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Neurology > Motor System > Flashcards

Motor System Flashcards

1
Q

What do central pattern generator circuits allow for?

A

rhythmic, alternating activity such as walking without us having to consciously think about it

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2
Q

How do central pattern generators work?

A

Inhibitory interneurons and excitatory neurons between motor flexor and extensor neurons allow for activation of one neuron to block the neighbouring neuron with the opposite action e.g. when flexed inhibitory neuron can block extensor neuron

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3
Q

What are the 3 levels of motor control hierarchy?

A
  • strategy
  • tactics
  • execution
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4
Q

What structures are involved in strategy level of motor control?

A
  • neocortical association areas

- basal ganglia

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5
Q

What structures are involved in tactics level of motor control?

A
  • motor cortex

- cerebellum

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6
Q

What structures are involved in execution level of motor control?

A
  • brainstem

- spinal cord

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7
Q

LMNs receive synaptic info from three sources. What are they?

A
  • UMNs
  • proprioceptors
  • spinal interneurones
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8
Q

Extrafusal fibres make up the bulk of the skeletal muscle and generate force. What type of LMNs supply them?

A

alpha motor neurones

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9
Q

Intrafusal muscle fibres are the sensory muscle spindles of skeletal muscle. What type of LMNs supply them?

A

Efferent gamma motor neurones

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10
Q

What is the difference between axial, proximal and distal muscles?

A
  • Axial control movements of trunk
  • proximal control movements of shoulder, pelvis, elbow and knee
  • distal control movements of hands, feet and digits
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11
Q

What is the difference between a motor unit and a motor neurone pool?

A
  • Unit: An alpha motor neurone and the muscle fibres it innervates
  • Pool: collection of a-MNs that innvervate a single muscle
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12
Q

What 3 factors affect to the activation of muscle fibres?

A
  • frequency of AP discharge in individual motor units
  • number of motor units within muscle that are simultaneously active
  • co-ordination e.g. activation of synergistic and antagonist muscles
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13
Q

In the ventral horn of the spinal cord, the cell bodies of the LMNs innervating axial muscles are medial/lateral to those innervation distal muscles and the cell bodies of the LMNs innervating flexors are ventral/dorsal to those supplying extensors.

A
  • medial

- dorsal

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14
Q

What are the two main factors muscle strength depends on?

A
  • activation of muscle fibres

- force production by innervated muscle fibres

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15
Q

What 2 factors affect the amount of force produced by a single muscle fibre?

A
  • the size of fibre

- type of fibre (fast/slow)

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16
Q

Explain why increasing the frequency of APs to a muscle fibre leads to a more force being produced by muscle fibre.

A

A single AP causes a muscle fibre to twitch. If you increase the rate of APs, these twitches don’t have time to relax again and so the twitches build on top of each other to get a bigger force produced

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17
Q

Motor units of muscles for fine movements (e.g. extraocular eye muscles) have one motor unit to loads of muscle fibres and motor units for large postural, antigravity muscles (e.g. quads) have one motor unit to a few muscle fibres. True/false?

A

False.

Small muscles motor units neurones supply only a few fibres and vice versa

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18
Q

Small motor units are innervated by small/large diameter a-MNs and large motor units are innervated by small/large diameter a-MNs.

A
  • small

- large

19
Q

How do slow-twitch and fast-twitch skeletal muscle fibres differ?

A

Differ in how quickly myosin ATPase splits ATP to provide energy for cross bridge cycling. They express different myosin heavy chains (MHC I and II)

20
Q

From what process is ATP mostly derived in slow-oxidative (Type I) fibres?

A

Oxidative phosphorylation

21
Q

List the 3 skeletal muscle fibre types in humans in order of fatigue resistance from most fatigue resistant to least.

A
  • Most resistant: Type I fibres
  • Type IIa fibres
  • Type IIx fibres
22
Q

Which fibre types are most vascularised and which least?

A

Type I most vascularised and so more red because more myoglobin
Type IIx least vascularised and so pale

23
Q

From what process is ATP mostly derived in fast-oxidative Type IIa fibres?

A

Oxidative phosphorylation

24
Q

From what process is ATP mostly derived in fast Type IIx fibres?

A

Glycolysis

25
Q

What type of action are Type I, Type IIa Type IIx fibres used for?

A
  • Type I: antigravity, sustained movement e.g. yoga
  • Type II: sustained locomotion e.g. jogging
  • Type IIx: Bursts of power e.g. weight lifting
26
Q

List the fibres (I, IIa, IIx) in order of threshold from high to low.

A

High threshold - Type IIx
Intermediate - Type IIa
Low - Type I

27
Q

What does the Henneman Size Principle state and what does this principle explain?

A

States that as more force is needed, motor units are recruited in order of increasing size.
It explains how a muscle can gradually increase force

28
Q

Explain how smaller a-MN units are recruited before larger a-MN units according to Henneman Size Principle.

A

Smaller a-MN units are more easily excited than the larger ones. Smaller a-MN units have smaller diameter so recruitment also correlates to diameter.

29
Q

How is it that one muscle can express a varying degree of force? (E.g. can be used for walking and sprinting)

A

One muscle can contain all 3 (I, IIa, IIx) fibre types and so when more recruited the faster ones are increased too which increases the force

30
Q

What is the myotatic reflex and give example?

A

When a skeletal muscle is stretched it pulls back e.g. knee jerk reflex

31
Q

What is the sensory organ within a skeletal muscle called and what modality is it involved in?

A

Muscle spindle involved in proprioception

32
Q

What is the only monosynaptic reflex in humans and describe the pathway.

A
  • Myotatic reflex
  • muscle spindle stretched -> Ia afferent activated -> transmission of glutamate at synapse in spinal cord -> activation of a-MN -> homonymous muscle contracted
33
Q

What do muscle spindles consist of? (Outer layer, insides and nerves)

A
  • outer fibrous capsule
  • intrafusal fibre inside
  • Ia sensory myelinated afferents at midway point of intrafusal fibre
  • gamma motor efferents that innervate intrafusal fibres
34
Q

In what type of skeletal muscles is myotatic reflex most prominent?

A

Extensor muscles

35
Q

When weight is applied to muscle, it only lengthens transiently before shortening back to original size. Explain how this happens.

A

When muscle is stretched Type Ia sensory afferents fire, this causes a-MN neurones to fire and contract muscle back to normal size. This causes Ia to stop firing and so does a-MN, so muscle re-adjusts to be same size despite carrying more load.

36
Q

Testing the biceps tendon reflex tests what spinal level?

A

C5-C6

37
Q

Testing the supinator tendon reflex tests what spinal level?

A

C5-C6

38
Q

Testing the triceps tendon reflex tests what spinal level?

A

C7

39
Q

Testing the quadriceps tendon reflex tests what spinal level?

A

L3-L4

40
Q

Testing the gastrocnemius (ankle) tendon reflex tests what spinal level?

A

S1

41
Q

What is Jendrassik manoeuvre?

A

Getting patient to pull fingers apart when testing tendon reflexes, it enhances reflexes

42
Q

Where do the gamma motor neurones attached to the polar ends of intrafusal muscle fibres receive input from?

A

From higher centres of spinal cord than the Ia afferents

43
Q

What is the function of gamma motor neurones that supply the intrafusal muscle fibres?

A

These contract in parallel with the extrafusal muscle fibres. When alpha-MNs are activated, so are gamma-MNs so that when the extrafusal muscle contracts the intrafusal fibres aren’t left slack. This allows the sensory Ia afferents to keep “broadcasting” i.e. keep sending APs and info

Neurology (34 decks)

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