Muscle Histology, and Physiology Flashcards
(39 cards)
Question/Term
Answer/Definition
What are the steps of the muscle contraction cycle?
1) ATP hydrolysis: Energy is released from ATP and forms ADP and a phosphate group. The energy energizes the myosin head and sets the head into a ‘cocked’ position, ready to bind to actin.
2) Calcium binds to the Troponin of the actin changing the shape of the tropomyosin, revealing the myosin-binding site.
3) The formation of the cross-bridge: The energized myosin attaches to the myosin-binding site on actin. Releases the phosphate group.
4) The power-stroke: ADP is released causing the myosin head to pivot changing the angle from 90 degrees to 45 degrees pulling the actin over the thick filament towards the m-line.
5) Detachment: ATP binds to the ATP binding site on myosin causing the myosin head to detach from the actin. And then step one is repeated.
What happens after the action potential reaches the muscle fiber?
The action potential travels along the sarcolemma and down the T-tubules, reaching the sarcoplasmic reticulum.
How is calcium released during muscle contraction?
Action potentials open the voltage-gated Ca ion channals (T-tubules) to open. Causing the Ca ions to be released from the Ca ion release channel. (Sarcoplasmic reticulum)
What role does calcium play in muscle contraction?
Calcium binds to troponin, causing a conformational change that shifts tropomyosin, exposing myosin-binding sites on the actin filament.
How do myosin heads interact with actin?
Myosin heads bind to the exposed sites on actin, forming a cross-bridge.
What is the power stroke in muscle contraction?
The myosin head pivots, pulling the actin filament toward the center of the sarcomere, shortening the muscle.
What causes myosin heads to detach from actin?
ATP binds to the myosin head, causing it to release from actin and reset for the next cycle.
How does muscle contraction stop?
When the nerve signal ceases, calcium is pumped back into the sarcoplasmic reticulum, and tropomyosin re-covers the binding sites on actin.
Myosin
A contractile protein that forms thick filaments. It has a head region that binds to actin and performs the power stroke during muscle contraction.
Actin
A contractile protein that forms thin filaments. It contains myosin-binding sites that interact with myosin heads during the contraction cycle.
Troponin
A regulatory protein attached to actin that binds calcium ions, triggering a shift in tropomyosin to expose myosin-binding sites.
Tropomyosin
A regulatory protein that covers myosin-binding sites on actin in a relaxed muscle, preventing cross-bridge formation until calcium binds to troponin.
Titin (Connectin)
A structural protein that extends from the Z-disc to the M-line, providing elasticity and stability to the sarcomere.
Nebulin
A structural protein that wraps around thin filaments and helps align actin within the sarcomere.
Dystrophin
A structural protein that connects the sarcolemma (muscle cell membrane) to the cytoskeleton, strengthening the sarcolemma, and helping to transmit force during contraction.
α-Actinin
A structural protein located at the Z-disc that anchors thin filaments and helps maintain sarcomere structure.
Myomesin
A structural protein located at the M-line that holds thick filaments in place and stabilizes the sarcomere.
Sarcomere
The basic functional unit of a myofibril in striated muscle, extending from Z-disc to Z-disc, responsible for muscle contraction.
Z-Disc (Z-Line)
The boundary of a sarcomere where thin filaments (actin) are anchored. It separates one sarcomere from the next.
M-Line
The middle of the sarcomere where thick filaments (myosin) are connected, providing structural support.
A-Band
The dark region of the sarcomere that spans the entire length of the thick filaments, including areas of overlap with thin filaments.
I-Band
The light region on either side of the Z-disc that contains only thin filaments (actin) and shortens during contraction.
