The Lower Motorneurone Flashcards

1
Q

What is a motorneurone?

A

It is a somatic efferent that supplies skeletal muscles to:

  • Bring about displacement of limbs (i.e. movements)
  • Set muscle tone
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2
Q

What are the two basic divisions of type of motorneurone?

A

Upper motorneurones
(Motorneurones that eventually supply skeletal muscles indirectly)

Lower motorneurones
(Motorneurones that supply skeletal muscles directly

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3
Q

Describe the variety of UMNs.

A

All descending tracts are UMN
All interneurons are UMNs
All upper motorneurones exert their actions via lower motorneurones

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4
Q

What is a lower motorneurone?

A

It is a somatic motor efferent with a cell body in either:

  • Lamina IX of the spinal cord (i.e. spinal motor nucleus)
  • Cranial nerve motor nucleus

Its axon supplies skeletal muscles of the body directly

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5
Q

What are some lower motorneurone signs?

A
Flaccid muscle weakness
Hypotonia or atonia
Hyporeflexia or areflexia
Denervation muscle atrophy
Fasciculation (acute phase)
Muscle wasting
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6
Q

What is the difference between a lower motorneurone and an alpha-motorneurone?

A

Alpha-motorneurones are a subdivision of lower motorneurones

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7
Q

What is a motor unit?

A

A motor unit consists of an alpha-motorneurone plus all the muscle fibres it supplies

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8
Q

What types of lower motorneurone are there?

A

Alpha-motorneurones

Beta-motorneurones

Gamma-motorneurones

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9
Q

Define a reflex.

A

It is an involuntary, unlearned, repeatable, automatic reaction to a specific stimulus that does not require the brain to be intact

(The neuronal pathway describing a reflex is known as a reflex arc)

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10
Q

What are the components to a reflex arc?

A

5 components:

  • A receptor (or transducer)
  • An afferent fibre
  • An integration centre
  • An efferent fibre
  • An effector
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11
Q

What are the different types of muscle stretch reflexes?

A

Monosynaptic stretch reflex
(Only has one synapse, i.e. one afferent fibre then one lower motorneurone)

Disynaptic stretch reflex
(Has two synapses, i.e. interneuron)

Oligosynaptic stretch reflex
(Has multiple synapses)

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12
Q

What is the relevance of different types of muscle stretch reflexes?

A

The more synapses ad intermediate neurones, then the more inhibition that can be on that reflex, and so it can make it harder to activate that reflex.

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13
Q

Why do we have muscle stretch reflexes?

A

To hold a bowl of soup

To keep a constant tone in our muscles
So if you have your arm outstretched, then gravity would make it fall, this would lengthen the stretch fibres I the muscle which would then send a reflex to increase motor tone and stop your arm from falling.

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14
Q

How does the muscle stretch reflex work?

A

When a muscle relaxes it effectively lengthens
This stretches muscle length fibres
They send an action potential down three routes:
- The brain via dorsal columns
- The cerebellum via spinocerebellar tracts
- Directly to spinal motorneurones
This keeps the body aware of muscle position and keeps tone.

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15
Q

What is muscle tone?

A

In a normal awake neurological status, lower motorneurones tonically supply muscles with background electrical impulses

These lead to background minimal contraction of the muscle

This gives the muscle a small amount of force

Also known as muscle tone

Muscle tone allows us to maintain body posture and hold our heads upright

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16
Q

What are the key spinal neural levels?

A
Diaphragm - C3-5
Biceps - C5-6
Wrist - C8-T1
Nipple - T4
Umbilicus - T10
Hip flexion - L1-2
Quadriceps - L3-4
Knee flexion - S1
Great Toe - L5 (Foot Dorsi-flexion)
Foot - S1-2 (plantar flexion)
Urinary sphincter and anal tone - S2-4
17
Q

What happens when muscles generate too little tone?

A

The body becomes limp
The body is unable to support its weight
Normal body posture is lost
This is anything between Hypotonia & atonia

18
Q

What happens when muscles generate too much tone?

A
Muscles become stiff
Joints become stiff
Normal body posture becomes altered
Ability to move affected limb will be lost
Fluidity of movements will be lost
Spastic paralysis will result