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Control Symposia > Control Term 3- Sensory and Motor Innervation of Muscles > Flashcards

Control Term 3- Sensory and Motor Innervation of Muscles Flashcards

1
Q

From where does the motor cortex receive regulatory input?

A

The basal ganglia.

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2
Q

What does the motor cortex do?

A

Initiates planned mov’s.

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3
Q

From where does the brainstem receive input?

A

Cerebellum - Sensory motor coordinatio

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4
Q

What does the brainstem do (terms of motor control)?

A

Basic movements and postural control

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5
Q

What are the brainstem centres?

A

Red nucleus, reticular formation and the vestibular nuclear complex

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6
Q

What are the UMN’s in the motor cortex?

A

Pyramidal cells in cortical layer 5.

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7
Q

Do more axons descend contralaterally or ipsilaterally?

A

Contralaterally - 85-95%

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8
Q

Where are lower motor neurones localised?

A

Laminae IX of ventral grey horn of SC.

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9
Q

How do LMN’s exit the grey horn?

A

As a ventral root of mixed spinal nerves.

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10
Q

What neurones are directly responsible for the generation of force by muscle?

A

Alpha motor neurons

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11
Q

Where is Laminae IX thickest?

A

Cervical and lumbosacral enlargements- reflects the muscle demand here.

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12
Q

What is a motor neurone pool?

A

A cluster of alpha motor neurones in the ventral grey horn.

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13
Q

In segmental organisation of LMNs in the ventral grey horn:

1) Where are the axial muscle compared to distal muscles LMNs?
2) Where are flexor muscle compared to extensor muscle LMN’s?

A

1) Axial is more medial compared to distal(makes sense)

2) Flexors are more dorsal compared to extensors.

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14
Q

What is a motor unit made up of?

A

> Alpha motor neuron

> Muscle fibres that the alpha motor neuron innervates

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15
Q

What is the advantage of having even spacing of the muscle fibres?

A

It ensures that having a single damaged motor axon won’t impair the overall muscles’ ability to contract.

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16
Q

What are the muscle fibres: alpha motor neuron ratios of:

1) Medium motor unit
2) Small motor unit
3) Large motor unit

A

1) 180:1
2) 3:1
3) 1000/2000:1

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17
Q

Posture muscles are what type of motor unit?

A

Slow motor unit - more resistant to fatigue

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18
Q

The biceps muscle is what type of motor unit?

A

Fast, fatiguable.

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19
Q

What does an electromyograph record?

A

Motor unit electrical activity.

20
Q

How can an EMG be used in clinical diagnosis?

A

Degradation of synchronous rhythm - used in clinical diagnosis.

21
Q

What contributes to a higher muscle tension?

A

Increased frequency of action potentials –> increase the firing rate –> increases the force.

22
Q

What are the 3 main sources of input to the alpha motor neurones?

A

1) Direct UMN synapse
2) UMN synapse through interneurons
3) Sensory input from peripheral proprioceptors.

23
Q

What is the muscle spindle?

A

Sensory apparatus of the muscle

24
Q

Where is the spindle located?

A

In the belly, parallel to muscle fibres

25
Q

What is the function of the spindle?

A

> Contribute to proprioception

> Match the muscle force generation to the motor task.

26
Q

What is the stretch reflex?

A

When you stretch a muscle and spindle –> contract in response. Makes up the basis for patella tap etc.

27
Q

What is muscle tone?

A

When the muscle is ALWAYS under some degree of stretch due to interaction between alpha motor neurones and muscle spindle.

28
Q

What are the classes of spindle and what afferent fibres do they give off?

A

Chain : Ia and II

Bag : Ia

29
Q

What is the function of a chain spindle?

A

Gives off information about sustained contraction - static.

A chain is continuous and the same, it is static

30
Q

What is the function of a bag spindle?

A

Gives off information about dynamic contraction.

31
Q

What type of muscle fibres are innervated by Alpha motor neurones?

A

Extrafusal fibres: Bulk of muscle body, generate tension

32
Q

What type of muscle fibres are innervated by Gamma motor neurones?

A

Intrafusal fibres: Spindle - sensory function.

33
Q

How is the length of the muscle spindle regulated?

A

A) The alpha motor neurons contract and shorten the muscle fibre.

2) Extrafusal fibres shorten and the spindle collapses.
3) Gamma motor neurones of the intrafusal fibres correct the length of the spindle to match extrafusal length.

34
Q

What is a golgi tendon?

A

It is a mechanoreceptor- detects changes in muscle tension

35
Q

How does A) A golgi tendon B) Spindle lie in relation to a muscle fibre?

A

Golgi is in series

Spindle lies parallel

36
Q

What is the innervation of a Golgi tendon?

A

Ib afferents

37
Q

What happens in an isotonic contraction?

A

Change in length, not tension

38
Q

What happens in an isometric contraction?

A

Change in tension, not length. (He weighed a “metric” ton and put tension on me)

39
Q

In which type of contraction (isometric or isotonic) is the Ia afferent activated and not the Ib:?

A

Isotonic

40
Q

Place these afferent fibres in order from fastest to slowest: Ib, II, Ia.

A

Ia, Ib, II

41
Q

What are the following receptors innervated by afferently:

1) Golgi Tendon Organ
2) Bag and chain spindle
3) Chain spindle only

A

1) Ib
2) Ia
3) II

42
Q

What is conduction velocity positively correlated with when speaking about afferent fibres?

A

Their axon diameter

43
Q

Which receptors are large diameter afferents associated with?

A

Low threshold mechanoreceptors

44
Q

Which receptors are small diameter afferents associated with?

A

Nociceptors and thermoceptors (not essential for survival).

45
Q

Damage to descending motor pathways causes what syndrome? And what are the clinical signs of this?

A

Upper motor neurone syndrome.

Signs: 
> Babinksis syndrome 
> Hyporeflexia
> Spasticity
> Loss of fine mov'ts
46
Q

What are the early manifestations of ALS? And what is the progression?

A

Early signs: Muscle weakness and atrophy.

Progression: Inexorable decline, lose voluntary movement, NO COGNITIVE FUNCTION LOSS (Stephen hawking)

47
Q

What is the incidence of ALS?

A

1:20,000

Control Symposia (12 decks)

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