Skeletal Muscle Contraction Action
Skeletal muscle contraction action describes the process by which the muscle
contracts, starting with calcium binding to troponin. The calcium enters the cell
through the opening of voltage-gated calcium channels and binds to troponin
within muscle cells. This causes an allosteric shift that moves tropomyosin and
exposes the active binding site on actin. The myosin head binds to the active site
and uses ATP hydrolysis (and phosphate release) to drive a conformational
change, which results in myosin pulling on actin, an action also known as the
power stroke. Finally, the release of ADP causes the myosin head to disengage
from actin. This process results in large amounts of ATP consumption, so muscle
cells must have many mitochondria producing ATP to adequately keep up with
energy demand.
PLAY PICMONIC
Characteristics
Calcium Binds Troponin
Cows grabbing the T-rope
An action potential in a motor neuron leads to acetylcholine release. Acetylcholine binds with receptors on the muscle fibers, opening sodium
channels, with release of calcium. Calcium influx from voltage-gated calcium channels results in calcium binding to troponin on the muscle fiber.
Active Site Exposed
Revealed Action-clapperboards
The calcium binding causes an allosteric change in troponin, shifting tropomysin, which was blocking the active site. This movement exposes the
binding sites on the actin filament.
Many Mitochondria Produce ATP
Mitochondria-factory Producing ATP-batteries
The power stroke of contraction requires ATP, so to keep up with muscle demands for ATP there are many mitochondria producing ATP in muscle
cells.
Myosin Head Binds
Mayo-sun Head Binds to active-site
The myosin head binds to the newly available active site, initiating the power stroke. They do so by breaking down ATP to ADP and a phosphate group.
Power Stroke
Swimming Stroke
The power stroke occurs when multiple myosin molecules generate force through ATP hydrolysis, which causes a conformational shift and myosin to
pull against actin.
Myosin Head Releases Active Site
Mayo-sun Head Disconnects from Action-clapper
The release of the ADP allows the myosin head to unbind from the active site on actin, until more ATP hydrolysis occurs with another power stroke.
