Muscle Physiology Flashcards
What is the tension generated in a muscle dependent on?
Dependent on the area of overlap as the greater the area of overlap, the more crossbridges that form and the greater the contraction
What is a motor unit?
1 motor neuron and the muscle fibres it innervates
How long is a skeletal muscle action potential?
1-2ms
The ion channel families in skeletal muscle cells and neuronal cells are different, T or F?
T
What is the Nernst potential for the Nicotinic AChR?
0mV
What does the Nernst potential of Nicotinic AChR suggest?
It causes depolarisation of the skeletal muscle cells
What does the activation of Nicotinic AChR lead to?
Depolarises the cell which leads to the activation of Na+ channels
What is the structure of Nicotinic AChR?
It has a pentameric structure but is made up of 4 types of subunits; 2 alpha, beta, gamma, delta
How many binding sites for ACh are there on the Nicotinic AChR?
2
How many transmembrane spanning domains does Nicotinic AChR have?
4
What do CHRNA1-9 code for?
They all code for the alpha subunit
Where are A1, A2-8 and A9 found?
A1 is found in skeletal muscle, A2-A8 are found in neuronal tissue and A9 isn’t known
What do CHRNB1-4 code for?
They all code for the beta subunit
Where are B1 and B2-4 found?
B1 is found in skeletal muscle, B2-4 are found in neuronal muscle
How many agonists need to bind to the AChR to cause it to open?
2
Myasthenia Gravis
An autoimmune disease
It makes antibodies that target A1 and B1 on AChR of the postsynaptic membrane of the neuromuscular junction - these stop the receptor working and lead to the degradation of AChR
Leads to weakness and tiredness in muscles
How does the incidence of Myasthenia Gravis differ between men and women?
Women - peak incidence in 30s
Men - peak incidence in 60-70s
What are the 2 different types of antibody evidence for Myasthenia Gravis?
Injection of mice with antibodies to AChR
Detection of antibodies to AChR in patients with Myasthenia Gravis and patients with other neuromuscular conditions - those with MG have increased levels of the antibody compared to those without
What is a treatment for mild Myasthenia Gravis and what is its action?
Acetylcholinesterase inhibitors such as pyridostigmine, it enhances ACh levels
What is a treatment for moderate to severe Myasthenia Gravis and what is its action?
Corticosteroids such as prednisolone, immunosuppressant that reduces antibody levels
Cyclosporins also act as immunosuppressants
What is a treatment for severe Myasthenia Gravis and what is its action?
IV immunogloblins that binds to antibodies, can only be administered for short periods of time
What method would be used to treat Myasthenia Gravis when acute intervention is needed?
Plasmapheresis to remove antibodies from plasma -filtration, immunoadsorption to reduce antibody levels
A tumour in what location can lead to Myasthenia Gravis and why is removal useful?
The thymus - a thymectomy removes AChR antibodies
What is the role of transverse tubules?
They invaginate into the into the muscle fibre so when an action potential arrives it travels deep into the muscle fibre, taking the action potential down the sarcoplasmic reticulum to release calcium from its stores as quickly as possible
