Skeletal Muscle Flashcards
What is the gross organisation of a skeletal muscle?
Muscle fibre is a cell. Wrapped by endomysium connective tissue.
Multiple muscle fibres together is a fascicle. Wrapped by perimysium.
All the fascicles together are wrapped by epimysium, which connects the whole muscle to the tendon which connects to bone.
True or false:
A muscle fibre is one cell
True
What is a muscle fibre made up of?
Myofibrils, composed of sarcomeres made of thick and thin myofilaments
Between what lines is a sarcomere defined?
Between two Z lines
What is an I band?
Light bands containing only actin (thin filament). (Disappears during contraction)
What is an A band?
Dark bands which contain myosin (thick filament) and (when contracting) actin.
What is an H band?
Very middle by M line, contains only myosin (unless sarcomere is fully contracted)
What is the function of titin?
Prevents over-extension of sarcomere
What are the names of the regulatory proteins attached to the actin?
Troponin and tropomyosin
What causes the myosin binding sites on the actin to become exposed?
After stimulation to contract, calcium enters the muscle and binds to troponin.
This causes the tropomyosin to uncover the myosin binding sites.
When the myosin binding sites are exposed, what forms between the myosin and actin?
A cross bridge
Describe the power stroke
ADP and phosphate are released, the potential (stored) energy in the hinge region of the myosin head is released and the head pivots, pulling the actin filament along.
What causes the crossbridge to break?
ATP binding to the myosin head
Describe myosin reactivation
After ATP binds to the myosin head, it is split into ADP + P, providing the myosin head with potential energy to re-cock ready to bind to actin again
Describe what causes calcium to be released
An action potential from the motor neuron initiates an action potential in the sarcolemma, depolarising the muscle fibre.
Action potential carries down the T-tubules to all the myofibrils.
Sarcoplasmic reticulum releases calcium
