Flashcards in Muscle Physiology Deck (93)
Recall the divisions of a muscle from largest to smallest?
Muscleà Muscle Fascicle à Muscle Fibre/Cell à Myofibril à Sarcomere à Myofilaments
What is defined as one sarcomere?
The length/distance between two successive Z-lines
What determines the degree of contraction in muscle?
Degree of overlap between the actin and myosin filaments
What is meant by the motor unit of a muscle?
The motor neuron and the muscle fibre it innervates
One motor neuron innervates a single muscle fibre, T or F?
F – one motor neuron innervates several muscle fibres
What attribute of motor units’ accounts for the ability to finely control muscle contraction?
Finer control of muscle contraction comes from the motor units where one motor neuron innervates a smaller number of muscle fibres
A single muscle has multiple motor units, T or F?
Which type of postsynaptic receptor is found on muscle cells and what class of receptor is it?
nAchR – ligand-gated ion channel
The skeletal muscle action potential has a very short duration, T or F?
At rest the membrane potential of skeletal muscle is more positive than normal due to open CLC1 and voltage-gated K+ channels, T or F?
F – membrane potential is very negative
Which channels mediate depolarisation in the action potential?
Which channels mediate repolarisation during the action potential?
There are different types of K+ channel that mediate the resting membrane potential and the repolarisation phase of the action potential, T or F?
nAchRs are Na+ ion channels, T or F?
F – they are cation selective but allow both Na+ and K+ through
Activation of the nAchRs causes depolarisation, T or F?
Describe the subunit composition of nAchRs?
Describe the subunit composition of nAchRs? nAchRs are pentameric structures consisting of 2α subunits, and 1 β, γ and δ subunit
What can be said about the acetylcholine binding site(s) of nAchRs?
There are two binding sites for acetylcholine that lie at the interface between the α and γ subunits. This means that two acetylcholine molecules have to be bound to the receptor before the ion channel opens
How many transmembrane domains are there in the nAchR?
What allows for the vast array of different nAchRs?
There are different types of each subunit
Describe the gating process of nAchRs?
Closed with no agonists bound à closed with one agonist bound à closed with two agonists bound à open
What type of disease is myasthenia gravis?
What are the symptoms of myasthenia gravis?
Weakness and tiredness in the skeletal muscle
What is the cause of myasthenia gravis?
Inappropriate antibodies against postsynaptic AchRs at the neuromuscular junction that prevent acetylcholine binding
What difference is seen in males and females with myasthenia gravis?
Female age of onset in much earlier (30s) whereas in males it occurs in 60s-70s
How can myasthenia gravis prove fatal?
Respiratory failure due to inability of the muscles to contract
Acetylcholinesterase inhibitors are used in the treatment of myasthenia gravis, how do these work?
By inhibiting acetylcholine breakdown you can prolong the effects of released acetylcholine allowing it to bind to the still functioning AchRs
How are corticosteroids effective in treating MG?
They are immunosuppressants that reduce levels of antibodies
Another treatment method for MG is using intravenous antibodies, how do these work?
They bind to the AchR antibodies and prevent them from binding to the receptors themselves
List two other treatment methods for MG?