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BMS 248 - Neural circuits > Motor control > Flashcards

Motor control Flashcards

1
Q

How is the motor system arranged?

A

Heirarchically

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2
Q

What is the highest level of the motor system hierarchy?

A

Primary motor cortex

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3
Q

What is the middle level of the motor system hierarchy?

A

Brain stem

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4
Q

What is the lowest level of the motor system hierarchy?

A

Spinal cord

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5
Q

How does the primary motor cortex directly interact with the spinal cord?

A

Projection via the CORTICOSPINAL tract

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6
Q

Other than project to the spinal cord, what else does the PMC do?

A

Regulates motor tracts that originate in the brainstem

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7
Q

What is the brainstem important in?

A

Goal directed movements of the hand/arm

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8
Q

How does the brainstem control distal limbs?

A

Via the lateral descending system

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9
Q

What neuronal pathway comes from the spinal cord?

What does this control?

A

Direct pathway to the muscles, via a neuronal circuit

Controls SIMPLE reflexes, such as walking/chewing

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10
Q

What are the simplest reflexes?

A

MONOSYNAPTIC:

  • Sensory neuron
  • Motor neuron
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11
Q

What is the structure of most of the reflexes in the body?

A

POLYSYNAPTIC:

  • Sensory neuron
  • Interneuron
  • Motorneuron
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12
Q

What happens if you artificially stimulate the motor cortex, brain stem or spinal cord?

A

NO complex movements (only twitches)

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13
Q

What does the brain stem do?

A

Feeds information into the primary motor cortex

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14
Q

Where do the basal ganglia and cerebellum receive input from?

Where do they relay this information to?

A

Many areas of the cortex, from ALL different sensory modalities

Relay this info to the motor cortex via the THALAMUS

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15
Q

What is the function of the basal ganglia and the cerebellum?

A

Monitor commands from the PMC to ensure they are appropriate

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16
Q

What are the basal ganglia and cerebellum ‘aware’ of?

A

The situation that the person is in (orientation of the limbs etc.)

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17
Q

What happens when the body orientation changes?

A

Signals from the PMC are no longer appropriate

Basal ganglia/cerebellum send error correction signals to the PMC for approval

Error correction signal from the PMC to the muscles

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18
Q

What is the difference between the basal ganglia and the cerebellum when sending error correction signals?

A

Basal ganglia can ONLY feedback to the PMC to SUGGEST changes

Cerebellum also does this but can also BYPASS the PMC and send signals straight to the muscles if it needs to (via the brainstem and spinal cord)

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19
Q

How does the basal ganglia feedback to the PMC?

A

Via a subcortical loop

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20
Q

Why does the motor cortex need input from the basal ganglia and cerebellum?

A

To produce coordinated responses

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21
Q

What does electrical stimulation of the frontal lobe cause?

A

Movements on the OPPOSITE side of the body

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22
Q

What is Brodmann’s area 4?

Where is it located?

A

The primary motor cortex

Located just before the central sulcus

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23
Q

What is the primary motor cortex sometimes called?

A

The precentral gyrus

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24
Q

How was the position primary motor cortex discovered?

A

By electrical stimulation:

Lowest intensity stimulation here elicited movement

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25
Q

How were motor maps produced?

A

Anatomical and clinical observations of lesions

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26
Q

What did the motor maps produced show?

A
  • Orderly arrangement along the gyrus (fingers close to hands, close to arms etc.)
  • Fingers, hand and face to have DISPROPORTIONATELY large representation
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27
Q

Why is there a disproportionately large area for fingers, hand and face in the precentral gyrus?

A

Need fine movements of these parts of the body - requires large brain control

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28
Q

What do lesions in a specific area of the cortex cause?

A

Degeneration in the associated spinal cord area and neuron tracts (Wallerian degeneration)

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29
Q

What kinds of movements does the PMC on its own produce?

What is needed for complex movements?

A

Simple voluntary movements

Complex movements require input to the PMC from many areas of the cortex (through the basal ganglia and cerebellum)
Also requires feedback from the BG and C

30
Q

What are the first motor neurons to project from the motor cortex?

A

Upper motor neurons

31
Q

What is the corticospinal tract?

A
  • Motor pathway starting at the cerebral cortex (involves UMN and LMN)
  • Terminates on lower motor neurons and interneurons in the spinal cord
  • Controlling movements of the limbs and trunk.
32
Q

What to upper motor neurons do?

A

Carry commands from the primary motor cortex to the spinal cord, though the brain and brainstem

33
Q

What do UMN synapse onto?

A

Lower motor neurons, via interneurons in the spinal cord

34
Q

Where do LMN originate?

Where do they travel to? What do they cause?

A

Originate in the spinal cord

Travel to the muscles and cause muscle contraction

35
Q

What are UMN involved in?

A

Planning,
Initiating,
Directing movements

36
Q

As well as from the primary motor cortex, where else do UMN originate from?

A

Ancient motor centres of the brain stem:

  • Red nuclei
  • Vestibular nuclei
  • Superior colliculus
  • Reticular formation
37
Q

What do the ancient motor centres of the brainstem regulate?

A
  • Maintain muscle tone
  • Control postural muscles
  • Maintain balance
  • Maintain the correct orientation of the head and body (keep head upright)
38
Q

What type of neurons are cranial nerves?

Where do they originate?

A

Upper motor neurons

Originate in the forebrain and brainstem

39
Q

What are the 2 types of UMN pathways?

