Disorders of the MotorU Flashcards
What is a motor unit
A alpha motor neurone (lower motor neurone) and all the extrafusal muscle fibres it innervates
What is denervation?
What is re-innervation?
Denervation is the state where a muscle has lost its nerve supply
Re-Innervation is the regrowth of the axon of a lower motor neurone to resupply and re-innervate the muscle
What is polio myelitis?
Infection caused by the polio virus
Is a communicable disease
Leads to infection of the Soma (cell bodies) in the ventral horn
Why does polio lead to damage?
Infection of cell bodies in ventral horn death of motor neurone cell body denervation of muscle paralysis loss of supply to respiratory muscles need assisted breathing
Where are the cell bodies of lower motoneurons located
In the ventral horn of the spinal cord
What is motor neurone disease?
unclear as to whether it is an upper motor neurone or lower motor neurone disease
Leads to spontaneous apoptosis and death of motor neurones
How can are car crash lead to motor neurone injury
severing of the spinal cord or extreme compression due to a car crash injury can lead to death of motor neurones loss of muscle innervation and paralysis
How can the axons of lower motor neurones be damaged?
complete transduction of the axon
crushing car crash injuries
stabbings
or Demyelination of axons
result in temporary faulty function of the axons and motor neurones e.g Gullian Barre syndrome
How do nerve gases and pesticides affect the NMJ?
orgnaophosphates act by blocking AChE in the NMJ ie acting as a permanent inhibitor
prevents ACH release continuous nervous transmission and stimulation leading to prolonged muscle contraction, salvation tearing and deification if it autonomic neurones affected too eventually leads to asphyxiation and death
What is Myasthenia Gravis
Autoimmune condition that result in destruction of nAChR’s on the post synaptic membrane
Disease of the skeletal msucles
Lead to paralysis of the motor system
Duchenne Muscular Dystrophy
defects in muscle proteins lead to progressive muscle weakness and eventual muscle death
leads to death of individual eventually
What are the characteristics lower motor neurone damage signs
Muscle weakness loss of muscle tone loss of stretch reflex muscle atrophy wasting fasciculations uncontrolled contractions
What is crocodile tears syndrome? What does this condition illustrate?
Where the regrowth of axon that used to supply the salivary glands innervates the lacrimal gland instead meaning when there is a stimulus such as taste smell or even sight of food the person begins to cry due to simulation of lacrimal gland
shows that even though regeneration may occur the re-innervation may be incorrect and go to the wrong effector
What is the most common cause of botulims?
eating incorrectly preserved homemade food provides ideal conditions for the culture of the Botulin bacteria
How does the toxin work and cause botulism?
Enters lower motor neurones that use ACh
favours highly active neurones
It is endocytosed by the presynaptic axon and one inside begins to cleave SNARE proteins involved in the release of ACh
this leads to reduced and eventually no postsynaptic action potentials and thus muscle paralysis
Can be fatal as can stop the muscles of respiration
Why is diplopia a common one of the first symptoms of botulism
Extraoccular muscles of the eye are incredibly active toxin favours and enters better into highly active neurones
What is the botulin toxin used for?
What happens if the toxin enters systemic circulation
Botox
Injected into the face at very high concentrations in localised areas leading to paralysis of muscles in the face and therefore reduction in wrinkles. This needs to be repeated regularly
Is rapidly metabolised if it enters systemic circulation so shouldn’t go onto effect other NMJ
Must be repeated as the toxin is broken down and metabolised over time
What is suxamethonium?
A drug used to cause muscle paralysis and relaxation
how does suxamethonium work?
What type of drug is it ?
It is a Agonist of the nACh receptor on the sarcolemma
Binds to nAChR on sarcolemma causing opening
leads to depolarisation and generation of an EPP and subsequent generation of an AP and initial muscle contraction
However unlike ACH it is not rapidly hydrolysed so leads to nACh channels to remain open this lead to the Em being constantly above threshold and the cell being unable to repolarise and thus the cell cannot fire any more AP’s
This leads to fasciculation’s and eventual muscle relation
Why may repeated does of suxamethonium cause long term paralysis?
Acts in two phase, phase 1 where there is prolonged depolarisation resulting in fasiculations and then relaxation
And phase 2 that leads to nAChR desensitisation where they are no longer sensitive to ACh
How can an overdose of suxamethonium be treated?
Add an antagonist of the nAChR to try and shut as many as possible preventing opening by suxamethonium
