L08 - Disorders of the LMN

Question 1

What is a motor unit?

Answer 1

The minimal functional unit of the motor system

Question 2

What is the motor unit comprised of?

Answer 2

1. An a-motoneuron

2. All extrafusal skeletal muscle fibres it supplies

Question 3

What is the innervation ratio between extra-ocular muscles and muscle fibres?

Answer 3

1:10 fibres

Question 4

What is the innervation ratio between quadricep muscles and muscle fibres?

Answer 4

1:1000 fibres

Question 5

What is the neuromuscular junction?

Answer 5

The site of communication between the motoneurone and muscle

Question 6

Define innervation

Answer 6

The normal state of nerve supply to a muscle or other target

Question 7

Define denervation

Answer 7

Depriving the muscle of its nerve supply (therefore will not survive for v long)

Question 8

Define re-innervation

Answer 8

Re-growth of the nerve to re-supply the muscle

Question 9

What is crocodile tears syndrome?

Answer 9

Occurs most often following facial paralysis

• Dmg to salivary gland mistakenly regrow into tear gland
• Shed tears whilst eating
• Re-innervate wrong effector

Question 10

What would happen to a motoneurone if the cell body (soma) was damaged?

Answer 10

Loss or damage of the cellbody would lead to death of motoneurone

Question 11

What is polio myelitis?

Answer 11

A communicable infection that targets cell bodies of LOWER motoneurones of the body
- aka infantile paralysis

Question 12

Cause of polio myelitis?

Answer 12

Infection by polio virus

- Any motoneurones of the spinal cord are susceptible to this virus

Question 13

Complications of polio myelitis?

Answer 13

• Leads to toxic infection (Death) of cell bodies of neurones of the ventral horn –> Death of motoneurones leads to denervation hence paralysis of muscles they supply
• If kill resp motoneurones, patient’s breathing has to be assisted for the rest of their lives
• Any muscle can become paralysed

Question 14

What effect could death to cell bodies of neurones of ventral horn do to the dorsal horn?

Answer 14

Toxic infection of cell bodies of neurones of the ventral horn an lead to death of the dorsal horn too

Question 15

What are the two possible variants of motoneurone disease?

Answer 15

1. Disease simultaneously kills both upper motoneurone and lower motoneurone (in American terms –> progressive supranuclear palsy)
2. The disease targets only the lower motoneurone

Question 16

What is motoneurone disease?

Answer 16

• Spontaneous genetically programmed death of motoneurones of body (apoptosis)
• Life-limiting, rapidly-progressing disease that affects the brain and spinal cord.
• Attacks the nerves that control movement so muscles no longer work. It does not usually affect senses, for example sight, sound and touch

Question 17

What is amyotrophic lateral sclerosis (Lou Gherig’s disease)?

Answer 17

Death of neurones responsible for controlling voluntary movement (deteriorate and gradually die)

Question 18

Which motoneurones of the body do not undergo apoptosis under MD?

Answer 18

1. Motoneurones supply extraocular muscles (eyes)

2. Motoneurones supplying the anal sphincter (S2-S4)

Question 19

What is Guillain-Barre syndrome?

Answer 19

• Rapid onset muscle weakness caused by the immune system damaging the PNS
• Acquired as a complication following a viral infection such as a common cold
• Axon demyelination of motoneurones
• Clinical signs reverse when condition is cured or foes into remission

Question 20

What is diabetic neuropathy?

Answer 20

• Possible nerve damage if you have diabetes
• Most often to legs and feet
• Caused by high blood glc levels over a long period of time
• Clinical signs reverse when condition is cured or foes into remission

Question 21

What is botulinum toxin and its effects on the NMJ?

Answer 21

• Neurotoxic protein produced by the bacterium Clostridium botulinum and related species.
• It prevents the release of ACh from axon endings at the NMJ and thus causes flaccid paralysis.
• Acts to deplete the presynaptic terminal of the NMJ of its neurotransmitter
• Infection with the bacterium causes the disease botulism.
• Emergency as can lead to death

Question 22

Possible causes of botulism or culturing of botulinum toxin?

Answer 22

• Unskilled domestic preservation of cooked food can lead to inadvertent culturing of botulinum toxin
• Badly preserved tinned foods are the most common cause of botulism

Question 23

How do nerve gases work in relation to the NMJ?

Answer 23

Act by blocking AChE from breaking down ACh in the NMJ

Question 24

What is myasthenia gravis and how does it affect the NMJ?

Answer 24

A rare genetic disease of the NMJ

• Nicotinic receptors of the post-synaptic membrane of the NMJ are selectively destroyed by the person’s immune system
• Affects any NMJ of the body in affected individuals
• Flaccid weakness of the affected muscles
• Can cause resp failure if muscle of resp are affected

Question 25

What is Duchenne muscular dystrophy?

Answer 25

- A genetic condition - Progressive muscle weakness - Muscle loss typically begins at pelvis and thighs --> arms (death of muscle tissue) - Defects in muscle protein --> Mutation in dystrophin (DMD) gene; Dystophin is primarily made in the muscle cells of the heart and skeletal muscle (vital for muscle strength and function) - Eventual death of individual if not treated - Diagnosis normally when younger than 5 years old ?

Question 26

What is dystrophy?

Answer 26

A disorder in which an organ/ tissue wastes away

Question 27

What are the different lower motoneurone signs of (damage)?

Answer 27

1. Flaccid muscle weakness 2. Hypotonia (atonia) 3. Hyporeflexia (areflexia)

Question 28

What are the different lower motoneurone signs of (damage)?

Answer 28

1. Flaccid muscle weakness 2. Hypotonia (atonia) 3. Hyporeflexia (areflexia) 4. Denervation muscle atrophy 5. Fasciculations (acute phase) 6. Muscle wasting