A

Direct - From primary motor cortex to interneuron/LMN

Indirect - From brainstem to spinal cord/LMN

40
Q

What do both UMN pathways do?

A

Govern the production of action potentials in LMN

41
Q

What is the ‘final common pathway’?

A

LMN from the interneurons in the spinal cord to the muscles, causing them to contract

42
Q

What makes up the basal ganglia?

A

Caudate
Putamen
Substansia Nigra
Subthalamic Nuclei

43
Q

What does the basal ganglia do?

In order to?

A
  • Provide sensory input to the UMN
  • Connect with the motor cortex

In order to:
- Initiate and terminate unwanted movements and establish a level of tone

44
Q

How does the basal ganglia establish a level of tone?

A

Inhibit antagonistic muscles - allow other muscles to work

45
Q

What does the cerebellum do?

A
  • Controls activity of UMN
  • Connects to the motor cortex via the brainstem and thalamus
  • Connects to the spinal cord itself

In order to:

  • Monitor movements, looking for differences in intended and actual movements
  • Tries to reduce discrepancies by sending error signal straight to muscle itself
46
Q

What is ‘proprioception’?

A

The ability to know the orientation of limbs in space (without any other visual information)

47
Q

What do muscle spindles do?

A

Tell the brain how long a certain muscle is

48
Q

What is the structure of a muscle?

A
  • Many fibres in a fibrous capsule
  • Many nerve inputs/outputs
  • Intrafusal and extrafusal nerve fibres
49
Q

Are muscle spindles intrafusal or extrafusal?

What does this mean?

A

Intrafusal (inside the capsule)

50
Q

What are the different types of intrafusal fibres?

A

Chain fibres

Bag fibres

51
Q

What are the differences between chain fibres and bag fibres?

A

Chain fibres - nuclei all in a straight line

Bag fibres - nuclei all gathered in the middle of the fibre, producing a bulge

52
Q

What are the similarities between chain fibres and bag fibres?

A
  • Have motor input through gamma fibres

- Have sensory output, through Ia and II afferents

53
Q

Where do the Ia and II afferent outputs from the muscle go to?

A

The brain

54
Q

What do the gamma motor neurons in the muscle do?

A

Contacts the muscle fibre and causes them to contract

55
Q

How do the Ia afferent fibres detect changes in muscle length?

A
  • Fibres coil around the muscle spindle
  • When the muscle is stretched, the coils become further/stretched apart
  • The afferent fibres then send action potentials to the brain
56
Q

What are the differences between the structure Ia and II afferent fibres?

A

Ia:

  • Anulospiral endings
  • Wrap around the middle of the BOTH bag and chain fibres

II:
- Flower spray endings that are embedded in the middle region of the BAG fibres

  • Anulospiral endings that are confined to CHAIN fibres
57
Q

What are the differences between the information that the Ia and II afferent fibres relay?

When do they fire?

A

Ia:

  • Relay information of the ‘dynamic’ phase of muscle stretch
  • Fire tonically at rest
  • As stretch is occurring - burst of action potentials

II:

  • Relay information about the FINAL length of the muscle (resting stretch)
  • Fire rapidly when stretch has finished
58
Q

How does the CNS receive useful information on muscle activity?

A

By viewing both the activity of Ia and II muscle fibres together

59
Q

When is the ONLY time that muscle spindles are useful?

Why?

A

When they are under TENSION

No tension - no stretch information to the brain

60
Q

When are gamma motor neurons coactivated?

Why is this needed?

A
  • Coactivated when the extrafusal muscle fibres contract

In order to:

  • Contract the intrafusal muscle fibres at the SAME TIME
  • So that the muscle spindle contracts at the same time as the extrafusal fibres
  • If this didnt happen, the intrafusal fibres would be unloaded and there would be no action potentials to the brain
61
Q

What does serotonin (5-HT) do to gamma motor neuron activity?

What does this cause?

A

Increases it

  • Causes the intrafusal fibres to become slightly STIFFER
  • Increasing sensitivity
62
Q

What does noradrenaline (NA) do to gamma motor neuron activity?

What does this cause?

A

Decreases it

  • Causes the intrafusal fibres to become more elastic
  • Decreasing sensitivity
63
Q

Where are serotonergic/adrenergic neurons in the muscle fibre?

A

In close proximity to gamma motor neurons

64
Q

What is used to fine-tune muscle fibres?

A

5-HT/ NA

  • Lots of 5-HT onto active nerves
  • Lots of NA onto inactive nerves
65
Q

What are the 3 synaptic relays between the periphery and the cortex?

A

1) DRG central processes synapse onto neurons in the GRACILE and CUNEATE nucleus in the lower MEDULLA
2) Axons from these nuclei ascend in the MEDIAL LEMNISCUS and synapse onto neurons in the ventral posterior lateral nucleus of the THALAMUS
3) Send projections to the primary somatosensory cortex

66
Q

Where is the motor cortex in relation to the central sulcus?

A

Infront (pre central)

67
Q

Where is the sensory cortex in relation to the central sulcus?

A

Behind (post central)

68
Q

Where is the secondary somatosensory cortex present?

A

Deep within the lateral sulcus

69
Q

Where is the primary somatosensory cortex present?

A

In the post central gyrus (anterior parietal lobe)

70
Q

What do lesions of the primary somatosensory cortex produce?

A

Proprioceptive deficits

BMS 248 - Neural circuits (16 decks)

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