pools arranged?

Answer 25

- 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

Question 26

How do the upper motor neurons in the cortical influence the spinal cord circuits?

Answer 26

- 2 different routes, both starting with planning and initiation in the premotor cortex Indirect projection Direct projection:

Question 27

What is the motor loop?

Answer 27

- 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

Question 28

What is the cerebellum required for?

Answer 28

Proper execution of planned voluntary multijoint movements

Question 29

What is the 'feedforward' mechanism?

Answer 29

Anticipatory, pre-adjusts body posture to compensate for forces that will be generated when doing an action

Question 30

Where are upper motor neurons from the brainstem located?

Answer 30

1) Reticular formation 2) Vestibular nucleus (vestibular coordination) 3) Superior colliculus (visual coordination)

Question 31

What do upper motor neurons of the motor cortex control?

Answer 31

- Muscles involved in precise limb movements (especially the hands) - Initiate complex voluntary movements via the corticospinal tract

Question 32

Where dos the input from many cortical regions converge?

Answer 32

On the striatum

Question 33

What is the direct pathway from the cortex which influences the spinal cord?

Answer 33

- To the spinal cord via the corticospinal tract | - Pyramidal decussation to the lateral CS tract

Question 34

What causes Huntington's disease?

Answer 34

- Degeneration of the striatum, resulting in reduced inhibition of the thalamus by the golbus pallidus - Increased initation of jerky movements (hyperkinesis)

Question 35

What causes Parkinson's disease?

Answer 35

- Degeneration of the substansia nigra - Leads to tonic inhibition of the thalamus and suppresed inhibtion of movement - Hypokinesis