Muscle Physiology

Question 1

What is the tension generated in a muscle dependent on?

Answer 1

Dependent on the area of overlap as the greater the area of overlap, the more crossbridges that form and the greater the contraction

Question 2

What is a motor unit?

Answer 2

1 motor neuron and the muscle fibres it innervates

Question 3

How long is a skeletal muscle action potential?

Answer 3

1-2ms

Question 4

The ion channel families in skeletal muscle cells and neuronal cells are different, T or F?

Answer 4

T

Question 5

What is the Nernst potential for the Nicotinic AChR?

Answer 5

0mV

Question 6

What does the Nernst potential of Nicotinic AChR suggest?

Answer 6

It causes depolarisation of the skeletal muscle cells

Question 7

What does the activation of Nicotinic AChR lead to?

Answer 7

Depolarises the cell which leads to the activation of Na+ channels

Question 8

What is the structure of Nicotinic AChR?

Answer 8

It has a pentameric structure but is made up of 4 types of subunits; 2 alpha, beta, gamma, delta

Question 9

How many binding sites for ACh are there on the Nicotinic AChR?

Answer 9

2

Question 10

How many transmembrane spanning domains does Nicotinic AChR have?

Answer 10

4

Question 11

What do CHRNA1-9 code for?

Answer 11

They all code for the alpha subunit

Question 12

Where are A1, A2-8 and A9 found?

Answer 12

A1 is found in skeletal muscle, A2-A8 are found in neuronal tissue and A9 isn’t known

Question 13

What do CHRNB1-4 code for?

Answer 13

They all code for the beta subunit

Question 14

Where are B1 and B2-4 found?

Answer 14

B1 is found in skeletal muscle, B2-4 are found in neuronal muscle

Question 15

How many agonists need to bind to the AChR to cause it to open?

Answer 15

2

Question 16

Myasthenia Gravis

Answer 16

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

Question 17

How does the incidence of Myasthenia Gravis differ between men and women?

Answer 17

Women - peak incidence in 30s

Men - peak incidence in 60-70s

Question 18

What are the 2 different types of antibody evidence for Myasthenia Gravis?

Answer 18

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

Question 19

What is a treatment for mild Myasthenia Gravis and what is its action?

Answer 19

Acetylcholinesterase inhibitors such as pyridostigmine, it enhances ACh levels

Question 20

What is a treatment for moderate to severe Myasthenia Gravis and what is its action?

Answer 20

Corticosteroids such as prednisolone, immunosuppressant that reduces antibody levels
Cyclosporins also act as immunosuppressants

Question 21

What is a treatment for severe Myasthenia Gravis and what is its action?

Answer 21

IV immunogloblins that binds to antibodies, can only be administered for short periods of time

Question 22

What method would be used to treat Myasthenia Gravis when acute intervention is needed?

Answer 22

Plasmapheresis to remove antibodies from plasma -filtration, immunoadsorption to reduce antibody levels

Question 23

A tumour in what location can lead to Myasthenia Gravis and why is removal useful?

Answer 23

The thymus - a thymectomy removes AChR antibodies

Question 24

What is the role of transverse tubules?

Answer 24

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

Question 25

Muscle triad

Answer 25

AP travels down the T tubule which activates L-type calcium channels causing calcium to move into the cell. The mechanical coupling of calcium with the ryanodine receptor causes calcium to move from the sarcoplasmic reticulum into the T tubule