L08 - Disorders of the LMN Flashcards
What is a motor unit?
The minimal functional unit of the motor system
What is the motor unit comprised of?
- An a-motoneuron
2. All extrafusal skeletal muscle fibres it supplies
What is the innervation ratio between extra-ocular muscles and muscle fibres?
1:10 fibres
What is the innervation ratio between quadricep muscles and muscle fibres?
1:1000 fibres
What is the neuromuscular junction?
The site of communication between the motoneurone and muscle
Define innervation
The normal state of nerve supply to a muscle or other target
Define denervation
Depriving the muscle of its nerve supply (therefore will not survive for v long)
Define re-innervation
Re-growth of the nerve to re-supply the muscle
What is crocodile tears syndrome?
Occurs most often following facial paralysis
- Dmg to salivary gland mistakenly regrow into tear gland
- Shed tears whilst eating
- Re-innervate wrong effector
What would happen to a motoneurone if the cell body (soma) was damaged?
Loss or damage of the cellbody would lead to death of motoneurone
What is polio myelitis?
A communicable infection that targets cell bodies of LOWER motoneurones of the body
- aka infantile paralysis
Cause of polio myelitis?
Infection by polio virus
- Any motoneurones of the spinal cord are susceptible to this virus
Complications of polio myelitis?
- 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
What effect could death to cell bodies of neurones of ventral horn do to the dorsal horn?
Toxic infection of cell bodies of neurones of the ventral horn an lead to death of the dorsal horn too
What are the two possible variants of motoneurone disease?
- Disease simultaneously kills both upper motoneurone and lower motoneurone (in American terms –> progressive supranuclear palsy)
- The disease targets only the lower motoneurone
What is motoneurone disease?
- 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
What is amyotrophic lateral sclerosis (Lou Gherig’s disease)?
Death of neurones responsible for controlling voluntary movement (deteriorate and gradually die)
Which motoneurones of the body do not undergo apoptosis under MD?
- Motoneurones supply extraocular muscles (eyes)
2. Motoneurones supplying the anal sphincter (S2-S4)
What is Guillain-Barre syndrome?
- 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
What is diabetic neuropathy?
- 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
What is botulinum toxin and its effects on the NMJ?
- 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
Possible causes of botulism or culturing of botulinum toxin?
- 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
How do nerve gases work in relation to the NMJ?
Act by blocking AChE from breaking down ACh in the NMJ
What is myasthenia gravis and how does it affect the NMJ?
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
What is Duchenne muscular dystrophy?
- 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 ?
What is dystrophy?
A disorder in which an organ/ tissue wastes away
What are the different lower motoneurone signs of (damage)?
- Flaccid muscle weakness
- Hypotonia (atonia)
- Hyporeflexia (areflexia)
What are the different lower motoneurone signs of (damage)?
- Flaccid muscle weakness
- Hypotonia (atonia)
- Hyporeflexia (areflexia)
- Denervation muscle atrophy
- Fasciculations (acute phase)
- Muscle wasting
