DISORDERS OF MOTOR UNITS

Question 1

What is a motor unit?

Answer 1

An alpha/lower motor neurone (somatic efferent) and all of the extrafusal muscle fibres that it supplies and the NMJ

Question 2

Where are alpha motor neurones found?

Answer 2

• Ventral horn of the spinal cord
• Motor nuclei of the cranial nerves

Question 3

What type of muscles do alpha motor neurones supply?

Answer 3

Skeletal muscles

Question 4

How do motor units vary?

Answer 4

Vary based on the amount of force they produce

Question 5

What are the two types of motor neurones?

Answer 5

• Upper motor neurones
• Alpha/ lower motor neurones

Question 6

How are the two types of motor neurones arranged?

Answer 6

Upper motor neurone is above the lower motor neurone. There is then a NMJ between the lower motor neurone and the skeletal muscle

Question 7

How do problems in the motor neurones present themselves?

Answer 7

Problems in upper –> upper motor neurone signs
Problems in lower –> lower motor neurone signs
Problems in both–> lower motor neurone signs

Presenting signs of upper and lower are different

Question 8

Where are upper motor neurones found and where are lower motor neurones found?

Answer 8

Upper motor neurone = Brain
Lower motor neurone = Ventral horn of spinal cord or motor nuclei of cranial nerves

Question 9

What are possible causes of lower motor neurone signs?

Answer 9

• Autoimmune destruction of receptors in skeletal muscle
• Death or dysfunction to muscle as this prevents communication between the neurone and the skeletal muscle cell

Question 10

What is de - nervation and its consequences

Answer 10

De- nervation is when a muscle loses its nerve supply. This can result in death of the muscle cell

Question 11

What is re- nervation?

Answer 11

Muscle looses nerve supply but then it is restored by either the same nerve or other nerves. Nerves may re- nervate effectors different to their original effector

Question 12

Give an example of a type of damage that can lead to death of the motor neurone

Answer 12

Damage to the cell body (soma) of the neurone as this can cause denervation

Question 13

Give the causes, effects and treatments of POLIO MYELITIS (aka infantile paralysis)

Answer 13

• Infection of the polio virus results in death to the cell body of lower motor neurones and this causes death to the muscle it supplies.
• It mainly affects the spinal cord region. There is paralysis of the muscles that are supplied. Lower motor neurones are located in the ventral horn of the spinal cord. Death to these neurones can also cause damage in the dorsal horn
• It can be treated by immunisation programs

Question 14

What happens if a patients respiratory system is affected by polio myelitis?

Answer 14

They need assistance breathing for the rest of their lives and may need iron lungs

Question 15

What is motor neurone disease?

Answer 15

Spontaneous programmed damage or death of cell bodies of either:
- Upper and lower motorneurones e.g ALS
- Just lower motorneurones e.g Lou Gehrig’s disease

Question 16

Which two types of motorneurones are not affected by motor neurone disease?

Answer 16

• Motorneurones supplying extraoculuar muscles
• Motorneurones supplying anal sphincter

Question 17

What is the effect of damage to the axon of the lower motor neurone?

Answer 17

It doesn’t lead to death of the motor neurone however it does lead to denervation

Question 18

What can cause damage to the axons of a motor neurone?

Answer 18

• Crushing injuries
• Stabbing injuries

Question 19

What is Guillain Barre syndrome?

Answer 19

There is damage to myelination of axons due to viral infection

Question 20

What effect can diabetic neuropathy have on motorneurones?

Answer 20

Can cause damage to myelination of sensory and motor axons

Question 21

how to treat problems with myelination of axons?

Answer 21

Plasma infusions to clean the blood and remove the virus

Question 22

What is the effect of Botulinum toxin on the NMJ?

Answer 22

Botulinum toxin prevents exocytosis and therefore prevents the release of acetyl choline. This results in weakness of the muscles that control the eyes, mouth, face and throat

Question 23

What can botulinum toxin be used in? (2)

Answer 23

• Botox
• spastic disorders

Question 24

What can cause botulism?

Answer 24

• Badly preserved tinned food
• Unskilled preservation of cooked food can culture growth of botulinum toxin

Question 25

What is myasthenia gravis and what effects does it have?

Answer 25

Autoimmune destruction of nicotinic acetylcholine receptors on the motor end plate. Results in flaccid weakness of muscles. If it affects respiratory muscles it can cause respiratory failure. it can affect any NMJ in affected people

Question 26

What is Duchenne muscular dystrophy?

Answer 26

This is when there is damage to the skeletal muscle supplied by a motor neurone. It is genetic and results in:
- Death of muscle tissue
- Progressive muscle weakness
- Defects in muscle proteins

It can eventually lead to death

Question 27

What is hypotonia and atonia (LMS)

Answer 27

Hypo - some loss of muscle tone but some still remain

Atonia = complete loss of muscle tone

Question 28

What are hyporeflexia and areflexia

Answer 28

Hypo = some reflexes still remain

Areflexia = complete loss of reflexes

Question 29

What are fasciculation’s?

Answer 29

A LMS where there are involuntary muscle twitches which are too weak to move a limb but can be seen and palpated by clinicians