Lecture 9 Flashcards
Which is the thin filament in a myofibril
Actin
Which is the thick filament in a myofibril
Myosin
Explain how Actin works
Actin forms the thin filament, a structural
scaffold that runs along the myofilament
(the rope)
Explain how Myosin works
Myosin forms the thick filament and acts a motor
molecule, attaching to actin and generating force to pull
What happens to actin and myosin in the presence of calcium
Actin and myosin bind together when calcium is present,
forming cross-bridges and allowing contraction to occur
What are the 5 states of cross-bridge cycling
Attached → Released → Cocked → Cross-Bridge → Power stroke
What happens in the attached state of Cross-Bridge cycling
The myofilament has just finished a power stroke (pulling on actin) and cross-bridges are still present
What happens in the released state of Cross-Bridge cycling
A molecule of ATP binds to the myosin in preparation for releasing some energy to prime the myosin head.
The ATP binding causes the myosin to release actin
What happens in the cocked state of Cross-Bridge cycling
The myosin head burns ATP
What happens in the cross-bridge state of Cross-Bridge cycling
If calcium is present and bound to the myofilament, the energized myosin head can bind to the actin.
This forms a cross-bridge
What happens in the power stroke state of Cross-Bridge cycling
Cross-bridge + energized myosin head. Myosin uses its stored energy to pull causing the actin filament to slide.
Thus the sarcomere shortens and contraction has occured
What two things does muscle tension depend on
The number of muscle fibers recruited
The rate at which the muscle is stimulated
What controls the number of fibers activated?
The number of fibers activated is regulated by how man neurons are active at one time
What is recruitment
The process of activating more fibers to make more force.
What is tetanus
When maximal signaling and contraction capability of the muscle is reached. At this point the force will plateau
What is the role of fast fibers. What attribute of their cells contribute to this
Cells that make up fast muscle fibres have large diameters. This is made to contract fast and to provide lots of contractual power
What is the role of slow fibers
Slow fibers are very fatigue resistant. They are used for many non explosive actions. They use up a lot of energy and are in constant need for supply from blood vesicles
