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Introduction to neuroscience > Motor control and disease > Flashcards

Motor control and disease Flashcards

1
Q

What are the two types of upper motor neurons? What do they both control?

A

Motor cortex- fine voluntary control of distal muscles

Brain stem- project to medial motor pools, concerned with postural movement

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2
Q

What are upper motor neurons? Where are they found?

A

Neurons in the brain that control motor function

Primary motor cortex- precentral gyrus

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3
Q

How is the motor cortex mapped somatotopically?

A

Lower body- medial
Upper body- lateral
Proportions reflect density of innervation and behavioral significance (like somatosensory cortex)

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4
Q

What do axial muscles control?

A

Trunk movement

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5
Q

What do proximal muscles control?

A

Shoulder, elbow, pelvis and knee movement

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6
Q

What do distal muscles control?

A

Movement of hands, feet and digits

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7
Q

What is a motor unit?

A

A motor neuron and all the muscle fibres it innervates

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8
Q

What is a motor neuron pool?

A

All the motor neurons that innervate a single muscle

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9
Q

What descending tract of the spinal cord controls voluntary movement? What kind of pathway is it?

A

Corticospinal tract
Lateral- distal muscles
Ventral- axial muscles

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10
Q

Where in the brain do axons of the CST originate?

A

Large pyramidal cells in layer V of the motor cortex

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11
Q

What tracts do upper motor neurons of the brain stem project in? What type of pathway are they?

A

Vestibulospinal and reticulospinal tracts

Ventromedial pathways

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12
Q

Where do lateral axons of the CST cross the midline? Where do they synapse onto?

A

Pyramidal decussation in the medulla

Laterally located motor neuron circuits that control distal muscles

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13
Q

Where do axons in the ventromedial pathways synapse onto?

A

Medially located motor neuron circuits that control axial muscles

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14
Q

What do the axons of the vestibulospinal tract control? What other system do they receive inputs from to do this?

A

Head balance and turning

Vestibular system via the vestibular nucleus

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15
Q

What do the axons of the tectospinal tract control? What other system do they receive inputs from to do this?

A

Orienting response

Visual system via the superior colliculus

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16
Q

What do the axons of the reticulospinal tracts control?

A

Anti-gravity reflexes

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17
Q

What directions do the two types of upper motor neurons project in the body?

A

Motor cortex neurons- contralateral

Brain stem- ipsilateral

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18
Q

What is anticipatory ‘feed forward’ mechanism?

A

Pre-adjustment of body posture to compensate for the forces that will be generated by movement (pulling a lever or stepping on a travelator)
This means there is a link between the upper MNs of the motor cortex and the brain stem

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19
Q

How is movement anticipated?

A

Anticipation starts in the premotor area

activates an indirect projection to axial muscles via the reticular formation

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20
Q

After anticipation how is movement initiated?

A

Initiated in the primary motor cortex

Activation of voluntary movement direct to spinal cord via corticospinal tract

21
Q

What becomes damaged in motor neuron disease?

A

Sclerosis of lateral spinal cord
Leads to degeneration of axons in the CST
Muscle atrophy

22
Q

What does ALS stand for?

A

Amyotrophic lateral sclerosis

23
Q

What is lower motor neuron disease characterized by? What do patients usually die from?

A

Muscle paresis
Loss of muscle tone due to lack of stretch reflexes
Muscle atrophy
Lung dysfunction

24
Q

What is upper motor neuron disease characterised by?

A

Muscle weakness
Spasticity due to increased muscle tone from failure of modulation of stretch reflexes
Hyperactive reflexes
Loss of fine voluntary movement

25
Q

What are the general consequences of motor neuron degeneration?

A

Almost always fatal

Intellect is not compromised

26
Q

What role do the basal ganglia and cerebellum play in motor control?

A

Influence movement indirectly by regulating the function of upper motor neurons

27
Q

What parts of the basal ganglia are involved in the initiation of movement?

A

Caudate
Putamen
Globus pallidus
Subthalamic nucleus

28
Q

What is the motor loop? What are the two pathways it consists of?

A

Motor cortex connects to the basal ganglia
Basal ganglia feed back to the premotor area via the ventrolateral complex of the thalamus (VLo)
Direct and indirect

29
Q

What happens in the direct pathway when there is no cortical input?

