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Z YEAR 2 BRS NEURO > Neuromuscular Control > Flashcards

Neuromuscular Control Flashcards

1
Q

Where are alpha motor neurons?

A

Occupy anterior horn - ventral horn of grey matter in spinal cord

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2
Q

What do the lower motor neurons of the brainstem and spinal cord inntervate? What does activation cause?

A
  1. extrafusal muscle fibres of the skeletal muscles

2. activation causes muscle contraction

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3
Q

What does the motor neuron pool contain?

A

all alpha motor neurons innervating a single muscle

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4
Q

What is a motor unit?

A

a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force

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5
Q

How many motor neurons and skeletal muscle fibres do humans have?

A
  • 420,000 motor neurons

- 250 million skeletal muscle fibres.

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6
Q

How many muscle fibres does each motor neurone supply on average?

A

600

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7
Q

What does the stimulation of one motor unit cause?

A

contraction of all the muscle fibres in that unit

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8
Q

What are the slow (S, type I) motor units?

A
  1. smallest diameter cell bodies
  2. small dendritic trees
  3. thinnest axons
  4. slowest conduction velocity
    - For posture muscles, as slow long time
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9
Q

What are the fast, fatigue resistant (FR, type IIA) motor units?

A
  1. larger diameter cell bodies
  2. larger dendritic trees
  3. thicker axons
  4. faster conduction velocity
    - Calf, high
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10
Q

What are the fast, fatiguable (FF, type IIB) motor units?

A
  1. larger diameter cell bodies
  2. larger dendritic trees
  3. thicker axons
  4. faster conduction velocity
    - Fast twitch muscle in calf
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11
Q

Is one single motor neuron innervate one muscle fibre?

A

An individual neuron may innervate 10 or 100 of muscle fibres, none of muscle fibres will innervated be motor neuron 1 will be innervated by motor neurons 2 - one neuron always wins (at baby more and then one neuron wins)

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12
Q

Why do you want more motor neurons to innervate muscle fibres?

A

If one motor neuron innervates thousands of muscle fibres the control over that muscle is not as refined as 10 muscle fibres by one motor neuron - innervation ratio relates to function of muscle - small ratio, fine control muscle

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13
Q

How are the 3 different motor unit types classfied?

A
  1. amount of tension generated
  2. speed of contraction
  3. fatiguability
    - Look at graphs
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14
Q

How does the CNS regulate the force that a single muscle can produce?

A
  1. Recruitment

2. Rate coding

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15
Q

How are motor units recruited?

A

Not random

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16
Q

By what principal are motor units recruited?

A
  • Size principal
  • Smaller units recruited first - generally slow twitch units
  • As more force required, more units are recruited
  • Slow then fast recurited
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17
Q

What does recruitment allow?

A

-Fine control - e.g. when writing, under which low force levels are required

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18
Q

At what frequencies to motor units fire at?

A
  • Motor unit can fire at range of frequencies

- Slow units fire at lower frequency

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19
Q

What happens as the firing rate increases?

A

Force produced by the unit increases

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20
Q

When does summation of rate coding occur?

A

When units fire at frequency too fast to allow the muscle to relax between arriving at action potentials

21
Q

When will a muscle waste?

A

Even when have arterial supply, need nerve supply otherwise will waste

22
Q

What do motor neurons supply?

A
  • Neurotrophic factors
  • Prevent neuronal death
  • Promote growth of neurons after injury
23
Q

What are motor unit and fibre characteristic dependent on?

A

the nerve which innervates them

24
Q

What happens in cross innervation?

A

If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.

25
Q

Can the motor neuron effect the properties of the muscle fibres it innervates?

A

Yes

26
Q

Can fibre types change properties under different conditions?

A

Yes

27
Q

What are some examples of fibre types changing conditions?

A
  1. Type IIB to IIA most common following training
  2. Type I to II possible in cases of severe deconditioning or spinal cord injury
  3. Microgravity during spaceflight results in shift from slow to fast muscle fibre types
28
Q

How do fibre types change with ageing?

A
  1. loss of type I and II fibres but also preferential loss of type II fibres
  2. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
29
Q

How are reflexes different from voluntary movements?

A

Can’t be stopped once started

30
Q

What is a reflex?

A
  1. An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness.
  2. An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.
31
Q

What is a monosynaptic (stretch) reflex?

A
  1. Sensory receptor
  2. Sensory neurone
  3. Motor neuron
  4. Motor neuron (to antagonist)
    - Inhibition of antagonist or other
    - Excitatory to muscle that needs to be contracted
32
Q

What are different types of reflexes?

A

automatic (knee jerk) and stereotyped behaviours (sneeze, cough) in response to stimulation of peripheral receptors

33
Q

Can reflexes be influenced?

A
  • Try clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped. The reflex becomes larger
  • Jendrassik manoeuvre
34
Q

Why does Jendrassik manoeuvre happen?

A

reducing amount of inhibition the the brain brain and upper regions on CNS exert on reflexes under normal conditions - removes descending inhibition form the brain

35
Q

What do the higher centres of the CNS exert on reflexes?

A

inhibitory and excitatory regulation upon stretch reflex

36
Q

What type of control domination in normal conditions?

A

Inhibitory (brain effect on reflex pathways)

37
Q

What does decerebration reveal?

A

The excitatory control from (descending) supraspinal areas - tonic contraction and higher reflex

38
Q

When can rigidity and spasticity result?

A

Brain damage giving over active or tonic stretch reflex

39
Q

Where do alpha neurons go out to?

A

Extrafusal muscles

40
Q

What do gamma neurons do?

A

Innervate intrafusal muscle (sensitise the sensory organ - don’t contribute to contraction of musucle)

41
Q

What action does descending (supraspinal) control have?

A
  1. Activating alpha motor neurons: by normal upper motors neurons lower motor neurons
  2. Activating inhibitory interneurons
  3. Activating propriosponal nuerons
  4. Activating gamma motor neurons
  5. Activating terminals of afferent fibres
42
Q

What are intrafusal muscle fibres?

A

Altering sensitively of sensory organs in muscle so when stretched cause signal to go back to spinal cord to generate reflex contraction of muscle

43
Q

What is hypereflexia?

A

Overactive reflex

44
Q

What happens in hyper-reflexia?

A

Loss of descending inhibition

45
Q

What is hyperfelxia associated with?

A

upper motor neuron lesions

46
Q

What is clonus?

A
  • Involuntary and rhythmic muscle contractions

- Hypereflexia

47
Q

What is babinski’s sign?

A

1; When sole stimulated with blunt instrument the big toe:
-Curls downwards - normal
-Curls upwards – abnormal in adults. This is a positive Babinski sign.
3. Associated with upper motor neuron lesions
Note: Toe curls upwards in infants – this is normal

48
Q

What is hypo-reflexia?

A
  • Below normal or absent reflexes

- lower motor neuron disease

49
Q

What happens in upper motor neuron lesion?

A
  • Loss of voluntary movement - pathway lost

- Inhibitory control removed so hypereflexia

Z YEAR 2 BRS NEURO (21 decks)

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