A

Globus pallidus internal segment (GPi) tonically inhibits the VLo

30
Q

Direct pathway

A

Input from many cortical regions converge on the striatum
Striatum inhibits the inhibitory activity of the GPi
This releases VLo to activate area 6 and initiate movement

31
Q

Why is the direct pathway set up like this?

A

Integration of cortical inputs to trigger a response

Rapidity of response – “engine is running”; inhibition of inhibition releases the “brake”

32
Q

What role does the substantia nigra play in the indirect pathway?

A

Acts via the striatum to maintain the balance between the inhibition and activation of the VLo

33
Q

Indirect pathway when SN input is excitatory

A

Excitatory input from the SN stimulates VLo activation by activating the inhibition of the GPi in the direct pathway
Inhibition of GPi by GPe is inhibited by the striatum
So the VLo is inhibited

34
Q

Indirect pathway when SN input is inhibitory

A

Inhibitory input by the SN decreases striatum inhibition of GPe
This inihibits the GPi
Allows activation of the VLo

35
Q

What are the symptoms of Parkinson’s disease?

A 
Hypokinesia (insufficiency of movement)
Bradykinesia (slow movement)
Akinesia
Increased muscle tone and 'mask like' expression
Resting tremor
Flexed posture and loss of balance
36
Q

What is Parkinson’s caused by?

A

Loss of dopamine due to the loss of dopaminergic neurons in the substantia nigra

37
Q

What are Lewy bodies?

A

Intracellular protein aggregates

Mark the loss of dopaminergic neurons in Parkinson’s

38
Q

How can L-DOPA treat Parkinson’s? Why is it only a temporary solution?

A

Boosts the capacity of existing dopaminergic neurons in the SN to make dopamine
Doesn’t stop the degeneration of neurons
So when there are insufficient neurons left it no longer has any benefits

39
Q

What does reduced dopaminergic output from the SN to the striatum lead to?

A

Increased activity of indirect pathway
Decreased activity of direct pathway
Less inhibition of the GPi so it’s inhibitory activity is increased
Decreased activity of VLo- less motor cortex activation

40
Q

What are the symptoms of Huntington’s disease?

A

Early- hyperkinesia or dyskinesia (involuntary jerking/twitching)
Late- akinesia and dystonia, dementia, psychosis/personality disorder

41
Q

What is Huntington’s disease caused by?

A

Autosomal dominant genetic disease causing neuronal degeneration
Initially in indirect pathway components of the striatum
Later on in direct pathway components + GPe

42
Q

In Huntington’s disease, what does degeneration in the striatum lead to? (early stages)

A

Reduces indirect pathway inputs to the GPe
Increases inhibition of Gpi
VLo is dis-inhibited as a result
Causes inappropriate initiation of movement

43
Q

Compare genetics of PD and HD

A

Both have a genetic element, but PD is mostly sporadic and HD is mostly genetic

44
Q

What genes presdispose you to developing PD? What are the differences between them?

A

SNCA is uncommon but has a high penetrance

GBA1 is common but has a low penetrance

45
Q

How can you be genetically predisposed to HD?

A

Mutations in the HTT gene which encodes the ‘Huntington protein’- 100% certainty of getting it but onset varies

46
Q

What do PD genes encode?

A

Proteins involved in either protein degradation pathways (Parkin, SNCA) which causes the formation of Lewy bodies
Or mitochondrial function (PINK1, DJ-1)

47
Q

What is the function of the HTT protein? What does the mutation lead to?

A

Remains unclear but is involved in intracellular transport
Mutant HTT protein contains extended stretches of poly-glutamine (polyQ) which contributes to aggregation of proteins in ‘inclusion bodies’ in affected neurons

48
Q

How is the cerebellum involved in motor control and learning?

A

Appears to instruct motor cortex neurons with respect to direction, timing and force of movement
Uses predictions based on past experiences
Compares what is intended and what actually happens- enables motor learning

49
Q

What is cerebellar ataxia?

A

Lesions to the cerebellum resulting in poorly integrated movement
Dyssynergia- inability to coordinate movements

Introduction to neuroscience (8 decks)

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